Human selection of elk behavioural traits in a landscape of fear

Abstract

Among agents of selection that shape phenotypic traits in animals, humans can cause more rapid changes than many natural factors. Studies have focused on human selection of morphological traits, but little is known about human selection of behavioural traits. By monitoring elk (Cervus elaphus) with satellite telemetry, we tested whether individuals harvested by hunters adopted less favourable behaviours than elk that survived the hunting season. Among 45 2-year-old males, harvested elk showed bolder behaviour, including higher movement rate and increased use of open areas, compared with surviving elk that showed less conspicuous behaviour. Personality clearly drove this pattern, given that inter-individual differences in movement rate were present before the onset of the hunting season. Elk that were harvested further increased their movement rate when the probability of encountering hunters was high (close to roads, flatter terrain, during the weekend), while elk that survived decreased movements and showed avoidance of open areas. Among 77 females (2-19 y.o.), personality traits were less evident and likely confounded by learning because females decreased their movement rate with increasing age. As with males, hunters typically harvested females with bold behavioural traits. Among less-experienced elk (2-9 y.o.), females that moved faster were harvested, while elk that moved slower and avoided open areas survived. Interestingly, movement rate decreased as age increased in those females that survived, but not in those that were eventually harvested. The latter clearly showed lower plasticity and adaptability to the local environment. All females older than 9 y.o. moved more slowly, avoided open areas and survived. Selection on behavioural traits is an important but often-ignored consequence of human exploitation of wild animals. Human hunting could evoke exploitation-induced evolutionary change, which, in turn, might oppose adaptive responses to natural and sexual selection.

Figure 1.

Predicted variation of step length over the time (from January through the hunting season) in male elk that survived or were harvested during the hunting season (a), in female elk irrespective of their hunting season fate (b), and estimated smoother predicting the effect of age on the variation of step length in female elk (c). Smoothed predicted values and approximate point-wise 95% CIs were calculated by adding the intercept value to the contribution of both fixed and random effects in GAMMs.

Figure 2.

Predicted variation of step length in male (a) and female elk (b) that survived or were harvested during the hunting season, and estimated smoothers for the effect of age on step length in female elk depending on hunting season fate (c). Smoothed predicted values and approximate point-wise 95% CIs were calculated by adding the intercept value to the contribution of both fixed and random effects in GAMMs.