RAPID: The role of disturbance in climate-driven hybrid zone dynamics

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Climate change is one of the most pressing issues of our time, yet the cascading effects of climate change on species and ecosystems remain unclear. Many species may be forced to shift their geographic range to escape unsuitable climates and pursue more favorable conditions. Range shifts may lead to novel interactions with other species including competition for food or other resources, and even interbreeding or hybridization. These new species interactions will play a critical role in determining whether or not species are able to colonize otherwise favorable habitats. Furthermore, punctuated disturbances such as fire may change the competitive balance at range edges via altered habitat structure and resource availability. In this project the PIs will examine the impact of a recent fire on the range-edge interactions between two closely related species of small mammals (woodrats). The PIs have previously documented how one species is overtaking the range of the other in response to climate conditions, especially drought. However, they predict the fire will substantially change how the species interact with the environment (e.g., feeding, nest-building) and with each other (e.g., competition and tendency to interbreed), dramatically changing and perhaps reversing the direction of range-edge movement. The PIs and their students will monitor the population using capture-mark-recapture to quantify individual survival, reproduction, dispersal, and resource use, especially dietary changes. This information will be used to build a predictive model of how disturbance interacts with annual weather variation to forecast how species’ distributional boundaries will shift under future conditions. Predicting how species’ distributions will respond to environmental change requires estimation of the mechanisms driving range edge dynamics. When distributional edges are also parapatric range boundaries between closely related species, a wide range of ecological and genomic interactions may govern species’ responses to environmental change. The role of climate in determining range edge boundaries and hybrid zone dynamics is only beginning to be understood in a few terrestrial vertebrate systems; nearly nothing is known of how punctuated disturbance may alter range edge and hybrid zone dynamics. In this project the PIs leverage long-term data collection at a parapatric range boundary between two closely related species to make informed predictions about how a recent fire will alter range edge dynamics via changes in individual fitness and competitive interactions. The PIs predict that the recent fire will substantially alter fitness and dispersal patterns in the contact zone, potentially leading to a reversal of the range edge movements they previously documented. The PIs will test these predictions using intensive capture-mark-recapture to quantify survival, reproduction, dispersal, and resource use. The PIs will integrate these data into a predictive model of how ecological and environmental processes interact to govern the shifting range margin between these two closely-related species. More generally, this work will provide a practical and conceptual framework for investigating and forecasting how climate change and local disturbance can alter a fundamental species-level characteristic (range-edge boundaries) via differential impacts on individual-level characteristics such as survival, reproduction, resource use and dispersal.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.