Effects Of Environmental And Anthropogenic Factors On The Range Contraction Of Bird And Mammal Species

The largest contributor to biodiversity loss is habitat destruction caused by humans. A common consequence of habitat destruction is a reduction in the geographic range of a species. Little research has been done to separate the contribution of anthropogenic and environmental variables to the extinction or persistence of species that have experienced range contraction. In this thesis, I examined the relative effects of several variables (elevation, mean annual precipitation, mean annual temperature, human population density, distance from roads, and proportion of land converted to built-up land, cropland, and rangeland) on the geographic ranges of declining bird and mammal species from all continents except Antarctica. Species were examined separately to determine which variables might have influenced the contraction in the ranges of individual species. The results of each variable were compiled both by individual species and by continent. My results suggest environmental variables have a greater effect on species persistence and extinction than do the anthropogenic variables I tested. Mean annual precipitation was most often identified as having a positive or negative influence on species persistence. The findings of this study provide a comprehensive assessment of the effects of environmental and anthropogenic variables on the persistence of both individual species and all species from each of the 6 continents included in the analyses. These findings could allow conservation biologists to better predict areas where a declining species will persist, thereby enabling the prioritization of areas for the establishment of wildlife reserves