Carabid beetle assemblages of rangeland and Conservation Reserve Program fields in western Kansas

Background/Question/Methods

The goal of the Conservation Reserve Program (CRP) is to convert low productivity agricultural fields to a more stable vegetative structure to control erosion.  CRP is often credited with improving the amount of habitat in regions dominated by agriculture.  Numerous studies have compared the mammal and bird inhabiting CRP fields with those other habitats, but few studies have examined how invertebrates respond to CRP.  In this study, we compare the carabid beetle assemblages inhabiting CRP and rangeland fields in western Kansas.  We wanted to investigate how vegetative structure influences the carabid community structure and to develop a baseline for more extensive landscape studies.  Using drift fence/pitfall arrays we sampled carabid beetle assemblages in 17 CRP and 17 rangeland fields (a paired sample design).  Traps were unbaited, but did contain a permethrin impregnated kill agent.  Specimens were collected weekly from the traps from June to September.  All specimens were identified to species.  Vegetation was described by quadrat sampling and plant height.

Results/Conclusions

We collected 4368 carabids over the study.  This sample consisted of 42 species. Nine species were captured only in rangeland and 10 species were captured only in the CRP fields.  Apparent species richness of the CRP was slightly greater than that of the rangeland.  Evenness and total abundance did not differ between the habitats sampled.  CRP and rangeland differed in vegetation composition and structure.  CRP vegetation was taller and less diverse and had a thicker layer of litter than did the rangeland.  The carabid assemblage structure was strongly influenced by vegetative structure (height and litter layer), but was relatively unaffected by vegetative composition.  However, the occurrence of Amara carinata was closely associated with the presence of western wheatgrass (Pascopyrum smithii).  CRP and rangeland fields could be differentiated by the abundance of Pasimachus elongatus. We found that while P. elongatus was among the most common species (896 specimens, captured in 29 of the 34 fields sampled) it was significantly more abundant in rangeland than CRP fields.  This research shows that CRP and rangeland fields differ in their carabid assemblages, but is it not clear if this difference is the result of their differing histories or the difference in current management practices.