The benefits of stealing from a predator: foraging rates, predation risk, and intraspecific aggression in the kleptoparasitic spider Argyrodes antipodiana

In the trade-off between food and safety, the role of aggressive intraspecific interactions has not been extensively examined. Here I present information on this system using a kleptoparasitic spider, Argyrodes antipodiana, and its host spider and potential predator, Eriophora pustulosa. A. antipodiana can feed either at a potentially dangerous site (the hub of its host's web with the host), or at a relatively safe site (on food bundles around the edge of the host's web). I found that A. antipodiana can gain food very quickly when feeding with the host, apparently by exploiting the host's ability to digest the prey. Thus A. antipodiana follows predictions based on foraging models in that it accepts a higher predation risk at the hub because of the higher food payoff. A. antipodiana also aggressively competes for access to more food. However, aggressive competition increases the predation risk from the host, especially at the hub where the host is very close. Consequently, A. antipodiana modifies its level of intraspecific aggressiveness in accordance with its position on the web: at the hub where the cost of aggression is high (due to predation risk), A. antipodiana reduces its aggressiveness, but it is aggressive away from the hub when competing for food bundles. The ability of A. antipodiana to change interaction intensity as a function of its position on the web enables it to exploit a rich, but risky, food source and provides a new angle for examining food and safety trade offs in light of intraspecific competition for food.