Although there is a clear link between emerging diseases and the survival of animal populations, few studies have focused on how a disease affects a specific population. USGS scientists Erin Muths and David Pilliod, along with Rick Scherer of Colorado State University, assessed the population-level effects of the chytrid fungus (linked to the worldwide decline of amphibians) on wild populations of boreal toads in western North America. They assessed how the chytrid fungus affected survival and recruitment of diseased boreal toads in Wyoming compared to a disease-free population in Colorado. Results published in the August 2011 issue of the Journal of Applied Ecology suggest that in the diseased-toad population, high recruitment rates of young are compensating for low survival of adults, thus allowing the diseased population to persist. In contrast, in the disease-free population, adults had high survival probability, but the population had a lower recruitment rate. The findings provide evidence that high recruitment rate may compensate for high mortality in populations challenged by disease, thus reducing the likelihood of catastrophic declines seen in some diseased populations. Further, the paper demonstrates how reliable estimates of both recruitment and survival can facilitate better management of wildlife populations.
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