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Ecology Desert Biome
by
David Ward

Introduction

Deserts are defined by their arid conditions. However, deserts are not necessarily dry. It is the high evaporation relative to the precipitation that makes a desert such a harsh environment. Such evaporation occurs because deserts are often, but not always, hot, and because precipitation is low. A result of this aridity is that most of the area occupied by deserts is barren and monotonous. However, biologists perceive deserts to be laboratories of nature, where natural selection is exposed at its most extreme. Scientists have long considered the many unique adaptations of plants and animals for surviving the harsh desert environment. More recently, researchers have focused on the biotic interactions among organisms. Thus, the harsh abiotic environment defines the desert and imposes the strong selection pressures on organisms that live there. However, it is the relative simplicity of desert ecosystems that makes them frequently more tractable for study than more complex environments such as forests. According to Gideon Louw and Mary Seely’s Ecology of Desert Organisms (Louw and Seely 1982, cited under General Overviews) and John Sowell’s Desert Ecology (Sowell 2001, cited under Specific Deserts), most deserts have an average annual precipitation of less than 400 mm. A common definition distinguishes between true deserts, which receive less than 250 mm of average annual precipitation, and semideserts or steppes, which receive between 250 mm and 400 to 500 mm. Four factors influence the lack of rainfall in deserts: (1) the global atmospheric circulation maintains twin belts of dry, high-pressure air over the edges of the tropics, called Hadley cells; (2) marine circulation patterns contribute to aridity when cold coastal waters on the west coasts of North and South America, Africa, and Australia chill the air, reducing its moisture-carrying capacity; (3) rain shadows are created by mountain ranges; and (4) if the distances to the interior of a continent are too great (such as in the Gobi and Taklamakan deserts of China), then water is limited. Many of these four factors act in tandem. An additional type of desert is the polar desert, which occurs in the McMurdo dry valleys of Antarctica. This desert has extremely low humidity and no snow cover. Katabatic winds, which occur when cold and dense air is pulled down by gravity, heat as they descend and evaporate all moisture (see Doran, et al. 2002, cited under Defining the Desert Biome). These winds can reach speeds in excess of 300 km per hour. Here too, rain shadows are created by mountain ranges that are sufficiently high that the seaward-flowing ice is blocked from reaching the sea, thereby reducing humidity.

General Overviews

Louw and Seely 1982 serves as an effective introduction to the topic. In many respects, Whitford 2002 and Ward 2009 build on this introduction, although Whitford 2002 has a strong ecosystem approach while Ward 2009 focuses on an evolutionary one. Ward’s approach considers natural selection to be an important cause of the adaptations of desert organisms. Mares 1999 is a very large tome with many aspects that one can dip into. Ezcurra 2006 covers many aspects of desert ecology and geomorphology (with a useful introduction to the issue of humans in deserts) and is a very good modern introduction to the topic. Of all the books listed here, Ezcurra 2006 is the easiest to access, although Mares 1999 also covers many fundamental issues. Shachak, et al. 2005 is an edited volume and suffers from some of the problems of conference proceedings in that not all contributions strictly relate to deserts. The World Wide Fund for Nature (formerly the World Wildlife Fund) maintains a very useful website that includes references to many deserts.

Specific Deserts

Several books have been published on specific deserts. A number of these books focus on North American deserts (Rundel and Gibson 1996; Sowell 2001; Havstad, et al. 2006; Hernández 2006). Sowell 2001 is the easiest book for the nonspecialist to access. There are also a few books on Middle Eastern deserts, with Evenari, et al. 1982 being relevant despite its age. Krasnov and Mazor 2001 is a more modern look at the central Negev desert, with a useful combination of geological and ecological studies. Two of southern Africa’s deserts are well described: Seely 1990 has attempted to cover a range of issues on the Namib desert, and Dean and Milton 1999 invited a number of highly respected authors to review issues on the Karoo. There is also an excellent series (some twenty-three books) titled “Adaptations of Desert Organisms,” published by Springer (Berlin). Some of the latter volumes may be a bit dated (and twelve are out of print), but they are worth reading in libraries nonetheless. See Shenbrot, et al. 1999 (cited under Biogeography: Animals), Smith, et al. 1997 (cited under Plants: Ecophysiology), and van Rheede van Oudtshoorn and van Rooyen 1999, cited under Plants: Population Dynamics).

Journals

Probably the most important of the journals on deserts is the Journal of Arid Environments, which covers all topics in this field. The journal Arid Land Research and Management focuses strongly on arid-zone soils. More general journals that also cover desert environments include Ecology, Rangeland Ecology and Management (formerly known as Journal of Range Management) and more recently, Global Change Biology, which focuses on causes of global change and desertification.

Government and University Publications

There are a number of websites where most research is desert related. Several of these are North American (Jornada, Sevilleta, and The Portal Project). Other institutes are located in different deserts such as Australia (CSIRO Sustainable Ecosystems), Israel (Mitrani Department for Desert Ecology, which is part of the Blaustein Institutes for Desert Research in Sede Boqer in the Negev desert) and India (Central Arid Zone Research Institute). There are, of course, many more researchers studying deserts, and specific details could be gleaned from the names listed in this bibliography.

Defining the Desert Biome

Deserts are widely spaced on the planet and have developed for different reasons. For example, the North American continental deserts are much hotter and wetter than African and Middle Eastern deserts, according to Louw and Seely 1982 (cited under General Overviews). Sowell 2001 (cited under Specific Deserts) notes that, in North America, the Intermountain desert (which includes the Great Basin desert) is temperate, while the southwestern deserts (Mojave, Sonoran, and Chihuahuan) are extremely hot. Furthermore, winter rainfall is experienced in the Mojave Desert in southwestern California, both winter and summer rainfall occur in the Sonoran Desert, and predominantly summer rainfall is seen in the Chihuahuan Desert in Texas. There are extremely dry but cold valleys in the McMurdo Sound of Antarctica that can be considered deserts because so little grows there (see Priscu 1998; Doran, et al. 2002). The Kalahari and Namib deserts in the Southern Hemisphere experience summer rainfall, while much of the adjacent Karoo desert experiences winter rainfall. Middle Eastern deserts experience winter rainfall. The coastal Namibian and Chilean deserts are driven by fog as the main form of precipitation, while runoff from winter floods is the main form of precipitation in the arid Middle East. Australian deserts are limited by phosphorus, according to Orians and Milewski 2007 (cited under Fire), while nitrogen is the limiting nutrient in other deserts (Ezcurra 2006, cited under General Overviews).

  • Doran, Peter T., John C. Priscu, W. Berry Lyons, et al. 2002. Antarctic climate cooling and terrestrial ecosystem response. Nature 415:517–520.

    DOI: 10.1038/nature710Save Citation »Export Citation »E-mail Citation »

    Details climate changes over the last two decades of the 20th century in a polar desert that is comprised of a mosaic of perennially ice-covered lakes, ephemeral streams, arid soils, exposed bedrock, and alpine glaciers, and whose biological activity is dominated by microbial processes.

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  • Priscu, John C., ed. 1998. Ecosystem dynamics in a polar desert: The McMurdo Dry Valleys, Antarctica. Washington, DC: American Geophysical Union.

    DOI: 10.1029/AR072Save Citation »Export Citation »E-mail Citation »

    Chapters on geomorphology, meteorology, geochemistry, soils, stream ecology, and limnology in the McMurdo Dry Valleys of Antarctica, with most of the focus being on glacial erosion processes and some coverage of freshwater aquatic systems.

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Historical Background

In general, desert ecologists believe that deserts are easier to study than other biomes because they contain fewer species. Although it is not necessarily true that they are less diverse than other biomes, there has been a large shift from foundational taxonomic, ecophysiological, and descriptive ecological studies to studies of interactions among organisms (see Abramsky and Rosenzweig 1984, cited under Productivity, Diversity, and Food Webs; Brown and Davidson 1977 and Friedman 1971 , both cited under Competition; and Polis 1991, cited under Community Ecology). There has also been a switch to ecosystem-based studies (Schlesinger, et al. 1996; Whitford 1996; both cited under Ecosystem Processes), particularly in the light of climate change (Jackson, et al. 2002 ; McAuliffe 1994; both cited under Ecosystem Processes; Schlesinger, et al. 1990, cited under Desertification). Initially, much research focused on adaptations of species to their environments. Prominent among desert plant ecophysiologists were Fritz W. Went and Park S. Nobel (see Hartsock and Nobel 1976 and Nobel 2003, both cited under Plants: Ecophysiology , and Franco and Nobel 1989, cited under Facilitation). A leading animal ecophysiologist who focused on desert research was Knut Schmidt Nielsen; Schmidt-Nielsen 1965 (cited under Animals: Ecophysiology ) spawned a generation of desert animal ecophysiologists. One of the earliest botanists and phytogeographers to work in deserts was Forrest Shreve. He was prominent from about 1910 onward. He and colleagues began publishing a journal, Plant World, which later became the major journal Ecology of the Ecological Society of America. His biography was written by Janice Bowers (Bowers 1988). Shreve worked at the University of Arizona Desert Laboratory and was responsible for setting up permanent research plots at Tumamoc Hill that are among the longest-studied desert plots anywhere in the world, having been protected from grazing since 1907.

  • Bowers, Janice E. 1988. A sense of place: The life and work of Forrest Shreve. Tucson: Univ. of Arizona Press.

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    Forrest Shreve (b. 1878–d. 1950) spent most of his career at the Carnegie Institution’s Desert Laboratory in Tucson, Arizona. He was an internationally known plant ecologist whose studies of plant ecology and biogeography laid the groundwork for modern studies.

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  • University of Arizona Desert Laboratory.Ongoing Field Research at Tumamoc Hill.

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    The first long-term study plots were placed on Tumamoc Hill near Tucson, Arizona, in 1903 by Frederic V. Coville of the US Department of Agriculture, based on his experiences in Death Valley in California in 1891. They represent the only systematic effort to monitor and analyze the long-term population dynamics of perennial plants in the Sonoran Desert. For a review of the vegetation change on these plots, see Goldberg and Turner 1986 (cited under Drought).

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Physical Background

The most important factors affecting the desert environment are the low and variable Precipitation and the high variability in Geology and soils. Much research has focused on the pulse-reserve model (see Noy-Meir 1973under Precipitation) and the more specific details of this general model of precipitation. With regard to geology, a lot of research has focused on the consequences of soil erosion, the removal of soil either by the little rain that falls or by wind as loess.

Precipitation

It is widely known that there is a negative correlation between the coefficient of variation and the median annual rainfall (Sharon 1972; van Etten 2009; Ward 2009, cited under General Overviews). There is also tremendous spatial variation in rainfall within deserts. Spatiotemporal variation in deserts is more extreme than in other biomes. A number of authors, starting with Immanuel Noy-Meir, have noted the importance of “pulses” of rainfall and their consequences for primary productivity (see Noy-Meir 1973; Reynolds, et al. 2004; Chesson, et al. 2004; Schwinning, et al. 2004; Collins, et al. 2008). More recently, attempts have been made to simulate predicted changes in precipitation due to anthropogenic climate change (Thomey, et al. 2011).

  • Chesson, Peter, Renate L. E. Gebauer, Susan Schwinning, et al. 2004. Resource pulses, species interactions, and diversity maintenance in arid and semi-arid environments. Oecologia 141:236–253.

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    These authors focus on the importance of pulsed events for creating the relatively high species diversity often encountered in deserts, and on the fact that species interactions are as important in deserts as they are elsewhere.

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  • Collins, Scott L., Robert L. Sinsabaugh, Chelsea Crenshaw, et al. 2008. Pulse dynamics and microbial processes in aridland ecosystems. Journal of Ecology 96:413–420.

    DOI: 10.1111/j.1365-2745.2008.01362.xSave Citation »Export Citation »E-mail Citation »

    In this review essay, Collins and colleagues consider an alteration of the pulse-reserve model that they call the Threshold-Delay Nutrient Dynamics model. Their model mediates responses to pulsed precipitation by a fungal loop that links carbon and nitrogen cycling, net primary production, and decomposition.

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  • Noy-Meir, Immanuel. 1973. Desert ecosystems: Environment and producers. Annual Review of Ecology and Systematics 4:25–51.

    DOI: 10.1146/annurev.es.04.110173.000325Save Citation »Export Citation »E-mail Citation »

    The first to comment on the importance of pulses of rainfall and how these influence growth of vegetation and their subsequent effects on higher trophic levels. See also Noy-Meir’s important review article in the same year in the same journal on higher trophic levels in deserts.

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  • Reynolds, James F., Paul R. Kemp, Kiana Ogle, and Roberto J. Fernández. 2004. Modifying the “pulse-reserve” paradigm for deserts of North America: Precipitation pulses, soil water, and plant responses. Oecologia 141:194–210.

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    It is the sequence of pulses of adequate magnitude that affects primary productivity (see also Evenari, et al. 1982, cited under Specific Deserts). The authors used a simulation model for the Mojave, Sonoran, and Chihuahuan deserts of North America and found that there was little separation of water access with depth.

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  • Schwinning, Susan, Osvaldo E. Sala, Michael E. Loik, and James R. Ehleringer. 2004. Thresholds, memory, and seasonality: Understanding pulse dynamics in arid/semi-arid ecosystems. Oecologia 141:191–193.

