title: Mechanistic variables can enhance predictive models of endotherm distributions: the American pika under current, past, and future climates.
abstract: How climate constrains species' distributions through time and space is an important question in the context of conservation planning for climate change. Despite increasing awareness of the need to incorporate mechanism into species distribution models (SDMs), mechanistic modeling of endotherm distributions remains limited in this literature. Using the American pika (Ochotona princeps) as an example, we present a framework whereby mechanism can be incorporated into endotherm SDMs. Pika distribution has repeatedly been found to be constrained by warm temperatures, so we used Niche Mapper, a mechanistic heat-balance model, to convert macroclimate data to pika-specific surface activity time in summer across the western United States. We then explored the difference between using a macroclimate predictor (summer temperature) and using a mechanistic predictor (predicted surface activity time) in SDMs. Both approaches accurately predicted pika presences in current and past climate regimes. However, the activity models predicted 8-19% less habitat loss in response to annual temperature increases of ~3-5 °C predicted in the region by 2070, suggesting that pikas may be able to buffer some climate change effects through behavioral thermoregulation that can be captured by mechanistic modeling. Incorporating mechanism added value to the modeling by providing increased confidence in areas where different modeling approaches agreed and providing a range of outcomes in areas of disagreement. It also provided a more proximate variable relating animal distribution to climate, allowing investigations into how unique habitat characteristics and intraspecific phenotypic variation may allow pikas to exist in areas outside those predicted by generic SDMs. Only a small number of easily obtainable data are required to parameterize this mechanistic model for any endotherm, and its use can improve SDM predictions by explicitly modeling a widely applicable direct physiological effect: climate-imposed restrictions on activity. This more complete understanding is necessary to inform climate adaptation actions, management strategies, and conservation plans.
authors: Department of Zoology, University of Wisconsin-Madison, Madison, WI, 53703, USA.
authors: Paul D
authors: PD
authors: Mathewson
authors: Department of Zoology, University of Wisconsin-Madison, Madison, WI, 53703, USA.|Department of Biology, University of Utah, Salt Lake City, UT, 84112, USA.
authors: Lucas
authors: L
authors: Moyer-Horner
authors: U.S. Geological Survey, Northern Rocky Mountain Science Center, Bozeman, MT, 59715, USA.|Department of Ecology, Montana State University, Bozeman, MT, 59715, USA.
authors: Erik A
authors: EA
authors: Beever
authors: School of BioSciences, University of Melbourne, Melbourne, VIC, 3010, Australia.
authors: Natalie J
authors: NJ
authors: Briscoe
authors: School of BioSciences, University of Melbourne, Melbourne, VIC, 3010, Australia.
authors: Michael
authors: M
authors: Kearney
authors: Department of Zoology, University of Wisconsin-Madison, Madison, WI, 53703, USA.
authors: Jeremiah M
authors: JM
authors: Yahn
authors: Department of Zoology, University of Wisconsin-Madison, Madison, WI, 53703, USA.
authors: Warren P
authors: WP
authors: Porter
mesh_terms: D000818:Animals; D002980:Climate; D057231:Climate Change; D003247:Conservation of Natural Resources; D017753:Ecosystem; D005544:Forecasting; D007793:Lagomorpha; D011157:Population Dynamics; D014481:United States
keywords: 
  Ochotona princeps
  ; American pika; activity; biophysical model; climate change; mechanistic model; physiology; species distribution model; temperature