SG: Ecological insights from range-expanding populations

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As the atmosphere and oceans warm, plants and animals are expanding their geographic distributions. For instance, the fiddler crab recently expanded its range north of its historic limit of Cape Cod, Massachusetts. While scientists have documented the range expansion of thousands of species, a big question remains: What is the impact of these organisms on the new habitats they occupy in their expanded ranges? Fiddler crabs live in salt marshes, which are economically important ecosystems that fuel fisheries and tourism. This research will focus on the impact that fiddler crabs will have on salt marshes in the newly expanded range (i.e., north of Cape Cod). Findings from this project will be made available to the public. Middle-school teachers and students in addition to undergraduate and graduate students will be directly involved in this research. The documented northern expansion of fiddler crabs (Uca pugnax) is an exceptional opportunity to test the effects of climate-driven species introductions on ecosystem functioning. In its native range, U. pugnax influences a range of marsh functioning including primary production, nutrient cycling, and food-webs. In terms of body size, fiddler crabs follow Bergmann's Rule (a positive relationship between body size and latitude) with individuals in Massachusetts being almost twice as large as those in Georgia. This biogeographic pattern may inform the relative effect of individual populations on ecosystem function in the context of climate change. The following hypotheses will be tested in this study: (1.) Fiddler crabs in the expanded-range populations (e.g., Massachusetts) will have larger per-capita effects on marsh functioning than those in the historic-range populations (e.g., Georgia) because of their larger size. (2.) At the landscape-scale, range-expanded crabs will have minor effects on marsh functioning relative to historic crabs because these populations are 10x smaller than historic-range populations. These hypotheses will be tested using a combination of field experiments and observational studies along a latitudinal gradient (Georgia, Virginia, Massachusetts) on a suite of ecosystem processes (e.g., primary production, decomposition, benthic animal diversity, plant stoichiometry). In addition, the targeted hypothesis that fiddler crab body size is correlated with ecosystem impacts will be tested in a mesocosm study.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.