Metapopulation and metacommunity structure in sandstone outcrop communities

David Barfknecht, Plant Biology, Southern Illinois University Carbondale, Carbondale, IL and David J. Gibson, School of Biological Sciences, Southern Illinois University Carbondale, Carbondale, IL

Background/Question/Methods: Land fragmentation and other detrimental processes continue to remain a concern for both land managers and ecologists, and the few extant natural grassland habitats remaining within southern Illinois have been diminished since pre-European settlement. Therefore, understanding how these discrete patches interact between each other by sharing populations and communities is crucial. The objective of this research was to describe which plant species exhibit metapopulation dynamics and to quantify metacommunity structure in a group of sandstone outcrops in Pope County, Illinois. These sandstone outcrops all occur within the Jackson Hollow Nature Preserve, and have been treated in previous years for exotic invasive species removal and woody encroachment. Vegetative surveys were conducted in the summer months of 2020. GPS coordinates were taken around the edges of each site to establish patch boundaries and plotted in ArcGIS over drone-collected ortho-mosaics for clarification. To determine metapopulations, an incidence function model allowing for varying patch area and isolation was conducted on all observed taxa. Metacommunity structure was analyzed using Leibold and Mikkelson’s approach, which required the calculation of metrics including coherence, absolute species turnover, and boundary clumping. Pearson’s correlations were calculated between total species, species with metapopulation dynamics, area, perimeter, and arear-to-perimeter ratio.
Results/Conclusions: From both vegetative surveys and drone ortho-mosiacs, 23 sandstone outcrop patches were identified distinct from the adjacent forest matrix. Vegetative surveys recorded 128 plant species. Of these, 20 species (15.7%) exhibited metapopulation dynamics including four of the five observed exotic invasive species. Most metapopulations were of species in Asteraceae or graminoids (Poaceae and Cyperaceae). Sites which had the most species exhibiting metapopulation dynamics were often closer to the road westward of the nature preserve and had a larger area. Based on significantly positive coherence, species turnover, and boundary clumping, the dominant metacommunity structure of these sandstone outcrops was Clementsian, with the potential for nested community subsets. Positive coherence indicates strong variation among patches based on the embedded absences of the community matrix, positive species turnover indicates discrete differences in species occurrence between sites, and positive boundary clumping shows species ranges are often similar across sites. Pearson’s correlations indicated significantly positive relationships between species exhibiting metapopulation dynamics and both total species richness and patch perimeter as well as between area, perimeter, and area-to-perimeter ratio. Given these findings, these sandstone outcrop communities exhibit an orderly progression of species over time, with few clades exhibiting movement between all suitable patches.