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    This editorial provides a fine general introduction to the other papers in this issue of Oecologia (see also Chesson, et al. 2004; Reynolds, et al. 2004) and provides a useful introduction to the ideas developed in Collins, et al. 2008. Accessible to students.

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  • Sharon, David. 1972. The spottiness of rainfall in a desert area. Journal of Hydrology 17:161–175.

    DOI: 10.1016/0022-1694(72)90002-9Save Citation »Export Citation »E-mail Citation »

    Shows convincingly that rainfall varies tremendously in space and time.

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  • Thomey, Michell L., Scott L. Collins, Rodrigo Vargas, et al. 2011. Effect of precipitation variability on net primary production and soil respiration in a Chihuahuan Desert grassland. Global Change Biology 17:1505–1515.

    DOI: 10.1111/j.1365-2486.2010.02363.xSave Citation »Export Citation »E-mail Citation »

    Under climate change scenarios currently proposed, there should be more extreme rainfall events punctuated by longer intervening dry periods in desert environments. The authors show that more extreme precipitation events will likely have a positive impact on some aridland ecosystem processes important for the carbon cycle.

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  • van Etten, Eddie J. B. 2009. Inter-annual rainfall variability of arid Australia: Greater than elsewhere? Australian Geographer 40:109–120.

    DOI: 10.1080/00049180802657075Save Citation »Export Citation »E-mail Citation »

    Tested the claim that Australia’s deserts experience more rainfall than other deserts. Found that the northern Australian (but not southern Australian) deserts, alongside the Thar, Namib-Kalahari, and Somali deserts, experienced more variable rainfall (see also Ward 2009, cited under General Overviews).

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Geology

There is high spatial variability in desert geology and soil types. The sand desert landscape is actually not as common as is often perceived and may account for as little as 15–20 percent of deserts. Some of the major landscape types are sand (Bagnold 1941, Pye and Tsoar 2009), stone (including desert pavement), rock (Friend 2000), plateau (Ben-David and Mazor 1988), and mountains. Louw and Seely 1982 and Ward 2009 (both cited under General Overviews) describe the major landscapes. Many desert environments have high levels of salts in them, which makes life difficult for many plants (Flowers and Colmer 2008, cited under Plants: Ecophysiology ) and means that many animals must become salt-tolerant. Soil nutrients and organic matter are concentrated in the upper 2–5 cm of desert soils, with most nutrients occurring under the canopies of desert shrubs and trees (Dean, et al. 1999, cited under Indirect Interactions; Aranibar, et al. 2004, cited under Ecosystem Processes). Erosion processes are fundamental aspects of deserts, and are well described by Bull 1981 and Avni, et al. 2006. Wind-borne dust deposits, called loess, make life in deserts during sandstorms rather unpleasant, but they can also provide unique insights into the interactions among biomes, such as the fact that loess from the Sahara desert in Africa reaches the Amazon rainforest (Swap, et al. 1992). Because of the shifting positions of the continents since the breakup of the supercontinent Pangea, deserts are seldom very old, although the Namib desert is at least 55 million years old (Ward, et al. 1983). Indeed, the Indian desert has become desertified over the past few centuries (Ward 2009, cited under General Overviews).

  • Avni, Yoav, Naomi Porat, Josef Plakht, and Gideon Avni. 2006. Geomorphic changes leading to natural desertification versus anthropogenic land conservation in an arid environment, the Negev Highlands, Israel. Geomorphology 82:177–200.

    DOI: 10.1016/j.geomorph.2006.05.002Save Citation »Export Citation »E-mail Citation »

    Superb investigation of natural changes in the erosion of loess (wind-borne dust) in the Negev desert highlands of Israel. The ancient Nabateans built structures that restricted the soil loss within the ephemeral rivers and constructed ridges on the hillsides to channel the water, leading to an increase in effective annual rainfall.

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  • Bagnold, Ralph A. 1941. The physics of blown sand and desert dunes. London: Methuen.

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    The classic work on sand formation and the creation of sand dunes.

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  • Ben-David, Rami, and Emanuel Mazor. 1988. Stages in the evolution of Makhtesh Ramon and its drainage system. Israel Journal of Earth Sciences 37:125–135.

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    In a desert land type known as mountain-and-basin (Ezcurra 2006, cited under General Overviews), there are notable repetitions of anticlines and synclines. Ben-David and Mazor describe in great detail how an erosion cirque has formed by erosion of an anticline by an ephemeral river.

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  • Bull, William B. 1981. Soils, geology and hydrology of deserts. In Water in desert ecosystems. Edited by D. D. Evans and J. L. Thames, 42–58. Stroudsburg, PA: Dowden, Hutchinson & Ross.

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    Brilliant introduction to the topic of soils, geology, and hydrology, with a very nice explanation of the causes of soil erosion in desert environments.

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  • Friend, William H. 2000. Revisiting William Morris Davis and Walther Penck to propose a general model of “slope evolution” in deserts. Professional Geographer 52:164–178.

    DOI: 10.1111/0033-0124.00215Save Citation »Export Citation »E-mail Citation »

    Davis proposed a steep decline in the evolution of slope, with steep upper slopes eroding more quickly, leading ultimately to progressively flatter slope angles. Contrastingly, Penck considered parallel retreat, with slope angles remaining constant. These data, from the arid southwestern United States, firmly support Penck’s theory of parallel slope evolution.

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  • Pye, Kenneth, and Haim Tsoar. 2009. Aeolian sand and sand dunes. Berlin: Springer.

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    A more modern discussion of the topic of Bagnold 1941.

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  • Swap, Robert J., Michael Garstang, Steven Greco, Robert Talbot, and Per Kållberg. 1992. Saharan dust in the Amazon Basin. Tellus, Series B 44:133–149.

    DOI: 10.1034/j.1600-0889.1992.t01-1-00005.xSave Citation »Export Citation »E-mail Citation »

    Classic study showing that Saharan dust, in plumes that accompany major wet-season rain events, can reach the Amazon rainforest. This clearly indicates the interconnectedness of the world’s major biomes.

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  • Ward, John D., Mary K. Seely, and Nicholas Lancaster. 1983. On the antiquity of the Namib. South African Journal of Science 79:175–183.

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    Provides evidence of the Namib in southwestern Africa as the oldest desert in the world, having been arid for 55 million years, and perhaps as much as 80 million years.

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Biogeography

The deserts of the world are widespread and, consequently, have different biogeographical origins. In most cases, the desert flora and fauna contain arid-adapted species from the local mesic regions (Ward 2009, cited under General Overviews).

Plants

Shreve 1942 and, much later, Shmida 1985 attempted to review the sources of the plants occurring either in North America or globally. In general, the desert floras have evolved from their mesic peripheries (Shmida 1985; Crisp, et al. 2001). Shmida 1985 considers only two families to be desert-adapted in their origins—the Chenopodiaceae and the Zygophyllaceae—although Ihlenfeldt 1994 stresses that the Mesembryanthemaceae (now a subfamily of Aizoaceae) have many unique features that make them so successful in African deserts. Many members of the Chenopodiaceae are salt-tolerant and hence do well under many desert conditions (see Flowers and Colmer 2008, cited under Plants: Ecophysiology ). The classic case of convergent evolution of succulent plants occurs in North America (Cactaceae) and Africa (Euphorbiaceae). Roig, et al. 2009 takes a more modern view of the differences and similarities in the Monte desert flora in South America and the North American Mojave and Sonoran desert floras, some 8,000 km apart. However, Roig, et al. 2009 recognizes that there are far more shared elements between the Monte and the adjacent Chaco and Patagonian floras than with the North American desert floras. Although deserts are renowned for their high local species richness (known as α diversity), their richness among habitats (called β diversity) is usually quite low. Cowling, et al. 1998 indicates that southern African deserts have far greater plant diversity than other deserts of their size.

  • Cowling, Richard M., Philip W. Rundel, Philip G. Desmet, and Karen J. Esler. 1998. Extraordinarily high regional-scale plant diversity in southern African arid lands: Subcontinental and global comparisons. Diversity and Distributions 4:27–36.

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    The Karoo-Namib region includes the winter-rainfall Succulent Karoo flora (including high diversity of geophytes), summer rainfall Nama Karoo and Kalahari Desert, and the winter-summer rainfall Namib region. The Succulent Karoo is far richer than equivalent-sized areas, having four times as many species as in North America, for example.

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  • Crisp, Michael D., Shawn Laffan, H. Peter Linder, and A. Monro. 2001. Endemism in the Australian flora. Journal of Biogeography 28:183–198.

    DOI: 10.1046/j.1365-2699.2001.00524.xSave Citation »Export Citation »E-mail Citation »

    All the major centers of endemism are near-coastal, possibly because Pleistocene expansions of the central desert have been a powerful limitation on the viability of refugia for narrowly endemic species. All the centers of endemism lay outside the estimated limits of the expanded arid zone at the last glacial maximum.

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  • Ihlenfeldt, Hans-Dieter. 1994. Diversification in an arid world: The Mesembryanthemaceae. Annual Reviews of Ecology and Systematics 25:521–546.

    DOI: 10.1146/annurev.es.25.110194.002513Save Citation »Export Citation »E-mail Citation »

    The biodiversity of this succulent group is the result of a complex interaction between the availability of diverse niches, often very small in extent, steep climatic gradients, and strong genetic drift caused by a very low rate of gene exchange among populations and frequent breakdown of populations.

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  • Quézel, Pierre. 1965. La végétation du Sahara, du Tchad à la Mauritanie. Stuttgart: Fisher Verlag.

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    Important book on the biogeography of the desert flora of the Sahara.

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  • Roig, Fidel A., Sergio Roig-Juñent, and V. Corbalan. 2009. The biogeography of the Monte desert. Journal of Arid Environments 73:164–172.

    DOI: 10.1016/j.jaridenv.2008.07.016Save Citation »Export Citation »E-mail Citation »

    This desert shows remarkable similarities with the Mojave and Sonoran deserts of Mexico and the United States. These authors consider this an exception because far more genera share affinities with the adjacent Chaco and Patagonian regions. Most enigmatic are the so-called paleo-endemics that are of either Pangean or Gondwanan origin.

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  • Shmida, Avi. 1985. Biogeography of the desert flora. In Hot deserts and arid shrublands. Edited by Michael Evenari, Imanuel Noy-Meir, and David W. Goodall, 23–77. Ecosystems of the World 12B. Amsterdam: Elsevier.

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    Unquestionably the magnum opus on desert phytogeography. Indicates some interesting patterns of origin of desert plants.

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  • Shreve, Forrest. 1942. The desert vegetation of North America. Botanical Review 8:195–246.

    DOI: 10.1007/BF02882228Save Citation »Export Citation »E-mail Citation »

    One of the earliest studies of desert vegetation and the biogeographic origins of North American desert plants.

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Animals

Owing to the largely mesic origin of many desert animal taxa, there is little comparison that can effectively be made across deserts. However, there are still some very important patterns that can be elucidated. Most importantly, species:area relationships and local diversity, interhabitat diversity, and regional diversity among continents can be compared. Mares 1993 has also stressed the importance of convergence of species resulting from the strong selection pressures on organisms imposed by the desert environment. Brown 1971, a classic study, shows that mammals can be “trapped” on mountaintops within deserts, leading to a process now known as “faunal relaxation.” Pianka 1986, Morton and Davidson 1988, Morton 1993, Kelt, et al. 1996, Shenbrot, et al. 1999, and James and Shine 2000 all discuss aspects of coexistence of desert organisms and why there are so many of certain types in particular deserts. James and Shine 2000 introduces an important point with regard to Australian desert diversity—there are so many species of desert lizard because the Australian deserts are so large—emphasizing the point that area alone is reason for such diversity. However, it does not explain why these species coexist (see Kotler and Brown 1988, cited under Competition), nor does it explain why lizards rather than other taxa are so dominant.

  • Brown, James H. 1971. Mammals on mountaintops: Nonequilibrium island biogeography. American Naturalist 105:467–478.

    DOI: 10.1086/282738Save Citation »Export Citation »E-mail Citation »

    Classic description of small mammals living on mountaintops (“islands”) surrounded by a “sea” of desert in Nevada, later known as “faunal relaxation.” Species are lost from these “islands” because they are surrounded by inhospitable desert climate, and small areas lose more species (i.e., higher extinction rate) than large areas.

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  • Kelt, Douglas A., James H. Brown, Edward J. Heske, et al. 1996. Community structure of desert small mammals: Comparisons across four continents. Ecology 77:746–761.

    DOI: 10.2307/2265499Save Citation »Export Citation »E-mail Citation »

    Kelt and colleagues recorded small mammal diversity in seven deserts across four continents. Deserts in the Northern Hemisphere possessed more granivores, the Turkestan desert of central Asia more folivores, and the Australian deserts more carnivorous small mammals than other deserts (see also Mares 1993).

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  • Mares, Michael A. 1993. Desert rodents, seed consumption and convergence: The evolutionary shuffling of adaptations. BioScience 43:372–379.

    DOI: 10.2307/1312045Save Citation »Export Citation »E-mail Citation »

    Mares believes that broad comparative studies that consider suites of characters across communities will tend to detect strong convergence, whereas those that search for perfect pairings of putative ecological equivalents will tend to conclude that convergence is uncommon.

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  • Morton, Steven R. 1993. Determinants of diversity in animal communities of arid Australia. In Species diversity in ecological communities: Historical and geographical perspectives. Edited by Robert E. Ricklefs and Dolph Schluter, 159–169. Chicago: Univ. of Chicago Press.

