Accessible habitat: an improved measure of the effects of habitat loss and roads on wildlife populations
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Habitat loss is known to be the main cause of the current global decline in biodiversity, and roads are thought to affect the persistence of many species by restricting movement between habitat patches. However, measuring the effects of roads and habitat loss separately means that the configuration of habitat relative to roads is not considered. We present a new measure of the combined effects of roads and habitat amount: accessible habitat. We define accessible habitat as the amount of habitat that can be reached from a focal habitat patch without crossing a road, and make available a GIS tool to calculate accessible habitat. We hypothesize that accessible habitat will be the best predictor of the effects of habitat loss and roads for any species for which roads are a major barrier to movement. We conducted a case study of the utility of the accessible habitat concept using a data set of anuran species richness from 27 ponds near a motorway. We defined habitat as forest in this example. We found that accessible habitat was not only a better predictor of species richness than total habitat in the landscape or distance to the motorway, but also that by failing to consider accessible habitat we would have incorrectly concluded that there was no effect of habitat amount on species richness.
KeywordsHabitat fragmentation Accessible habitat Road ecology Ontario Amphibians Species richness Habitat loss GIS Barriers Deforestation
This study would not have been possible without the co-operation of many private landowners. We would also like to thank Kristen Keyes and Alison Callahan for their help in the field, many volunteers (especially Katy Heady, Wes von Papineau, Paul Sokoloff and Anne and Dean Keyes) for their help with the fieldwork and with logistic support, and the members of the GLEL for their helpful comments on the manuscript. Funding was provided through a Natural Sciences and Engineering Research Council of Canada (NSERC) Doctoral Scholarship and Carleton University scholarships to Felix Eigenbrod, and NSERC Discovery Grants to Stephen J. Hecnar and Lenore Fahrig.
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