Effectiveness of a vegetation-based approach to insect conservation

We used plant and insect data from 50 prairie reserves in the Chicago region to assess the extent to which reliance on plant criteria for conservation planning might result in the conservation of insect biodiversity within the tallgrass prairie ecosystem. Three of nine plant measures-plant community richness, plant species richness,and plant genus richness-were found to explain significant levels of variation in conservation (reserve-requiring) insect species richness in best-fit regressions. Native plant species richness explained from 28% to 49% (80-85%, on average, when coupled with area) of the variance in conservative insect species richness among sites,suggesting that plants are a useful indicator taxon. Conservative insect species were well represented within the botanically selected Chicago-area reserve system, providing additional support for the vegetation-based "coarse-filter" preserve selection approach. We found no evidence of concurrence between either conservative plant species richness or rare plant richness and conservative insect species richness,suggesting that the use of additional "fine-filter" plant data may not increase capture rates for reserve-requiring insects. Among nine plant measures, only plant community richness showed (limited) promise as a surrogate for rare insect richness. We found no coincidence between either plant species richness or common insect species richness and rare insect species richness, supporting earlier suggestions that a "hot spot" approach might fail to capture rare species at finer spatial scales. Low levels of coincidence between plant family richness and insect species richness suggest that the use of higher taxa for cost-effective reserve selection may not be an effective conservation strategy. We conclude that a vegetation-based coarse-filter approach, emphasizing native plant species and plant community richness, can contribute substantially to the consevatioin of insect biodivesity in tallgrass prairie regions, and perhaps within temperate regions generally. We caution,however, that effective protection of rare insect species will require a detailed knowledge of their identity and distribution within the region under consideration.