|dc.description.abstract||As human populations continue to expand and grow, ecosystems and the
species that inhabit them face ever-increasing stress. To conserve these
ecosystems, scientists use indicator species to try to measure the impact of
human-induced pressures on the environment. Anurans are exceptional indicator
species because they are often the first vertebrates to respond to the direct and
indirect effects of land use by humans. Sparse historical data have made it
difficult to map the ‘natural’ distribution of many species and, therefore, to map
any changes in distribution range as a result of human expansion.
This study sought to address the lack of data coverage by using a
predictive model to map the distribution of anuran species across the southeastern
U.S.A. based on their response to environmental parameters. Historical (prior to
1960), transitional (1960-1989), and modern (1990-2013) distributions were
mapped for each anuran species, and the expansions and contractions of
distribution ranges were calculated between time blocks. Species life-history traits were analyzed as potential predictor variables to determine whether a species had
increased or decreased its total range size in recent history.
Results suggest that six species (60%) had a large decrease in range size
from their historical distributions; three species (30%) had a large increase in
range size, and one species (10%) had almost no change in range size. Most
species that gained range size, from the historical to the modern block, expanded
to the interior of the southeastern U.S.A. during the transitional-time block.
Model results indicate that precipitation, temperature, and elevation are more
important for determining frog distributions than human population density across
all time blocks. Trait analysis did not indicate any traits were able to determine
whether the species had range expansions or contractions. Distribution range
trends suggest that the Atlantic Multidecadal Oscillation (AMO), a low-frequency
climatic oscillation, may have a role in distribution expansions and contractions,
but more long-term data are required to explore this possibility properly.
Overall the study shows that historical distributions can be accurately
mapped, despite the lack of landscape-scale historical surveys of individual
species. Whether anuran species increase or decrease in range size from their
historical distribution cannot yet be explained using species traits. Compounded
effects from a changing climate cannot be ruled out.||en_US