Doctoral Dissertations

Date of Award

5-2000

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

Susan E, Riechert, Thomas G. Hallam

Committee Members

David A. Buehler, Paul A. Delcourt, Michael L. McKinney

Abstract

This dissertation addresses issues surrounding the inclusion of terrestrial arthropods in conservation planning. There are potentially disastrous consequences of basing all of our conservation priorities and strategies on what we know of the ecology of a minority of species (vertebrates). Vertebrate species do not provide enough information to be good indicators of ecosystem health, particularly if we are interested in those ecosystem processes which involve invertebrates. We need to leam more about those organisms which comprise the bulk of biodiversity (arthropods) and develop methods which facilitate the inclusion of terrestrial arthropods (or other hyperdiverse groups) in conservation planning. In this dissertation, I begin the process of developing analytical tools appropriate to a representative arthropod group, the spiders (Order Araneae). Spiders were chosen in part because they show particular promise as an indicator group. One of the difficulties associated with studying a hyperdiverse taxonomic group is ensuring accurate and timely species identification. Using technology similar to that employed in handwriting analysis and/or face recognition, I present an automated species identification system which makes use of neural networks. This technology, once perfected, will increase the accuracy of identifications by non-specialists and thereby reduce the need to burden systematists with routine identifications of ecological collections. This technology could also be used to catalog species which have yet to be identified or even described (morphospecies), thus allowing accurate ecological studies to take place prior to naming all the component species in the assemblage. Using data collected in the Southern Appalachians, I review and evaluate some commonly used analytical techniques in biodiversity studies: rarefaction (scaling down all samples to the size of the smallest), diversity indices, and extrapolation (estimating the total richness of a site based on a sample taken from the site). Rarefaction was essential to correct for differences in samples size between samples, particularly when using indices calculated using only presence/absence data. The diversity indices, Shannon-Weiner and Simpson's, were surprisingly robust to differences in sample size and they detected both successional and disturbance-induced changes in spider assemblages. Directional trends in the diversity indices through time proved to be most informative in conjunction with pair-wise statistical tests. My results suggest, however, that extrapolation techniques should be used cautiously, as they were sensitive to differences in sample size and yielded very different richness estimates for surveys taken at the same sites. Using the same datasets, I identify and discuss potential sources of error which are characteristic of studies involving hyperdiverse taxa and make recommendations for eliminating or reducing this error. I find that collector bias is a significant problem, in that each collector is not sampling a statistically random subset of the community. But, as expected, some collection techniques are more subject to this kind of bias than others. I recommend that if turnover of collectors is likely, methods such as pitfall traps, litter samples, and vegetation beating/sweeping should be emphasized. Also, inclusion of juveniles in diversity estimates and analysis should be avoided as much as possible as their presence appears to obscure ecological trends. I used the datasets to investigate the intra-annual (early vs. late summer) and inter-annual (yearly vs. decadal) variability of spider assemblages in six Southern Appalachian habitats. Spider assemblages show greater seasonal variation than yearly variation. The diversity and variability of the spider assemblages I studied were closely tied to gross habitat structure. In conclusion, terrestrial arthropods can and should be included in conservation planning and/or community-level analyses. Techniques exist and are currently being perfected, which address the peculiarities and difficulties associated with working with such hyperdiverse groups.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS