Coexistence within an endangered predator–prey community in California vernal pools

Abstract

Abstract Globally endangered ecosystems, such as ephemeral wetlands, are often critical habitat for multiple interacting imperilled species. To conserve this biodiversity, managers must consider both species‐specific resource requirements and mechanisms for endangered species coexistence under variable habitat conditions. We examined communities native to California playa pools, ephemeral wetlands that have declined by >90% from their historic extent. Specifically, we describe the diet of a federally Threatened amphibian (Ambystoma californiense), and characterise interactions between this amphibian and two federally Endangered macrocrustaceans (Branchinecta conservatio and Lepidurus packardi) across three rain years to understand how these imperilled species coexist. We examined the dietary preferences of A. californiense larvae, metamorphs, juveniles, and breeding adults, and determined how prey electivity by larval A. californiense differs between natural playa pools and human‐modified stock ponds. Within playa pools, both breeding adult and larval A. californiense preyed extensively on L. packardi, whereas fully terrestrial juveniles had relatively empty stomachs. We provide evidence for size‐moderated optimal foraging by larval A. californiense, and show that larval prey differed dramatically between playa pools and stock ponds. Additionally, an ontogenetic progression from smaller to larger prey gave the relatively large, endangered macrocrustaceans an early‐season temporal refuge, during which they reached maturity in all three rain years. Consistent with complex life cycle theory, our results suggest that ephemeral wetland habitat offers abundant food resources for A. californiense relative to terrestrial habitat. Our findings also suggest that diet flexibility facilitates the persistence of this imperilled amphibian in human‐modified stock ponds. Temporal offsets in prey maturation rates and ontogenetic shifts in predator diets are likely to facilitate coexistence among the focal endangered species. We highlight the importance of accounting for spatial and temporal variation in interspecific interactions when predicting the effects of environmental change on biodiversity, particularly in highly threatened ecosystems.