Invertebrate Diversity In Old-Field Sites In Southwest Michigan: Assessment of Indicator Taxa and Examination of Ecological Correlates of Diversity

Abstract

Insects and invertebrates comprise a substantial portion of earth’s diversity, representing 72.8%, and 95.8 % respectively of all known animal species. In the soil environment invertebrates perform many important functions, including but not limited to; pest management, decomposition of organic matter, soil aeration, assist in growth, development and reproduction of plants, and provide a food source for higher trophic level organisms. Because of the immense level of biodiversity contained within invertebrates, conducting studies examining insect or invertebrate diversity can become time consuming and difficult. In order to analyze diversity on a large scale entomologists have begun to use certain indicator taxa as representative of greater taxonomic diversity (Balmford et al. 1996, Cleary 2004). This is the use of one monophyletic group as representative in at least one aspect of greater taxonomic diversity. This allows studies to be conducted with more manageable sorting and identification but with implications that expand far beyond that of the taxa examined. In order for a taxon to be to be considered a good representative of greater taxonomic diversity, it should meet four criteria. It should, 1) be easily sampled and monitored, 2) be representative of important groups within the ecosystem examined, 3) have known relationships to the diversity of other taxa and, 4) should respond similarly to environmental change as the groups they represent (Alonso et al. 2000). As ecological succession within old-field sites proceeds the total number of species present increases (Bazzaz 1968). This increase in species diversity makes cataloguing invertebrate diversity more and more difficult. By finding and then using an indicator taxon diversity could be more efficiently monitored and examined in its relationship to outside factors, such as invasive species. One such invasive species is Spotted knapweed (Centaurea maculosa). Spotted knapweed is an herbaceous forb that is native to Eastern Europe and Western Asia. Knapweed infests non-native habitats with the aid of an allelopathic toxin that it secretes from its roots called (-)-catechin (Bais et al. 2003). Over the past century knapweed has spread to occupy over 2.8 million hectares of the western United States (Story et al. 2001), though it can be found in many other habitats including old-field sites in Michigan. Invasive plants like knapweed cost an estimated $2 billion annually (Bovey 1987). The discovery of a valid indicator taxon could be used to track invertebrate diversity in relation to changes in habitat due to factors such as knapweed infestation.