Ana D. Davidson1, Eduardo Ponce1, Sandra L. Brantley2, Juan Cruzado1, Ed L. Fredrickson3, Rodrigo Sierra1, Rurik List1, David C. Lightfoot2, and Gerardo Ceballos1. (1) Universidad Nacional Autónoma de México, (2) University of New Mexico, (3) USDA-ARS, Jornada Experimental Range
Background/Question/Methods Humans have dramatically altered grassland ecosystems worldwide through the widespread replacement of native ungulates with domestic livestock and anthropogenic grazing regimes, yet, little is known about the interactive effects of these important exotic herbivores with native keystone herbivores. In the central grassland ecosystems of North America, cattle (Bos taurus) have supplanted bison (Bison bison), and now co-exist with prairie dogs (Cynomys spp.), a burrowing-herbivorous keystone rodent. An ongoing and intense debate exists on how cattle can co-exist with native herbivores like prairie dogs. Indeed, understanding the ecological relationships between cattle and prairie dogs and how they together and separately affect the grassland ecosystem has become one of the most important conservation issues facing this grassland system. To address these issues, we established a long-term, manipulative study in the Janos region of northern Chihuahua, Mexico, which supports one of the largest remaining complexes of black-tailed prairie dogs (C. ludovicianus). Using a 2x2 factorial design we established experimental plots with prairie dogs only (+P-C), cattle only (-P+C), both prairie dogs and cattle (+P+C), and without either species (-P-C), collecting pre-treatment data in 2006 and post-treatment data in 2007 and 2008. Results/Conclusions
Our initial results show large increases in prairie dog abundance in the areas with cattle compared to areas where prairie dogs occurred alone. We also saw dramatic changes in vegetation on the plots where both animals occurred together compared to areas where each species occurred alone or were not present. Vegetation height and cover was lowest where both animals occurred, while the plots without prairie dogs (-P-C, -P+C) experienced particularly large increases in exotic forb species. The changes in vegetation already have had large, cascading effects on other grassland animals as well. Our results indicate that cattle and prairie dogs are having important, synergistic effects on the grassland that differ from the effects either animal species alone. Short-term and long-term studies can reveal very different insights into community dynamics, and therefore, it will be essential to follow the effects of these herbivore manipulations over the long-term.
