1. Ant Community Changes Associated With Introduced Plant Species. Daniel S. Kjar and Edward M. Barrows Introduction Since colonial times, biodiversity has markedly changed in the Washington, D.C., area as a result of disturbances from humans. Unlike direct human threats such as encroachment, frag- mentation, overuse, and pollution, introduced organisms cannot be stopped by simply passing legislation or by lawsuits against parties guilty of introducing these organisms. Alien, invasive organisms will continue to grow, fill our natural areas, and consume resources needed to support our native populations. Arthropods are ideal for studying changes in eastern deciduous forests. Arthropods are abundant, have short generation times, and are sensitive to local changes. We have caught and identified (to various taxonomic levels) nearly 300 species in over 90 families of arthropods in this study. For this poster we concentrate on the ant community (Insecta: Hymenoptera: Formici- dae). Ants are attractive indicators of change as they are easy to catch and identify, are diverse, generally do not travel more than a few meters from their nests, and move nests away from areas which are no longer suitable. The aim of this research is to quantify changes in the arthropod community associated with the invasion of alien plants in the low forest of Dyke Marsh Wildlife Preserve (DMWP). Associations among plant coverage and richness, soil moisture and structure, tree abundance and richness, and the arthropod community are examined using several methods. We hypothesize that increased alien invasive plant coverage decreases native plant richness and changes the abundance and diversity of native arthropods. Materials and Methods We utilized satellite imagery and Geographic Imaging System data (GIS) with ArcView® and the AlaskaPak to generate 60 random sites within the DMWP. We used a Global Positioning System (GPS) to locate these sites (Figure 1). We placed a pitfall trap at the center of each 1- m 2 site (Figure 2). Pitfalls were run for 24 hr during a warm night at the end of each trapping month (June, August, October during 2002–2003). We recorded all plant species and relative coverage for each site during early August of 2002 and 2003 (Figure 2). We recorded the dbh and species of all trees within a 6-m diameter circle of each site. We took one soil core (40 x 80 mm) from each site at the end of each trapping period. We used a modified Berlese-Tullgren design to extract arthropods from the 60 soil cores (Figure 2). Soil cores were used to determine soil moisture and soil structure. The results presented here are preliminary. These data are from 40 sites, do not include soil core samples, and do not include the 2003 trapping year. A.B. C.D. Figure 2. (A) Soil core tool, (B) plant coverage grid, (C) pitfall trap, (D) modified Berlese-Tullgren funnel setup. Images from the low forest in Dyke Marsh Wildlife Preserve: (A) a tree fall area dominated by Porcelainberry, (B, D) areas of relatively native forest, (C) an Asiatic bittersweet vine strangling a tree. Figure 4a. Percent invasion, tree richness, and soil moisture account for nearly half the variance in ant abundance (Hierarchical Linear Regression). Table 2. Regression models for ant community associations. a,b,c Figure 4b. Ants and soil moisture. Figure 4c. Ants and tree richness. Table 3. ANOVA table for ant community associations. a,b,c,d Tree Richness Ants Invasive Plants Soil Moisture - + + A model of environmental factors significantly associated with changes in ant abundance. Arrow width represents amount of variance explained by the association. Arrow direction represents hypothesized direction of relationship. Table 4. Regression models for A. rudis associations. a,b,c Table 5. ANOVA table for A. rudis associations. a,b,c Figure 5a. Aphaenogaster rudis abundance and alien plant coverage. Figure 5b. Aphaenogaster rudis abundance and total plant richness. Trees A. rudis Invasive Plants Plant Richness Soil Moisture - + - A model of environmental factors significantly associated with changes in A. rudis abundance. Soil moisture, tree richness, and abundance were not associated with A. rudis abundance. Arrow width represents amount of variance explained by the association. Arrow direction represents