Site-specificity and site tenacity in a wolf spider: A serological dietary analysis

Summary

The wolf spider Pardosa ramulosa is a dietary specialist on aquatic insects. Site tenacity of this species was determined by serological analysis of spiders collected on the margins of and at known distances from each of eight closely-spaced pools whose prey compositions were known. Remains of a mosquito species found uniquely in three of these pools were found only in spiders closely associated with them, despite the presence of otherwise suitable pools less than 10 m away. This indicates that spiders stay at specific pools for at least two weeks, the detectability period of this marker species in the assay.

The only exception to this site tenacity, except for inadvertant rafting during high tides, is the movement of adult females with egg cases away from pools. This is attributed to selection for avoidance of spiderling cannibalism, rather than a search for sunning or foraging sites as in some other lycosids.

The extreme site-tenacity of P. ramulosa is attributed to the high productivity of all pools, such that spiders from the most and least productive pools differ little if at all in fitness, and the high costs of moving to other pools, which are widely dispersed. The situation in crab spiders may be analogous. Conversely high and biologically significant variances in web site productivity, low distances between acceptable web sites, and low moving costs reduce site tenactiy in north temperate second growth orb weavers and a desert funnel web weaver.