COS 96-4 - CANCELLED - The impact of food supplementation and cycle phase on the stress physiology of snowshoe hares

Tuesday, August 16, 2022

2:15 PM – 2:30 PM EDT

Location: 515C

Presenting Author(s)

YM

Yasmine N. Majchrzak

University of Alberta, Canada

Coauthor(s)

MP

Michael Peers

Memorial University of Newfoundland, Canada
SL

Sophia Lavergne

University of Toronto Scarborough, Canada
ES

Emily Studd

Post-Doctoral Fellow
University of Toronto Mississauga, Canada
AM

Allyson Menzies

McGill University, Canada
SS

Shotaro Shiratsuru

University of Alberta, Canada
MH

Murray Humphries

Associate Professor
McGill University, MacDonald Campus, Centre for Indigenous Peoples' Nutrition and Environment (CINE), Canada
TJ

Thomas Jung

Department of Environment, Government of Yukon, Canada
AK

Alice Kenney

University of British Columbia, Canada
CK

Charles Krebs

University of British Columbia, Canada
SB

Stan Boutin

Department of Biological Sciences, University of Alberta
Edmonton, Alberta, Canada
RB

Rudy Boonstra

University of Toronto Scarborough, Canada

Background/Question/Methods

Understanding the causes behind population cycles is a fundamental issue in ecology. One of the most prominent examples of cyclic species is the snowshoe hare (Lepus americanus), a prey species in the North American boreal forest that fluctuates in abundance every 9-11 years. According to the chronic stress hypothesis, demographic changes associated with the cycle are thought to be driven by direct and indirect predation, with predator induced stress being the major cause of decreased reproduction during the decline and low phases. However, food limitation has recently been shown to impact hare demography through behaviour and condition, but the impact of food on stress physiology remains unknown. We examined the effect of food on the stress physiology of hares using an individual based food-supplementation experiment over-winter across three cycle phases that naturally varied in predation risk. We assessed various measures of stress and condition in late winter in both treatments using hormone challenges and measured hematological indices of body condition. The goal was to 1) determine if access to abundant high-quality food may buffer against the effects of chronic stress, and 2) evaluate the physiological measures of stress and condition in hares during different cycle phases when predation risk varies.

Results/Conclusions

We found that food supplementation increased hare stress response to a hormone challenge but simultaneously increased their ability to buffer against this heightened response, through increased corticosteroid binding capacity. We also found that food supplementation improved the overall body condition of hares as supplemented individuals had higher % packed red-blood cell volume (indicator of condition) and lower body mass loss over winter. Most notably, we found that indicators of stress in snowshoe hares did not track the yearly changes in predator density nor predator-prey ratio, as predicted by the chronic stress hypothesis. Overall, the indicators of chronic stress were more prominent during the increase phase of the cycle. In conclusion, our results showed no clear pattern between population level stress physiology and demography, and instead provided evidence that increased stress, in regards to the parameters measured here, is not required to cause population declines.