PRAIRIE DOG EFFECTS ON PLANT COMMUNITY STRUCTURE IN SOUTHERN MIXED-GRASS PRAIRIE

Black-tailed prairie dogs (Cynomys ludovicianus) influence ecosystem s tructure and function through their burrowing and grazing activities, and reportedly increase plant species diversity relative to uncolonize d portions of the landscape. Consequently, systematic eradication of p rairie dogs-a widespread practice over much of the Great Plains-may ul timately reduce plant species diversity. To determine the effects of p rairie dogs and associated fauna on herbaceous vegetation in a souther n mixed-grass prairie ecosystem, we quantified herbaceous standing cro p, species composition, and plant species diversity on and off a prair ie dog colony in north-central Texas in 1988 and 1989. Total live herb aceous standing crop was 3 times to 4 times greater off the prairie do g colony than on the prairie dog colony in 1988 and 1989, respectively . Midgrass biomass was 6 and 15 times greater off-colony than on-colon y in 1988 and 1989, respectively. Shortgrass biomass did not differ be tween on-colony and off-colony zones in either year. Principal compone nts analysis (PCA) revealed plant species distribution patterns attrib utable to colonization by prairie dogs. Axis I sample scores were stro ngly correlated with midgrass biomass bur not shortgrass biomass. Stat istical analyses of jack-knifed Shannon's and Simpson's diversity indi ces indicated that plant species diversity was greater off than on the prairie dog colony. Thus, black-tailed prairie dogs and associated fa una substantially altered the relative distribution, abundance, and co mposition of herbaceous vegetation at this southern mixed-grass prairi e site.