Wolf spider feeding strategies: optimality of prey consumption in Pardosa hortensis.

Abstract

Feeding behaviour of the wolf spider Pardosa hortensis Thorell (Araneae, Lycosidae) was studied in the laboratory. Characteristics of feeding were measured while prey availability was increased and the results were compared with the predictions of three models: the marginal value theorem (MVT), gut limitation theory (GLT) and the digestion rate limitation model (DRL). As a result of more frequent encounters with prey, the wolf spiders were able to modify their feeding behaviour so that their net energy intake rate increased substantially. Handling time decreased by 30%, and consumption rate increased by 40%. Partial consumption of prey did not occur until the spiders became nearly satiated. This indicated that spiders did not reach the optimum predicted by MVT. The most plausible mechanism for the increased efficiency was prey-stimulated digestive enzyme production as suggested in DRL. The predictions of GLT were not applicable for most of the feeding session, though gut satiation had an influence on the final stages of feeding. P. hortensis seemed to apply a "responsive but cautious" strategy: (i) spiders improved feeding efficiency on entering the higher quality habitat, but (ii) feeding times appeared to be sub-optimal and (iii) spiders were also willing to continue feeding when, as they approached satiation, the previously high efficiency could not be maintained. Such feeding behaviour optimizes long-term energy intake when food is scarce and unpredictable, which corresponds well with the known degree of natural food limitation of these animals.