The advantage of starving: success in cannibalistic encounters among wolf spiders

Both hunger and body size differences increase the likelihood that an encounter between 2 predators turns into a cannibalistic event. Two hypotheses with opposite predictions can be proposed to explain how hunger influences cannibalism. The first claims that starvation weakens individuals, which then fall victim more easily to conspecifics that are more successful foragers or in better condition. The other suggests that starvation increases aggressiveness and willingness to take risks, so that starved individuals might more often become cannibals. We staged encounters between pairs of wolf spiders (Pardosa prativaga) of different body mass ratios, where either one was satiated and the other was starved or both were satiated. In 2 experiments, we found that in encounters between a hungry and a satiated spider of the same mass, the hungry spider was most often the cannibal. We also found an interaction between hunger asymmetry and body mass asymmetry in the likelihood of cannibalism occurring and the time taken until the cannibalistic event. These results support the second hypothesis that predicts that success in cannibalism will result from increased aggression and risk taking induced by hunger. Our results have implications for the consequences of cannibalism at population and community levels because they assign an increased emphasis on intracohort cannibalism resulting from food limitation. Copyright 2010, Oxford University Press.