Date of Award

12-2005

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

Susan E. Riechert

Committee Members

Christine Boake, Gordon M. Burghardt, Joseph H. Williams

Abstract

Widely distributed species are exposed to different environmental forces throughout their range. As a response to differences in local environmental conditions, these species are expected to present geographic variation in phenotypic traits (e.g., behavioral, physiological, anatomical) in order to better adapt to these conditions. Parawixia bistriata (Araneidae) is a colonial spider distributed in a variety of habitats in South America. This species is unusual in two respects: contrary to most social species found in tropical wet forests, P. bistriata’s distribution extends from tropical to temperate latitudes; and it exhibits facultative group foraging, a behavioral pattern absent in territorial colonial spiders. In this dissertation, I examined the existence of geographic variation in life history and behavioral traits of P. bistriata’s populations inhabiting sites with distinctive environmental conditions and estimated success of populations. I performed reciprocal transplants of colonies to evaluate the influence of genetic and environmental forces on the variation exhibited in both life history and behavioral traits in populations from different habitats. When examining behavioral traits, I focused on foraging behavior as I wished to evaluate whether the expression of this behavioral pattern could explain the success of populations in diverse habitats types. Phenology of populations from the different habitats was out of phase. The differences exhibited in the phenology were a response of juvenile developmental traits to resources levels and possibly climatic factors such as temperature. Populations from the different habitats were equally successful as judged by the reproductive output of individuals and by the size of colonies. Data from the reciprocal transplants, however, suggested that populations constituted ecotypes: while individuals from dry habitat origin were successful in both native and foreign habitat, individuals of a wet habitat origin failed at reproduction in the foreign habitat. Analysis of foraging behavior showed that while some of the behavioral aspects that differed geographically exhibited plasticity, others, such as the tendency to capture and feed on prey as a group, exhibited divergence between populations from the different habitats. Individuals from populations with low resources exhibited plasticity for this trait: they tended to capture prey and feed as a group when resources are low, but solitarily when prey levels are high. On the other hand, individuals from high resource habitats did not change between solitary and group foraging in response to different prey levels. The correspondence between reproductive effort and plasticity in group foraging suggests that the expression of this behavior is in part responsible for the success of populations of P. bistriata in habitats with low resources.

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