Date of Award:

5-1-1984

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Biology Ecology

Committee Chair(s)

James A. MacMahon

Committee

James A. MacMahon

Abstract

The effects of altered prey availability and shrub architecture on spider community parameters were studied in a field experiment in northeastern Utah. Treatments of 2 states of foliage density--"normal" and tied (= high density)--and 2 states of insect attractant-- control and baited--were applied to big sage shrubs (Artemisia tridentata) using a factorial experimental design. Temperature and humidity were not significantly different between the 2 types of shrub architecture. The species array and abundance of shrub insects were not significantly altered by the foliage density treatment. Shrubs with insect attractant had significantly larger insects (as measured by body length) than control shrubs. These shrubs also had proportionately more saprovore and omnivore insects than control shrubs. Numbers of spider "sit-and-wait" hunters (Ambushers) increased significantly in tied shrubs with increased foliage density. Numbers of active foraging spiders (Jumpers) increased significantly in shrubs with insect attractant-altered prey base. Differences in foraging technique characteristics such as spider activity, size of area in which prey is sensed and prey selection may account for the differential response by spider hunters to vegetation architecture and shrub insect composition. High density foliage in shrubs may increase the number of hiding site, necessary for successful prey captures by Ambushers. The increase in Jumpers in shrubs with insect attractant appears to be in response to higher prey concentrations. When compared with other shrub spider hunting-types, Jumpers appear to be more versatile hunters because they are more mobile and have larger areas of prey detection. These characteristics enable them to detect and respond to increases and concentrations of shrub insect numbers.

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