AUTHORS: Lily Thompson, University of Missouri; Gregory Jacobs, Cornell University; Brandon Gerig, University of Wisconsin-Madison; Allison Pease, University of Missouri
ABSTRACT: Species introductions and biodiversity loss can result in the global change phenomenon of biotic homogenization, or the process of ecological community assemblages becoming more similar to each other over time. Freshwater fish communities are understood to be particularly at risk for biotic homogenization and shifts in fish community composition can jeopardize the distinctiveness of native communities and the ecosystem services they provide. The US National Parks Service (NPS) is tasked with preserving unimpaired natural and cultural resources, including fish community assemblages. Therefore, there is a clear interest in understanding levels of biotic homogenization in the fish communities within NPS properties. We evaluated changes in fish community assemblages in midwestern National Parks using data from the NPS Heartland Inventory and Monitoring Network in two time periods: 2006–2008 and 2021–2023. Our goals were to characterize variation in fish assemblage structure among Parks, to test whether biotic homogenization has occurred over the approximately 15 years between sampling periods, and evaluate whether some Parks have shifted assemblage structure more than others. We explored both taxonomic and functional changes in local contributions to beta diversity of these sites to understand the potential for loss of unique species identities and ecosystem functions, respectively. We compared Park specific estimates of beta diversity change and assessed whether these differences could be explained by associated environmental variation. Overall, we found evidence for both homogenization and differentiation among these midwestern National Parks depending on whether taxonomic or functional homogenization metrics were used. This suggests that ecosystem function may be maintained in these locations even if the species’ identities in the fish assemblages change.
