What ants are in our pants?!?… Oh wait, on campus trees: Ant Community Composition and Abundance on Campus Trees

                                                                                                                                             Will Bebee

             As the world's human population continues to climb and industries expand, urbanization is becoming more of a threat than ever to biodiversity. The shift from natural habitat to concrete, buildings, and roads leads to negative impacts for many organisms including, habitat loss and fragmentation, alterations in microclimates, and contamination due to pollution. However, many organisms are very adaptive, and ecology and conservation biology do not rest as the lush green grasses and forests transform to gray concrete jungles. As Uno, Cotton, and Philpott (2010) note, species generally inhabit four types of habitats in urban spaces; built habitat (i.e., buildings and pavement), managed vegetation, unmanaged green spaces (i.e., vacant lots and farmland), and natural leftover vegetation. Understanding which species and how many of them occupy these habitats along with how they utilize the urban space will be essential for conservation management and planning.

Arthropods, specifically ants, are a good model organism for assessing biodiversity in urban landscapes (Uno, Cotton, and Philpott 2010). To begin with, they play an essential role in the food web of the environment and provide multiple ecological services acting as decomposers and nutrient cyclers.  Their short generation time is also advantageous for observing the dynamics of urban ecology as they can quickly respond to environmental change. Also, different ant species are affected uniquely depending on the habitat structure like leaf litter, habitat disturbance, vegetation structure, plant species richness, etc. Additionally, the presence of dominant competitors and exotic species can influence ant community structure. There are mixed results on how habitat loss and fragmentation impact ant richness within urban spaces. However, there is a consensus that ant species composition is affected when comparing urban habitats versus natural rural areas (Uno, Cotton, and Philpott 2010).

In this study, Uno, Cotton, and Philpott (2010) asked how ant abundance, richness, and species composition change depending on the urban habitat and whether ant biodiversity and species composition correlate with specific habitat characteristics. To perform this study, they surveyed ants in three urban green spaces: community gardens, vacant lots, and forest remnants in Detroit, Michigan, and Toledo, Ohio. Ant sampling methods utilized tuna baits at “baiting stations” approximately in the center of each habitat. They inspected the baits 30 min. after placement, where the authors assessed the number of ant species and their abundance. They also measured 24 habitat and vegetation characteristics to explore potential effects on ant richness and abundance (Table 1). This involved measuring the size of the habitat, estimating the percent of the area covered with concrete, buildings, bare ground, grass or herbs, and shrubs, and counting the number of trees. Different habitat characteristics were assessed at varying spatial scales (100x100 m plots, 20x20 m plots, and 1x1 m plots).

The authors found that forests displayed the highest ant richness (26) compared to vacant lots (20) and gardens (14) (Fig. 1). They contribute these findings to two potential causes, habitat and landscape factors, and competitive interactions (Uno, Cotton, and Philpott 2010). Regarding habitat and landscape factors, the authors found habitat type significantly influences ant community composition, abundance being lowest in forests. This is largely due to site characteristics differing in the three habitats. In general, forests had more woody plants and leaf litter, and less concrete than gardens and vacant lots. Vacant lots contained taller herbaceous vegetation while gardens consisted of higher forb richness and more bare ground. Interestingly, the differences in the vegetation structure and factors of the habitats significantly influenced ant species composition, but not ant richness. Additionally, the size of the habitat may affect ant community structures as dispersal limitation may be more prevalent in larger habitats. In terms of competitive interactions, the authors found the abundance of exotic ant species negatively influences ant richness in gardens and vacant lots, impacting native ant richness in urban spaces. This is likely because, in urban habitats, the most successful ants are generalist and opportunistic species, dominant competitors, and form sizeable, aggressive colonies. Therefore, the introduction of an exotic species that is more competitive (i.e., Tetramorium. caespitum in this paper) can lead to the local displacement of native ant species.

Figure 1: Rarefaction curves for ant species richness observed in urban forests, community gardens, and vacant lots sampled in Detroit, MI (b), Toledo, OH (c), and across both cities (a). Thin lines show upper and lower 95% confidence intervals for symbols of the same color.

This research article is relevant to my group’s urban ecology project in Grinnell, Iowa, since we are asking how different managed tree species on campus (native vs. non-native) act as habitats for ants and impact ant community structure and abundance. Different tree species may be utilized as a habitat by specific ant species depending on whether there is a mutualistic relationship between the two or whether the ants require a specific tree species for foraging needs. Furthermore, due to the mixing of native and non-native tree species on campus, it will be interesting to observe whether native trees are compromised primarily of native species of ants in higher abundance than non-native trees. Additionally, identifying whether any exotic ant species are present on campus and how their competitive interactions with native species impact the species composition and abundance of ants on the trees will be valuable information for the potential addition of management procedures. The distance between trees may also provide valuable information by impacting the dispersal patterns and abilities of the ants to colonize some trees.

 

References

Uno, S., Cotton, J., & Philpott, S. M. (2010). Diversity, abundance, and species composition of ants in urban green spaces. Urban Ecosystems, 13(4), 425-441