ASPECTS OF HABITAT CHOICE AND FITNESS IN PROLINYPHIA MARGINATA (ARANEAE: LINYPHIIDAE): WEB-SITE SELECTION, FORAGING DYNAMICS, SPERM COMPETITION, AND OVERWINTERING SURVIVAL

Investigations were conducted on proximate and ultimate factors of web-site selection in the filmy dome spider, Prolinyphia marginata. The influence of food supply on site selection and tenacity was examined by contrasting choice of web-sites relative to prey density in a laboratory aquarium with disappearance rates in abandoned, food-supplemented abandoned, and permanent field web-sites. Laboratory differential feeding rate experiments plus comparison of food-supplemented and non-food-supplemented field spiders, provided data on the influence of food supply on spider development rate and weight gain. Web size measurements, plastic cups coated with insect adhesive, and spider response to introduced prey were used to determine the relative importance of web size, prey density, and prey capture rate in accounting for different spider prey availabilities in the field. The importance of rapid development in males was examined by determining the degree of multiple mating and sperm use patterns in females using electrophoretic data from field-captured mating pairs of spiders. The influence of development stage and weight on overwintering success was analyzed using spiders of different development stages and weights overwintering in outdoor jars with leaf litter or field cages.; The results indicate that spiders permanently reside at web-sites with high prey densities. This strategy maximizes the percent net energetic return and promotes a temporally constant food supply. Spiders which have access to a large number of prey develop faster and weigh more than individuals with lower prey availabilities. Large variability in web size rather than prey density or prey capture rate, appears largely responsible for differences in spider prey availability. Most females multiply mate and primarily use sperm from early matings for fertilization, placing a premium on fast male development. Overall winter survivorship is low, with older stages (instars) having a higher survival rate than younger stages. There is no effect of weight variability, within a stage, on survivorship. I suggest that habitat selection is best described as microhabitat selections in response to resource requirements. The structure of microhabitat selections are related to r- and K- life history traits.