Effect of habitat area and isolation on fragmented animal populations

Abstract

Habitat destruction has driven many once-contiguous animal populations into remnant patches of varying size and isolation. The underlying framework for the conservation of fragmented populations is founded on the principles of island biogeography, wherein the probability of species occurrence in habitat patches varies as a function of patch size and isolation. Despite decades of research, the general importance of patch area and isolation as predictors of species occupancy in fragmented terrestrial systems remains unknown because of a lack of quantitative synthesis. Here, we compile occupancy data from 1,015 bird, mammal, reptile, amphibian, and invertebrate population networks on 6 continents and show that patch area and isolation are surprisingly poor predictors of occupancy for most species. We examine factors such as improper scaling and biases in species representation as explanations and find that the type of land cover separating patches most strongly affects the sensitivity of species to patch area and isolation. Our results indicate that patch area and isolation are indeed important factors affecting the occupancy of many species, but properties of the intervening matrix should not be ignored. Improving matrix quality may lead to higher conservation returns than manipulating the size and configuration of remnant patches for many of the species that persist in the aftermath of habitat destruction.incidence function ͉ island biogeography ͉ logistic regression ͉ metaanalysis ͉ occupancy H abitat loss and fragmentation are major threats to terrestrial biodiversity (1). Globally, Ϸ40% of land has been converted for agricultural use (2), and regions as diverse as the eastern United States, the Philippines, and Ghana have lost Ͼ90% of their natural habitat (3, 4). Conservation theory and practice are founded on the principle that large habitat patches have more species than small ones and connected patches have more species than isolated ones (5). Although few would dispute this basic premise, we still do not know the general value of patch area and isolation as predictors of species occupancy in fragmented terrestrial systems. Despite hundreds of patch occupancy studies over Ͼ4 decades, there has been no quantitative synthesis of these findings. Several syntheses have examined species-area and diversity relationships (6, 7), but the species occupancy patterns that underlie diversity patterns in fragmented landscapes have been overlooked (8). How important is patch isolation relative to patch size in determining where species occur, and how consistent are these effects across diverse taxonomic groups? These are foundational, yet unanswered, questions for ecology and conservation biology.We synthesized patch occupancy data from 89 studies of terrestrial fauna on 6 continents (Table S1) to determine how patch area and isolation affect species' occurrence patterns. Collectively, these studies recorded the occurrence of 785 animal species (Table 1) in 1,015 population networks surveyed in 12,370 discrete habitat p...

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“…This is in agreement with previous studies showing the importance of the bad patches (habitat matrix) [45,46]. For both kernels, increasing the landscape period L reduces the total proportion of good habitat required for an invasion to occur.…”

Importance of matrix habitats in maintaining biological diversity

“…We strongly agree with Prugh et al (1) that resource management practices that maintain or improve the suitability of the matrix are fundamental to the conservation of biodiversity. Many studies have highlighted the importance of the matrix in agricultural areas (13), temperate forests (11), and tropical forests (e.g., 14 and 15), such as through work on countryside biogeography (16).…”

“…This is an important result given the centrality of the patch size-isolation tenet to much of academic conservation biology and its wide application in conservation planning and resource management. In fact, the findings of Prugh et al (1) are largely congruent with other analyses, such as the extensive assessment of fragmentation experiments by Debinski and Holt (2). Collectively these analyses raise significant questions about the merits of island biogeographic theory as a basis for conservation biology.…”

“…This will often blur the distinction between ''habitat patches'' and the surrounding ''matrix'' [sensu Forman (10)]; this, in turn, weakens the effect of patch size and isolation effects. Hence, it is not surprising that Prugh et al (1) found that the type of land cover separating habitat patches most strongly affected sensitivity of species to patch area and isolation. Many of these species may be responding to the overall suitability of landscapes because the landscape matrix surrounding the habitat patches is actually functioning as breeding or foraging habitat or both, rather than simply defining and isolating the patches.…”

The concept of green infrastructure and urban landscape planning: a challenge for urban forestry planning in Belgrade, Serbia

“…However, this metric has several limitations, among which is that it cannot illustrate spatial properties and the distribution of elements across the analysed landscape (Botequilha Leitao et al 2006). Furthermore, working with a metric class which refers only to the size or number of NSN elements yields weaker results than using an integral metric of the structural relationship inside a landscape matrix that is hostile to natural processes (human dominated matrix types - Prugh et al 2008). We can, therefore, conclude that the thrust of our analysis is focused on the zones in which the influence of NSN elements is reduced or absent.…”