How Wolves Respond to Changes in Climate and Prey

Although wolf natality increases with abundant prey, wolf population numbers actually decreased due to territoriality and fewer packs.

We investigated predator-prey dynamics in Denali National Park and Preserve using data from 30 years of research on wolves and caribou. We found that the number of wolves added to pack (wolf natality) increased when caribou were plentiful, when there was an abundance of caribou calves, and when hare were also plentiful. We also found that wolves were more likely to survive in years of heavy snowfall when there were more young caribou. The amount of snowfall can indicate how vulnerable caribou are to predation because deep snow impacts their ability to move through the snow and limits access to food. Wolves that are lighter and can travel on top of deep snow have the advantage over weakened caribou that are struggling to get through the snow. Plentiful and vulnerable prey keep wolves healthy and increases the survival of pups.

Interestingly, we found that when the caribou population increased, the number of wolves added to packs increased, but the wolf population size declined. The decline in the population is attributed to fewer packs in the same area, suggesting that the number of packs that an area can support can play a vital role in limiting population growth for wolves. Territoriality plays a role in regulating the overal number of wolves. The results from this study provide a valuable baseline and comparison for other studies.

The Role of Weather and Long-Term Prey Dynamics as Drivers of Wolf Population Dynamics in a Multi-Prey System

Abstract

As climate change accelerates in northern latitudes, there is an increasing need to understand the role of climate in influencing predator-prey systems. We investigated wolf population dynamics and numerical response in Denali National Park and Preserve in Alaska, United States from 1986 to 2016 under a long-term range of varying climatic conditions and in the context of prey vulnerability, abundance, and population structure using an integrated population modeling approach. We found that wolf natality, or the number of wolves added to packs, increased with higher caribou population size, calf:cow ratio, and hare numbers, responding to a 1-year lag. Apparent survival increased in years with higher calf:cow ratios and cumulative snowfall in the prior winter, indicators of a vulnerable prey base. Thus, indices of prey abundance and vulnerability led to responses in wolf demographics, but we did not find that the wolf population responded numerically. During recent caribou and moose population increases wolf natality increased yet wolf population size declined. The decline in wolf population size is attributed to fewer packs in recent years with a few very large packs as opposed to several packs of comparable size. Our results suggest that territoriality can play a vital role in our study area on regulating population growth. These results provide a baseline comparison of wolf responses to climatic and prey variability in an area with relatively low levels of human disturbance, a rare feature in wolf habitat worldwide.

Borg, B. L. and D. W. Schirokauer. 2022. The role of weather and long-term prey dynamics as drivers of wolf population dynamics in a multi-prey system. Frontiers in Ecological Evolution 10: 791161.