title: High adult mortality in disease-challenged frog populations increases vulnerability to drought.
abstract: 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.
authors.affiliation: Fenner School of Environment and Society, College of Medicine, Biology and Environment, Australian National University, Canberra, ACT, 0200, Australia. ben.scheele@anu.edu.au.|One Health Research Group, College of Public Health, Medical and Veterinary Sciences, James Cook University, 1 James Cook Drive, Townsville City, QLD, 4811, Australia. ben.scheele@anu.edu.au.
authors.forename: Ben C
authors.initials: BC
authors.lastname: Scheele
authors.affiliation: NSW Office of Environment and Heritage, PO Box 544, Albury, NSW 2640, Australia.
authors.forename: David A
authors.initials: DA
authors.lastname: Hunter
authors.affiliation: Fenner School of Environment and Society, College of Medicine, Biology and Environment, Australian National University, Canberra, ACT, 0200, Australia.
authors.forename: Sam C
authors.initials: SC
authors.lastname: Banks
authors.affiliation: Fenner School of Environment and Society, College of Medicine, Biology and Environment, Australian National University, Canberra, ACT, 0200, Australia.
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Pierson
authors.affiliation: One Health Research Group, College of Public Health, Medical and Veterinary Sciences, James Cook University, 1 James Cook Drive, Townsville City, QLD, 4811, Australia.
authors.forename: Lee F
authors.initials: LF
authors.lastname: Skerratt
authors.affiliation: One Health Research Group, College of Public Health, Medical and Veterinary Sciences, James Cook University, 1 James Cook Drive, Townsville City, QLD, 4811, Australia.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Webb
authors.affiliation: Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Burwood, Vic 3125, Australia.
authors.forename: Don A
authors.initials: DA
authors.lastname: Driscoll
mesh_terms: D000818:Animals; D001001:Anura / Q000502:physiology; D001315:Australia / Q000453:epidemiology; D008411:Chytridiomycota / Q000502:physiology*; D003710:Demography; D055864:Droughts; D056727:Endangered Species; D005260:Female; D008297:Male; D009181:Mycoses / Q000382:microbiology / Q000401:mortality / Q000662:veterinary*; D011157:Population Dynamics
keywords: amphibian declines; chytrid fungus; demography; environmental stochasticity; life history; niche contraction; population dynamics; recruitment failure