Experimental influence of population density and vegetation biomass on the movements and activity budget of a large herbivore

Population density could influence herbivore foraging decisions as it affects the availability of preferred plant species and intraspecific competition. We tested the effect of density on white-tailed deer (Odocoileus virginianus) movements and activity budgets at controlled densities of 7.5 and 15 deer/km². We also measured the activity budget of deer and plant biomass in an unfenced area at >20 deer/km². Deer in the unfenced area spent less time active than those at controlled densities, possibly because of the greater time required to process a low quality diet. Biomass of preferred plant species significantly increased through years but did not differ between controlled densities. Adults were less active than yearlings at 7.5 but not at 15 deer/km² but, otherwise, movements and activity budgets were similar between densities. Deer at controlled densities responded to the increase of plant biomass by increasing the number of activity bouts and shortening their duration. When vegetation was less abundant, adults at 7.5 deer/km² spent more time active. Augmentation of population density and, thus, of intraspecific competition, can have direct effects on deer foraging behavior. Increases in plant biomass, however, revealed that plant biomass appears to have a stronger influence on deer foraging behavior than population density.

Affiliations: 1: NSERC-Produits forestiers Anticosti Industrial Research Chair, Département de biologie & Centre d'études nordiques, Université Laval, Québec, Québec, Canada G1K 7P4