Species distribution modeling of North American beavers from the late Pliocene to the future

Aim: Beavers play a profound role in altering their environments by dam building, effectively creating habitats for other organisms as a result. These ‘ecosystem engineers’ represent one of the best examples of conservation success, but are at risk like many other organisms due to anthropogenic climate change. The presence of beavers in North America extends back over seven million years, but relatively little is known about their dispersal throughout the continent. In this study, we model the distributions of beavers in the past and present to: 1) understand their dispersal across North America, 2) predict future distributions, and 3) interpret their possible response to future climate and habitat changes.<br>Location: North America<br>Taxon: Beavers (extinct <i>Castor californicus</i> and extant <i>Castor canadensis</i>; Rodentia: Castoridae).<br>Methods: We downloaded and rarified species occurrence data for <i>Castor canadensis</i> within North America from Global Biodiversity Information Facility (GBIF). We used those data points with modern (1970-2000) and modeled future (EC-Earth-Veg 2081-2100) bioclimatic variables from WorldClim and past (Pliocene Marine Isotope Stage M2, Pleistocene Last Interglacial, Pleistocene Last Glacial Maximum) bioclimatic variables from PaleoClim. We overlaid fossil locality points (with corrected time ranges) for <i>Castor</i> (from the NOW, NEOTOMA, and Paleobiology Databses) on past projection models to use as validation points. We ran our models using MaxEnt with post processing in ArcGIS.<br>Results: During periods cooler than those today (mid to late Pliocene cooling period and Last Glacial Maximum), <i>Castor</i> habitat suitability tended to shift further south into Mexico and peninsular Florida and away from more periglacial, northern regions. Warmer periods than those today (Last Interglacial period and EC-Earth-Veg 2081-2100) show higher suitability in cooler coastal and central regions in North America and lower suitability in warmer southern regions.<br>Main Conclusions: Beaver habitat suitability has shifted substantially in the past and will continue to do so in the future. At a large scale, beavers were most affected by precipitation seasonality, isothermality, and mean annual temperature. These bioclimatic variables influence vegetation and water presence, which could impact beaver habitation and dam building. Observing the shifts during warmer periods may help identify areas which may have been more suitable for beavers in the late Miocene and encouraged them to disperse into North America.