hypothesized direction of relationship. Conclusions Preliminary data show that alien plants are associated with changes in native plant richness and ant abundance in the low forest of the Dyke Marsh Wildlife Preserve. Lonicera japonica and Celastrus orbiculatus appear to present the larger threats to native plant species and the terrestrial arthropod community within the forest. Modern computer software and GPS provide an effective method of randomly sampling a large area without the use of transects, haphazard sampling, or other potentially flawed forms of site selection. Aphaenogaster rudis (a common ant species) Increased abundance of A. rudis is associated with increased levels of alien plant coverage and total plant species richness. Biology Department Georgetown University Washington, D.C. 20057 Table 1. Increased alien plant coverage is associated with decreased native plant richness. a,b Appendix Table 2. Increased alien plant coverage is associated with increased ant abundance. a Table 3. Increased alien plant coverage is associated with increased A. rudis abundance. a Statistical Analysis Each site’s trap catches are summed across all trapping dates (n=40). Hierarchical Linear Regression was used for analysis where appropriate. Simple regression was used for the analysis of invasive plant coverage and native plant richness. Acknowledgments We greatly appreciate help from Maya Patel, Philip Sze, Martha Weiss, John Sauer, Barry Wood (NPS), Smithsonian and USDA specialists, and support from Friends of Dyke Marsh, Georgetown University, the National Park Service, and the Washington Biologists’ Field Club. References Crisp, P. N., K. J. M. Dickinson, and G. W. Gibbs. 1998. Does native invertebrate diversity reflect native plant diversity? A case study from New Zealand and implications for conservation. Biological Conservation 83: 209–220. Gremmen, N. J. M., S. L. Chown, et al. 1998. Impact of the introduced grass Agrostis stolonifera on vegetation and soil fauna communities at Marion Island, sub-Antarctic. Biological Conservation 85(3): 223 – 231. Panzer, R. and M. W. Schwartz. 1998. Effectiveness of a vegetation-based approach to insect conservation. Conservation Biology 12: 693– 702. Perfecto, I. and R. Snelling 1995. Biodiversity and the transformation of a tropical agroecosystem: Ants in coffee plantations. Ecological Applications 5: 1084–1097. Preliminary Results The study plots had 55 plant species of different abundances, including 10 invasive species. We found that the average level of coverage by invasive plant species for the DMWP forest was 45%, ranging from 0-94% at each site. Lonicera japonica and Celastrus orbiculatus were the more common alien plants (Table 1). Invasive plant coverage is correlated with decreasing native plant richness (Figure 3, Appendix: Table 1). Increasing alien plant coverage is associated with increasing abundances in the native ant community. Tree richness and soil moisture are also highly correlated with ant abundance (ANOVA, P < 0.05, Figures 4a, 4b, 4c, Tables 2 and 3). Aphaenogaster rudis may be a good indicator of ecological change caused by invasion of alien plants (ANOVA, P < 0.05, Figures 5a, 5b, Appendix: Table 3). Invasive plant coverage is associated with decreasing native plant richness. In our model of coverage, increasing coverage by one species does not require decreasing coverage of other species. Coverage was determined by the presence of a species in a grid of nine subplots. Maximum coverage of a species at a single site is nine; many species may have a score of 9 at any one site. 2.09% Rosa multiflora 0.70% Lonicera maackii 56.38% Lonicera japonica 0.23% Ligustrum sp. 3.25% Hedera helix 0.93% Euonymus fortunei < 0.01% Duchesnea indica 2.55% Clemitis terniflora 24.59% Celastrus orbiculatus 9.28% Ampelopsis brevipedunculata Table 1. Invasive alien plant species found in this study and their contribution to the total alien plant species coverage. Figure 3. Decreasing native plant species richness is associated with increasing alien plant coverage. Figure 1. (A) To locate sites we used a Trimble® GPS unit (left, Keith Post with GPS). (B) Satellite imagery and ArcView® with AlaskaPak were used to generate random field site loactions in the Dyke Marsh Wildlife Preserve low forest. A.B.