DOI: 10.5061/dryad.qz612jm9b
title: Vanishing islands in the sky? A comparison of correlation- and mechanism-based forecasts of range dynamics for montane salamanders under climate change

description: Forecasting the effects of climate change on species and populations is a
 fundamental goal of conservation biology, especially for montane endemics
 which seemingly are under the greatest threat of extinction given their
 association with cool, high elevation habitats. Species distribution
 models (also known as niche models) predict where on the landscape there
 is suitable habitat for a species of interest. Correlative niche modeling,
 the most commonly employed approach to predict species’ distributions,
 relies on correlations between species’ localities and current
 environmental data. This type of model could spuriously forecast less
 future suitable habitat because species’ current distributions may not
 adequately represent their thermal tolerance, and future climate
 conditions may not be analogous to current conditions. We compared the
 predicted distributions for three montane species of Plethodon salamanders
 in the southern Appalachian Mountains of North America using a correlative
 modeling approach and a mechanistic model. The mechanistic model
 incorporates species-specific physiology, morphology, and behavior to
 predict an annual energy budget on the landscape. Both modeling approaches
 performed well at predicting the species’ current distributions and
 predicted that all species could persist in habitats at higher elevation
 through 2085. The mechanistic model predicted more future suitable habitat
 than the correlative model. We attribute these differences to the
 mechanistic approach being able to model shifts in key range-limiting
 biological processes (changes in surface activity time and energy costs)
 that the correlative approach cannot. Choice of global circulation model
 (GCM) contributed significantly to distribution predictions, with a
 tenfold difference in future suitability based on GCM, indicating that GCM
 variability should be either directly included in models of species
 distributions or, indirectly, through the use of multi-model ensemble
 averages. Our results indicate that correlative models are over-predicting
 habitat loss for montane species, suggesting a critical need to
 incorporate mechanisms into forecasts of species’ range dynamics.
description: Localities of Plethodontid salamanders in the southern Applachian
 Mountains are from the US National Museum of Natural History Herpetology
 Collection. Ground temperature input rasters for radiative heating and
 topographic convergence were developed using GRASS and the provided
 digital elevation model. Stream distance calculated from the USGS stream
 vectors datasets for each state.
description: Localities for presence and absence occurance points for three
 montane species, <em>Plethodon jordani, Plethodon metcalfi,
 </em>and <em>Plethodon montanus. </em>Absences are
 locations where a plethdontid salamander, but not the species of interest
 is found.  Ascii files necessary for running ground
 temperature model for the southern Appalachians developed by Fridley 2009
 for the Smoky Mountains. Each species has ascii files for elevation (dem),
 average monthly radiative heating (numbered by julian date), total yearly
 radiative heating, stream distance, and topographic convergence index.
 Ascii headers were removed for running the code but available in a
 header.txt file. Example R code for computing ground temperature for
 <em>Plethodon jordani.</em>