CAREER: Do urban heat islands facilitate tropical species invasions? A test integrating course-based undergraduate research and a multi-institution researcher network

About This Grant

Tropical freshwater fishes are popular aquarium pets throughout the United States and often become invasive when aquarists release unwanted pets into lakes, streams, and wetlands where they consequently impact native species and the freshwater resources upon which humanity depends. Most of these tropical fishes are intolerant of cold winters and subsequently establish invasive populations only within subtropical regions like Florida and southern portions of California, Arizona, and Texas. However, environmental change and the growth of cities that absorb solar heat are causing freshwater environments to warm, and this warming may facilitate the northward expansion of invasive tropical fishes. This research will use laboratory experiments to measure the cold tolerance and growth potential of three tropical freshwater fishes in order to understand their ability to expand their invasive range northward. A subset of these experiments will be performed by students enrolled in course-based undergraduate research at the University of Texas at San Antonio. At the same time, research teams composed of undergraduate students and faculty from three universities in south, central, and north Texas will monitor winter water temperatures in streams to understand baseline temperatures in their respective regions as well as the urban heat island effects that increase temperatures beyond the baseline and therefore potentially facilitate the expansion of the three tropical invasive fishes. Lastly, the laboratory physiology and field temperature data will be combined with climate models to build forecast maps of future invasion risks for the three focal species. This research will test two key hypotheses. First, tropical species differ from temperate species in thermal physiology. Second, urban heat islands in temperate climates create thermally suitable conditions in the winter for tropical invasive species, which facilitate population persistence and spread. Conversely, urban heat islands create thermally stressful conditions in the summer for temperate native species, which cause population extirpations and range contractions. The first hypothesis will be tested using a species comparative framework, specifically exploiting three tropical-temperate species pairs from three different phylogenetic lineages. Researchers will characterize the thermal niche dimensions of these three tropical and three temperate species by measuring acute cold and heat tolerance, acclimation potential, and organismal energy budgets. To test the second hypothesis, researchers will use the aforementioned thermal niche dimensions to build process-based species distribution models and simulate geographic range shifts under alternative scenarios of climate change and urbanization. These simulations will be validated using field-based population monitoring and will be carried out for three urban centers arrayed along a latitudinal climate gradient in Texas, thus providing a space-for-time substitution to understand drivers of range limits. The broad aim of this research is to identify the mechanistic underpinnings of species range edges to advance biogeographic knowledge of ecologically- and phylogenetically-diverse fishes and to forecast range shifts caused by global change. 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.