Evaluating Multiple Arthropod Taxa as Indicators of Invertebrate Diversity in Old Fields

evaluate and monitor the health of ecosystems and as a tool for conservation planning. The use of one or more focal taxa as surrogates or indicators of larger taxonomic diversity can greatly expedite the process of biodiversity measurement. This is especially true when studying diverse and abundant invertebrate fauna. Before indicator taxa are employed, however, research into their suitability as indicators of greater taxonomic diversity in an area is needed. We Correlation analysis was used to assess species richness relationships between focal arthropod taxa and general invertebrate diversity. Relationships were four sampling patches. Cumulative richness of all assessed taxa increased proportionately with cumulative invertebrate richness as sampling intensity Hemiptera and Coleoptera as effective indicator taxa of greater invertebrate richness. Although Hymenoptera, Araneae and Diptera exhibited high species richness, their total richness within patches was not associated with overall invertebrate richness among patches. Increased sampling throughout the active season and across a greater number of habitat patches should be conducted invertebrate richness in the Great Lakes region. Multiple sampling techniques, in addition to pitfall trapping, should also be added to overcome capture biases associated with each technique. ____________________ Biodiversity measurement is commonly used to evaluate and monitor the health of ecosystems and as a tool for conservation planning (Magurran 1988, Hoffmann 2010). Species richness is often used for these purposes, wherein standardized methods are used to sample and catalog species-level diversity within a designated area (Magurran 1988). Accurate species richness results can also be obtained quickly and at lower cost using morphospecies designaThe use of morphospecies is not without limitations, however. Error rates for 2012 THE GREAT LAKES ENTOMOLOGIST 57 morphospecies determinations can be high for speciose taxa such as beetles and spiders (Derraik et al. 2002) but can be reduced if sorters are trained in morphospecies determinations lack actual species names, however, information on species ecology and conservation status is lost (Goldstein 1997). Despite these limitations, the use of morphospecies allows quick sorting of specimens and can provide gross level information on the effects of invasion, disturbance or land use change on community composition and diversity. provide, the sheer magnitude and variety of specimens that result from survey collections often necessitates the use of one or more focal taxa as diversity intaxon is an appropriate surrogate taxon or ‘bioindicator’ of greater taxonomic diversity when its own diversity, usually expressed in terms of species richness, is positively correlated with greater taxonomic diversity in the same area (Duelli when relationships are tested, assumed correlations are not always upheld (Duregions (Lindenmayer et al. 2000), or at certain spatial scales (Weaver 1995, Hess et al. 2006, Gaspar et al. 2010). When seeking to use focal taxa as indicators of greater taxonomic diversity, preliminary assessments of their usefulness must be made at scales relevant to desired use. The purpose of this study was to identify focal arthropod taxa whose attempt to investigate the effects of an invasive plant species, spotted knapweed (Centaurea stoebe L.), on the local invertebrate community and consequently on ecosystem health and functioning (Coleman and Hendrix 2000, Weisser and Siemann 2004, Harvey et al. 2010). In a pilot study, we were quickly overwhelmed with the diversity and abundance of invertebrate specimens retrieved by pitfall trapping (Waller 2006) and realized a need for suitable indicator taxa for this purpose. The diversity and abundance of arthropod taxa such as ants, beetles and spiders, coupled with their relative ease of collection, suggested that these, and possibly other taxa, might be good indicators of greater arthropod and general invertebrate diversity (Waller 2006). To test the suitability of these and additional arthropod taxa as indicators of invertebrate biodiversity, we used pitfall sampling to collect invertebrates and assessed species richness relationsampling patches, and locally across four sampling patches. Materials and Methods Field sites. This study was conducted in Kalamazoo County, Michigan between June and August 2005. We used pitfall trapping to sample invertebrates from three locations within the Lillian Anderson Arboretum (ARB) in in Comstock, approximately 19 km distant from the ARB site. Sampling was but which had not been actively managed by human enterprise for at least ten years prior to our study. Consequently, all patches were undergoing ecological succession. Habitat patches varied in size from ca. 1400 m2 to 15000 m2 and all patches were bordered by hardwood trees, predominantly oak (Quercus), hickory (Carya), maple (Acer) and wild black cherry (Prunus serotina Ehrh.). CHIP patch was composed of grasses and mixed forbs, with spotted knapweed (Centaurea stoebe) as the predominant forb. Vegetation cover in the three ARB 58 THE GREAT LAKES ENTOMOLOGIST Vol. 45, Nos. 1 2 patches (ARB1-ARB3) varied from primarily grasses (ARB2) with a few mixed forbs such as horse nettle (Solanum carolinense L.), pokeweed (Phytolacca americana L.) and thistle (Cirsium) to predominantly mixed forbs with goldenrod (Solidago), vetch (Vicia Daucus carota L.), spotted knapweed and Rubus as the most common forbs present. The three ARB patches were separated from one another by a 300-500 m expanse of forested vegetation. Invertebrate sampling. We sampled invertebrates using pitfall traps consisting of plastic cups measuring 7.5 cm diam × 8.5 cm deep. Pitfall traps were installed between 1000 and 1200 h at the start of a sampling period and percent isopropyl alcohol was used as the trapping liquid in all cases except at period. However, we found that slugs captured in soapy water secreted profuse amounts of slime that hindered specimen sorting. At CHIP, we initially added several drops of mineral oil to alcohol to reduce evaporation but this caused evaporation of untreated 70% isopropyl alcohol was not found to be a problem in subsequent trapping. At each patch, pitfall traps were installed at 10 m intervals along two parallel 50 m transects, for a total of 12 traps per patch. Parallel transects were separated by 15 m distance. Two rounds of sampling were conducted within each patch. Sampling period I occurred in early summer, between 20 June and 9 July 2005; the second round of sampling (period II) occurred in late summer, 2-4 August 2005. Weather during both sampling periods was seasonably warm (ca. 22-28 oC), generally sunny and without precipitation. Specimens were identiinsects, spiders) or genus (ants only). We discarded larvae of holometabolous to family and matching these with adult counterparts. For hemimetabolous insects and spiders, we could not reliably assign immatures of different instars treated all immatures within a family as a single morphospecies distinct from Among hemimetabolous families with immatures represented in collections, immatures accounted for 7.8% of all individuals collected, with two families (Araneae: Lycosidae and Hemiptera: Cicadellidae) accounting for 77.8 % of immature specimens. Data analysis. cients (r) to assess the strength of associations between focal taxa and remaining invertebrate diversity (see Gotelli and Ellison 2004). Analyses were conducted using JMP ver. 9.0 (SAS Institute). Associations were evaluated at two spatial scales: within and among patches. For within-patch evaluation of indicator taxa, we plotted the cumulative number of species per focal taxon against the corresponding cumulative number of all remaining invertebrate species (total invertebrate richness minus focal taxon richness) as successive pitfall contents were added. This allowed us to determine whether accumulated focal taxon richness was strongly correlated with accumulated invertebrate richness as sampling area increased. Plotting proceeded in order of pitfall number along transects. Data from the two sampling periods were analyzed separately to assess usefulness of focal taxa as indicators in different periods of the season. To evaluate the usefulness of focal taxa as indicators of greater invertebrate diversity over the larger among-patch spatial scale we plotted total focal taxon 2012 THE GREAT LAKES ENTOMOLOGIST 59 richness per patch against corresponding total remaining invertebrate richness per patch, with each sampling period (n=2) and patch (n=4) representing a single data point for a total of eight observations per focal taxon assessment.