Lichens occur worldwide in all terrestrial and even in some aquatic and marine habitats, where they often occupy locations inhospitable for vascular plants. The more extreme the habitat, the more important the ecological roles that lichens play. While lichens function like photosynthetic plants and often compete with plants of similar size, biologically they are a symbiosis of a fungus with an alga and/or a nitrogen-fixing cyanobacterium. With few exceptions, their vegetative body, the thallus, has a morphology and physiology radically different from the symbionts growing alone. There are approximately 19,000 fungi (lichens are named from the fungus) forming lichens, belonging to several unrelated lineages within the kingdom Fungi, specifically the phyla Ascomycota and Basidiomycota. In contrast, far fewer algal and cyanobacterial lineages are involved in the lichen symbiosis. Lichens are quintessential stress-tolerators for natural environmental factors: most species can tolerate wide temperature fluctuations and complete desiccation for prolonged times. Lichens lack specialized structures such as roots for water and nutrient acquisition, and their outer layers do not substantially reduce water loss. This limits the time when conditions are favorable for physiological activity, leading to slow growth since, without physical protection, lichens tolerate environmental extremes through desiccation. Lack of protective structures also means lichens readily absorb environmental chemicals. Thus, while their stress-tolerating strategy allows lichens to grow on substrates such as bare rock and tree trunks, it also renders them especially vulnerable to competition from plants in more favorable habitats and to anthropogenic stressors such as pollution; on the other hand, ecological niches of lichens often overlap with those of bryophytes except in wet or shady conditions. Lichens have been popular bioindicators of many kinds of pollution since before the start of the 20th century, but more recently they have also been recognized as bioindicators for other kinds of anthropogenic stressors to natural habitats, such as habitat fragmentation and climate change.
Modern approaches to lichen ecology consider that we live in a changing world. While the study of lichen ecology has progressed along with lichenology since early days (see History of Lichen Ecology), we chose the late 1980s to define the start of modern lichen ecology: with more than two thousand papers published in this field, almost two- thirds of these appeared since 1988. Thus, our overview and review of this area are limited to selected references among many, favoring geographic distribution. One of the major challenges to lichen ecology studies is the fact that massive and continuing revisions of lichen taxonomy and species delineation from molecular studies since the late 1980s generate substantial nomenclatural and taxonomic changes. Hence, both classical and modern ecological studies on lichens routinely need to be reinterpreted in light of modern phylogenies and species concepts. Examples include the interpretation of presumed infraspecific phenotypic variation as response to environmental parameters, when molecular studies resolve such variation as distinct taxa, or the opposite case where species distinguished based on morphology or chemistry are reinterpreted from molecular studies to be the same taxon. Nash 2008 provides updated reviews of lichen physiology and ecology as well as anatomy, morphology, and reproduction. Purvis 2000 emphasizes many aspects of general lichen ecology as well as lichenology applications in this readable introduction for beginners. Kranner, et al. 2002 provides summaries of modern quantitative methodology for ecophysiology, biomonitoring, and biodiversity information systems. Upreti, et al. 2015 is built on the aformentioned reference, with some new topics and with emphasis on new quantitative methods for surveys and data analyses. A classic review of the impact of environmental changes on mosses and lichens, Bates and Farmer 1992 provides a thorough survey of literature on lichen ecology to 1990, bringing together studies on nitrogen and sulfur air pollution, anthropogenic land use, and climate change. Introductions to modern regional taxonomy treatments, such as Brodo, et al. 2001 for North America or McCarthy and Mallet 2004 for Australia, summarize both ecology and basic biology reflecting these modern concepts. Modern reviews of lichen ecology in particular biomes incorporate pollution, climate change, and loss of natural habitats as major stressors on lichens; Galloway 1991 on all aspects of lichens in the tropics is an example.
Bates, J. W., and A. M. Farmer, eds. 1992. Bryophytes and lichens in a changing environment. Oxford: Clarendon.
Several chapters in this well-edited book for professionals and amateurs emphasize the ecological similarities of bryophytes and lichens. Lichen succession and response to changing climate, pollution load, and land management are reviewed, with special attention to forests and to Europe and North America.
Brodo, I. M., S. D. Sharnoff, and S. Sharnoff. 2001. Lichens of North America. New Haven, CT: Yale Univ. Press.
This fabulously illustrated overview (not complete) flora of the continent for both amateurs and professionals includes an extensive 113-page introduction to lichen biology and ecology.
Galloway, D. J., ed. 1991. Tropical lichens: Their systematics, conservation, and ecology. The Systematics Association Special Volume 43. Oxford: Clarendon.
This edited publication was the first comprehensive review of lichenology in the tropics. While aimed for professionals, most chapters are quite readable for amateurs.
Kranner, I., R. P. Beckett, and A. K. Varma, eds. 2002. Protocols in lichenology: Culturing, biochemistry, ecophysiology and use in biomonitoring. Berlin: Springer.
Mostly for professionals, this book focuses on methodology; five chapters on aspects of ecophysiology, three on biomonitoring with emphasis on element content of lichens, and four chapters on biodiversity and information management. Most information is currently relevant, though see Upreti, et al. 2015 for updates to some methods.
McCarthy, P. M., and K. Mallet. 2004. Flora of Australia V56A. Lichens 4. Canberra and Melbourne, Australia: ABRS and CSIRO.
The introduction to this comprehensive flora includes an introduction to lichen biology and ecology.
Nash, T. H. III, ed. 2008. Lichen biology. 2d ed. Cambridge, UK: Cambridge Univ. Press.
This relatively recent general book for professionals and advanced amateurs emphasizes physiology and physiological ecology but includes five chapters on other ecological topics.
Purvis, W. 2000. Lichens. London: Natural History Museum.
This beautifully illustrated book for a beginner general audience introduces lichens in three chapters, covers lichen biodiversity and ecology for six chapters, and finishes with chapters on lichen uses and projects. This is one example of many similar books published worldwide.
Upreti, D. K., P. K. Divakar, V. Shukla, and R. Bajpai, eds. 2015. Recent Advances in Lichenology. Modern Methods and Approaches in Biomonitoring and Bioprospection 1. New Delhi, India: Springer India.
This edited volume is a modern successor to Kranner, et al. 2002 for some chapters while reviewing new methods in other chapters. Geographic representation of lichenology is quite broad, with ten of twenty-three chapters by lichenologists outside Europe and North America. Online only, chapters can be purchased separately.
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- Accounting for Ecological Capital
- Allocation of Reproductive Resources in Plants
- Animals, Functional Morphology of
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