Spatial connectivity moderates the effect of predatory fish on salamander metapopulation dynamics

In predator-prey metapopulations, persistence of prey in patches with predators may depend on the rescue effect in which immigration from nearby sources prevents local extinction. Thus, constraints on spatial connectivity may have important implications for predator-prey coexistence. We tested the hypothesis that metapopulation dynamics of Ambystoma tigrinum (tiger salamander) depend on combined effects of predatory fish and spatial connectivity. Because matrix heterogeneity can influence dispersal, we also considered how a proximate constraint on amphibian dispersal-desiccation risk-scales up to influence metapopulation dynamics for A. tigrinum . Occupancy and subsequent turnover patterns were quantified in a network of 90 wetlands for three years in an agricultural landscape in Illinois. Our previous field experiments demonstrated that desiccation risk varies among matrix habitats, and that individuals orient movements towards habitat with low desiccation risk. We used cost-distance modeling to generate a connectivity metric that accounted for desiccation risk. Occupancy and colonization probabilities were related negatively to fish occupancy and positively to connectivity. Matrix structure had a strong influence on colonization, and the connectivity metric based on desiccation risk was a better predictor of colonization than alternative metrics. The positive effect of desiccation-informed connectivity on colonization was strongest in wetlands with fish, indicating matrix composition can moderate the effects of predation on amphibians. We detected a rescue effect in which extinction probability was related negatively to connectivity, and this effect was strongest in sites with fish. The matrix did not have a strong effect on occupancy or extinction probabilities, and we discuss why matrix effects may vary for different aspects of population turnover. Our results suggest effects of fish predators on metapopulation dynamics of amphibians depend on spatial connectivity, and that immigration may be essential for maintaining persistence of amphibians in systems with fish. This study also demonstrates that the mechanisms underlying dispersal limitation for A. tigrinum may include desiccation risk.