Species extinction is a poorly understood process, particularly at local scales, because there are few ecological data sets that span long enough time periods to reveal patterns of extinction. There is perhaps no single place on Earth where changes in the local assemblage of species have been carefully observed and documented continuously over several centuries. As a consequence, many basic questions about patterns and rates of species extinction following environmental change are difficult to answer. For example, how many species have been lost from specific local areas? Do extinctions follow immediately after a disturbance, or are post-disturbance extinctions delayed, resulting in an 'extinction debt' to be paid in the future? Data collected by this project will begin to fill a deficit that has limited scientists' ability to answer these basic questions. Paleontological techniques that have traditionally been used to study changes in plant communities over many thousands of years will be used to examine changes in plant communities in the past few hundred years. Seeds, leaf fragments, and pollen will be analyzed in sediment cores from disturbed wetlands in the Indiana Dunes to create a long-term ecological data set for approximately ten-year intervals from the present day to about 300 years ago. Analysis of these long-term data will advance ecological theory and aid conservation practice by supplying information critically needed to gauge what current patterns of ecosystem change mean for the future.
This project will provide training and mentorship for several undergraduate students, a high school student, a high school teacher, a technician, and a postdoctoral researcher. The project will also support the development of educational and outreach material for K-12 programs.
Ecologists and conservation biologists are interested in understanding how local assemblages of species (hereafter referred to as 'communities') will respond to environmental change and whether changes elicited by particular impacts are likely to manifest quickly or slowly through time. For example, an ecologist might ask, "If a pond is disturbed by development (or an invading species) then what will happen to the community of plants that live in that pond and how long will any changes that eventually occur take to manifest?". Because most communities have only been studied for a few decades at most and because many major disturbances to these communities happened many decades or centuries earlier, it has been very difficult to answer such questions. In this study we took the novel approach of constructing long-term ecological data. We did this by examining seeds from plant species that are preserved in the sediment found at different depths beneath ponds. Specifically, we collected nearly 100 sediment cores across a series of ponds at the Miller Woods Section of the Indiana Dunes National Lakeshore (Figure 1; Photo 1). These ponds vary in whether, when and how they were initially disturbed by human activities, such that some ponds are largely undisturbed, while others have been cut into smaller pieces by the creation of utility lines, railroad lines and other disturbances (Figure 2). By cutting individual cores of sediment into smaller cookie-sized sections, and by dating the material in those sections using a variety of modern scientific approaches, we were able to determine the age of any given portion of any given sediment core. This allowed us to examine the many seeds preserved in each of these sections and develop, for any given pond, how the vegetation has changed in approximately 5-year intervals over the past 300 years. Our work provided a number of important insights about how ecological systems respond to disturbances. First, we found that species vary tremendously in how quickly they respond to disturbances. Some species dropout of these systems or show large drops in their abundance relatively quickly, that is, within just a few years of a particular disturbance. Other species take many decades to respond. This is an important finding because it suggests that studies conducted within a few years of any given perturbation, are unlikely to detect the full suite of changes that will eventually occur within that system. This means, for instance, that following an oil spill or some other major change to an environment, that we cannot know what sorts of major changes might eventually play out in those systems until many decades have passed. Second, we found that in the first couple decades following a disturbance that what appeared to be a newly altered, but stable community type was present, but that this eventually gave way to a different community, one with a different constellation of relative abundances of species, and in some cases with some different species as well. This finding is consistent with our first finding, but provides further context not just for changes observed with individual species, but with whole assemblages of species. Third, we found that some of the 'native' species in this particular system we studied had in fact become established at these sites only after the disturbances had occurred. This is an important finding because it helps to clarify what the historical assemblages looked like at these sites, but also because it emphasizes that many species (both native and not native to North America) will often be relatively new members of a given community. Finally, we found a series of important findings that can help clarify the challenges and interpretation of future data collected using the sort of approaches employed here. Our study also provided benefits with regard to training scientists to conduct future work and in educating high school students about ecological systems, including building an understanding of how ecological systems change over time. This project trained a recently graduated PhD student in how to conduct this type of ecological research and that individual is now a professor at a university, conducting their own research and educating the next generation of students. The project also exposed a whole series of undergraduate students, and even a high school student, to ecological research. Further, by partnering with a high school science teacher, the project was able to aid in the development of a series of educational modules for high school science teachers in Illinois, Indiana and Michigan - the three states bordering the site where the work was conducted.