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    Morton showed that Australian arid regions are dissimilar to North American deserts in local and regional diversity in ants, termites, reptiles, birds, and small mammals. Australian termites, ants, lizards, granivorous birds, and insectivorous small mammals had higher diversity than in North America, but Australian rodent communities were less diverse.

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  • James, Craig D., and Richard Shine. 2000. Why are there so many coexisting species of lizards in Australian deserts? Oecologia 125:127–141.

    DOI: 10.1007/PL00008884Save Citation »Export Citation »E-mail Citation »

    Australian desert skinks of the genus Ctenotus are far more diverse locally than their mesic counterparts. The arid-zone species are more widely distributed than the mesic species because of the greater climatic homogeneity in the arid zone, and they have a wider range to disperse over. Consequently, more species can coexist.

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  • Morton, Steven R., and Diane W. Davidson. 1988. Comparative structure of harvester ant communities in arid Australia and North America. Ecological Monographs 58:19–38.

    DOI: 10.2307/1942632Save Citation »Export Citation »E-mail Citation »

    There are more harvester ant species and fewer mammalian granivores in Australian deserts than in North American deserts. The authors found that Australian and North American harvester ant communities were similar in species richness, species diversity, numbers of common species, and abundance of ants.

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  • Pianka, Eric R. 1986. Ecology and natural history of desert lizards. Princeton, NJ: Princeton Univ. Press.

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    Classic study written by the doyen of desert lizard researchers. Strong focus on the effects of competition on lizard ecology (contra Huey and Bennett 1987, cited under Animals: Ecophysiology, which emphasizes running speed to escape predators as a factor of key importance).

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  • Shenbrot, Georgy, Boris Krasnov, and Konstantin A. Rogovin. 1999. Spatial ecology of desert rodent communities. Berlin: Springer.

    DOI: 10.1007/978-3-642-60023-4Save Citation »Export Citation »E-mail Citation »

    Covers the biogeography and small-scale interactions among desert rodents, with an important contribution on little-known Asian desert rodents.

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Population Processes

One can essentially divide research into population processes into two sections: ecophysiology and population dynamics. This partly reflects the history of research into this biome, where there was much interest in the adaptations of Plants and Animals to this extreme environment; considerably later, interest developed in what was perceived to be relatively simple population dynamics. The apparent simplicity of population dynamics in deserts has not always proved to be so (see Indirect Interactions, for example). There has also been considerable interest more recently in removing the effects of phylogeny from statements claiming particular adaptations of organisms.

Plants

Much interest in population processes of plants has centered on discovering the ecophysiological mechanisms that plants employ to survive in desert environments. Nonetheless, there is considerable interest in the factors that cause populations to change in size and how populations may trade off mean and variance in reproductive output. More recently, there has been considerable interest in the evolution of species, particularly with regard to adaptive radiation.

Ecophysiology

Here, as in the subsection Animals: Ecophysiology, there has been emphasis on adaptations to extreme environments. In many ways, in the case of plant ecophysiology, it is the use of unique technical approaches that has led to valuable insights (Smith, et al. 1997). Various techniques have been used to understand mechanisms such as water and nutrient uptake (Richards and Caldwell 1987; Ehleringer 1993; Schulze, et al. 1998; Nobel 2003) and salinity tolerance (Flowers and Colmer 2008). However, even such elementary techniques such as distribution maps (Hattersley 1983) and watering experiments (Hartsock and Nobel 1976; Smith, et al. 1997) have revealed new insights.

  • Ehleringer, James R. 1993. Carbon and water relations in desert plants: An isotopic perspective. In Stable isotopes and plant carbon/water relations. Edited by James R. Ehleringer, Anthony E. Hall, and Graham D. Farquhar, 155–172. San Diego, CA: Academic Press.

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    A classic review of the use of stable isotopes to demonstrate the effectiveness of various nutrient and water uptake strategies.

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  • Flowers, Timothy J., and Timothy D. Colmer. 2008. Salinity tolerance in halophytes. New Phytologist 28:89–121.

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    Halophytes constitute about 1 percent of the world’s flora and are highly concentrated in desert environments. The tolerance of all halophytes to salinity relies on controlled uptake and compartmentalization of salts and the synthesis of organic “compatible” solutes, even where salt glands are operative.

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  • Hartsock, Terry L., and Park S. Nobel. 1976. Watering converts a CAM plant to daytime CO2 uptake. Nature 262:574–576.

    DOI: 10.1038/262574b0Save Citation »Export Citation »E-mail Citation »

    Conventionally, plants with CAM photosynthesis take up CO2 at night. However, when Agave deserti was watered, it switched to a more conventional CO2 uptake pattern, indicating that there is plasticity in this mode of photosynthesis that is dependent on the availability of water.

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  • Hattersley, Paul W. 1983. The distribution of C3 and C4 grasses in Australia in relation to climate. Oecologia 57:113–128.

    DOI: 10.1007/BF00379569Save Citation »Export Citation »E-mail Citation »

    Grasses with C4 photosynthesis tend to be most abundant in hot, dry places. Hattersley found that C4 grass species in Australia increase in number with increasing rainfall, within their “preferred” temperature regime. C3 grass species are most numerous where the spring is cool and wet.

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  • Nobel, Park S. 2003. Environmental biology of agaves and cacti. Cambridge, UK: Cambridge Univ. Press.

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    First published in hardcover in 1988, this new paperback version by one of the doyens of desert plant ecophysiology is a very effective summary of his contributions to the ecophysiology and ecology of agaves and cacti.

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  • Richards, James H., and Martyn M. Caldwell. 1987. Hydraulic lift: Substantial nocturnal water transport between soil layers by Artemisia tridentata roots. Oecologia 73:486–489.

    DOI: 10.1007/BF00379405Save Citation »Export Citation »E-mail Citation »

    This is the first paper to demonstrate that deep-rooted plants brought water to the surface and then, at night, lost the surface water to the surroundings. Often this water was taken up by surrounding plants.

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  • Schulze, E.-Detlef, Martyn M. Caldwell, Josep Canadell, et al. 1998. Downward flux of water through roots (i.e. inverse hydraulic lift) in dry Kalahari sands. Oecologia 115:460–462.

    DOI: 10.1007/s004420050541Save Citation »Export Citation »E-mail Citation »

    Here, unlike the Richards and Caldwell 1987 hydraulic lift study, water is used to provide a moist area for new root growth in dry sands.

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  • Smith, Stanley D., Russell K. Monson, and Jay E. Anderson. 1997. Physiological ecology of North American desert plants. Berlin: Springer.

    DOI: 10.1007/978-3-642-59212-6Save Citation »Export Citation »E-mail Citation »

    An important contribution that effectively lays the framework for understanding the ecophysiology of many desert plants, not just those of North America.

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Population Dynamics

Belnap and Lange 2003 and Eldridge and Tozer 1997 introduce frequently ignored groups of organisms—lichens and bryophytes, which are extremely important in desert environments, especially because lichens, in particular, retard the rate of soil runoff and reduce subsequent evaporation. Zohary 1937 and Ellner and Shmida 1981 approach the issue of the absence of long-distance dispersal mechanisms in desert plants from different points of view (see also van Rheede van Oudtshoorn and van Rooyen 1999), although probably these arguments are not mutually exclusive (see Ward 2009, cited under General Overviews). Two other studies examine the nature of adaptation to desert environments. Sandquist and Ehleringer 2003 performed a common garden experiment, a classic approach to discovering adaptive characteristics of organisms, and showed that two populations of Encelia have diverged. Ellis, et al. 2006, a study of the evolution of plants in the Aizoaceae (formerly Mesembryanthemaceae), echoes some of the points made by Willert, et al. 1992 and Ihlenfeldt 1994 (cited under Biogeography: Plants) with regard to the small spatial scale over which radiation can be achieved. Venable 2007 introduces a fascinating topic, the interplay between mean reproductive output and its variance, showing that annual plants bet-hedge—that is, they trade off mean and variance against each other.

  • Belnap, Jayne, and Otto L. Lange. 2003. Biological soil crusts: Structure, function, and management. Berlin: Springer.

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    Biological soil crust consists of a variety of organisms such as cyanobacteria, algae, fungi, and lichens which aggregate with soil particles. This crust influences water runoff and infiltration, protects the soil surface from erosion, and contributes nutrients. Disturbing the soil breaks up the crust, compromising its stability, structure, and productivity.

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  • Eldridge, David J., and Merrin E. Tozer. 1997. A practical guide to soil lichens and bryophytes of Australia’s dry country. Sydney, Australia: Department of Land and Water Conservation.

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    Richly illustrated, with a very interesting text on the roles of biological soil crusts in dry environments, the components of the soil crust, and their roles under grazing, fire, mining, and cultivation. Accessible to the nonspecialist.

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  • Ellis, Allan G., Arthur E. Weis, and Brandon S. Gaut. 2006. Evolutionary radiation of “stone plants” in the genus Argyroderma (Aizoaceae): Unraveling the effects of landscape, habitat and flowering time. Evolution 60:39–55.

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    Convincing demonstration of fine-scale heterogeneity and its effects on the evolution in this genus of stone plants from Namaqualand, South Africa.

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  • Ellner, Stephen P., and Avi Shmida. 1981. Why are adaptations for long-range seed dispersal rare in desert plants? Oecologia 53:133–144.

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    There are five possible alternative reasons to the “mother plant” hypothesis in Zohary 1937 that are essentially due to either low benefits to be derived from long-distance dispersal rather than a benefit of short-distance dispersal. Adaptations to prevent dispersal are a side effect of mechanisms whose adaptive value is not directly related to dispersal.

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  • Sandquist, Darren R., and James R. Ehleringer. 2003. Carbon isotope discrimination differences within and between contrasting populations of Encelia farinosa raised under common-environment conditions. Oecologia 134:463–470.

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    There was selection imposed by variation in rainfall and drought that resulted in genetic divergence of these Encelia populations. Leaf pubescence reduces heat load and reduces the need to rely on transpirational cooling. There is a tradeoff with leaf hair production and the reflection of photosynthetically active radiation.

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  • van Rheede van Oudtshoorn, Karen, and Margaretha W. van Rooyen. 1999. Dispersal biology of desert plants. Berlin: Springer.

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    Very useful descriptions of dispersal mechanisms employed by plants.

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  • Venable, D. Lawrence. 2007. Bet hedging in a guild of desert annuals. Ecology 88:1086–1090.

    DOI: 10.1890/06-1495Save Citation »Export Citation »E-mail Citation »

    Convincing demonstration of the tradeoff between mean and variance in reproductive output (called “bet-hedging”) in annuals in the desert of Arizona.

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  • Willert, Dieter J. von, Benno M. Eller, Marinus J. A. Werger, Enno Brinckmann, and Hans-Dieter Ihlenfeldt. 1992. Life strategies of succulents in deserts, with special reference to the Namib desert. Cambridge, UK: Cambridge Univ. Press.

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    A useful introduction to succulents. Some of the text is accessible to nonspecialists, and much of it is accessible to senior undergraduate students. Largely focuses on the physiological mechanisms behind Crassulacean Acid Metabolism (CAM) and the ecological significance thereof.

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  • Zohary, Michael. 1937. Die verbreitungsokologischen verhaltnisse der pflanzen Palaestinas. Beihefte zum Botanischen Zentralblatt A56:1–155.

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    In German. Superb introduction to the issue of plant dispersal in deserts. Claims that dispersal is not selected for because the ideal living circumstances are right next to the “mother plant.” Compare this with the arguments in Ellner and Shmida 1981 (see also Ward 2009, cited under General Overviews).

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Animals

As is the case in Plants, there has been much interest in discovering unique features of desert animals that are adaptive characteristics. More recently, scientists have realized that they need to account for phylogenetic effects that mask the detection of these unique adaptations. With regard to animal population dynamics, there are unique adaptations for desert existence that warrant changes in the timing of development and dispersal within the desert environment.

Ecophysiology

Much interest in desert animal ecophysiology stems from the pioneering work of Knut Schmidt-Nielsen, summarized in Schmidt-Nielsen 1965. This has ranged from discoveries of fog basking in Namib desert beetles (Hamilton and Seely 1976) to mammals that are effectively ectotherms in the cold Namib nights (Fielden, et al. 1990). There has been much progress in discoveries of adaptations of desert organisms since Schmidt-Nielsen 1965, when species were considered to have desert adaptations merely because they had low basal metabolic rates and effective evaporation mechanisms. With the discovery that species evolved within clades that were already desert-adapted, much recent focus has turned to removing the effects of phylogeny to discover the adaptive nature of physiological mechanisms (Huey and Bennett 1987; Garland, et al. 1991; Ward and Seely 1996; Tieleman, et al. 2003; Williams, et al. 2004).

  • Fielden, Laura J., Jon P. Waggoner, Michael R. Perrin, and Graham C. Hickman. 1990. Thermoregulation in the Namib Desert golden mole, Eremitalpa granti namibensis (Chrysochloridae). Journal of Arid Environments 18:221–237.

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    An important study showing that a desert mammal could also be an effective ectotherm, lowering its body temperature at night to that of the ambient, thereby reducing its energetic costs.

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  • Garland, Theodore, Raymond B. Huey, and Albert F. Bennett. 1991. Phylogeny and coadaptation of thermal physiology in lizards: A re-analysis. Evolution 45:1969–1975.

