Effects of hydroperiods and predator communities on Pseudacris maculata: A model species for climate change impacts on amphibians

Amphibians are particularly sensitive to environmental conditions due their permeable skin and their reliance on aquatic environments for breeding and larval development, making them highly susceptible to climate change. Climate change has been previously associated with amphibian declines directly by altering habitat suitability or indirectly by changing community interactions within altered habitats.;Hydroperiod, or the amount of time water is present in a pond, is crucial to larval development, and climate change is predicted to reduce ephemeral hydroperiods in some regions, truncating the time available for larval development. Some amphibian species can plastically respond to reduced hydroperiod by accelerating rates of development and potentially compromising overall growth in order to reach metamorphosis faster. Little is known as to how rapidly organisms may adapt to climate change altered conditions, and plasticity may serve as a buffer to the immediate effects of climate change, allowing for increased survival without rapid adaptation. However, plasticity may not be present in all species and the costs and limits of plasticity are largely unknown. Climate change still may negatively impact populations that can plastically respond through reduced size at metamorphosis resulting from accelerated development, compromised immune system function post metamorphosis, and decreased larval, juvenile, or adult survival. By better understanding the current limits and costs of plasticity, better predictions concerning amphibian persistence and survival can be made.;In addition to hydroperiod, climate change will likely alter community assemblages and interactions, and these altered interactions could also cause declines. Some species of amphibian larvae have been show to plastically respond to predator presence by altering developmental rate in response to the stress of potential predation. Predator presence, denoted by a released, chemical cue, is also associated with altered behavior such as decreased foraging that affects larval growth and development by altering resource use. Many amphibian predators are also reliant on aquatic environments, suggesting that predator-prey interactions will likely be altered by climate change. Predators may be concentrated in reduced habitats with their prey and may serve as a secondary pressure to accelerate metamorphosis. By better understanding the effect predator cue has on amphibian development in concert with hydroperiod reductions, we can better predict and ameliorate the detrimental effects of climate change.;Specifically, my work has focused on understanding the effects of climate change on amphibians by focusing on the complex interactions in communities in concert with altered habitat conditions. I have focused on the impact of hydroperiod in concert with predator assemblages in the lab and in nature, utilizing Pseudacris maculata (the boreal chorus frog) as a model system. P. maculata are distributed nearly statewide in Colorado, USA, across a wide range of elevations and habitat types and across much of the northwestern USA upwards into Canada. Populations exist along an elevational gradient spanning over a 1280 m difference in altitude in Colorado and exist in a range of hydroperiods and predator communities. Common pond-dwelling predators in this system are primarily fish (native and introduced), Ambystoma tigrinum (tiger salamanders), and odonate larvae. Due to P. maculata's wide and varied distribution, they are ideal for investigating the effects of various habitat components on persistence and survival. P. maculata also have a limited dispersal distance, making them particularly sensitive to fine-scale changes in their local habitats and potentially facilitating local adaptation.;In my first chapter, I analyzed the effects of truncated hydroperiod and odonate larvae predator cues, individually and combined, on metamorphosis of P. maculata. In a climate-change scenario where hydroperiod is drastically reduced and predator cue is concentrated within the remaining habitat, tadpoles responded plastically by accelerating development with no difference in size at metamorphosis. However, mortality was much higher in treatments experiencing hydroperiod reductions, indicating that, while plasticity may facilitate escape from suboptimal conditions, populations may still be negatively impacted through heightened mortality.;In my second chapter, I surveyed a broad spectrum of natural conditions to better understand the impact of current habitat and landscape characteristics on occupancy by P. maculata. We focused on modeling presence of tadpoles in order to identify likely breeding sites important for population persistence. Using a robust occupancy analysis design that corrects for imperfect detection, I was able to clarify the current factors most important to describing patterns in occupancy. Predator communities strongly impact presence by P. maculata tadpoles, with fish excluding tadpoles almost exclusively. Odonate larvae and tadpoles frequently co-occurred, highlighting the relevance of my first chapter and the role predator cue might play in future climate-altered conditions. In addition, intermediate hydroperiod ponds that do not dry rapidly but exclude fish had the highest levels of occupancy probability, though hydroperiod was not well supported in the analyses. (Abstract shortened by UMI.).