Abstract
Environmental change associated with anthropogenic disturbance can lower habitat quality, especially for sensitive species such as many amphibians. Variation in environmental quality may affect an organism's physiological health and, ultimately, survival and fitness. Using multiple health measures can aid in identifying populations at increased risk of declines. Our objective was to measure environmental variables at multiple spatial scales and their effect on three indicators of health in ornate chorus frog (Pseudacris ornata) tadpoles to identify potential correlates of population declines. To accomplish this, we measured a glucocorticoid hormone (corticosterone; CORT) profile associated with the stress response, as well as the skin mucosal immune function (combined function of skin secretions and skin bacterial community) and bacterial communities of tadpoles from multiple ponds. We found that water quality characteristics associated with environmental variation, including higher water temperature, conductivity and total dissolved solids, as well as percent developed land nearby, were associated with elevated CORT release rates. However, mucosal immune function, although highly variable, was not significantly associated with water quality or environmental factors. Finally, we examined skin bacterial diversity as it aids in immunity and is affected by environmental variation. We found that skin bacterial diversity differed between ponds and was affected by land cover type, canopy cover and pond proximity. Our results indicate that both local water quality and land cover characteristics are important determinants of population health for ornate chorus frogs. Moreover, using these proactive measures of health over time may aid in early identification of at-risk populations that could prevent further declines and aid in management decisions.
Highlights
As the human population continues to increase, land-use conversion has altered habitat suitability for many species (Vitousek et al, 1997; McKinney, 2002)
An ordination plot based on the Bray–Curtis method of non-metric multidimensional scaling (NMDS) showed bacterial community similarities within Sites and across Properties (Fig. 10). We found that both water quality and land cover characteristics were associated with increased CORT release rates and altered skin bacterial communities among populations of P. ornata
We found that CORT release rates were highest in tadpoles from a pond within Lafayette Forest Wildlife Environmental Area (LF1), which had some of the warmest water temperatures and was dominated by shrubby vegetation, a result of infrequent prescribed fires
Summary
As the human population continues to increase, land-use conversion has altered habitat suitability for many species (Vitousek et al, 1997; McKinney, 2002). Fragmentation and degradation, coupled with climate change and other anthropogenic factors, are among the most significant drivers of population declines and species by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Landscape-level disturbances such as habitat loss and degradation affect populations by altering habitat connectivity, composition and quality (Fahrig, 2003). Local impacts on water quality such as changes in temperature, pH, contaminant, nutrient and sediment levels (Meybeck, 2004) can pose significant consequences to population health and resilience. Examining physiological responses of individuals to such factors can provide insight into the mechanisms by which environmental stressors can lead to population declines (Wikelski and Cooke, 2006). Understanding the consequences of these factors on populations could aid in better management practices for declining species
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