    DOI: 10.2307/2409846Save Citation »Export Citation »E-mail Citation »

    A reexamination of Huey and Bennett 1987, a classic study of the effects of phylogeny on coadaptation in lizards, using a more sophisticated phylogenetic approach. Some of the claimed significant effects were rejected in this analysis.

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  • Hamilton, William J., and Mary K. Seely. 1976. Fog basking by the Namib Desert beetle Onymacris unguicularis. Nature 262:284–285.

    DOI: 10.1038/262284a0Save Citation »Export Citation »E-mail Citation »

    Showed that an insect could use the coastal fogs to acquire water in an otherwise dry environment by allowing water to dribble down its back into its mouth. A similar paper was published by the same authors on fog catchment trenches of Lepidochora beetles in Science (193:484–486) in the same year.

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  • Huey, Raymond B., and Albert F. Bennett. 1987. Phylogenetic studies of coadaptation: Preferred temperatures versus optimal performance temperatures of lizards. Evolution 41:1098–1115.

    DOI: 10.2307/2409194Save Citation »Export Citation »E-mail Citation »

    Important study examining the importance of removing the effects of phylogeny on the body temperatures of lizards. First study to examine this in an ectotherm. Coadaptation of preferred body temperatures and optimal performance temperatures was found. See Garland, et al. 1991 for refinements.

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  • Schmidt-Nielsen, Knut. 1965. Desert animals: Physiological problems of heat and water. London: Clarendon.

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    The classic study that prompted so many animal ecophysiologists to enter this field.

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  • Tieleman, B. Irene, Joseph B. Williams, and Paulette Bloomer. 2003. Adaptation of metabolism and evaporative water loss along an aridity gradient. Proceedings of the Royal Society of London B: Biological Sciences 270:207–214.

    DOI: 10.1098/rspb.2002.2205Save Citation »Export Citation »E-mail Citation »

    These authors examined basal metabolic rate and evaporative water loss in twenty-two species of larks, including desert-dwelling larks, mostly from Saudi Arabia and Iran, and mesic species from Europe and elsewhere. They removed the effects of phylogeny and found that basal metabolic rate declined with increasing aridity.

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  • Ward, David, and Mary K. Seely. 1996. Adaptation and constraint in the evolution of the physiology and behavior of the Namib desert tenebrionid beetle genus Onymacris. Evolution 50:1231–1240.

    DOI: 10.2307/2410663Save Citation »Export Citation »E-mail Citation »

    In the first study of an insect genus, showed adaptations to the harsh Namib desert environment once the effects of phylogeny had been removed. Desert-interior beetle species evolved longer legs to raise themselves out of the hot boundary layer, and some species evolved wax to reduced evaporative water loss.

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  • Williams, Joseph B., Agusti Muñoz-Garcia, Stephane Ostrowski, and B. Irene Tieleman. 2004. A phylogenetic analysis of basal metabolism, total evaporative water loss, and life-history among foxes from desert and mesic regions. Journal of Comparative Physiology B 174:29–39.

    DOI: 10.1007/s00360-003-0386-0Save Citation »Export Citation »E-mail Citation »

    Desert foxes have a basal metabolic rate comparable to other, more mesic species, although they have a lower total evaporative water loss. Mostly these differences could be ascribed to the smaller body sizes of these foxes, reducing total energy requirements.

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Population Dynamics

Caughley and Gunn 1993 stresses that short-term fluctuations in the weather can lead to long-term fluctuations in the dynamics of animals. Lubin, et al. 1993 shows how movements of spiders improve their reproductive success, while both Williams 1985 and Newman 1994 show how key features of aquatic organisms can be altered in an adaptive way to maximize their fitness. Jones and Shachak 1990 shows how tiny snails can de facto alter the nutrient status of deserts, benefiting the surroundings with increased nitrogen levels.

  • Caughley, Graeme, and Anne Gunn. 1993. Dynamics of large herbivores in deserts: Kangaroos and caribou. Oikos 67:47–55.

    DOI: 10.2307/3545094Save Citation »Export Citation »E-mail Citation »

    Caughley and Gunn showed that long-term fluctuations without obvious periodicity are a consequence of unpredictable short-term fluctuations in weather. Even when the weather had no time trend, there were noticeable trends in numbers of kangaroos, varying over ten to twenty years.

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  • Jones, Clive G., and Moshe Shachak. 1990. Fertilization of the desert soil by rock-eating snails. Nature 346:839–841.

    DOI: 10.1038/346839a0Save Citation »Export Citation »E-mail Citation »

    On days with dew, small desert snails consume rock-dwelling lichens. They also consume and defecate on the rocks surrounding the lichens. This amounts to soil formation similar to wind-borne dust deposited in the Negev desert. The snails transferred about 10 percent of total annual soil nitrogen inputs.

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  • Lubin, Yael, Stephen Ellner, and Mandy Kotzman. 1993. Web relocation and habitat selection in desert widow spider. Ecology 74:1915–1928.

    DOI: 10.2307/1940835Save Citation »Export Citation »E-mail Citation »

    These Negev desert spiders relocate their webs to progressively larger shrubs as they grow, which results in larger webs being built and ultimately higher fitness. The main cost to relocation was the high mortality of the spiders (otherwise the spiders would presumably have all entered large shrubs from the onset).

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  • Newman, Robert A. 1994. Genetic variation for phenotypic plasticity in the larval life history of spadefoot toads (Scaphiopus couchii). Evolution 48:1773–1785.

    DOI: 10.2307/2410507Save Citation »Export Citation »E-mail Citation »

    Spadefoot tadpoles responded adaptively to pond duration by metamorphosing earlier in short-duration ponds but delayed metamorphosis and were larger when they emerged in long-duration ponds. When either the temperature was high or there was little food available, there was a genetic correlation between age and size at metamorphosis.

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  • Williams, William D. 1985. Biotic adaptations in temporary lentic waters, with special reference to those in semi-arid and arid regions. Hydrobiologia 125:85–110.

    DOI: 10.1007/BF00045928Save Citation »Export Citation »E-mail Citation »

    Williams reviews floral and faunal adaptations to life in temporary waters in arid and semiarid zones, focusing on the adaptations to stressful conditions such as might occur in temporary ponds.

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Community Ecology

Interest in the biotic interactions among species has been considerable in deserts, particularly because they are perceived to be simple ecosystems. This is not always true (see Indirect Interactions, for example). There has been considerable progress in our understanding of desert communities over the past fifty years (compare, for example, Orians and Solbrig 1977, Polis 1991, and Miriti 2006, the last cited under Facilitation).

  • Orians, Gordon H., and Otto T. Solbrig, eds. 1977. Convergent evolution in warm deserts. Stroudsburg, PA: Dowden, Hutchinson & Ross.

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    Useful summary of the Desert Scrub project of the International Biological Program. There are lots of interesting natural history and ecological issues that were examined. Chapters include “The strategies and community patterns of desert plants,” “The strategies and community patterns of desert animals,” and “Degree of convergence of ecosystem characteristics.”

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  • Polis, Gary A., ed. 1991. The ecology of desert communities. Tucson: Arizona Univ. Press.

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    Superb papers on various aspects of desert communities. No longer in print, but photocopies are available from the publisher.

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Competition

Some of the most important demonstrations of competition between species come from deserts (e.g., Brown and Davidson 1977; Kotler and Brown 1988; Heske, et al. 1994). Usually, these studies have involved small mammals, particularly in the North American and Middle Eastern deserts (Abramsky and Rosenzweig 1984, cited under Productivity, Diversity, and Food Webs; Mitchell, et al. 1990 and Veech 2001, both cited under Indirect Interactions). Demonstrations of interspecific competition among plant species are less common, but there are a number of prominent examples (Friedman 1971). Goldberg and Novoplansky 1997 stresses that competition, at least among annual plants, may be restricted to periods of maximal resource availability. There are also some studies that have not shown interspecific competition, particularly among birds (Repasky and Schluter 1996), despite claims to the contrary (Dunning 1986).

  • Brown, James H., and Diane W. Davidson. 1977. Competition between seed-eating rodents and ants in desert ecosystems. Science 196:880–882.

    DOI: 10.1126/science.196.4292.880Save Citation »Export Citation »E-mail Citation »

    A classic study indicating intraguild competition in desert-dwelling species. There were extensive overlaps in diet, and reciprocal increases when one taxon was excluded. Carlos Galindo viewed this as pseudoreplication and lack of replication (Do desert rodent populations increase when ants are removed? Ecology 67:1422–1423).

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  • Dunning, John B. 1986. Shrub-steppe bird assemblages revisited: Implications for community theory. American Naturalist 128:82–98.

    DOI: 10.1086/284541Save Citation »Export Citation »E-mail Citation »

    The role of interspecific competition in structuring shrub-steppe communities of birds was hotly debated, because no evidence was found of competition among breeding birds in these North American habitats. This absence of competition may occur because they are competing on their wintering grounds (but see Repasky and Schluter 1996).

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  • Friedman, Jacob. 1971. The effect of competition by adult Zygophyllum dumosum Boiss. on seedlings of Artemisia herba-alba Asso in the Negev desert of Israel. Journal of Ecology 59:775–782.

    DOI: 10.2307/2258139Save Citation »Export Citation »E-mail Citation »

    First study to show that interspecific competition occurred among desert perennial plants.

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  • Goldberg, Deborah E., and Ariel Novoplansky. 1997. On the relative importance of competition in unproductive environments. Journal of Ecology 85:409–418.

    DOI: 10.2307/2960565Save Citation »Export Citation »E-mail Citation »

    Grime considered competition to be important only in productive environments, while Tilman considered competition to be important in unproductive environments. Goldberg and Novoplansky believe that competition may be restricted to brief periods of the year when large amounts of resources are available.

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  • Heske, Edward J., James H. Brown, and Shahroukh Mistry. 1994. Long-term experimental study of a Chihuahuan Desert rodent community: 13 years of competition. Ecology 75:438–445.

    DOI: 10.2307/1939547Save Citation »Export Citation »E-mail Citation »

    Four rodent species showed direct competitive effects of kangaroo rat removal, one species showed both direct and indirect effects (due to vegetation changes and habitat selection), and two species responded indirectly to vegetation changes (see also Brown and Heske 1990, cited under Indirect Interactions).

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  • Kotler, Burt P., and Joel S. Brown. 1988. Environmental heterogeneity and the coexistence of desert rodents. Annual Review of Ecology and Systematics 19:281–307.

    DOI: 10.1146/annurev.es.19.110188.001433Save Citation »Export Citation »E-mail Citation »

    Excellent review of the coexistence of desert rodents, with a strong emphasis on optimal foraging assumptions.

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  • Repasky, Richard R., and Dolph Schluter. 1996. Habitat distributions of wintering sparrows: Foraging success in a transplant experiment. Ecology 77:452–460.

    DOI: 10.2307/2265621Save Citation »Export Citation »E-mail Citation »

    Found that sparrows in the Sonoran Desert in southern California did not forage most efficiently in their favored habitats, contra expectations of interspecific competition. The authors concluded that immediate foraging gains do not explain habitat distributions of these birds (i.e., inconsistent with claims in Dunning 1986).

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Facilitation

There was a strong focus on the role of competition in structuring desert communities. More recently, however, there has been a switch to examining the role of facilitation, where one species benefits another. In many cases there was no cost to the benefactor (Franco and Nobel 1989), but in other cases, when the recipient grows larger it competes with the benefactor (McAuliffe 1984, Aguiar and Sala 1994, Miriti 2006).

  • Aguiar, Martín R., and Osvaldo E. Sala. 1994. Competition, facilitation, seed distribution and the origin of patches in a Patagonian steppe. Oikos 70:26–34.

    DOI: 10.2307/3545695Save Citation »Export Citation »E-mail Citation »

    Aguiar and Sala showed that when shrubs are young and small, facilitation results in the formation of a dense ring of grasses underneath the shrubs. When the shrub grows larger, competition overshadows facilitation.

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  • Franco, Augusto C., and Park S. Nobel. 1989. Effect of nurse plants on the microhabitat and growth of cacti. Journal of Ecology 77:870–886.

    DOI: 10.2307/2260991Save Citation »Export Citation »E-mail Citation »

    Nurse plants facilitated seedling establishment of two species of cactus by reducing high temperatures near the soil surface and provided a microhabitat with a higher soil nitrogen level. However, shading and competition for water with the nurse plants markedly reduced cactus seedling growth.

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  • McAuliffe, Joseph R. 1984. Sahuaro-nurse tree associations in the Sonoran Desert: Competitive effects of sahuaros. Oecologia 65:82–85.

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    Sahuaro cacti are dependent on a nurse tree, the foothill paloverde. McAuliffe found that there was increased stem dieback as well as greater mortality in this common nurse tree. This interaction accelerates the local loss of individual nurse trees, indicating a significant cost of competition to the nurse tree.

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  • Miriti, Maria N. 2006. Ontogenetic shift from facilitation to competition in a desert shrub. Journal of Ecology 94:973–979.

    DOI: 10.1111/j.1365-2745.2006.01138.xSave Citation »Export Citation »E-mail Citation »

    A fine study showing how desert shrubs may benefit from the presence of adult plants when they are young but compete once they become adults.

