MEG Research
Ecology at the University of Wisconsin, Madison, spans more than 20 different departments and institutions. Every semester we highlight several students from different departments.
Ashley Shade, Microbiology Doctoral Training ProgramAshley Shade, Microbiology Doctoral Training Program
Ashley Spade will be presenting her research at the Spring Ecology Symposium on April 4th.
Do microbes follow the same rules? Aquatic bacterial community assembly following disturbance.
Because of their ubiquity, rapid generation time, and quick response to environmental stimuli, microbial communities may serve as convenient models for testing traditional ecological theory, such as disturbance. Disturbance is the periodic disruption of ecosystem, community, or population structure, or changes in resource availability or the physical environment. In lakes, mixing acts as disturbance because it destroys water column gradients in temperature, oxygen, and nutrient availability. Previous work suggests that mixing events “re-set” the bacterial community to a pioneer composition. Then, as stratification in temperature and dissolved oxygen re-establish, a distinct bacterial community develops in each thermal layer. Guided by these results, we devised a transplant experiment to better understand community assembly following disturbance. We collected upper-layer, bottom-layer, and mixed water as inocula, and then incubated these in dialysis-tubing mesocosms in each thermal layer. We sacrificed three replicates of each treatment daily for five days. We used molecular techniques to fingerprint the bacterial communities, and multivariate analyses to examine community dynamics. We hypothesized that some populations would be robust to environmental conditions in either layer, and able to serve as pioneer species in the post-transplant community. At the end of the experiment, we found that the mesocosm communities most closely resembled the source layer community rather than the local ambient community. This suggests compositional history had a stronger influence than habitat filtering. However, mixed transplant communities became more similar to the local ambient community, suggesting that interactions (e.g. competition) deterministically selected for a climax community. We found populations capable of surviving in either layer, as well as layer-specialists. Our results advocate microbial community models for investigating disturbance and species sorting theories, and provide a springboard for build ing predictive models of community assembly.
Ben Werling, Entomology
Ben Werling will be presenting his research at the Spring Ecology Symposium on April 4th.
Influence of off-crop natural areas on predation of crop pests in an annual crop at local and landscape scale
Predaceous arthropods have limited impact on populations of insect herbivores in most annual crops. This may be because crop habitats lack key resources that limit the abundance and diversity of these predators. Conserving natural areas outside of crops may be one way to increase the impact of predators on herbivorous pests and reduce the need to use insecticides, since natural habitats may provide diverse resources that enhance the abundance and diversity of predators. We examined if the presence of natural areas in the landscape surrounding potatoes affects predation on eggs of the Colorado potato beetle (CPB), Leptinotarsa decemlineata, a key pest of potatoes. To accomplish this, we compared predation on CPB eggs in potato fields set in landscapes that varied at both local and large spatial scales. At a local scale, we hypothesized that the grassy field margins that border potato fields are reservoirs of predators that enter the crop and attack pests. We expected predation to be greater in field margins than potatoes and to be greater in potato fields surrounded by large amounts of field margin. At a larger scale, we hypothesized that predation in both potatoes and field margins would be positively related to the percentage of the surrounding 1.5 km composed of uncultivated habitat. Our results suggest that local habitats like field margins do harbor predators of CPB eggs: 10% more eggs were killed by predators in field margins compared to potatoes. Furthermore, predation within the crop increased from 0 to 10% as the area of field margin surrounding potatoes increased; however, this increase in predation only occurred when potato fields were small in area compared to field margin habitats. In contrast, we found no evidence that predation on CPB is affected by the amount of uncultivated habitat within 1.5 km of potatoes and field margins. Overall, our results suggest that off-crop natural areas do support predators that attack pests in potatoes, but that the influence of these predators becomes significant only when potato fields are small and all parts of the crop are relatively close to field margin.
Amy Kamarainen, Center for Limnology
Amy Kamarainen will be presenting her research at the Spring Ecology Symposium on April 4th.
The history and fate of ecosystem services in a human-dominated landscape: A case study from Lake Wingra, Wisconsin.
