Dynamic approaches to modeling wetland community responses to changing water availability

Open Access
Davis, Courtney Lynn
Graduate Program:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 10, 2015
Committee Members:
  • David Andrew Miller, Thesis Advisor
  • Amphibian communities
  • climate change
  • multispecies occupancy
Of the myriad of issues facing amphibian populations worldwide, the direct and indirect effects of climate change are among the most difficult to isolate and predict. The effects of climate change on distributions of individual species do not occur in isolation but instead are the outcome of interactions between climate, co-occurring species, and the physical environment in which interactions occur. However, current models do not consider community dynamics or complex interactions between climate and the physical environment, making it difficult to predict how community assemblages will be affected. For wetland communities, in particular, shifts in regional climate are likely to have profound and ongoing effects on site suitability and as a result, species composition. We examined how patterns of amphibian occurrence responded to extreme climate events at St. Marks National Wildlife Refuge from 2009 – 2014, where fluctuations in precipitation have resulted in periods of extreme drought as well as expansive flooding. High rainfall associated with Tropical Storm Debby in 2012 allowed for the colonization of predatory fishes to many previously isolated wetlands. Using long-term monitoring data, we parameterized a set of dynamic multispecies occupancy models that incorporate habitat dynamics and species interactions to investigate the occurrence dynamics of three representative amphibian species in response to changing water availability (Chapter 1). Additionally, we investigate how an adaptation to variable environmental conditions – facultative paedomorphism, as exhibited in one of these three species – further structures responses to these disturbance events (Chapter 2). Drought and predatory fishes had differing effects on amphibian occurrence dynamics for each of the three species we examined. The occupancy of ornate chorus frogs (Pseudacris ornata), a species that preferentially selects ephemeral wetlands to breed, increased from 30% to 50% of surveyed wetlands during periods of drought in 2010 – 2011. Mole salamander (Ambystoma talpoideum) occupancy, however, decreased from 40% to 25% due to the reduction of wetland hydroperiod at this time. For both of these species, fishes negatively impacted occurrence; wetlands occupied by fish were rarely, if ever, colonized by either the ornate chorus frog or the mole salamander. Despite the ability to modify its phenotype in favorable environmental conditions, the mole salamander occupied less than 20% of wetlands by 2014, suggesting that conditions remained unfavorable for this species, in particular. Pig frog (Rana grylio) occupancy, however, was not influenced by changes in climate during the study or changes in fish presence on the refuge. Projecting community composition under various climate scenarios (i.e., future increases in drought and/or flood frequency), we further demonstrate that responses to changing water availability are linked to species traits, characteristics of individual wetlands, and the interaction between climate and the physical environment.