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Predation

Although some of the literature focuses on the direct and negative consequences of predation on populations (see Shachak, et al. 1981; Groner and Ayal 2001; Johnson, et al. 2007), desert ecology has been prominent for stressing that it is also the risk of being eaten that affects the use of habitats and the time of activity. Thus, in deserts, much work has focused on the facts that animals are less active on dark nights than on moonlit nights (see Bouskila 1995, Brown 1988, Kotler 1984).

  • Bouskila, Amos. 1995. Interactions between predation risk and competition: A field study of kangaroo rats and snakes. Ecology 76:165–178.

    DOI: 10.2307/1940639Save Citation »Export Citation »E-mail Citation »

    Two species of kangaroo rats preferred to forage in the exposed microhabitat and avoided bush microhabitat in the Mojave Desert, opposite to the preference of the main rodent-eating snake. Where snakes were present, one kangaroo rat avoided the bush microhabitat because of competition with the other kangaroo rat.

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  • Brown, Joel S. 1988. Patch use as an indicator of habitat preference, predation risk, and competition. Behavioral Ecology and Sociobiology 22:37–47.

    DOI: 10.1007/BF00395696Save Citation »Export Citation »E-mail Citation »

    Key theoretical reference showing that it is not only the direct (negative) impact of predation that affects community dynamics, but also the risk of predation that determines how and when habitats are used.

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  • Groner, Eli, and Yoram Ayal. 2001. The interaction between bird predation and plant cover in determining habitat occupancy of darkling beetles. Oikos 93:22–31.

    DOI: 10.1034/j.1600-0706.2001.930102.xSave Citation »Export Citation »E-mail Citation »

    Darkling beetles in the Negev desert of Israel exhibit size-related habitat segregation, with larger species found in denser cover. Greater plant cover reduced the predation efficiency of the most common predatory birds, white storks and stone curlews. They also found that these birds preferred larger species.

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  • Johnson, Christopher N., Joanne L. Isaac, and Diana O. Fisher. 2007. Rarity of a top predator triggers continent-wide collapse of mammal prey: Dingoes and marsupials in Australia. Proceedings of the Royal Society of London B: Biological Sciences 114:341–346.

    DOI: 10.1098/rspb.2006.3711Save Citation »Export Citation »E-mail Citation »

    A very good example of “mesopredator” release effects on marsupial mammal prey in Australia, where top predators in terrestrial ecosystems may reduce populations of smaller predators (called “mesopredators”) that could otherwise become over-abundant and cause declines and extinctions of some prey.

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  • Kotler, Burt P. 1984. Risk of predation and the structure of desert rodent communities. Ecology 65:689–701.

    DOI: 10.2307/1938041Save Citation »Export Citation »E-mail Citation »

    Very convincing study of the effects of the risk of predation (rather than the population effects of predation per se) in the US state of Nevada.

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  • Shachak, Moshe, Uriel N. Safriel, and Richard Hunum. 1981. An exceptional event of predation on desert snails by migratory thrushes in the Negev desert, Israel. Ecology 62:1441–1449.

    DOI: 10.2307/1941500Save Citation »Export Citation »E-mail Citation »

    A remarkable description of the effects of predation by migratory thrushes passing through the Negev desert that subsequently affected the population dynamics of desert snails for many years thereafter.

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Mutualism

Some of the most convincing examples of mutualism come from desert organisms, such as the yucca and yucca moth (Pellmyr 2003), senita cactus and senita moth (Fleming and Holland 1998), which are obligate mutualisms, and the facultative mutualisms between cacti and cactus-tending ants (Miller 2007). All mutualisms assume that the mutualism entails a cost to both parties, but the benefits outweigh the costs, otherwise the partners would not engage in the mutualism (Rasa 1983).

  • Fleming, Ted H., and J. Nathaniel Holland. 1998. The evolution of obligate pollination mutualism: Senita cactus and senita moth. Oecologia 114:368–374.

    DOI: 10.1007/s004420050459Save Citation »Export Citation »E-mail Citation »

    The senita cactus is a night-blooming, self-incompatible columnar cactus. Beginning at sunset, its flowers are visited by senita moth females, which oviposit a single egg. The moth larvae destroy about 30 percent of the seeds resulting from pollination by senita moths. There are many similarities with the yucca/yucca moth mutualism.

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  • Miller, Tom E. X. 2007. Does having multiple partners weaken the benefits of facultative mutualism? A test with cacti and cactus-tending ants. Oikos 116:500–512.

    DOI: 10.1111/j.2007.0030-1299.15317.xSave Citation »Export Citation »E-mail Citation »

    Interspecific facultative mutualisms typically involve guilds of interacting species. Only one ant species provided protection against herbivores and seed predators. Simulations of cactus lifetime reproductive output indicated that associating with high- and low-quality mutualists did not significantly reduce plant benefits relative to an exclusive single ant species-cactus association.

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  • Pellmyr, Olle. 2003. Yuccas, yucca moths and coevolution: A review. Annals of the Missouri Botanical Gardens 90:35–55.

    DOI: 10.2307/3298524Save Citation »Export Citation »E-mail Citation »

    Important review article on the best-known mutualist species.

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  • Rasa, O. Anne E. 1983. Dwarf mongoose and hornbill mutualism in the Taru Desert, Kenya. Behavioral Ecology and Sociobiology 12:181–190.

    DOI: 10.1007/BF00290770Save Citation »Export Citation »E-mail Citation »

    Both the dwarf mongooses and two hornbill species have very high overlap in their food items. These three species face high predation from raptorial birds. The hornbills and the mongooses flock together when alarmed and alter their behavior to more effectively avoid predation.

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Indirect Interactions

There are a number of ways in which one species can have indirect effects on other species. For example, keystone species affect many other species via predation or facilitation (Brown and Heske 1990; Dean, et al. 1999). Apparent competition occurs where two species seem to be competing with each other (they have negative effects on each other’s densities), but it is actually caused by predation by a third species (Veech 2001). In priority effects, the first species to occupy a habitat dominates that habitat (Blaustein and Margalit 1996). Finally, there is exploitation competition, where one species has a net negative effect on the density of the other species by virtue of a shared food resource (Mitchell, et al. 1990).

  • Blaustein, Leon, and Joel Margalit. 1996. Priority effects in temporary pools: Nature and outcome of mosquito larva–toad tadpole interactions depend on order of entrance. Journal of Animal Ecology 65:77–84.

    DOI: 10.2307/5701Save Citation »Export Citation »E-mail Citation »

    This novel study showed that the first predator in a temporary pond, either a mosquito larva or a tadpole, would eat the other predator. These authors showed experimentally by manipulating the order of entry that this interaction was a priority effect.

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  • Brown, James H., and Edward J. Heske. 1990. Control of a desert–grassland transition by a keystone rodent guild. Science 250:1705–1707.

    DOI: 10.1126/science.250.4988.1705Save Citation »Export Citation »E-mail Citation »

    Twelve years after three kangaroo rat species were removed, the density of tall perennial plants and annual grasses increased. Rodent species typical of arid grasslands then invaded the desert areas. Brown and Heske consider this as evidence that these kangaroo rats are keystone species.

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  • Dean, W. Richard J., Suzanne J. Milton, and Florian Jeltsch. 1999. Large trees, fertile islands, and birds in arid savannas. Journal of Arid Environments 41:61–78.

    DOI: 10.1006/jare.1998.0455Save Citation »Export Citation »E-mail Citation »

    Very nice demonstration of keystone species effect in a Kalahari desert tree, Acacia erioloba.

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  • Mitchell, William A., Zvika Abramsky, Burt P. Kotler, Berry Pinshow, and Joel S. Brown. 1990. The effect of competition on foraging activity in desert rodents: Theory and experiments. Ecology 71:844–854.

    DOI: 10.2307/1937356Save Citation »Export Citation »E-mail Citation »

    Interesting study comparing the effects of competition between two Negev desert rodents, which resulted in a reduction in the activity of the weaker competitor due to the reduced benefit of foraging. This is exploitation competition, an indirect effect where the species compete for food but do not directly interact.

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  • Veech, Joseph A. 2001. The foraging behavior of granivorous rodents and short-term apparent competition among seeds. Behavioral Ecology 12:467–474.

    DOI: 10.1093/beheco/12.4.467Save Citation »Export Citation »E-mail Citation »

    This Nevada study involved the apparent competition of one plant species on another; there was a negative correlation between the densities of the two plant species. However, this was mediated by the predator, a granivorous desert rodent.

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Productivity, Diversity, and Food Webs

Much recent research has found that there is a linear relationship between productivity and species diversity, indicating that competition is unlikely to restrict the number of species that can occur at high productivity levels. However, Tilman has stressed that interspecific competition should reduce the number of species once productivity is high. Abramsky and Rosenzweig 1984 show that the curvilinear response occurs, at least for Negev desert rodents. Much recent research has attempted to relate the productivity of the desert environment with the number of trophic levels (see Ayal, et al. 2005) and with food web complexity (Polis, et al. 1991). Ayal, et al. 2005 introduces the role of macrodetritivory and the structure of the habitat as major influences on trophic structure, while Polis, et al. 1991 shows how there is tremendous complexity even in relatively simple desert food webs. This complexity arises for several reasons, not least being the fact that one cannot break down species according to size alone, and also because of ontogeny reversals where some animals eat other animals when they are small and the effect is reversed when they grow (see also “priority effects” recorded by Blaustein and Margalit 1996, cited under Indirect Interactions).

  • Abramsky, Zvika, and Michael L. Rosenzweig. 1984. Tilman’s predicted productivity–diversity relationship shown by desert rodents. Nature 309:150–151.

    DOI: 10.1038/309150a0Save Citation »Export Citation »E-mail Citation »

    David Tilman showed that there should be a unimodal relationship (rather than a positive correlation) between productivity and diversity. Abramsky and Rosenzweig showed, in Negev desert rodents, that there was indeed a curvilinear relationship between primary productivity and desert rodent diversity.

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  • Ayal, Yoram, Gary A. Polis, Yael Lubin, and Deborah E. Goldberg. 2005. How can high animal diversity be supported in low-productivity deserts? The role of macrodetritivory and habitat physiognomy. In Biodiversity in drylands: Toward a unified perspective. Edited by Moshe Shachak, James R. Gosz, Steward T. A. Pickett, and Avi Perevolotsky, 15–29. Oxford: Oxford Univ. Press.

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    Another effective description of the limitations of major trophic level hypotheses in desert environments, such as the Hairston-Smith-Slobodkin “Green World” hypothesis.

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  • Polis, Gary A. 1991. Complex trophic interactions in deserts: An empirical critique of food web theory. American Naturalist 138:123–155.

    DOI: 10.1086/285208Save Citation »Export Citation »E-mail Citation »

    An effective description of the complexity of desert ecosystems despite their apparent simplicity. Describes a number of reasons why the description of trophic levels is too elementary to encompass food webs.

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Ecosystem Processes

Many superb studies of nutrient levels and their effects on ecosystem processes have been done in deserts, largely because of their simplicity (few interacting species). Much of the focus has been on the role of nitrogen and phosphorus as soil nutrients (Schlesinger, et al. 1996; Aranibar, et al. 2004; Austin 2010; O’Halloran, et al. 2010), although other studies have considered the importance of soil biota (Whitford 1996). Many of these studies have been done at small spatial scales (e.g., Schlesinger, et al. 1996), largely because of the enormous spatial variation in nutrient availability. However, McAuliffe 1994 has shown that even at a landscape scale, significant and sometimes abrupt differences in vegetation type can occur, most of which are related to abrupt changes in geology. Another factor that can have large effects on ecosystem processes is the ratio of C3 to C4 plants in desert environments (Jackson, et al. 2002). Trees are C3 plants and appear to be benefiting from the heavy grazing imposed by domestic livestock in particular on the C4 grasses that are dominant in deserts and from changes in CO2 levels, mostly caused by humans (see Ward 2010, cited under Climate Change).

  • Aranibar, Julieta N., Luane Otter, Stephen A. Macko, Christopher J. W. Feral, Howard E. Epstein, Peter R. Dowty, Frank D. Eckardt, Herman H. Shugart, and Robert J. Swap. 2004. Nitrogen cycling in the soil–plant system along a precipitation gradient in the Kalahari sands. Global Change Biology 10:359–373.

    DOI: 10.1111/j.1365-2486.2003.00698.xSave Citation »Export Citation »E-mail Citation »

    Soil and plant N was more 15N enriched in arid than in humid areas and more so during wet than during dry years, indicating a strong effect of annual precipitation variability on nitrogen cycling. As found in other deserts, soil organic carbon and carbon:nitrogen ratios decreased with aridity.

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  • Austin, Amy T. 2010. Has water limited our imagination for aridland biogeochemistry? Trends in Ecology and Evolution 26:229–235.

    DOI: 10.1016/j.tree.2011.02.003Save Citation »Export Citation »E-mail Citation »

    This review of recent studies notes that there are alternative mechanisms to the concept that all soil processes in aridlands are proximately water-limited, as originally laid out by Noy-Meir 1973 (cited under Precipitation; see also Chesson, et al. 2004 under Precipitation). Spatial heterogeneity in soil nutrients is a modulator of biotic responses to water availability.

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  • Jackson, Robert B., Jay L. Banner, Esteban G. Jobbágy, William T. Pockman, and Diana H. Wall. 2002. Ecosystem carbon loss with woody plant invasion of grasslands. Nature 418:623–626.