Amy M. Kamarainen and Stephen R. Carpenter
As urban landscapes expand, they often surround formerly natural ecosystems and thereby alter their structure, function and ecosystem services. The ability of ”natural areas” embedded in urban landscapes to continue to provide ecosystem services may depend on management and policy decisions made by the surrounding municipality. Here we examine Lake Wingra, Wisconsin as a case study of aquatic ecosystem services (water regulation, recreation, water quality, education, fish production, biodiversity, and cultural amenities) provided by a lake in a watershed that is mostly urban. There is a long history of monitoring and management within Lake Wingra and its watershed; in many cases these management actions have altered ecosystem services. Through spatial analysis of aerial photos and summary of historical written accounts, agency records, scientific research and monitoring data we were able to reconstruct changes in ecosystem services in concert with changes in land use, public policy, and human demograph ics over the past century. Our findings include a shift in the hydrologic balance of the watershed from groundwater domination to surface water runoff, a shift in fish production from a community dominated by game fish to one dominated by invasive carp and panfish, and a shift in recreational use of the lake. Ecological changes have altered the mix of ecosystem services provided by the lake, and constrained potential future ecosystem services. Nonetheless, present policy options for restoration and management imply different future outcomes for ecosystem services provided by Lake Wingra.
Matt Kornis, Center for Limnology
Matt Kornis will be presenting his research at the Spring Ecology Symposium on April 4th.
Forecasting the distribution of the round goby in Wisconsin tributaries to Lake Michigan
The spread of the invasive round goby (Apollonia melanostomus) in the Laurentian Great Lakes has been well documented, though their distribution in streams is less well known. During the summer of 2007 we sampled 73 distinct Wisconsin tributaries of Lake Michigan to determine the spatial extent of goby presence and associate their presence/absence with a suite of site and watershed scale variables. Round goby presence was detected in 24 streams (33% of streams sampled), and was identified at sites >10km upstream of Lake Michigan in eight watersheds. We used multiple logistic regression to determine the habitat variables correlated with goby presence/absence and used a best subsets analysis to select the best model. The best model incorporated watershed area, slope, gradient, and conductivity and correctly predicted round goby presence/absence at 80 % of sampled sites. Based on this model, we identified sites suitable for round goby that have not yet been invaded. Our results provide empirical estimates for the range expansion of this non-native fish into Lake Michigan tributaries and suggest a need to further study the round goby in lotic systems.
Jaquelyn Gill, Geography
Jacquelyn Gill will be presenting her research at the Spring Ecology Symposium on April 4th.
Were late-glacial no-analog vegetation communities driven in part by herbivory release following the local extinction of megaherbivores?
Late-glacial pollen assemblages from eastern North America are often characterized by plant communities that lack a modern analog; these so-called “no-analog communities” have previously been explained by differences in climate seasonality due to orbital forcing at the end of the last glaciation. However, peak vegetation dissimilarity is coeval with rapid climatic warming, the arrival of the first humans to the continent, and the extinction of 33 genera of large mammals, complicating the search for a cause. Possible biotic drivers (e.g. herbivores) have typically been ignored, largely because uncertainties in the dating of mammalian fossils and lake sediments have hindered the establishment of precise lead-lag relationships. Megaherbivores are an important component of many landscapes, and can affect vegetation directly through grazing and disturbance, or indirectly by modifying competition or fire regimes. In this study, I used spores from the coprophilous fungus Sporormiella, which persist in lake sed iments, as a proxy for megafaunal populations. A sediment core from Appleman Lake in northeastern Indiana was analyzed for changes in pollen abundance, vegetation dissimilarity from present, charcoal (to reconstruct fire regimes), and Sporormiella to test hypotheses about the vegetation response to megaherbivore removal locally and its environmental context.
At Appleman Lake, Sporormiella declined below the extinction threshold (4% of the total upland pollen sum) within the fossil-inferred interval of the megafaunal extinction (~13,000 years ago) and did not recover during the Holocene. This decline occurs slightly earlier than the most-recent dated fossils in the region, suggesting that Sporormiella is a qualitative proxy for viable populations, rather than a quantitative proxy of individual presence. Immediately after the decline in spores, pollen assemblages reached peak dissimilarity due to a rise in Ostrya/Carpinus and Fraxinus components; this is interpreted as the release of palatable hardwoods following the relaxation of herbivory pressure. Charcoal data indicates low fire frequency during the late Pleistocene, with a moderate increase in accumulation immediately following the extinction, and a large increase at the end of the no-analog interval and coeval with the transition to a Quercus-Ulmus-Carya complex. Additionally, this work can also comme nt directly on the cause of the megafaunal extinction; at Appleman, Sporormiella decreased before the transition from Picea to Pinus, suggesting that climate-driven habitat change was not the main driver of the extinction at this site.