Selective predation in a euryphagous invertebrate predator, Pardosa vancouveri (Arachnida, Araneae)

Abstract

Selective predation (i.e., non-random feeding) was studied in a laboratory system that allowed individual lycosid spiders, Pardosa vancouveri, to feed on prey populations consisting of one or two kinds of insects. Various combinations of male and female fruit flies (Drosophila melanogaster), "small" and "large" beetle larvae (Tenebrio molitor), and nymphal milkweed bugs (Oncopeltus fasciatus) were used as prey. Female adult and subadult spiders were used as predators. Generally, fruit flies were selected by the spiders over mealworms or milkweed bugs, and small mealworms over large ones. No selection occurred between male and female flies. Very weak or no selection occurred between small beetle larvae and milkweed bugs. Spiders of both age classes showed similar selective tendencies. Prior feeding experiences did not alter feeding selections, but minor changes in the physical complexity of the environment did. Twelve criteria related to development, survival, growth, and fecundity were monitored for 12 groups of spiders fed either single or two-prey combinations of the five kinds of prey. The hierarchy of benefits conferred by the five kinds of prey was the same as that for selection. Male and female fruit flies equally benefited the spiders. The fruit flies yielded the most and large beetle larvae the least number of statistically superior benefits. Small beetle larvae and milkweed bugs were intermediate and about equal. There was no evidence that a mixed (i.e., two) prey diet is better than a single prey diet. It is hypothesized that selective predation by P. vancouveri involves prey sampling, memory of prey attributes, and selection of prey that possess attributes that are associated with high fitness.