Species and Ecosystem Responses To Human-Dominated Landscapes

Matthew Rich – Ant Community Composition Associated with Urban Lawn and Trees

Globally, rapid human population growth has accelerated the expansion of urban landscapes. Urbanization affects ant communities but few studies exist describing the impact that isolated endemic and ornamental trees have on ant community composition and diversity in urban landscapes. The objective of this research was to determine the composition of ant communities in human-dominated landscapes and describe the diversity, and distribution of ants under individual closed-canopy trees in an urban landscape. Ant communities found under trees (closed-canopy) are compared to those found in unshaded lawns.  It is hypothesized that ant species richness and abundance will be greater under closed-canopy tree cover than in an adjacent exposed lawn. Furthermore, as soil moisture content increases, so should ant abundance.  Berlese funnels were used to extract ant from soil samples collected from specifically chosen ornamental and/or native trees on Miami University Campus in Oxford, OH from 11 June – 10 July 2008.  A total of 759 ant specimens belonging to 15 species and 14 genera were collected from 51 samples.  Seventy-three percent of tree cover samples and 67% of lawn samples contained ants. The four most abundant species were Solenopsis molesta (75.49%), Ponera pennsylvanica (6.98%), Brachymyrmex depilis (6.46%), and Lasius alienus (6.32%). Eight ant species were found exclusively under tree cover, 2 were found in lawn only, and 5 were collected in both habitats. Shannon-Wiener Indices were calculated for low closed-canopy, high closed-canopy, and lawn localities resulting in H’ values of 0.786, 0.552, and 0.178, respectively.

Viankie Pagan –Effect of Burning on Composition and Diversity of Herbaceous Plant Communities in Southwest Ohio

High diversity herbaceous plant communities may provide a source of biofuel feedstock, but the maintenance of such communities depends on active management. Periodic burns can help maintain open landscapes, enhance soil composition and reduce the number of invaders while favoring native species and diversity. Preserving high diversity in natural plant communities is important because it can lead to both greater animal diversity and greater productivity. For this study, we measured the effects of burning on composition and diversity of herbaceous plant communities in Southwest Ohio. We predicted that a late spring burn would yield higher grass abundance, higher diversity and a greater number of annual species than the unburned fields. The burning treatment was applied in late spring of 2007 and samples were taken during summer 2008. We identified species composition and diversity by using percent cover. Although our results show that plant diversity decreased it was not significant. Grasses composition and abundance decreased for most species. The abundance of Big Bluestem(Andropogon gerardii) increased significantly. This increase may be due in part because fire promotes species with high relative growth rate and tall grasses also take advantage of open spaces and high soil nitrogen. Annual species composition did not vary significantly between burn and unburned plots. Our results suggest that a late spring burn might favor some tall grasses species but decrease the abundance of some forbs in herbaceous plant communities.

Darin Alexander –Effects of Light and Nutrients on Daphnia Growth

 The goal of this research was to test the importance of food quality and quantity for the aquatic grazer, Daphnia parvula. As a primary consumer, Daphnia represent the link between producers and secondary consumers (i.e. fish). The elemental composition of algae is affected by light intensity and nutrient composition. Under high levels of light and low nutrient concentrations, carbon fixation and photosynthesis are at their highest levels and the algal C:nutrient ratio are high. On the other hand, under low light intensities and high nutrient concentrations C:nutrient ratios are low. Phosphorus is generally the most limited nutrient in an aquatic ecosystem. For Daphnia, this is a major concern because phosphorus is thought to be the growth limiting factor. Therefore, Daphnia growth is lower when feed with algae of a high C:P ratio. We conducted three experiments using algae grown under different light and nutrient conditions. In experiment 1 we used algae cultured under low light, high nutrients (LLHN) and high light, low nutrients (HLLN). We predicted Daphnia growth to be greater under (LLHN) due to the high quality of food (low C:P). Our results supported our prediction. In experiment 2, we used the same algae cultures (LLHN and HLLN) but created a gradient of food quantity (LLHN = 5.31, 2.38, 1.28, HLLN = 2.38, 1.28). We predict that at a given quantity Daphnia growth will be greater under LLHN than HLLN. In this experiment Daphnia growth was similar under both food quality conditions (p = 0.37). However, within each food quality treatment Daphnia growth decreased with decreasing quantity. However, this trend did not have statistical significance (HN p = 0.56, LN p = 0.84). In experiment 3, we tested the same hypotheses as in experiment 2. However, we used different algae cultures under high nutrients with low light and high light intensities and a gradient of food quantities (HLHN = 7.32, 4.53, 2.27 and LLHN = 4.53, 2.27). At any given food concentration, Daphnia growth was greater under HL than under LL condition. Food quantity had no effect on Daphnia growth (p > 0.05) however; our results suggest that food quality had a stronger effect on Daphnia growth than quantity. These experiments are beneficial in helping to understand how light and nutrient conditions can affect foraging conditions for fish populations.

Kenneth Kellner – Effects of Urbanization on the Hydrology of Southwestern Ohio Watersheds: A Comparative Historical Approach

Urbanizing watersheds typically exhibit altered hydrological characteristics, which affect flood control, water quality, and ecosystem health.  Impervious surfaces created through human activity are the cause of much of this alteration; therefore, the presence of impervious surfaces has become an important indicator of urbanization.  The objective of this study was to compare the hydrology of four Southwestern Ohio (USA) watersheds with varying degrees of urbanization over a 20-yr time period (1988-2007).  We expected more change in urbanized watersheds than in rural watersheds.  Percent cover of impervious surfaces was quantified in each watershed for three dates in the study period using a subpixel classification of remotely sensed images.  Monthly watershed runoff coefficients, a measure of runoff normalized for precipitation and drainage area, were calculated using daily USGS streamflow data and NCDC precipitation data.  Groundwater levels, a measure of infiltration and water withdrawal, were also obtained from USGS stations.  Overall, the most heavily urbanized watershed had the highest median coefficient of runoff, and showed significant increases in coefficient of runoff over time.  The runoff coefficients of the other three watersheds were not significantly different from each other and did change significantly over the study period.  Simultaneously, depth to groundwater in urbanized areas of the study region showed an increasing trend, indicating less infiltration and/or greater water withdrawal.  These results support a relationship between impervious surface cover and the hydrological characteristics of these Southwestern Ohio watersheds, with implications for landscape management and ecosystem health.