Plague and the black-tailed prairie dog: An introduced disease mediates the effects of an herbivore on ecosystem structure and function

I investigated the effects of black-tailed prairie dogs (Cynomys ludovicianus) on plant communities and nutrient cycling on the shortgrass steppe of Colorado and how those effects are mediated by an introduced disease, sylvatic plague. I first studied five colonies before (1997-1999) and after (2000-2001) a plague outbreak. Total plant canopy cover and cover of functional groups did not differ significantly between on- and off-colony before or after the plague-outbreak. However, total plant biomass and graminoid biomass were lower on than off of colonies before, but not after the plague-outbreak. Using herbivore exclosure cages on active colonies, I found that graminoid production decreased and forb production increased with prairie dog grazing.; To further elucidate how colony age and activity influence the role of prairie dogs, I studied plant communities and nutrient cycling on and off three young (3-7 years), three old (∼20 years), and three plague-extirpated (7-12 years) colonies from 2002-2004. Active colonies, but not plague-extirpated colonies, had shorter canopy and lower graminoid cover and biomass than off-colony sites. Bare ground cover and forb cover and biomass were greater and biomass of standing dead plants and litter were lower on than off old colonies only. Root biomass did not differ on and off colony for any colony type. Total plant species richness and forb richness was greater on than off old and plague-extirpated colonies. Shoot [N] of dominant plants was greater on than off active, but not plague-extirpated colonies. Although there was a trend toward higher root [N] on than off colonies, it was not significant for any colony type. N mineralization was greater on prairie dog mounds compared to the rest of the colony or to off-colony sites. Soil organic matter pools were relatively unaffected by prairie dogs, with differences seen only for older colonies, which had lower organic C than off-colony sites.; My results suggest that effects of prairie dogs on the shortgrass steppe are generally similar to, but of lower magnitude than, their effects on the more mesic mixed-grass prairie. My research also suggests that plague may be altering the role of prairie dogs in shaping ecosystem structure and function.