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  • Potential Terrestrial Arthropod Indicators for Tallgrass Prairie Restoration in Iowa
  • Jessica M. Orlofske, Wayne J. Ohnesorg, and Diane M. Debinski

Prairie management and restoration have traditionally emphasized plant communities but could benefit from the development of ecological indicators that incorporate animal communities to provide tangible benchmarks of ecosystem function and process (Hodkinson and Jackson 2005). Arthropods are useful bioindicators in terrestrial and aquatic systems because, in addition to being diverse and abundant, they represent key components in food webs, nutrient cycles, plant reproduction, and soil formation (Hodkinson and Jackson 2005, Kremen et al. 1993).

A more comprehensive understanding of arthropod habitat specificity and resilience is needed before defining holistic ecological indicators for tallgrass prairies. Previous research has focused on either responses of prairie arthropods to management practices, specifically prescribed fire, or the status of particular taxa (Shepherd and Debinski 2005). Panzer and colleagues (1995) provide a preliminary list of remnant-dependent insects that qualify as potential ecological indicators. This list could be improved by 1) eliminating a priori assumptions regarding potential indicators; 2) using consistent sampling across prairie sites; and 3) comparing indicator response at restored and reconstructed prairies. Our objective is to identify insect and spider families that are informative bioindicators of tallgrass prairie condition—a surrogate of biotic integrity—for use as measures of restoration progress. We accomplish this objective by 1) broadly examining insect and spider taxa without assuming their indicator potential; 2) collecting invertebrates using a standardized method; and 3) comparing the indicators at a suite of sites relevant to those interested in prairie conservation and restoration.

In June–August of 2006–2007, we sampled arthropods in central Iowa at prairie remnants (n = 9), isolated restorations/reconstructions (n = 10), and integrated reconstructions (n = 11). Site types are defined according to Shepherd and Debinski (2005) (Figure 1). The surrounding landscape was primarily agricultural, but integrated reconstructions were nested within larger managed prairies. We selected sites to minimize geographical, soil type, and size variation; however, specific management practices varied across the sites. This approach allowed us to characterize taxa based on their association with a particular prairie type, providing a way to evaluate consistency among managed prairies.

Sweep net transects were used to collect arthropods from foliage. Sweep net collections provide a rapid, inexpensive, and easily standardized protocol, although they do not sample the entire arthropod community, missing arthropods found on or below the ground surface. At each site, three 25 × 2 m belt transects were chosen with a random starting point and direction during each monthly visit. Transects were located at least 10 m from edges, trails, or water and were nonintersecting. Sampling occurred between 9:30 a.m. and 4:30 p.m. on days above 18°C with less than 60% cloud cover and calm winds (gusts less than 17 kph; Shepherd and Debinski 2005). Each transect was swept with a canvas net (diam. 30.5 cm) with 20 pendulum sweeps. Collected arthropods were transferred to labeled zip-top bags and stored in a −20°C freezer until identified.

Insect and spider specimens were identified to family according to Triplehorn and Johnson (2005) and Ubick and others (2005). We excluded taxa that were considered impractical for practitioners to identify based on [End Page 250] size (Collembola, Thysanoptera, Psocoptera, and micro-Hymenoptera) and taxa primarily associated with aquatic habitats (Ephemeroptera, Odonata, Plecoptera and primarily aquatic families of Diptera and Coleoptera). We also excluded Lepidoptera owing to the high proportion of indistinguishable larval specimens. To identify insect and spider families representative of each prairie type, we used indicator species analysis (ISA), which evaluates a taxon’s site specificity, the abundance of the taxon at a specific subset of sites, and site fidelity, the number of sites of a particular type where the taxon occurs, in order to calculate an indicator value for each taxon for each site type (see equation in Dufrêne and Legendre 1997). Arthropod abundances were log transformed to reduce skewness, and data from each sampling year were analyzed separately and combined to determine if there were effects attributable to sampling year. The ISA was performed using the duleg function in the labdsv package in the R statistical environment (version 2.6.0, R...

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