    DOI: 10.1038/nature00910Save Citation »Export Citation »E-mail Citation »

    Although individual trees are far heavier than grasses, when woody plants encroach desert grasslands, the net effect is a loss of carbon and nitrogen.

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  • McAuliffe, Joseph R. 1994. Landscape evolution, soil formation, and ecological patterns and processes in Sonoran desert bajadas. Ecological Monographs 64:111–148.

    DOI: 10.2307/2937038Save Citation »Export Citation »E-mail Citation »

    Syntheses such as this one allow for more effective understanding of arid ecosystems due to the linking of basic ecological processes with a landscape perspective. These geomorphic mosaics on alluvial fans (bajadas) correspond closely to vegetation patterns and produce abrupt juxtapositions of soils of different ages.

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  • O’Halloran, Lydia R., Herman H. Shugart, Lixin Wang, Kelly K. Caylor, Susan Ringrose, and Barney Kgope. 2010. Nutrient limitations on aboveground grass production in four savanna types along the Kalahari Transect. Journal of Arid Environments 74:284–290.

    DOI: 10.1016/j.jaridenv.2009.08.012Save Citation »Export Citation »E-mail Citation »

    Despite higher levels of nutrients (especially foliar phosphorus), O’Halloran and colleagues found no change in aboveground biomass. This may be explained by luxury uptake or allocation to belowground resources.

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  • Schlesinger, William H., Jane A. Raikes, Anne E. Hartley, and Anne F. Cross. 1996. On the spatial pattern of soil nutrients in desert ecosystems. Ecology 77:364–374.

    DOI: 10.2307/2265615Save Citation »Export Citation »E-mail Citation »

    Superb study of the spatial distributions of soil nutrients, showing remarkable small-scale variation in their distributions.

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  • Whitford, Walter G. 1996. The importance of the biodiversity of soil biota in arid ecosystems. Biodiversity and Conservation 5:185–195.

    DOI: 10.1007/BF00055829Save Citation »Export Citation »E-mail Citation »

    In arid ecosystems, the subset of soil biota that is active at any point in time is determined by the soil water potential and soil temperature. Soil microarthropod abundance and diversity were directly related to quantity of litter accumulations and soil organic matter.

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Disturbances

Various disturbances affect the nature of desert species interactions. Among these, Drought and Herbivory and Granivory are most important. Several long-term vegetation studies have documented the importance of drought as a natural disturbance in desert ecosystems, which may take many years before suitable periods of high rainfall reset the ecosystem to its original position. Herbivory and granivory are both important ecosystem effects, with granivory probably being the more important of the two because there are too few plants in desert ecosystems to warrant the presence of large mammalian herbivores. Contrastingly, there are many granivores in deserts, be they insects, lizards, birds, or small mammals. Fire is less common and is often considered to be unimportant as a disturbance because of the low fuel load. Physical Disturbances are often related to the presence of agricultural systems in the past, but military maneuvers can be a source because deserts are often considered suitable for activities where agriculture is not achievable.

Herbivory and Granivory

Herbivory involves removal of vegetative growth (Milton 1991; Ward 2006; Miller, et al. 2009; Browning and Archer 2011) and granivory involves seed removal (Davidson, et al. 1985; Lopez de Casenave, et al. 1998). Both have important effects in deserts, especially because seed removal can cause competition between various granivores such as rodents, birds, and ants (Lopez de Casenave, et al. 1998). Herbivory, particularly by domestic livestock, may also have very important negative consequences for plant species diversity (Milton 1991; Browning and Archer 2011; reviewed in Ward 2006), although Miller, et al. 2009 shows that insect herbivory can also have significant effects along an environmental gradient.

  • Browning, Dawn M., and Steven R. Archer. 2011. Protection from livestock fails to deter shrub proliferation in a desert landscape with a history of heavy grazing. Ecological Applications 21:1629–1642.

    DOI: 10.1890/10-0542.1Save Citation »Export Citation »E-mail Citation »

    Contrary to widely held assumptions, protection from livestock since 1932 not only failed to deter woody plant proliferation but actually promoted it relative to grazed areas (see Ward 2010, cited under Climate Change).

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  • Davidson, Diane W., D. A. Samson, and Richard S. Inouye. 1985. Granivory in the Chihuahuan desert: Interactions within and between trophic levels. Ecology 66:486–502.

    DOI: 10.2307/1940397Save Citation »Export Citation »E-mail Citation »

    Three seasonally distinct classes of annual plants (winter, summer, and year-long) produce the seeds used by granivorous ants and rodents. Rodents reduced ant resources through their effects on seeds of both summer annuals and winter annuals. Ants of one species increased in number while another ant species declined.

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  • Lopez de Casenave, Javier, Victor R. Cueto, and Luis Marone. 1998. Granivory in the Monte desert, Argentina: Is it less intense than in other arid zones of the world? Global Ecology and Biogeography Letters 7:197–204.

    DOI: 10.2307/2997375Save Citation »Export Citation »E-mail Citation »

    Granivory was as common as in other deserts, with the exception of North American deserts where it was exceptionally high.

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  • Miller, Tom E. X., Svata M. Louda, Karen A. Rose, and James O. Eckberg. 2009. Impacts of insect herbivory on cactus population dynamics: Experimental demography across an environmental gradient. Ecological Monographs 79:155–172.

    DOI: 10.1890/07-1550.1Save Citation »Export Citation »E-mail Citation »

    Insects had a highly significant negative impact (depressing the asymptotic rate of population increase) on the life history of the tree cholla cactus in the Chihuahuan desert. The impact was most significant at low elevations and progressively less so at middle and high elevations.

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  • Milton, Suzanne J. 1991. Plant spinescence in arid southern Africa: Does moisture mediate selection by mammals? Oecologia 87:279–287.

    DOI: 10.1007/BF00325267Save Citation »Export Citation »E-mail Citation »

    Milton found that spinescence tended to increase with aridity in moist, nutrient-rich habitats. Spinescence in plants of drainage lines and pans in arid southern Africa appears to have been selected by the effect of large mammals that concentrate on these moist patches.

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  • Ward, David. 2006. Long-term effects of herbivory on plant diversity and functional types in arid ecosystems. In Large mammalian herbivores, ecosystem dynamics, and conservation. Edited by Kjell Danell, Roger Bergström, Patrick Duncan, and John Pastor, 142–169. Cambridge, UK: Cambridge Univ. Press.

    DOI: 10.1017/CBO9780511617461Save Citation »Export Citation »E-mail Citation »

    A review of the major effects of herbivory on arid ecosystems.

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Fire

Fire seldom has an important effect on desert communities because there is insufficient fuel load and there may be an absence of a source of ignition (although lightning forms a natural source). Nonetheless, there are a few occasions, mostly in Australia (Orians and Milewski 2007; Morton, et al. 2011) and some of the North American deserts (McLaughlin and Bowers 1982, Abella 2009) where it can be an important driver of vegetation change. In Australia, it is the combination of low nutrients and fire that occurs as a result of nutrient poverty (Orians and Milewski 2007; Morton, et al. 2011).

  • Abella, Scott R. 2009. Post-fire plant recovery in the Mojave and Sonoran deserts of western North America. Journal of Arid Environments 73:699–707.

    DOI: 10.1016/j.jaridenv.2009.03.003Save Citation »Export Citation »E-mail Citation »

    A very useful review of post-fire recovery in the Mojave and Sonoran deserts. In five of six studies with the longest post-fire period, percentage cover returned to within 10 percent of the unburned values after forty years, but there was little similarity in species composition.

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  • McLaughlin, Steven P., and Janice E. Bowers. 1982. Effects of wildfire on a Sonoran desert plant community. Ecology 63:246–248.

    DOI: 10.2307/1937048Save Citation »Export Citation »E-mail Citation »

    Fascinating description of the effects of a wildfire similar in consequence to fires in desert peripheries, causing high mortality and a significant reduction in population density and cover of dominant plants. This was only possible because there was sufficient fuel load after two winters of above-average rainfall.

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  • Morton, Steven R., D. Mark Stafford Smith, Christopher R. Dickman, et al. 2011. A fresh framework for the ecology of arid Australia. Journal of Arid Environments 75:313–329.

    DOI: 10.1016/j.jaridenv.2010.11.001Save Citation »Export Citation »E-mail Citation »

    Most features of the Australian deserts are explicable in terms of rainfall variability and widespread soil nutrient poverty. Low levels of phosphorus (together with abundant soil moisture on irregular occasions) favor plants producing a relative excess of carbohydrate, which sometimes leads to fire-prone ecosystems.

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  • Orians, Gordon H., and Antoni V. Milewski. 2007. Ecology of Australia: The effects of nutrient-poor soils and intense fires. Biological Reviews 82:393–423.

    DOI: 10.1111/j.1469-185X.2007.00017.xSave Citation »Export Citation »E-mail Citation »

    Most anomalous features of Australian ecosystems are the evolutionary consequences of adaptations to nutrient poverty, compounded by fire that tends to occur as a result of nutrient poverty. Accumulation of nutrient-poor biomass, which is a result of low rates of herbivory due to well-defended plants, provides fuel for intense fire.

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Drought

A number of long-term studies have illustrated the changes in desert vegetation (e.g., Goldberg and Turner 1986; Ward, et al. 2000) (and some changes in the animals: Brown, et al. 2001) that show that deserts are not static in their structure. This may have large-scale consequences; thus Tucker, et al. 1991 showed that the world’s largest desert, the Sahara, shrank in size between 1980 and 1990 while many other studies indicate that it has grown (Sinclair and Fryxell 1985, cited under Pastoralism). In one of the longest-term studies, Gibbens, et al. 2005 showed changes in shrub and grass cover in the Jornada basin of the Chihuahuan Desert since 1858. However, in some cases, drought has not affected the dominance of plant species (Milton and Dean 2000). Reynolds, et al. 1999 found that simulated drought affected one of the two shrub species they studied, causing a change in the seasonality of maximal growth. A number of studies of individual deserts (e.g., Rundel and Gibson 1996; Dean and Milton 1999; Havstad, et al. 2006; all cited under Specific Deserts), also illustrate such changes.

  • Brown, James H., Thomas G. Whitham, S. K. Morgan Ernest, and Catherine A. Gehring. 2001. Complex species interactions and the dynamics of ecological systems: Long-term experiments. Science 293:643–650.

    DOI: 10.1126/science.293.5530.643Save Citation »Export Citation »E-mail Citation »

    Drought is an important factor causing changes in densities of certain species, but so is very high rainfall (the banner-tailed kangaroo rat almost became extinct during very high rainfall periods). Of great importance was the role of keystone and dominant species (see Brown and Heske 1990 and Dean, et al. 1999, both cited under Indirect Interactions).

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  • Gibbens, Robert P., Robert P. McNeely, Kris M. Havstad, Reldon F. Beck, and Barbara Nolen. 2005. Vegetation changes in the Jornada Basin from 1858 to 1998. Journal of Arid Environments 65:651–668.

    DOI: 10.1016/j.jaridenv.2004.10.001Save Citation »Export Citation »E-mail Citation »

    There has been a general increase in shrub cover since 1858 and a concomitant decrease in grass cover in the Jornada basin unrelated to grazing (see also Jackson, et al. 2002, cited under Ecosystem Processes; and Ward 2010, cited under Climate Change).

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  • Goldberg, Deborah, and Turner, Raymond M. 1986. Vegetation change and plant demography in permanent plots in the Sonoran Desert. Ecology 67:695–712.

    DOI: 10.2307/1937693Save Citation »Export Citation »E-mail Citation »

    Elegant study of long-term change (seventy-two years) in plant population dynamics in a desert environment. Coverage of most species responded strongly to regimes of extremely wet or extremely dry years. Total cover, density, and species diversity have increased more or less continuously in many plots between 1906 and 1978.

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  • Milton, Suzanne J., and W. Richard J. Dean. 2000. Disturbance, drought and dynamics of desert dune grassland, South Africa. Plant Ecology 150:37–51.

    DOI: 10.1023/A:1026585211708Save Citation »Export Citation »E-mail Citation »

    In a seven-year study, perennial grass recruitment was dependent upon disturbances that reduced the density of living perennial grass tussocks. However, a drought in 1992 lead to widespread mortality of the perennial grass, killing almost 60 percent of established tufts. However, drought had little long-term effect on community composition.

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  • Reynolds, James F., Ross A. Virginia, Paul R. Kemp, Amrita G. de Soyza, and David C. Tremmel. 1999. Impact of drought on desert shrubs: Effects of seasonality and degree of resource island development. Ecological Monographs 69:69–106.

    DOI: 10.1890/0012-9615(1999)069[0069:IODODS]2.0.CO;2Save Citation »Export Citation »E-mail Citation »

    In the absence of drought, both creosote bush (evergreen) and mesquite (drought deciduous) exhibited maximal growth and photosynthetic rates in late spring. Mesquite shrubs did not change their strategy when simulated drought was applied, but creosote bushes that experienced drought in winter/spring shifted their maximal growth and activity to the summer.

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  • Tucker, Compton J., Harold E. Dregne, and Wilbur W. Newcomb. 1991. Expansion and contraction of the Sahara Desert from 1980 to 1990. Science 253:299–301.

    DOI: 10.1126/science.253.5017.299Save Citation »Export Citation »E-mail Citation »

    Satellite imagery shows that the Sahara Desert both grows and shrinks. The greatest annual north-south latitudinal movement of the southern Saharan boundary was 110 km from 1984 to 1985 and resulted in a “decrease” in desert area of 724,000 km2.

