Doctoral Dissertations

Date of Award

5-1989

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

Susan E. Riechert

Committee Members

Sandy C. Echternacht, Paris L. Lambdin, M. L. Pan

Abstract

The effect of dispersal on the structure of animal communities was examined by studying the recolonization of disturbed habitats by spider species assemblages. Disturbance results in a disruption of the relative abundance of species in the community and produces new patterns. Spiders are a good choice as the experimental group because they are among the first arthropods to invade a disturbed habitat. Spiders exhibit many of the characteristics used to define successful invaders: abundance, polyphagy, a high dispersal potential achieved by active and passive modes, dispersal of fertilized females, high reproductive potential, and a broad range of physical tolerances.

The first aspect of my research was to determine the community reassembly process of spiders invading an agroecosystem, and to compare this to less disturbed communities - old field and woods. I sampled the spider fauna weekly for eight months in each of these three habitats. Ground dispersers were collected by pitfall traps, and airborne dispersers were collected by vertical sticky traps. Results demonstrate peaks in dispersal and a complete description of spider species composing each habitat through time. There is a trend for the species composition in the garden to be more similar to that of the old field than to that of other adjacent habitats. However, the similarities between these habitats were always low. The garden habitat was higher in species richness and turnover than adjacent, more stable habitats. Species persistence was lower in the garden than in other habitats early in the season, but was independent of habitat type later in the season.

Secondly, I examined the effect of differential dispersal abilities of invading spider species on the recolonization of agroecosystems. Two mark - recapture experiments demonstrate that cursorial spiders will disperse into a garden habitat fix>m adjacent old fields, however, recapture rates were very low. The relative significance of aerial vs ground dispersal was examined by comparing plots with sheet metal flashing enclosures, which limit arrival to airborne spiders only, with control plots. There was no significant iv difference between the mean number of spiders in each plot, which demonstrates that most dispersal was by aerial ballooning. Further evidence for long distance dispersal was that high percentages of species in garden habitats were unique and not found in adjacent habitats.

For the ballooning spiders, I determined what climatological factors influence aerial dispersal. I studied aerially dispersing spiders from a 45 meter forest meteorology tower. Spiders were collected daily on sticky traps suspended from the tower at various heights within and above the forest canopy. Climatological data were continuously collected from the tower, including temperature, wind velocity, wind vectors, and humidity. Most spiders trapped in the autumn were collected at 22m, immediately above the forest canopy, whereas in the spring the highest catch was at 33m and 44m. Spider ballooning activity was most affected by abrupt changes in temperature, a maximum range between dew point temperature and air temperature, and low wind fluctuations.

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