Tuesday, August 7, 2007

PS 21-5: Selective foraging and the functional response of Pardosa milvina (Araneae: Lycosidae) fed on different diets

Peter J. Sebastian and Ann L. Rypstra. Miami University, Ohio

One assumption of prey selection theory is that prey quantity is important while nutritional content of the prey is generally ignored.  The goal of this work was to quantify the functional response of the wolf spider, Pardosa milvina, when provided with diets that differed in quality.  In all cases, we manipulated prey quality by using Drosophila melanogaster reared on Carolina medium (low quality) or medium augmented with dog food  (high quality). In one experiment, spiders were offered varying densities of low or high quality Drosophila and the number killed and amount ingested (based on change in abdomen width) was measured. In a second experiment, spiders were maintained on a diet of high or low quality prey for two weeks and then provided with varying densities of high quality prey.   In both experiments, spiders displayed a linear Type II functional response.   In the first experiment spiders killed similar numbers of high and low quality prey but consumed more of the low quality prey across all densities.  These results suggest spiders ingest more low quality prey to meet nutrient requirements. In the second experiment, spiders pre-fed on a high quality diet killed more prey than those pre-fed on low quality prey.  These results suggest spiders maintained on a better diet were in better physiological condition and more effective predators.  Thus, the foraging of this generalist predator, and its potential impact on the food web, is influenced by the quality of prey in the environment.