Climate driven variability in the demography and physiology of the Uinta ground squirrel

Falvo, Caylee, author; Aubry, Lise, advisor; French, Susannah, committee member; Aldridge, Cameron, committee member

Climate driven variability in the demography and physiology of the Uinta ground squirrel

Files

Falvo_colostate_0053N_14970.pdf (2.62 MB)

Date

2018

Authors

Falvo, Caylee, author

Aubry, Lise, advisor

French, Susannah, committee member

Aldridge, Cameron, committee member

Abstract

Climate change is impacting the phenology of many species, ultimately altering their fitness and population dynamics. Shifts in phenology have been documented across a variety of taxa and ecosystems, but few studies have considered the effects of pertinent season-specific climatic variables on phenology and fitness. Hibernators may be particularly susceptible to changes in climate since they have a relatively short active season in which to reproduce and gain enough mass to survive the following winter. To understand whether and how climatic changes may be affecting hibernator fitness, we analyzed historical (1964-1968) and contemporary (2014-2017) mark-recapture data taken from the same population of Uinta ground squirrels (UGS, Urocitellus armatus). Although survival of UGS has not changed significantly over time, annual survival seems to fluctuate strongly in response to climate and phenology. Population density also increased, suggesting resources are less limited today than they used to be. Cheatgrass is now dominating low-elevation UGS habitat and seems to provide a better food source than native plants did historically. Although the phenology of UGS has not changed significantly over time with a locally warming climate (3.22ºF over 50 years), season-specific climatic variables were important in determining over-winter survival rates. To understand the role that physiological processes play in shaping the life history of UGS in light of warming temperatures, we studied UGS life history trade-offs near the extremes of their elevation range (6200 ft. versus 8000 ft.) which offer contrasted micro-climatic conditions. Specifically, we quantified trade-offs between body mass dynamics and immune function in two populations of UGS that experience different phenologies and active season lengths. UGS at the high elevation had a shorter active season, largely driven by extended snow cover into spring. UGS at this elevation also weighed less at emergence from hibernation than UGS at the lower elevation. Despite this, UGS at the high elevation gained mass faster than UGS at the low elevation, entering estivation at a similar weight. This accelerated mass gain was associated with a decline in immune function at the higher elevation, but not at the lower elevation where UGS experience a much longer active season and are not food-limited. Juveniles generally gained mass faster than adults and yearlings, but did not demonstrate a decrease in immune function at either elevation, possibly because they do not have to bear the energetic burden of reproduction. Our results improve our understanding of how hibernators respond to climate change, and how these plastic responses lead to contrasted life history strategies. Our results have implications for the conservation of this species and similar ones that are sensitive and responsive to even small changes in climate.