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  • Ward, David, David Saltz, and Linda Olsvig-Whittaker. 2000. Distinguishing signal from noise: Long-term studies of vegetation in Makhtesh Ramon erosion cirque, Negev desert, Israel. Plant Ecology 150:27–36.

    DOI: 10.1023/A:1026529126729Save Citation »Export Citation »E-mail Citation »

    Their long-term vegetation studies in permanent plots, initiated in 1990, showed that there is high spatial and temporal variance in plant species’ incidences and abundances related to droughts. However, they found significant negative effects of herbivory by the Asiatic wild ass on plant cover and on vegetation community composition.

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Physical Disturbance

There are various physical disturbances to desert soils, such as those created by agriculture (Milton and Dean 2000, cited under Drought). More recently, a number of studies have indicated that military maneuvers (Kade and Warren 2002; Belnap, et al. 2007) and various multiple land uses that includes motor vehicles (Webb, et al. 2009) may have serious negative consequences on the vegetation. Some of the most effective examples of protection from physical disturbance come from the protection afforded to desert soils by cyanobacteria (see Eldridge and Tozer 1997, cited under Plants: Population Dynamics). However, there are areas, particularly in sandy soils, where such protection of soils does not occur.

  • Belnap, Jayne, Susan L. Phillips, Jeffrey E. Herrick, and Jeffrey R. Johansen. 2007. Wind erodibility of soils at Fort Irwin, California (Mojave Desert), USA, before and after trampling disturbance: Implications for land management. Earth Surface Processes and Landforms 32:75–84.

    DOI: 10.1002/esp.1372Save Citation »Export Citation »E-mail Citation »

    Undisturbed sites had greater cyanobacterial biomass, soil surface stability, threshold friction velocities (wind speed required to move soil particles), and sediment yield than sites that had been more recently disturbed by military maneuvers.

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  • Kade, Anja, and Steven D. Warren. 2002. Soil and plant recovery after historic military disturbances in the Sonoran Desert, USA. Arid Land Research and Management 16:231–243.

    DOI: 10.1080/153249802760284784Save Citation »Export Citation »E-mail Citation »

    Military training exercises in desert areas have resulted in various types of disturbance. Foot traffic disturbance did not show full recovery of vegetation and biological soil crust. Most plant species disturbed by vehicular traffic exhibited higher density and greater foliar cover than was found at the control site.

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  • Webb, Robert H., Lynn F. Fenstermaker, Jill S. Heaton, Debra L. Hughson, Eric V. McDonald, and David M. Miller, eds. 2009. The Mojave Desert: Ecosystem processes and sustainability. Reno: Univ. of Nevada Press.

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    A number of very useful review chapters on the effects of physical disturbance on the soils and vegetation of the Mojave Desert, such as “Rates of soil compaction by multiple land use practices in southern Nevada” and “Ecological effects of vehicular routes in a desert ecosystem.”

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Applied Ecology

Very little agriculture takes place in the desert biome, with the exception of extensive Pastoralism, although some irrigated agriculture occurs near rivers. Heavy livestock presence, in concert with global Climate Change, is leading to major problems of Desertification, particularly around the desert margins. Nonetheless, there are many areas where substantial Conservation is effectively occurring, most frequently because deserts are perceived as “wastelands.” We also need to recognize that people have been an integral part of the desert for many thousands of years and have altered them to suit their needs (People in Deserts).

Pastoralism

It is extremely difficult for arid land pastoralists to manage their herds in an optimal way because there are such large fluctuations in primary productivity (Westoby, et al. 1989), which is driven by precipitation. This problem may mean that an optimal herd is below the size required to maintain a breeding group in drought years (Friedel, et al. 1990). Much pastoralism is perceived to have negative effects on the vegetation (Milton, et al. 1994), particularly around water points (James, et al. 1999). A major cause of problems with vegetation denudation for communal pastoralists occurs because people are no longer allowed to migrate (Hardin 1968, cited under Desertification; Sinclair and Fryxell 1985; Ellis and Swift 1988). However, some ecologists believe that this is more an issue of perception than a reality (Ellis and Swift 1988, Behnke and Abel 1996), although Behnke and Abel 1996 recognizes that the heavy stocking rates so frequently recorded on desert lands may exacerbate the problems of vegetation declines. Ellis and Swift 1988 considers the shuttling of people engaged in extensive pastoralism to cities when droughts occur to be an effective way of managing the problem of a lack of food in a household, although the individuals involved may not consider this to be an optimal strategy.

  • Behnke, Roy, and Nick Abel. 1996. Revisited: The overstocking controversy in semiarid Africa. World Animal Review 87:4–27.

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    An important consideration of the problems faced by communal pastoralists and their need to keep large herds for a variety of purposes. This has led to the concept of “overstocking,” although many prefer to use the term “heavy stocking” since the classic paper Westoby, et al. 1989.

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  • Ellis, James E., and David M. Swift. 1988. Stability of African pastoral ecosystems: Alternate paradigms and implications for development. Journal of Range Management 41:450–459.

    DOI: 10.2307/3899515Save Citation »Export Citation »E-mail Citation »

    An important review paper that focuses on the authors’ long-term study of the communal pastoralists of the arid Turkana region of East Africa. Livestock herds slowly build up after sporadic droughts and then are cut back again when droughts strike. They see this as part of a natural process.

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  • Friedel, Margaret H., Barney D. Foran, and D. Mark Stafford Smith. 1990. Where the creeks run dry or ten feet high: Pastoral management in Australia. Proceedings of the Ecological Society of Australia 16:185–194.

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    Illustrates the boom-or-bust pastoral situation in arid Australia, showing how difficult it is for pastoralists to manage their herds.

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  • James, Craig D., Jill Landsberg, and Steven R. Morton. 1999. Provision of watering points in the Australian arid zone: A review of effects on biota. Journal of Arid Environments 41:87–121.

    DOI: 10.1006/jare.1998.0467Save Citation »Export Citation »E-mail Citation »

    Watering points create piospheres, which are areas of heavy grazing close to these points. Typically, they have virtually no vegetation adjacent to the watering point, with unpalatable vegetation slightly farther away followed by annual plants still further away because perennial plants are removed by livestock.

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  • Milton, Suzanne J., W. Richard J. Dean, Morné A. du Plessis, and W. Roy Siegfried. 1994. A conceptual model of arid rangeland degradation. BioScience 44:70–76.

    DOI: 10.2307/1312204Save Citation »Export Citation »E-mail Citation »

    Rangeland degradation proceeds in steps, each step being increasingly difficult to reverse (Schlesinger, et al. 1990, cited under Desertification). In the first two steps, arid systems demand that managers understand variation in annual rainfall and necessitate adaptive management to control stocking rates and then stricter grazing control.

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  • Sinclair, Anthony R. E., and John M. Fryxell. 1985. The Sahel of Africa: Ecology of a disaster. Canadian Journal of Zoology 63:987–994.

    DOI: 10.1139/z85-147Save Citation »Export Citation »E-mail Citation »

    These authors show that the major reason for the problems associated with pastoralism in the arid Sahel that surrounds the Sahara desert in Africa is that people are no longer able to migrate with their herds.

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  • Westoby, Mark, Brian Walker, and Immanuel Noy-Meir. 1989. Opportunistic management for rangelands not at equilibrium. Journal of Range Management 42:266–274.

    DOI: 10.2307/3899492Save Citation »Export Citation »E-mail Citation »

    This was the first paper to recognize that arid rangelands might not be at equilibrium and that an opportunistic strategy may be more effective than a conventional one that is based on fixed concepts of carrying capacity and a single optimal stocking density.

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Climate Change

One of the most difficult issues to quantify in desert is climate change, because of the inherent variability in rainfall and the high spatial variability of soil nutrients in desert ecosystems. Nonetheless, climate change can still be detected despite this variability. Giannini 2010 has developed two scenarios for climate change in the Sahara that both have negative consequences for primary productivity, while Martin 2006 goes back further in time to demonstrate that such changes have been occurring since the Cenozoic in Australia. Climate change has many potentially negative consequences, including increased woody plant encroachment (e.g., Jackson, et al. 2002, cited under Ecosystem Processes; Wiegand, et al. 2006, cited under Desertification; Ward 2010), reduced distributions of species (e.g., Foden, et al. 2007), and the need to change the shape of nature reserves (Cowling 1999). A number of models have shown that more extreme environments are predicted under climate change models, with larger, more intense storms being more frequent. Whitford and Steinberger 2011 shows that the size and frequency of rain events affect availability of soil nutrients, which can produce unexpected growth responses of perennial herbs and grasses.

  • Cowling, Richard M. 1999. Planning for persistence: Systematic reserve design in southern Africa’s Succulent Karoo desert. Parks 19:17–30.

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    Accessible to students and nonspecialists. Stresses that, in the face of climate change, conservation should focus on preserving climatic gradients rather than specific habitats.

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  • Foden, Wendy, Guy F. Midgley, Greg Hughes, et al. 2007. A changing climate is eroding the geographical range of the Namib desert tree Aloe through population declines and dispersal lags. Diversity and Distributions 13:645–653.

    DOI: 10.1111/j.1472-4642.2007.00391.xSave Citation »Export Citation »E-mail Citation »

    From a detailed population census throughout the entire geographical range of Aloe dichotoma, a long-lived Namib desert tree, together with data from repeat photographs, Foden and colleagues showed that a developing range shift in this species is due to anthropogenically induced climate change.

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  • Giannini, Alessandra. 2010. Mechanisms of climate change in the semiarid African Sahel: The local view. Journal of Climate 23:743–756.

    DOI: 10.1175/2009JCLI3123.1Save Citation »Export Citation »E-mail Citation »

    Giannini sketches two scenarios for climate change in the Sahel, both of which have negative consequences for the main activity in this region, pastoralism.

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  • Martin, Helene A. 2006. Cenozoic climatic change and the development of the arid vegetation in Australia. Journal of Arid Environments 66:533–563.

    DOI: 10.1016/j.jaridenv.2006.01.009Save Citation »Export Citation »E-mail Citation »

    Fascinating description of the changes in vegetation in arid Australia since the Cenozoic. Aridity in Australia started in the early Miocene. She describes the change in the vegetation from elements that were dominant in humid times and that have managed to tolerate aridity.

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  • Ward, David. 2010. A resource-ratio model of the effects of elevated CO2 on woody plant encroachment. Plant Ecology 209:147–152.

    DOI: 10.1007/s11258-010-9731-zSave Citation »Export Citation »E-mail Citation »

    Details the change from C4 grasses typically dominant in arid areas to C3 trees under increased CO2 levels predicted under global climate change models and relates this to the potential for woody plant encroachment. This effect of elevated CO2 need not be linked to levels of grazing.

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  • Whitford, Walter G., and Yosef Steinberger. 2011. Effects of simulated storm sizes and nitrogen on three Chihuahuan Desert perennial herbs and a grass. Journal of Arid Environments 75:861–864.

    DOI: 10.1016/j.jaridenv.2011.03.007Save Citation »Export Citation »E-mail Citation »

    Increasingly extreme climatic events could result in patterns such as less total rainfall but infrequent but more intense storms. This study used simulated rainfall events to examine responses in plant productivity to different amounts and timing of rainfall.

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Desertification

Desertification is a change in state of an ecosystem such that a return to the original better-vegetated state is unlikely. Desertification is often linked with the margins of desert regions, such as the Sahel that surrounds the Sahara desert in North Africa. Although the term “desertification” is new, it is a process that has been occurring for a very long time (Guo, et al. 2002). There are many potential causes of desertification (Schlesinger, et al. 1990). However, in much of the world, desert biomes are mostly affected by pastoralism (see Hardin 1968 and Hardin 1998, both cited under People in Deserts) and its consequences for changes in woody plant encroachment (Peters, et al. 2004; Wiegand, et al. 2006), by some irrigation close to rivers (Saiko and Zonn 2000), and by anthropogenically induced climate change (Giannini 2010, cited under Climate Change). Ultimately, it is increasing human population density that is the greatest cause of desertification, as emphasized by Middleton and Thomas 1997 and Geist and Lambin 2004.

  • Geist, Helmut, and Eric F. Lambin. 2004. Dynamic causal patterns of desertification. BioScience 54:817–829.

    DOI: 10.1641/0006-3568(2004)054[0817:DCPOD]2.0.CO;2Save Citation »Export Citation »E-mail Citation »

    Desertification is driven by a relatively limited suite of core variables, of which the most prominent at the underlying level are climatic factors, economic factors, institutions, national policies, population growth (the most obvious but seldom discussed), and remote influences such as dam-building upstream. Accessible to students and nonspecialists.

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  • Guo, Z. T., W. F. Ruddiman, Q. Z. Hao, et al. 2002. Onset of Asian desertification by 22 Myr ago inferred from loess deposits in China. Nature 416:159–163.

    DOI: 10.1038/416159aSave Citation »Export Citation »E-mail Citation »

    Desertification is not a new process; it was happening at least 22 million years ago. Using palaeomagnetic measurements and fossil evidence they show that large source areas of eolian dust and winter monsoon winds to transport the material must have existed in the interior of Asia by the early Miocene epoch.

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  • Middleton, Nicholas J., and David S. G. Thomas, eds. 1997. World atlas of desertification. 2d ed. London: Edward Arnold.

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    Comprehensive atlas of global desertification.

