Seasonal Weather Effects on Mass Variation and Torpor Expression in an Obligate Hibernator
Date
2023-10-24
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0002-1161-2307
Type
Thesis
Degree Level
Masters
Abstract
Global climate change, characterized by long term changes in temperature and precipitation patterns, can present an energetic challenge to terrestrial species. Seasonal hibernators are potentially vulnerable to projected changes because their annual energy management is tightly connected to predictable fluctuations in environmental resources. I studied the relationships between environmental factors and seasonal energy management in a wild population of Columbian ground squirrels (Urocitellus columbianus) between 2009 and 2020. I hypothesized that vegetation availability and torpor expression mediated the direct relationships between weather (i.e., temperature and precipitation) and ground squirrel energy budgets (measured as seasonal mass variation). I found that separate weather patterns influenced summer mass gain for each sex immediately following reproductive investment. As measured, vegetation availability did not significantly influence the total summer mass gain of either sex. Males lost more mass in cold winters (-11.49 1.64 g body mass/1°C decrease in mean air temperature between Oct 2 and Mar 28), but female mass loss was more strongly influenced by entry mass and emergence phenology than winter weather.
I conducted a two-way factorial field experiment to test the influences of entry mass and hibernation microclimate on torpor expression and over-winter mass loss. I manipulated pre-hibernation entry mass by supplementally feeding a treatment group of females prior to hibernation. On average, fed females weighed 40 g more than unfed females entering hibernation (fed mean mass 567 51 g, unfed mean mass 527 40 g, t25 = 2.33, df = 25.09, p = 0.03) . I manipulated the hibernation microclimates of a treatment group containing fed and unfed females by installing snow fences upwind of their hibernacula. The snow fences created deep snowpack, which raised and stabilized the ambient temperature of the hibernacula compared to females hibernating without snow fences. Females in colder hibernacula increased torpor expression (e.g., expressed colder torpid skin temperatures, Tsks), but females with larger pre-hibernation energy stores reduced torpor expression. Thus, warmer winters may reduce hibernation thermoregulatory costs and allow large ground squirrels to invest energy in torpor reduction. This study shows that the effects of projected climate changes on seasonal hibernator energy management will have complex and opposing effects for separate demographic classes depending on when the changes occur within the calendar year.
Description
Keywords
hibernation, torpor, weather, climate change, mass, energy, snow, temperature, ground squirrel, seasonality, NDVI, thermoregulation
Citation
Degree
Master of Science (M.Sc.)
Department
Biology
Program
Biology