Geology topics

Scott C. Schneider

Publications and source records attributed to Scott C. Schneider.

3 recordsLinked to original sources

USGS2022

Compensatory recruitment unlikely in high-elevation amphibian populations challenged with disease

Understanding the causes of population variation in host response to disease, and the mechanisms of persistence, can serve as vital information for species conservation. One such mechanism of population persistence that has gained support is the demographic process of compensatory recruitment. Host populations may persist by increasing recruitment to compensate for reduced survival due to infection, thus limiting the negative effects of the disease on population trajectories. However, high-elevation populations are inherently vulnerable to stochastic processes and may be limited in their ability to exhibit compensatory recruitment relative to lower elevation populations. We use long-term mark–recapture data from five populations of boreal toads Anaxyrus boreas boreas , across an elevational gradient in Colorado, before and after pathogen arrival to assess whether populations can persist with Batrachochytrium dendrobatidis ( Bd ) via compensatory recruitment. Prior to pathogen arrival, we found a life-history trade-off between survival and recruitment across elevations, where high-elevation toads have high survival but lower recruitment and vice versa at lower elevations. Pathogen arrival had a strong negative effect on apparent annual survival and recruitment leading to negative population growth rates and dramatically reduced host abundances. The data did not support the occurrence of compensatory recruitment. Synthesis and applications . Our unique dataset indicates that demographic responses to pathogens may be environmentally (i.e. elevationally) context dependent and highlights the value of long-term monitoring. We recommend that practitioners verify that potential persistence mechanisms occur across multiple populations and relevant environmental gradients to counter any assumptions of the mechanism existing species-wide. Quantifying variation in population responses to disease will aid in understanding the bounds of such persistence mechanisms and identify particularly vulnerable populations where mechanisms are nonexistent.

Journal of Applied Ecology↗

USGS2018

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

Movement of individuals has been described as one of the best studied, but least understood concepts in ecology. The magnitude of movements, routes, and probability of movement have significant application to conservation. Information about movement can inform efforts to model species persistence and is particularly applicable in situations where specific threats (e.g., disease) may depend on the movement of hosts and potential vectors. We estimated the probability of movement (breeding dispersal and permanent emigration) in a metapopulation of 16 breeding sites for boreal toads ( Anaxyrus boreasboreas ). We used a multi‐state mark–recapture approach unique in its complexity (16 sites over 18 yr) to address questions related to these movements and variation in resident survival. We found that individuals had a 1–2% probability of dispersing in a particular year and that approximately 10–20% of marked individuals were transient and observed in the metapopulation only once. Resident survival probabilities differed by season, with 71–90% survival from emergence from hibernation through early post‐breeding and >97% survival from mid‐/late active season through hibernation. Movement‐related probabilities are needed to predict species range expansions and contractions, estimate population and metapopulation dynamics, understand host–pathogen and native–invasive species interactions, and to evaluate the relative effects of proposed management actions.

Colorado↗

USGS2016

Influence of demography and environment on persistence in toad populations

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.

Journal of Wildlife Management↗