The aim of this study was to compare the effects of arginine vasotocin (AVT) administration in the endangered boreal toad (Bufo boreas boreas) and common Fowler’s toad (Bufo fowleri). The objectives of this study were to determine if AVT could elicit: 1) calling, and 2) amplexus behaviors. Toads were paired into single male:female groups and administered AVT at varying concentrations: 0.1, 1.0, 5.0, 10.0 and 25.0 μg/g and in different combinations: 1) only male was treated; 2) only female was treated, and 3) both male and female treated. AVT failed to stimulate any breeding behavior in the boreal toad, but the administration of AVT to both B. Fowleri genders significantly affected the duration of amplexus (p<0.0347). Also, the concentration of AVT significantly affected the length of amplexus (p<0.0429) and call frequency (p<0.0294). These results will be valuable for breeding programs where animals are failing to show natural reproductive behavior.

Two of the most pervasive threats to species biodiversity are invasive species and habitat loss and degradation. Invasive species are often relatively insensitive to disturbance and many expand their range into disturbed and fragmented habitats. This dissertation uses an interdisciplinary approach to investigate how anthropogenic habitat disturbance is precipitating a range expansion in an invasive toad species, Bufo nebulifer, which is driving a decline in its native congener, B. fowleri. I employed a remote sensing and GIS study using historical data to compare changes in the two species distributions and habitat changes, a molecular genetic study to identify interspecific hybrids and their potential effects on the parental species, and an experimental ecology study to look at the effects of competition and predation on the two species. The results of the landscape level analyses of species' distributional changes in different disturbance levels showed that both species' distributions have changed significantly. The distributions of the two species are inversely affected by habitat disturbance; the distribution of B. fowleri in highly degraded habitat has contracted while the expansion of B. nebulifer increased substantially. The molecular genetic study successfully demonstrated the use of nuclear and mitochondrial markers to identify cryptic hybrids and their maternal lineage. Three hybrids were detected using nuclear introns and a morphologically cryptic hybrid was identified using mitochondrial DNA as the progeny of a cross that was previously thought to be inviable. Although relatively few hybrids were currently found, the identification of a cryptic hybrid implies that the rate of historical hybridization may have been drastically underestimated. Ecological studies showed that competition with B. nebulifer tadpoles had a negative effect on both body size measures and survival to metamorphosis for B. fowleri tadpoles. The addition of predators to experiment did not favor the survival of B. fowleri over B. nebulifer. Bufo fowleri's inability to compete with its invasive congener could be a driving mechanism for the decline of B. fowleri and the expansion of B. nebulifer. The methods discussed in this dissertation offer promising and practical new approaches for evaluating and managing changes in the distribution of species of conservation concern.