Oral Paper

         Ecology

Investigating the Turnover in Plant Species Biodiversity on Gypsum Soil Outcrops

Presenting Author
Lilly Osterday
Description
Gypsum soils have unique chemical properties that restrict edaphic communities of plants to them. Soils containing high levels of gypsum occur in patchy outcrops that form island chains throughout the southwestern deserts in North America. Island biogeography theory suggests that island communities should have higher species turnover than mainland communities due to isolation limiting dispersal events that would otherwise homogenize them. We tested the hypothesis that because of their discontinuous, island distributions, gypsum outcrops would have greater differences in species composition (beta diversity) than comparable populations from the surrounding non-gypsum floral communities. This result would show that the community assemblage of gypsum is governed by the same processes that lead to high species turnover in insular systems. We analyzed species presence/absence data collected from 148 gypsum sites and 148 paired nearby non-gypsum sites and compared the calculated beta diversity values between them using a paired t-test. We then ran a linear regression to determine whether beta diversity is influenced by the distance between sites. Beta diversity was not significantly different between gypsum outcrops and the surrounding non-gypsum communities. Both soil types had high beta diversity indicating low levels of similarity between sites whether the community was on or off gypsum. As expected, distance between the sites significantly influenced the beta diversity among non-gypsum sites. As distance increased, the differences in species composition increased. This pattern was not observed in the gypsum results. Distance had no effect on the beta diversity among gypsum sites. This result suggests that all gypsum sites were so isolated from each other that no matter the distance between sites, beta diversity is high. The equally high beta diversity among the non-gypsum sites, was not expected, but may be explained by the high environmental heterogeneity found in the landscape of southwestern North American deserts.