Antler Size of Alaskan Moose Alces Alces Gigas: Effects of Population Density, Hunter Harvest and Use of Guides

Abstract

Moose Alces alces gigas in Alaska, USA, exhibit extreme sexual dimorphism, with adult males possessing large, elaborate antlers. Antler size and conformation are influenced by age, nutrition and genetics, and these bony structures serve to establish social rank and affect mating success. Population density, combined with anthropogenic effects such as harvest, is thought to influence antler size. Antler size increased as densities of moose decreased, ostensibly a density-dependent response related to enhanced nutrition at low densities. The vegetation type where moose were harvested also affected antler size, with the largest-antlered males occupying more open habitats. Hunts with guides occurred in areas with low moose density, minimized hunter interference and increased rates of success. Such hunts harvested moose with larger antler spreads than did nonguided hunts. Knowledge and abilities allowed guides to satisfy demands of trophy hunters, who are an integral part of the Alaskan economy. Heavy harvest by humans was also associated with decreased antler size of moose, probably via a downward shift in the age structure of the population resulting in younger males with smaller antlers. Nevertheless, density-dependence was more influential than effects of harvest on age structure in determining antler size of male moose. Indeed, antlers are likely under strong sexual selection, but we demonstrate that resource availability influenced the distribution of these sexually selected characters across the landscape. We argue that understanding population density in relation to carrying capacity (K) and the age structure of males is necessary to interpret potential consequences of harvest on the genetics of moose and other large herbivores. Our results provide researchers and managers with a better understanding of variables that affect the physical condition, antler size, and perhaps the genetic composition of populations, which may be useful in managing and modelling moose populations.

Selective harvesting of large mammals: how often does it result in directional selection?

“…meat, recreation or trophy), level of knowledge and skill (use of guides), cultural background, religion (taboos), individual ethics and animal trait variation. For example, trophy hunters using guides shot larger moose Alces alces L. in Alaska, because guides took client hunters to areas with lower population densities and therefore larger moose (Schmidt, Ver Hoef & Bowyer 2007). More importantly, strong directional selection for size is often unlikely because of limited (or redirected) opportunities for hunter selection because of both direct and intentional factors such as quotas or economic costs of high pricing and also time limitations, cost of lost opportunity, and indirect and non‐intentional factors through animal behaviour and abundance (Table 2).…”

“…rutting males, affecting selectivity. The spatial hunting behaviour of humans may also influence the selective pressures exerted (Schmidt, Ver Hoef & Bowyer 2007).…”

Human selection of elk behavioural traits in a landscape of fear

“…However, while research has focused on human-mediated selection of morphological traits in wild populations (e.g. selection of large-antlered or largehorned ungulate males [10,11]), little is known about human-mediated selection of behavioural traits. Here we predict that prey, depending on individual personality traits, can adopt anti-predator behavioural strategies in response to human hunting pressure, and thus humans directly influence prey behavioural traits.…”

Changes in horn size of Stone's sheep over four decades correlate with trophy hunting pressure

“…moose (Alces alces) with larger antlers compared to non-guided hunters because guides had a 80 better knowledge of low-density areas producing large-antlered moose (Schmidt et al 2007). 81 Most guided hunters are non-residents, who pay substantial fees to obtain large trophies.…”

“…103 Guides try to satisfy their clients by providing an opportunity to harvest a large trophy 5 MATHIEU DOUHARD ET AL. Ecological Applications (Schmidt et al 2007). Therefore, we expected non-residents to harvest older males with larger 105 horns (H3, Table 1).…”