From Lynx to Coyotes: How Climate Change Has Impacted Hare Predation

Climate change increases predation risk for a keystone species of the boreal forest

By: Michael J.L. Peers, Yasmine N. Majchrzak, Allyson K. Menzies, Emily K. Studd, Guillaume Bastille-Rousseau, Rudy Boonstra, Murray Humphries, Thomas S. Jung, Alice J. Kenney, Charles J. Krebs, Dennis L. Murray, and Stan Boutin

Summarized by: Anna Geldert

What data were used? Researchers observed 321 snowshoe hares in southwestern Yukon from 2015-2018. Researchers also monitored changes in weather and snow conditions within the study region, including temperature, snow depth, snow hardness and daily snowfall.

Methods: Hares were captured in live traps and given collars with mortality sensors before being released back into the wild. In the event of hare death, researchers visited the site to identify any predators responsible for the death by looking for tracks, scat, and other indicators in the surrounding area. Researchers recorded data on weather and snow conditions at three different sites throughout the study region on a nearly daily basis, as well as at each kill site. They then used a computer model to compare the likelihood of hare death under different weather conditions (e.g., temperature, snow depth, and snow hardness), and generated a best fit line to model these relationships. Similar models compared weather conditions to hare predation from lynx and coyote, hare death by age group, and hare foraging time by age group. The models were tested by inputting randomized data and estimating uncertainty.

Results: Researchers found that 153 hares died of predation. Lynx and coyote were the most common predators, accounting for 59.4% and 25.5% of deaths respectively. Hare survival was lowest in 2015-2016, countering the predicted increase in hare populations based on predator-prey cycles. Low survival rates were correlated with shallow snow depth and high snow hardness. . The relationships between hare survival and these weather conditions are most likely due to changes in predator threats, not changes in foraging behavior. While lynx predation remained relatively constant across a wide range of snow conditions, coyote predation increased by a factor of 1.155 with higher snow depth and 1.244 with lower snow hardness.

The figure graphs the relationship between snow depth and hare predation risk by lynx and coyotes. The x-axis is labeled “snow depth (cm),” and ranges from 20 to 70, increasing at intervals of 10. The y-axis is labeled “risk (relative to baseline),” and ranges from 0 to 15, increasing at intervals of 5. A legend indicates that the purple line represents risk from lynx while the red line represents risk from coyotes. At a risk measurement of 1, a dotted line runs horizontally (slope=0) across the graph; this represents baseline risk. The risk from lynx almost exactly coincides with the baseline risk, indicating that snow depth has little impact. On the other hand, the risk for coyote has an inverse relationship with snow depth. At a snow depth of 20 centimeters (the lowest depth represented), risk from coyotes is approximately 10. The risk line then decreases exponentially, crossing the baseline risk at approximately 35 centimeters and plateauing close to a risk of zero around 50 centimeters.
Fig. 1. Hare predation risk by lynx and coyotes at different snow depths. The dotted line represents a baseline risk, while shaded regions represent standard errors.

Why is this study important? This study is an important example of the cascading effects that climate change can have on ecosystems in the boreal forest. Increasing temperatures due to climate change have altered traditional snow conditions in the Yukon, leading to lower snow depth and snow hardness in recent years. Coyotes – who, unlike lynx, are not well adapted to harsh winters – have gained a relative advantage in these milder conditions, leading to increased hare predation. Risk has increased so much, in fact, that they disrupted the natural rise and fall of hare populations due to existing predator-prey cycles. If these trends continue, they could potentially impact other aspects of boreal forest ecosystems.

The big picture: It is widely recognized that climate change threatens the survival of many species and ecosystems around the globe. However, this is most often talked about in terms of direct threats, such as increasing temperature, increasing severe weather conditions, etc. This article demonstrates that a further concern, particularly in boreal forests, is the impact of changing climatic conditions on food webs and predation threats. Further research is needed to determine if the changing predator-prey relationships between hares and coyotes in this study are consistent in other regions of boreal forest, and whether similar trends are reflected in other biomes as well.

Citation: Peers, M. J. L., Majchrzak, Y. N., Menzies, A. K., Studd, E. K., Bastille-Rousseau, G., Boonstra, R., … Boutin, S. (2020). Climate change increases predation risk for a keystone species of the boreal forest. Nature Climate Change, 10(12), 1149–1153.

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