Small cumulative survival costs of enzootic disease could suppress long-term population size

Abstract

Fungal pathogens can cause epizootics that result in widespread mortality and rapid population declines in some species. However, even in the absence of high disease-induced mortality, enzootic mycoses could have large-scale impacts on host population dynamics. Here, we examined the effects of ophidiomycosis, an enzootic fungal disease, on a Louisiana snake community over a 3-year period using a multi-state Jolly–Seber model with disease-state misclassification. We did not detect a difference between the average weekly apparent survival probability of uninfected and infected hosts for either Nerodia species or Thamnophis proximus . We also found a strong positive association between snout-to-vent length and weekly apparent survival probability across all species. We found that recruitment of infected hosts was slightly higher than recruitment of uninfected hosts for two of the three species. Population projections suggested divergent trajectories between disease-present and disease-absent scenarios, where disease-absent populations had higher abundance than disease-present populations. Our results highlight that small differences in survival can accumulate over time, as well as the challenges of quantifying population-level impacts of enzootic diseases when survival differences are not readily detected, underscoring the importance of continued long-term monitoring to assess whether ophidiomycosis affects snake population dynamics.