Nonlinear effects of food aggregation on interference competition in mallards

Abstract

Previous studies of interference competition have shown an asymmetric effect on intake rate of foragers on clumped resources, with only subordinate individuals suffering. However, the food distributions in these studies were uniform or highly clumped, whereas in many field situations, food aggregation is intermediate. Here we investigated whether food distribution (i.e., uniform, slightly clumped, and highly clumped) affects the behavioral response of mallards foraging alone or competing with another. Although the amount of food was the same in all distributions, the mallards reached higher intake rates, visited fewer patches, and showed longer average feeding times in the highly clumped distribution. Competing mallards had lower intake rates on the slightly clumped than on the uniform or highly clumped food distributions. Subordinates generally visited more patches and had shorter feeding times per patch, but their intake rates were not significantly lower than those of dominants. Therefore, we propose that subordinates do not necessarily suffer from interference competition in terms of intake rate, but do suffer higher search costs. In addition, although dominants had significantly higher average feeding times on the best quality patches of the highly clumped food distribution, such an effect was not found in the slightly clumped distribution. These findings indicate that in environments where food is aggregated to a lesser extent, monopolization is not the best strategy for dominants. Our results suggest that interference experiments should use food distributions that resemble the natural situation animals are faced with in the field.

Time allocation of bison in meadow patches driven by potential energy gains and group size dynamics

“…When biomass of C. atherodes exceeded 2500 kg over the area, the difference in risk of departure between small and large groups was weak. This response is consistent with previous studies showing that an increase in the abundance of resources or a decrease in the spatial distribution of preferred food types can balance the effects of social factors on intake rate and food preferences (Vahl et al 2007, Sibbald et al 2008, Gyimesi et al 2010). For example, domestic sheep Ovis aries prefer to feed on larger grass patches offering greater biomass of their favourite food, because they can graze in social groups (Sibbald et al 2008) without the foraging costs of competition being as strong as when they are on relatively small patches (Dumont et al 2002).…”

Human disturbance of Bewick's Swans is reflected in giving‐up net energy intake rate, but not in giving‐up food density

“…, , Gyimesi et al . ). Consequently, grazing pressure is low or absent in patches at low initial food densities and below the threshold GUN (Olsson & Brown ).…”

Mallards Feed Longer to Maintain Intake Rate under Competition on a Natural Food Distribution

“…In a homogeneous environment for example, where all patches have the same quality, foragers gain an equal intake rate and dominance status has little to no effect on the foraging success of individual flock members (Vahl et al. 2005a; Gyimesi et al. 2010).…”

“…2010). However, when food is highly clumped, interference competition reduces the intake rate of group‐foraging birds (Gyimesi et al. 2010), and dominant birds are able to monopolise the high‐quality patches, hereby reducing the foraging success of subordinate birds (Vahl et al.…”