Environmental and demographic drivers of a rapidly expanding sub-arctic moose population

Abstract

Anthropogenic forces are dramatically altering the dynamics of many populations and ranges. A thorough understanding of drivers and mechanisms underlying population dynamics is needed to better understand reasons for range shifts and broaden our understanding of how environmental and demographic drivers affect population trajectories. In this thesis, I present two chapters that investigate the population dynamics of a rapidly colonizing moose (Alces alces) population in southwest Alaska. In the first chapter, I correlated environmental variables with demographic rates estimated using a multistate model and found that annual patterns of vegetation productivity and winter severity affected calf survival most strongly, followed by twinning rate. In the second chapter, I applied transient life table response experiments (tLTREs) to demographic rates and components of population structure estimated using an integrated population model (IPM). I found that, although calf survival did not have the highest sensitivity out of all other parameters, variation in calf survival contributed the most to variation in population growth rate. Together, these chapters suggest that variation in environmental conditions drove variation in population growth rate via effects on calf survival. Results uphold and add nuance to the demographic buffering hypothesis (DBH), which states that species evolve to buffer highest sensitivity demographic rates against variation that could otherwise decrease individual fitness and population sustainability. My research indicates that an outcome of the DBH is that lower sensitivity vital rates ultimately have a higher actual impact on population growth rate. Additionally, I found that the environmental drivers that currently limit population growth exhibit long-term trends consistent with climate change in ways that are amenable to moose, which suggests climate change facilitated moose colonization of the region. The lack of shortterm trends, lower adult survival in the most heavily hunted part of the study area, and the abrupt colonization that aligned with the irruption of a local caribou (Rangifer tarandus) herd indicate that human hunting pressure also played an important role in allowing moose to establish themselves at high density. These findings pertaining to drivers and mechanisms of population dynamics are relevant for conservation and management of large herbivores across the world that might similarly expand into new areas.