Ecological Dynamics in Fragmented Landscapes

by

Jaboury Ghazoul

• LAST REVIEWED: 29 May 2014
• LAST MODIFIED: 29 May 2014
• DOI: 10.1093/obo/9780199830060-0079

Introduction

Dramatic changes in landscape composition and increasing concerns about global biodiversity losses through the 20th century motivated the emergence of the field of landscape ecology, which addresses ecological dynamics in relation to the spatial pattern of landscapes. Landscape fragmentation, the breaking up of contiguous landscapes or their elements by human activities, is a principal outcome of human transformation of natural landscapes. This process leads to habitat loss and habitat isolation, as well as associated changes in the overall composition and spatial distribution of landscape elements, and is one of the primary driving forces behind biodiversity loss. Landscape and habitat fragmentation affect demographic and genetic processes of populations. Large patches tend to have larger populations (and therefore lower extinction probabilities) and more species (due to the area effect and greater habitat heterogeneity). Habitat area loss generally has stronger effects on population demography and persistence than does habitat isolation. Habitat isolation is more relevant to genetic effects and also becomes increasingly important when there is little remaining habitat in the landscape and when species have poor dispersal capabilities. Species responses to landscape fragmentation are, however, complex, because habitat patches have multiple attributes. Size and shape, for example, affect the ratio of patch perimeter to area, and hence the relative importance of “edge effects” at habitat boundaries, where there may be changed abiotic conditions and increasing vulnerability to disturbances, pests, and predators. The nature of the surrounding habitat matrix might also be more or less suitable in supporting species or facilitating movement between patches. Ecosystem processes are mediated by species, and thus edges and boundaries created by fragmentation also affect the distribution and flow of energy and resources (e.g., biomass, productivity, and nutrients) within and among ecosystems. Consequently, landscape fragmentation has wide relevance to biodiversity and ecosystem processes, and central importance to ecosystem management, land use planning, and conservation.

General Overviews

The field of ecological dynamics in fragmented landscapes sits at the intersection of landscape ecology, conservation, and population biology, and overviews of the subject necessarily draw on aspects from all these fields. Principles of landscape ecology are summarized in Turner 1989 and treated more fully in Turner, et al. 2001. Collinge 2009 provides an excellent nontechnical overview of fragmentation effects on species, and species-mediated processes. The implications of habitat fragmentation for species loss and biodiversity conservation are treated in Lindenmayer and Fischer 2006 and Fahrig 2003. Both these references emphasize that fragmentation and fragmentation processes have many attributes and conceptual interpretations (see Conceptualizing Fragmentation and Connectivity). Understanding ecological outcomes requires the segregation of the effects of these attributes, and failing to do so, as Fahrig 2003 points out, risks ambiguous conclusions. Ecologists have used a variety of experimental approaches to study the consequences of habitat fragmentation, but a review in McGarigal and Cushman 2002 concludes that limitations in the design of these studies greatly restricts the strength of inferences, and the authors propose recommendations for improving the design of fragmentation studies.

• Collinge, S. K. 2009. Ecology of fragmented landscapes. Baltimore: Johns Hopkins Univ. Press.

  A nontechnical and highly accessible overview of species responses to fragmented landscapes, including a summary of fragmentation experiments (chapter 4, pp. 63–92) and modeling work (chapter 9, pp. 195–218), and two chapters on restoration (chapter 9, pp. 219–245) and ecological planning (chapter 11, pp. 246–272).

• Fahrig, L. 2003. Effects of habitat fragmentation on biodiversity. Annual Review of Ecology, Evolution, and Systematics 34:487–515.

  DOI: 10.1146/annurev.ecolsys.34.011802.132419

  Discusses several conceptual interpretations of fragmentation and evaluates how different attributes of fragmentation affect biodiversity. Has a strong animal bias.

• Lindenmayer, D. B., and J. Fischer. 2006. Habitat fragmentation and landscape change: An ecological and conservation synthesis. Washington, DC: Island.

  Explores ecological problems stemming from landscape fragmentation, with an emphasis on species and ecosystems of conservation interest. The book draws on examples, albeit mostly of animals, from around the world.

• McGarigal, K., and S. A. Cushman. 2002. Comparative evaluation of experimental approaches to the study of habitat fragmentation effects. Ecological Applications 12.2: 335–345.

  DOI: 10.1890/1051-0761(2002)012[0335:CEOEAT]2.0.CO;2

  Discusses the reasons for the failure of many manipulative and mensurative fragmentation experiments to provide clear insights into the ecological mechanisms and effects of habitat fragmentation.

• Turner, M. G. 1989. Landscape ecology: The effect of pattern on process. Annual Review Ecology and Systematics 20:171–197.

  DOI: 10.1146/annurev.es.20.110189.001131

  A very readable introduction to the main concepts of landscape ecology, including an evaluation of the principal effects of landscape fragmentation on population and ecosystem dynamics.

• Turner, M. G., R. H. Gardner, and R. V. O’Neill. 2001. Landscape ecology in theory and practice: Pattern and process. New York: Springer.

  A comprehensive textbook on landscape ecology that explores the causes of landscape patterns and their implications for disturbance dynamics, organismal responses, and ecosystem processes. Also includes an introduction to landscape modeling.