Doctoral Dissertations

Date of Award

6-1986

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major Professor

Susan E. Riechert

Committee Members

Gordan M. Burghardt

Abstract

Behavioral adaptations for resource acquisition in the long jawed orb weaving spider Tetragnatha elongata Walckenaer (Araneae: Tetragnathidae) are documented in this study. It examines the form and mechanism of spider foraging behavior, an essential prerequisite to the realization of the commercial use of spiders in integrated pes t management. Being the most common and ubiquitous of insect predators, spiders offer tremendous potential as stabilizers in agro ecosystems with unstable cycling of phytophagous insects. The initial part of this study examines the mechanisms employed by T. elongata in selecting a habitat, and demonstrates that spiders do not build webs where the abiotic environment is unsuitable; under these circumstances there is increased random locomotion. Where the immediate physiological requirements of the spider are satisfied, web building may occur when a spider can locate suitable support structures. Residence time at a site is determined by an interaction of spider hunger level and prey availability.

The nature of this interaction is fur the r examined in the second part of this study by comparing two populations with marked differences in behavioral activity patterns and prey capture rate. The specific foraging strategy adopted in any given situation is highly plastic. Where prey availability is low, a "'sit-and-wait'' strategy is adopted; where high, they are "'mobile"' predators. A mode l is developed to explain this dichotomy in terms of "'risk"‘; i.e., hunger-specific responses to variability in resource abundance. The mode l is validated. The behavior of s it -and-wait foragers is "'risk prone"': predators capitalize on variability in resource abundance by remaining for extended periods at any site offering a sustainable prey capture rate. A mobile predator is "'risk averse", avoiding variability in resource abundance by continual sampling to exploit the habitat average.

The mode l developed also suggests a positive advantage to aggregative behavior in T. elongata at high prey densities. The extent and form of this behavior is examined in the final part of this study through experimental manipulation to allow the establishment of very high levels of prey availability. Such conditions induce a degree of cooperation: reduced individual web building and silk sharing.

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