Disease and climate effects on individuals drive post‐reintroduction population dynamics of an endangered amphibian

Abstract

The emergence of novel pathogens often has dramatic negative effects on previously unexposed host populations. Subsequent disease can drive populations and even species to extinction. After establishment in populations, pathogens can continue to affect host dynamics, influencing the success or failure of species recovery efforts. However, quantifying the effect of pathogens on host populations in the wild is challenging because individual hosts and their pathogens are difficult to observe. Here, we use long‐term mark–recapture data to describe the dynamics of reintroduced populations of an endangered amphibian (Rana sierrae) and evaluate the success of these recovery efforts in the presence of a recently emerged pathogen, the amphibian chytrid fungus Batrachochytrium dendrobatidis. We find that high B. dendrobatidis infection intensities are associated with increases in frog detectability and reductions in survival. When average infection intensities are high, adults are more likely to gain infections and less likely to lose infections. We also find evidence for intensity‐dependent survival, with heavily infected individuals suffering higher mortality. These results highlight the need in disease ecology for probabilistic approaches that account for uncertainty in infection intensity using imperfect observational data. Such approaches can advance the understanding of disease impacts on host population dynamics, and in the current study will improve the effectiveness of species conservation actions.

Survival cost to relocation does not reduce population self‐sustainability in an amphibian

“…) but few studies have evaluated relocation success using capture–recapture data (Howell et al. , Joseph and Knapp ). Our study is one of the few to highlight age‐dependent survival loss associated with amphibian relocation using a comparative demographic approach.…”

“…Relocation have become increasingly popular among wildlife managers, especially in conservation programs dedicated to mitigate the effect of pathogens (Garner et al 2016) and habitat loss and degradation on amphibian populations (Harding et al 2016). To date, dozens of relation programs have been implemented (Germano andBishop 2009, Harding et al 2016) but few studies have evaluated relocation success using capture-recapture data (Howell et al 2016, Joseph andKnapp 2018). Our study is one of the few to highlight age-dependent survival loss associated with amphibian relocation using a comparative demographic approach.…”

Population dynamics ofRana sierraeat Dusy Basin: influence of non‐native predators, drought, and restoration potential

“…With evidence of persistence with Bd emerging in some nearby populations (Joseph and Knapp 2018) as well as active treatment methods to counteract the effects of Bd (Woodhams et al 2011, Knapp et al 2016, there is growing interest in re-introducing frogs to areas where they were extirpated. We found significant effects of drought-related environmental variables on frog abundance during the 14 yr prior to extirpation, including lake surface area and the propensity of lakes to dry out.…”

“…Translocation experiments in Yosemite National Park are underway in an attempt to re-populate suitable, historic habitat (Joseph and Knapp 2018). Translocation experiments in Yosemite National Park are underway in an attempt to re-populate suitable, historic habitat (Joseph and Knapp 2018).…”

“…Translocation experiments in Yosemite National Park are underway in an attempt to re-populate suitable, historic habitat (Joseph and Knapp 2018). This variation has recently also been shown to exist across populations of R. sierrae (Joseph and Knapp 2018). Important to reintroduction efforts is the observation that different frog species show varying degrees of susceptibility to chytridiomycosis (Fisher et al 2009).…”