Influence of demography and environment on persistence in toad populations

Abstract

Effective conservation of rare species requires an understanding of how potential threats affect population dynamics. Unfortunately, information about population demographics prior to threats (i.e., baseline data) is lacking for many species. Perturbations, caused by climate change, disease, or other stressors can lead to population declines and heightened conservation concerns. Boreal toads (Anaxyrus boreas boreas) have undergone rangewide declines due mostly to the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd), with only a few sizable populations remaining in the southern Rocky Mountains, USA, that are disease‐free. Despite the apparent region‐wide occurrence of Bd, our focal populations in central Colorado were disease free over a 14‐year capture‐mark‐recapture study until the recent discovery of Bd at one of the sites. We used recapture data and the Pradel reverse‐time model to assess the influence of environmental and site‐specific conditions on survival and recruitment. We then forecast changes in the toad populations with 2 growth models; one using an average lambda value to initiate the projection, and one using the most recent value to capture potential effects of the incursion of disease into the system. Adult survival was consistently high at the 3 sites, whereas recruitment was more variable and markedly low at 1 site. We found that active season moisture, active season length, and breeding shallows were important factors in estimating recruitment. Population growth models indicated a slight increase at 1 site but decreasing trends at the 2 other sites, possibly influenced by low recruitment. Insight into declining species management can be gained from information on survival and recruitment and how site‐specific environmental factors influence these demographic parameters. Our data are particularly useful because they provide baseline data on demographics in populations before a disease outbreak and enhance our ability to detect changes in population parameters potentially caused by the disease. © 2016 The Wildlife Society.

Estimating the probability of movement and partitioning seasonal survival in an amphibian metapopulation

“…The survival probability estimates given above apply only to resident individuals and are similar, but slightly higher than previous estimates that did not account for transience (0.52-0.88, Lambert et al 2016,~0.77, Scherer et al 2008, 0.75-0.78, Muths and Scherer 2011.…”

“…Boreal toads (A. boreas boreas) are one of a handful of species in North America that are affected by Bd (Muths 2003. Investigations have focused on (1) demography of a few, well-studied populations, largely ignoring dispersal (Muths et al 2006, 2008, Lambert et al 2016, and (2) monitoring breeding and disease status in known historic populations (Loeffler 2001, Muths 2003. Investigations have focused on (1) demography of a few, well-studied populations, largely ignoring dispersal (Muths et al 2006, 2008, Lambert et al 2016, and (2) monitoring breeding and disease status in known historic populations (Loeffler 2001, Muths 2003.…”

“…Conservation of boreal toads in the southern Rocky Mountain (SRM) region has been a concern for decades (e.g., Carey 1993, Loeffler 2001. Investigations have focused on (1) demography of a few, well-studied populations, largely ignoring dispersal (Muths et al 2006, 2008, Lambert et al 2016, and (2) monitoring breeding and disease status in known historic populations (Loeffler 2001, Muths 2003. With the recent observation of Bd in the largest known remaining set of breeding sites in the SRM (the metapopulation described below), questions about movement and its role in disease spread are of elevated interest.…”

Twenty‐nine years of population dynamics in a small‐bodied montane amphibian

“…, Lambert et al. ), and reduce genetic connectivity among chorus frog populations because of reduced moisture (Watts et al. ).…”

“…Specifically, shifts in the form and timing of precipitation (MacCracken et al 2003, Barnett et al 2005, Parry et al 2010 have the potential to affect breeding phenology (Corn and Muths 2002), precipitating increased probability of reproductive failure (Corn 2005, Amburgey et al 2014. Climate change may affect adult survival via reductions in snowpack (Scherer et al 2008, Williams et al 2015, Lambert et al 2016, and reduce genetic connectivity among chorus frog populations because of reduced moisture (Watts et al 2015).…”