Glenn and Collins determined the relationships between local annual immigration and extinction rates of plant species and total species richness using long-term data in permanent plots in tallgrass and shortgrass prairies of Kansas. Immigration rates were significantly correlated with species richness only at the site level. Extinction rates were not significantly correlated with growing season precipitation at any scale. Immigration rates were only significantly correlated with precipitation at the transect level. The equilibrium number of species, as defined when immigration equals extinction, increased with spatial scale. Transect data were divided into burned and unburned years to test for effects of burning on immigration and extinction rates. Average species richness, immigration rates, and extinction rates were higher on unburned versus burned years. Extinction rates were significantly correlated with species richness and the regressions were not significantly different in burned versus unburned years. Immigration rates were not significantly correlated with species richness, possibly because the true relationship has a shallow slope. Equilibrium numbers of species were greater on unburned versus burned transects. Extinction rates were not significantly correlated with growing season precipitation and immigration rates were significantly correlated with growing season precipitation only on unburned treatments. On grazed sites in western Kansas, average species richness, immigration rates, and extinction rates were not different in grazed versus ungrazed sites. Immigration rates were not significantly correlated with species richness in grazed or ungrazed sites; but extinction rates were significantly positively correlated with species richness.
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