Predator presence alters prey diet composition but not quantity in tide pool fish interactions

Understanding species interactions and how they change in the presence of a predator or competitor is a fundamental goal for ecologists. We tested such interactions in an intertidal soft sediment pool system where both the sand goby Favonigobius lentiginosus and post-settlement whiting Sillago spp. consume meiofaunal prey, but F. lentiginosus also consumes Sillago spp. We quantified changes in fish gut content volumes and composition (i.e. meiofaunal group diversity and abundances) in response to the presence of a predator/prey and to different fish densities (two, four or six total individuals) in experimental aquaria. We found no significant density-dependent effects on either the predator or prey species, likely due to meiofaunal prey oversupply; however, the diet composition of the prey species Sillago spp. changed significantly in the presence of their potential predator. We conclude that lower consumption of meiofaunal amphipods in the presence of gobies suggests that whiting perhaps maintain their gut fullness by preferentially targeting larger amphipods.Griffith Sciences, Griffith School of EnvironmentNo Full Tex

The evolution of food sharing in primates

The aim of this study is to explain the occurrence of food sharing across primates. Defined as the unresisted transfer of food, evolutionary hypotheses have to explain why possessors should relinquish food rather than keep it. While sharing with offspring can be explained by kin selection, explanations for sharing among unrelated adults are more controversial. Here we test the hypothesis that sharing occurs with social partners that have leverage over food possessors due to the opportunity for partner choice in other contexts. Thus, we predict that possessors should relinquish food to potential mates or allies, who could provide or withhold matings or coalitionary support in the future. We used phylogenetic analyses based on both maximum likelihood and Bayesian approaches in a sample of 68 primate species to test these predictions. The analyses strongly indicate that (1) sharing with offspring is predicted by the relative processing difficulty of the diet, as measured by the degree of extractive foraging, but not overall diet quality, (2) food sharing among adults only evolved in species already sharing with offspring, regardless of diet, and (3) male–female sharing co-evolved with the opportunity for female mate choice and sharing within the sexes with coalition formation. These results provide comparative support for the hypothesis that sharing is “traded” for matings and coalitionary support in the sense that these services are statistically associated and can thus be selected for. Based on this, we predict that sharing should occur in any species with opportunities for partner choice