Nutritional stress and population density influence risk/reward decisions by elk

Abstract

Context Optimal foraging strategies can be influenced at the group level by population density, which can increase competition, hunger, and activity levels. Optimal foraging can also be influenced at the individual level by personality, which in part governs how individuals assess risk versus reward. Aims The purpose of this study was to quantify the influence of population density on risk-taking. I focused on captive elk that had previously been studied in tandem with wild elk in order to quantify personality trait characteristics. I hypothesised that risk-taking would be shown to be a density-dependent affect, in addition to varying individually. Methods Automated cameras recorded visitation to four rotating treatments sites in each of high and low density pens, and which had either: forage, a novel object, forage + novel object, or a control site. Novel objects were regularly changed to elicit a spectrum of responses ranging from neofilia to neophobia. Selection or avoidance of sites was determined by comparing elk visitation to visits to control sites. The experiment was done in summer when natural forage was most abundance, and in again in autumn when natural forage was limited. Key results High density elk showed year-round selection for all treatment sites. In summer low density elk showed weak selection for forage and forage + novel and no selection for novel objects, and no selection for any site in autumn. These patterns showed that elk in the high density pen, which were in poorer condition, had to increase their levels of both activity and risk taking. Neither elk pen exhibited any group-wide avoidance of novel objects, indicating a group-wide gradient of neophobia to neofilia, known personality traits in elk. Conclusions These results show that risk-taking behaviour can be a density dependent effect. This increase in neofilia may be driven by hunger stress, but also through increases in competition that may favour elk of certain personalities. Implications Increasing density may increase the prevalence of both neofilia and other personality traits correlated with neofilia, which include aggression, and so may contribute to increasing human–wildlife conflicts in areas where human disturbance has resulted in ungulate hyperabundance.