Highly variable rates of survival to metamorphosis in wild boreal toads (Anaxyrus boreas boreas)
Life history theory suggests that long-lived, pond-breeding amphibians should have low and highly variable early life-stage survival rates, but this theoretical expectation is often untested and the causes of variation are usually unknown. We evaluated the impact of hydroperiod, presence of a pathogen (Batrachochytrium dendrobatidis [Bd]), presence of a potential predator (cutthroat trout Oncorhychus clarki stomias), and whether animals had been reintroduced into a site, on survival of early life stages of boreal toads (Anaxyrus boreas boreas). We used a multi-state mark-recapture framework to estimate survival of boreal toad embryos from egg to metamorphosis at four sites over five years. We found substantial spatial and temporal variation in survival to metamorphosis and documented some evidence that monthly tadpole survival was lower in sites with Bd, and without trout, and at permanent sites. Our results support theories of amphibian life history, aid in the management of this species of conservation concern, and contribute to our knowledge of the ecology of the species. Additionally, we present methodology that allows practitioners to account for different lengths of time between sampling periods when estimating survival probabilities and which is especially applicable to organisms with distinct biological stages.