Integrating Museum and GIS Data to Identify Changes in Species Distributions Driven by a Disturbance-Induced Invasion

Two topics of great importance to conservation biologists and managers are the impact of habitat degradation on species' distributions and the effects of invasive species on the decline of other species. I evaluate the interaction of these threats by comparing the impact of a native invasive amphibian species on a formerly allotopic amphibian species in disturbed versus undisturbed habitat. Fowler's Toad (Anaxyrus fowleri) historically thrived in a range of habitats including urban and suburban areas in the mid-twentieth century, but has recently undergone a range contraction concurrent with the spread of the Coastal Plain Toad (Incilius nebulifer) into recently disturbed habitat. Contemporary surveys of historical collection sites obtained from museum records of vouchered specimens were used to document changes in the distribution of both species over the past half-century. Temporal changes in habitat disturbance at collection sites were detected by comparing historical aerial photographs with current remote sensing data. Analysis of species' distribution in different disturbance levels showed that A. fowleri is unaffected by disturbance in areas where I. nebulifer is absent, but at sites where the species are sympatric the distribution of A. fowleri in degraded habitat contracted while the expansion of I. nebulifer increased substantially. This study demonstrates that anthropogenic habitat alteration can facilitate dispersal and colonization by an invasive species, resulting in the significant decline of a native species that is otherwise tolerant of disturbance.