Data from: High adult mortality in disease-challenged frog populations increases vulnerability to drought

Pathogen emergence can drive major changes in host population demography,
with implications for population dynamics and sensitivity to environmental
fluctuations. The amphibian disease chytridiomycosis, caused by infection
with the fungal pathogen Batrachochytrium dendrobatidis (Bd), is
implicated in the severe decline of over 200 amphibian species. In species
that have declined but not become extinct, Bd persists and can cause
substantial ongoing mortality. High rates of mortality associated with Bd
may drive major changes in host demography, but this process is poorly
understood. Here, we compared population age structure of Bd-infected
populations, Bd-free populations and museum specimens collected prior to
Bd emergence for the endangered Australian frog, Litoria verreauxii alpina
(alpine tree frog). We then used population simulations to investigate how
pathogen-associated demographic shifts affect the ability of populations
to persist in stochastic environments. We found that Bd-infected
populations have a severely truncated age structure associated with very
high rates of annual adult mortality. Near-complete annual adult turnover
in Bd-infected populations means that individuals breed once, compared
with Bd-free populations where adults may breed across multiple years. Our
simulations showed that truncated age structure erodes the capacity of
populations to withstand periodic recruitment failure; a common challenge
for species reproducing in uncertain environments. We document previously
undescribed demographic shifts associated with a globally emerging
pathogen and demonstrate how these shifts alter host ecology. Truncation
of age structure associated with Bd effectively reduces host niche width
and can help explain the contraction of L. v. alpina to perennial
waterbodies where the risk of drought-induced recruitment failure is low.
Reduced capacity to tolerate other sources of mortality may explain
variation in decline severity among other chytridiomycosis-challenged
species and highlights the potential to mitigate disease impacts through
minimizing other sources of mortality.