Document Type

Thesis - University Access Only

Award Date

2004

Degree Name

Master of Science (MS)

Department / School

Animal Science

First Advisor

Patricia S. Johnson

Abstract

Prairie dogs have been viewed as pests by ranchers on grazing lands in the V western United States since the late 1800's and as a critical keystone species in the short[1]and mixed-grass prairies by some wildlife ecologists. Studies evaluating the effects of prairie dogs on grassland plant communities have produced variable results. Some differences between studies may be explained by location (shortgrass vs. mixed-grass prairie), however many studies failed to ensure that their on- and off-town plant communities were on similar soils, and others have collected data from on- and/or off[1]town sites in only one year. Forage losses caused by prairie dogs are a major concern for ranchers. However, studies have not documented the proportion of total forage disappearance on-town attributable to prairie dogs and to livestock. The objectives of this study were: 1) to quantify differences in plant species composition and richness between on-town and off-town sites, and 2) to estimate forage removal on prairie dog towns by prairie dogs and by cattle in southcentral South Dakota. During the summers of 2002 and 2003, species richness, utilization, and biomass data were estimated in June and July on three mixed-grass prairie pastures in southcentral South Dakota. On-town and off-town sites had similar soils. Exclosures that excluded cattle and others that excluded both cattle and prairie dogs were used in conjunction with unprotected plots. Forage removed by prairie dogs was two to three times greater than forage removed by cattle on prairie dog towns. Cattle removed two times more forage on off-town sites than on on[1]town sites. Graminoids dominated both the on- and off-town sites, but the species making up the graminoid biomass differed between prairie dog towns and off-town sites. Very few differences in percent composition between on- and off-town sites were found in an extremely dry year (2002), however, composition of forbs was greater on on-town sites and graminoid composition was greater on off-town sites in a more favorable year (2003) on the same plots. Total species richness varied with season and year, however, total graminoid species richness was greater on off-town sites and total forb species richness was greater on on-town sites for both sampling periods in both years. As expected, annual species were more abundant on on-town sites for both sampling dates in both years. There were very few consistent patterns of species richness between locations within prairie dog towns (center, mid-radius, and edge). This study demonstrated that 1) great care must be used when comparing prairie dog towns and off[1]town sites for percent composition and species richness because these parameters are heavily influenced by season and precipitation, 2) grasses dominated both the on- and off-town sites, however, prairie dog towns tend to have greater forb and annual species components, while off-town sites have greater grass and perennial components, 3) prairie dogs were responsible for 2/3 of forage disappearance on prairie dog towns, and 4) each hectare of prairie dog towns provided only about half the forage for cattle as that same site would have provided if not colonized. Thus, prairie dogs significantly alter the composition of plant communities resulting in less desirable forages for livestock, and they reduce the forage available to cattle, thereby reducing the carrying capacity of pastures with prairie dog towns.

Library of Congress Subject Headings

Prairie dogs.
Plant communities.
Forage plants -- Ecology.
Grazing.

Publisher

South Dakota State University

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Rights Statement

In Copyright