A Tale of Two Species -- Species distribution models for two cryptic Cricket Frog (Acris) species in syntopy

Enigmatic species decline is arguably the most alarming aspect of the global amphibian population collapse. The Cricket Frogs (genus Acris) are common species that are exhibiting enigmatic declines at their northern range limits, a well-documented progression that has remained unexplained for decades. Though many researchers have offered hypotheses, the true causes of decline are difficult to isolate due to noise from a variety of external factors that may or may not be contributing. In Virginia and North Carolina, the population dynamics of A. gryllus (Southern Cricket Frog) have been obscured by its syntopy and sympatry with its sibling species, A. crepitans (Northern Cricket Frog). However, recent surveys using acoustic technology and analysis of historic data have uncovered the disappearance of A. gryllus from a large portion of northern North Carolina. This area is adjacent to the northern limit of the range of A. gryllus in Virginia, where a 2010 survey of Acris species revealed southward recession of the range of A. gryllus in the presence of thriving A. crepitans populations. Because the two species prefer similar habitat, the disappearance of A. gryllus is enigmatic. Using the unique syntopic and sympatric dynamic between these species in conjunction with distribution modeling techniques in a Geographic Information System (GIS), I identified factors affecting habitat use of A. gryllus and A. crepitans in their overlapping ranges. Specifically, I developed a species distribution model (SDM) that predicts the difference in habitat use between the two species, then used multinomial logistic regressions to relate three levels of abundance for each species to environmental variables and potential anthropogenic stressors. I found that A. gryllus prefers pine forests, lowland forested swamps, and is less tolerant of anthropogenic stressors than A. crepitans, which tolerates drier and less pristine habitats. The results from this paper can be used to develop hypothesis regarding the range contraction of A. gryllus and can be implemented into a framework of adaptive management to curb the disappearance of A. gryllus until further data become available that allow fine-tuning of management actions