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  • Peters, Debra P. C., Roger A. Pielke, Brandon T. Bestelmeyer, Craig D. Allen, Stuart Munson-McGee, and Kris M. Havstad. 2004. Cross-scale interactions, nonlinearities, and forecasting catastrophic events. Proceedings of the National Academy of Sciences of the United States of America 101:15130–15135.

    DOI: 10.1073/pnas.0403822101Save Citation »Export Citation »E-mail Citation »

    Using examples from desertification (albeit with a narrow view that it results from woody plant encroachment only) and wildfires, and associated with global change, recognizes that we need to traverse disciplinary boundaries to include interactions and feedbacks at multiple scales to increase our ability to predict catastrophic events.

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  • Saiko, Tatyana A., and Igor S. Zonn. 2000. Irrigation expansion and dynamics of desertification in the Circum-Aral region of Central Asia. Applied Geography 20:349–367.

    DOI: 10.1016/S0143-6228(00)00014-XSave Citation »Export Citation »E-mail Citation »

    A superb graphical account of the relationship between irrigation, consequent salinization, and the dramatic reduction in size of the Aral Sea and associated environments.

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  • Schlesinger, William H., James F. Reynolds, Gary L. Cunningham, et al. 1990. Biological feedbacks in global desertification. Science 47:1043–1048.

    DOI: 10.1126/science.247.4946.1043Save Citation »Export Citation »E-mail Citation »

    The classic study indicating the feedbacks in desertification. Accessible to students.

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  • Wiegand, Kerstin, David Saltz, and David Ward. 2006. A patch-dynamics approach to savanna dynamics and woody plant encroachment: Insights from an arid savanna. Perspectives in Plant Ecology, Evolution and Systematics 7:229–242.

    DOI: 10.1016/j.ppees.2005.10.001Save Citation »Export Citation »E-mail Citation »

    Woody plant encroachment can be an important part of desertification because it may take so long to return to its previous state. Important theoretical work on the details of patch dynamics, a spatially explicit approach that models the degree of encroachment of arid regions (see also Peters, et al. 2004).

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Conservation

Although there are many reasons why deserts are expanding and there are negative consequences of pastoralism and irrigation of desert lands, there are some success stories. One reason for this is that many people perceive that these are wastelands and thus not worth their concern. Stanley-Price 1989 tells a highly successful tale of the reintroduction of the Arabian oryx into Oman, as does Saltz and Rubenstein 1995 for the Asiatic wild ass in Israel. Of crucial importance to our understanding of effective conservation measures is the development of effective population models, as was done by Godínez-Alvarez and Valiente-Banuet 2004 for a columnar cactus, and by Saltz and Rubenstein 1995 for the Asiatic wild ass. Rohner and Ward 1999 considers it important to conserve wild ungulates together with scarce Acacia trees because germination of these trees is rare without the benefits of seed scarification by ungulates. Barnard, et al. 1998 demonstrates that although much desert habitat is protected, far more can be effectively protected if transboundary biospheres in both South Africa and Namibia are included. They also show that conservancies by private and communal landholders can contribute substantially to effective conservation. Robbins 1998 considers the use of rules for resource preservation by rural women in Rajasthan in India, and finds that women will abide by these rules if there is equity in rule enforcement and if they could gain by rule enforcement. On the negative side, Cunningham and Berger 1997 considers the conservation problems faced by the black rhino in Namibia; simple strategies such as dehorning this endangered species have not always proved effective. Similarly, Letnic and Dickman 2006 shows that predation by non-native wildlife coupled with the increased risk of wildfires during peak rainfall years can cause boom years for the vegetation to turn into bust years for native mammals.

  • Barnard, Phoebe, Christopher J. Brown, Alice M. Jarvis, Antony Robertson, and Leon van Rooyen. 1998. Extending the Namibian protected areas network to safeguard hotspots of endemism and diversity. Biodiversity and Conservation 7:531–547.

    DOI: 10.1023/A:1008831829574Save Citation »Export Citation »E-mail Citation »

    The national parks in the Namib desert make up about 70 percent of the protected areas network of Namibia. Two important endemism zones, the arid Kaoko escarpment (northwest) and the Sperrgebiet succulent steppe (southwestern coastal Namibia) offer valuable opportunities for regional consolidation of protected areas into transboundary biosphere reserves.

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  • Cunningham, Carol, and Joel Berger. 1997. Horn of darkness: Rhinos on the edge. New York: Oxford Univ. Press.

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    Discusses the critical status of the African black rhinoceros. This husband-and-wife team spent years in arid Namibia studying this species. They consider the ill-advised consequences of dehorning this species because the females are less capable of defending their young and because horns ultimately regrow. Accessible to the nonspecialist.

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  • Godínez-Alvarez, Héctor, and Alfonso Valiente-Banuet. 2004. Demography of the columnar cactus Neobuxbaumia macrocephala: A comparative approach using population projection matrices. Plant Ecology 174:109–118.

    DOI: 10.1023/B:VEGE.0000046052.35390.59Save Citation »Export Citation »E-mail Citation »

    This long-lived columnar cactus is endemic to a single valley in south central Mexico. Very few recruitment events have been detected. Survival was the process with the highest relative contribution to population growth rate. Seeds and seedlings had high mortality caused by seed predation and death of germinated seeds.

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  • Letnic, Michael, and Christopher R. Dickman. 2006. Boom means bust: Interactions between the El Niño/Southern Oscillation (ENSO), rainfall and the processes threatening mammal species in arid Australia. Biodiversity and Conservation 15:3847–3880.

    DOI: 10.1007/s10531-005-0601-2Save Citation »Export Citation »E-mail Citation »

    Large rainfall events in arid Australia associated with El Niño/Southern Oscillation events are often viewed as the good (“boom”) periods for wildlife. However, predation by introduced species and the risk of wildfire causes years including and immediately after floods to be critical (“bust”) periods for mammals in arid Australia.

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  • Robbins, Paul. 1998. Authority and environment: institutional landscapes in Rajasthan, India. Annals of the Association of American Geographers 88:410–435.

    DOI: 10.1111/0004-5608.00107Save Citation »Export Citation »E-mail Citation »

    Women maintain some rules for resource preservation but disregard others when they believe that men are making decisions for them. Resource preservation occurred if the women perceived that the enforcing authority was legitimate, if they could gain from resource maintenance, and if there was a reasonable expectation of equal rule enforcement.

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  • Rohner, Christoph, and David Ward. 1999. Large mammalian herbivores and the conservation of arid Acacia stands in the Middle East. Conservation Biology 13:1162–1171.

    DOI: 10.1046/j.1523-1739.1999.97300.xSave Citation »Export Citation »E-mail Citation »

    High mortality and poor recruitment in Acacia tree populations in many parts of the Middle East result in loss of biodiversity. Ungulates were the main seed dispersers of these Acacia species. However, bruchid beetles damaged more than 95 percent of seeds not consumed by ungulates.

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  • Saltz, David, and Daniel I. Rubenstein. 1995. Population dynamics of a reintroduced Asiatic wild ass (Equus hemionus) herd. Ecological Applications 5:327–335.

    DOI: 10.2307/1942025Save Citation »Export Citation »E-mail Citation »

    Important study that nicely integrates field studies of the Asiatic wild ass with simulation models to make predictions about the impacts of reintroduction on these animals in the central Negev desert of Israel.

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  • Stanley-Price, Mark R. 1989. Animal re-introductions: The Arabian oryx in Oman. Cambridge, UK: Cambridge Univ. Press.

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    Highly successful reintroduction of the endangered Arabian oryx to its native lands. A similar program is currently underway in several other Middle Eastern nations.

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People in Deserts

People have been an integral part of the desert for a very long time. In some cases, people have sought refuge there (Yellen 1977), while in other places people have manipulated the desert for their benefit (Bruins, et al. 1986; Fuller, et al. 2010). Anthropogenic fires, particularly in the arid spinifex grasslands of Australia where there is sufficient fuel available, may also be an important source of landscape transformation by the aboriginal peoples (Bliege Bird, et al. 2008). There are some serious negative consequences of communal ownership of land (Hardin 1968; Burwell 1995; Hardin 1998; Ward, et al. 2000) and the need for people to migrate to optimize their use of areas that have recently experienced rain (Yellen 1977, Leslie and Little 1999). An interesting perspective on pastoralists as conservationists is provided by Ruttan and Borgerhoff Mulder 1999.

  • Bliege Bird, Rebecca, Doug W. Bird, Brian F. Codding, Christopher H. Parker, and James H. Jones. 2008. The “fire stick farming” hypothesis: Australian aboriginal foraging strategies, biodiversity, and anthropogenic fire mosaics. Proceedings of the National Academy of Sciences of the United States of America 105:14796–14801.

    DOI: 10.1073/pnas.0804757105Save Citation »Export Citation »E-mail Citation »

    Anthropogenic fires made by the aboriginal peoples of Australia have long been assumed to be a resource management strategy. By combining ethnographic observations of current burning practices and satellite imagery analyses, the authors showed how aboriginal burning practices affect desert landscapes. Small-scale habitat mosaics increase small-animal hunting productivity.

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  • Bruins, Hendrik J., Michael Evenari, and U. Nessler. 1986. Rainwater-harvesting agriculture for food production in arid zones: The challenge of the African famine. Applied Geography 6:13–32.

    DOI: 10.1016/0143-6228(86)90026-3Save Citation »Export Citation »E-mail Citation »

    Fascinating insight into the use of runoff water from rain to plant crops in arid areas receiving little rain. The authors show that techniques have been used in arid zones in many countries since the Neolithic.

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  • Burwell, Trevor. 1995. Bootlegging on a desert mountain: The political ecology of agave (Agave spp.) demographic change in the Sonora river valley, Sonora, Mexico. Human Ecology 23:407–432.

    DOI: 10.1007/BF01190139Save Citation »Export Citation »E-mail Citation »

    Wild agave plants are being overexploited in Sonora, leading to a “tragedy of the commons” (Hardin 1968). All producers are aware of the problem, but population growth, expansion of agriculture onto ecologically marginal lands, and increasing dependence on wild-harvested products from communal lands has led to increased demand.

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  • Fuller, Dorian Q., Robin G. Allaby, and Chris Stevens. 2010. Domestication as innovation: The entanglement of techniques, technology and chance in the domestication of cereal crops. World Archaeology 42:13–28.

    DOI: 10.1080/00438240903429680Save Citation »Export Citation »E-mail Citation »

    Many cereal crops were domesticated in the arid Middle East, including wheat, barley, and oats. Key changes in human behaviors such as soil preparation and harvesting must be linked with key genetic innovations in the cereals, such as large seed size and non-shattering infructescences that allowed for easy harvesting.

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  • Hardin, Garrett. 1968. The tragedy of the commons. Science 162:1243–1248.

    DOI: 10.1126/science.162.3859.1243Save Citation »Export Citation »E-mail Citation »

    Classic paper that details why communally held land is so often misused. The benefits to the individual are always greater than the cost to the community. Accessible to students.

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  • Hardin, Garrett. 1998. Extensions of “The tragedy of the commons.” Science 280:682–683.

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    Follow-up to the classic paper, written thirty years later. Recognizes that he left the adjective “unmanaged” out of the original essay. “Managed” commons can be controlled, although they may still fail. Accessible to students.

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  • Leslie, Paul W., and Michael A. Little. 1999. Turkana herders of the dry savanna: Ecology and biobehavioral response of nomads to an uncertain environment. Oxford: Oxford Univ. Press.

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    Important long-term study of the nomadic Turkana people of arid northwestern Kenya, including research on their cultural and social habits, as well as the pressure being placed on them to change their society. This study should be read in conjunction with Ellis and Swift 1988 (cited under Pastoralism).

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  • Ruttan, Lore M., and Monique Borgerhoff Mulder. 1999. Are East African pastoralists truly conservationists? Current Anthropology 40:621–652.

    DOI: 10.1086/300086Save Citation »Export Citation »E-mail Citation »

    The authors use a game-theoretic approach to assess whether pastoralists are conservationists who benefit the environment, and whether it is possible to effectively manage common property (cf. Hardin 1968, Hardin 1998). There is a very interesting discussion by a number of prominent authors about the suitability of this game-theoretic approach.

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  • Ward, David, Ben T. Ngairorue, André Apollus, and Hermanus Tjiveze. 2000. Perceptions and realities of land degradation in arid Otjimbingwe, Namibia. Journal of Arid Environments 45:337–356.

    DOI: 10.1006/jare.2000.0647Save Citation »Export Citation »E-mail Citation »

    These pastoralists perceived that land degradation had occurred but said that a decline in rainfall was the cause. However, no change in rainfall was recorded. Management options are limited because of high human population growth rate and immigration, restricted water availability, and limited movement opportunities for livestock in drought periods.

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  • Yellen, John E. 1977. Long term hunter-gatherer adaptation to desert environments: A biogeographical perspective. World Archaeology 8:262–274.

    DOI: 10.1080/00438243.1977.9979672Save Citation »Export Citation »E-mail Citation »

    Uses a unique biogeographical perspective to look for common features in hunter-gatherer groups from desert ecosystems in Australia, Africa, and the United States, and records the consistencies in their behavior. In particular, they alter group size to suit the local environment, splitting up into smaller groups when rain is scarce.

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LAST MODIFIED: 05/23/2012

DOI: 10.1093/OBO/9780199830060-0044

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