Invasive species cause many extinctions today, but there is still a lot scientists do not know about how new, non-native species can change the way an ecosystem works. The researchers will enter information from the fossil record into computer models of food webs to understand what happened when new species arrived in ancient marine ecosystems. What the investigators learn from the past can benefit society because it can lead to determining consequences of similar species invasions today and in the future. The fossil food web models are helping researchers understand the connection between number of species in ecosystems and their stability, as well as how and why ecosystems have changed over the last 500 million years. So that others can use fossil food web modeling in paleontology, the new software program is free and available online. <br/><br/>The Cincinnati Series (USA) preserves a well-documented influx of species that is being used to construct food web models of shallow marine paleocommunities from the Late Ordovician before, during, and after the Richmondian Invasion to test hypotheses determining the effects of biotic immigrations on ecosystem structure and functioning. Comparisons between Paleozoic and polar ecosystems are being made to provide insight into the consequences of anticipated immigrations and invasions expected to occur in the near future. Modeled food web stability and resistance are compared to (1) identify changes in ecosystem dynamics resulting from asymmetrical biotic interchange, (2) isolate properties promoting stability and resistance, and (3) make explicit predictions regarding the outcome of polar invasions. These data are providing crucial insights into the drivers of the Great Ordovician Biodiversification Event, one of the most significant prolonged increases of marine diversity in Earth history. Training of undergraduate interns and mentoring of graduate students are advancing discovery and understanding. Broad dissemination of the software program is enhancing scientific and technological understanding.<br/><br/>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.