Evaluating current and future range limits of an endangered, keystone rodent (Dipodomys ingens)

Ivy V Widick,William T Bean,Alexandra Syphard

doi:10.1111/ddi.12914

Abstract

AbstractAimWe use current models of species distribution to predict the future habitat suitability for an endangered, keystone rodent (Dipodomys ingens, giant kangaroo rat). We incorporate the possibility of local adaptation and novel competitive interactions to improve the predictive accuracy of our Maxent models.LocationSan Joaquin Valley, California, USA.MethodsWe created Maxent models of two isolated populations of D. ingens. Using local surveys and state‐wide data, we also modelled California ground squirrels (Otospermophilus beecheyi), a potential novel competitor. Models included landscape variables (slope and soil composition) and climate variables (temperature, precipitation and climatic water deficit). We used Warren's I to evaluate niche overlap between species as well as between isolated populations of the same species. We then projected each set of models into the future to evaluate D. ingens response to climate change.ResultsNiche overlap between the D. ingens populations was moderate (I = 0.44), suggesting that they already experience different climatic regimes and providing support for population‐level modelling. Projecting individual populations separately into the future, under a high emission climate change scenario (CCSM4, rcp8.5), resulted in less predicted range contraction than modelling the species as a whole. However, forecasted distributions showed areas of increasing niche overlap between the Panoche population of D. ingens and O. beecheyi (I = 0.63 to 0.74), indicating competition could be a novel range limit.Main conclusionsModelling the distributions of isolated populations separately provides a more accurate estimation of the species’ contemporary niche, capturing not just overlap between the populations, but individually suitable areas as well. Projecting the individual contemporary and historical models into the future allows us to estimate future habitat suitability. Predicting the distribution of a novel competitor characterizes areas of potential competition. Subsequently, management can target suitable areas for preservation and avoid areas of potential novel competition.

Highlights

Climate is often considered the single most important factor limiting species’ ranges (e.g. Merriam 1894, Peterson 2011)
In total 301 of these sites resulted in a positive detection; 197 presence locations were in the Panoche Natural Area (Panoche) population, 101 in the Carrizo, and three in the range between populations
Driving surveys for O. beecheyi resulted in 228 thinned locations overall, 165 in the Panoche and 34 in the Carrizo

Summary

Introduction

Climate is often considered the single most important factor limiting species’ ranges (e.g. Merriam 1894, Peterson 2011). Most contemporary approaches to modeling species distributions and predicting range shifts under climate change suggest species will relocate to track their climatic niches (Parmesan 2006). This response is governed by niche conservatism, which occurs when species retain ecological traits related to their niche over time (Wiens et al 2010). Species may shift their range through space to follow the conditions to which they are adapted, or they may locally express retained traits in response to change. The interaction between abiotic and biotic factors is important in determining whether species follow or deviate from niche conservatism

Methods

Results

Conclusion