Emily Mitchell Ayers, Luc Hebou, and Karen Needham

1. Parking Lot Forest Raingarden edge Raingarden USING ANTS AS BIOINDICATORS TO ASSESS HABITAT QUALITY Emily Mitchell Ayers, Luc Hebou, and Karen Needham DEPARTMENT OF BIOLOGICAL RESOURCES ENGINEERING, UNIVERSITY OF MARYLAND, COLLEGE PARK, MD 20742 • RESULTS AND DISCUSSION • Figure 5 shows that more ants were found in the forest (F) than in other patches (RG, RGE and PKL), and Table 1 shows significant differences in ant populations between the forest and all other habitats (p < 0.5). This confirms our first hypothesis. No significant differences were found in ant populations between RG, RGE and PKL, so we are unable to confirm our second hypothesis. • BACKGROUND • Raingardens, or bioretention cells, represent a new paradigm in stormwater management: distributed treatment using natural systems. These mesocosms filter pollutants out of stormwater runoff and promote infiltration. They may also provide valuable habitat for insects and small animals. Ants create large burrows that may function as macropores, improving infiltration rates (Wang et al. 1996). Figure 1 illustrates the important roles that ants may play in raingardens. • MATERIALS AND METHODS • 4.1. Study Area • The study was carried out in and around two raingardens located in the southwest corner of Lot 11b at UMCP. Samples were collected in the raingardens, the parking lot (PKL), the surrounding woods (F), and the raingardens’ edges (RGE) (Figure 3). 4.2. Data Collection and Analysis A total of 8 baiting positions (two in each of the above-mentioned areas), were selected. Data collection was carried out in October, on 4 afternoons, between 1 pm and 6 pm. The ants were baited using tuna fish set in Petri dishes. The baits were checked every 30 minutes. Ant specimens were counted and preserved in a 80% ethanol solution for future identification. Ant specimens were identified and classified by the Systematic Entomology Laboratory (SEL)/USDA in Beltsville, MD. Multiple F-tests were performed to test relationships between ants and patch habitats. Figure 3. Study Area Figure 5. Distribution of ant populations in F, RG, and PKL. Average numbers from four collection days. Table 1. Comparison of means Paratrechina sp. appears to be the most abundant ant species in the study area (86%), followed by Tapinoma sessile (6%), Aphaenogaster rudis (4%), and others (4%) (Figure 6). To investigate the effect of choice of bait on the species of ants collected, on trial was conducted using grape jelly rather than tuna fish as the bait source. As Figure 8 shows, the relative abundance of ant species attracted to the grape jelly bait was very different from the relative abundance of ant species attracted to the tuna bait (Figure 6). This suggests that it may be advisable to use multiple different bait types in order to obtain a full picture of the true ant diversity at the site. There are two possible explanations for the lower than expected numbers of ants in the raingardens. First, these raingardens are recessed and lined; this may retard the immigration of ants into the raingardens, and may also prevent them from taking refuge in dry areas during rain events (Figure 7). Second, the raingardens are newly built and have not yet developed substantial plant cover, which might provide a better habitat for ants. Forest Figure 1. Relationships between ants, plants and soil (adapted from Wang et al. 1996). 2. OBJECTIVE To assess habitat quality in two newly built raingardens (Figure 2). Ants were used as indicators of habitat quality, as they have been used previously to evaluate the recovery of ecosystems after severe disturbance (Andersen 1991 & 1993). Figure 7. Raingarden, showing liner and depth. Paratrechina sp. (86 %) • CONCLUSION AND RECOMMENDATIONS • This study suggests that ant populations prefer forest habitats to raingardens and parking lots. This is probably because the forest offers better conditions (less pollution, less disturbance and greater availability of food and other resources needed by ants). The influence of pollutant loading on ant populations in the raingardens is not known. • Raingarden habitat value may be improved by creating a greater connection to surrounding upland areas, so that insects are able to escape to dry land during rain events. Raingarden Figure 6. Relative abundance of ant species Figure 2A. Typical Raingarden schematic (A. Davis, 2003) Tapinoma sessile (6%) REFERENCES Andersen, A.N. 1991. Responses of ground-foraging ant communities to three experimental fire regimes in a savanna forest of tropical Australia. Biotropica v. 23, pp. 575-585. Andersen, A.N. 1993. Ants as indicators of restoration success at a uranium mine in tropical Australia. Restoration Ecology v.1, pp.156-157. Davis, A.P. 2003. Bioretention: A Low Impact Stormwater Best Management Practice. [online] http://www.ence.umd.edu/~apdavis/Bioret.htm. Wang, D., B. Lowery, J.M. Norman, and K. McSweeney. 1996. Ant burrow effects on water flow and soil hydraulic properties of Sparta sand. Soil & Tillage Research, v.37 no.2-3 p.83-93. Parking Lot Aphaenogaster rudis (4%) Figure 8. Distribution of ant species using a different bait (grape jelly). ACKNOWLEGMENTS Dr. P. Kangas, Associate Professor, University of Maryland Dr. Ethan C. Kane, Entomologist, SEL/USDA in Beltsville, MD Figure 2b. Study Area showing a raingarden • HYPOTHESIS • More ants will be found in the forest patches (F) than in the raingardens (RG), and more ants in the raingardens than in the parking lots (PKL). Figure 4. Use of tuna fish, set in Petri dishes, to bait ants in various habitats Figure 9. Photographs of some of the most abundant ant species.