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Inter-annual differences in abundance of thirteen-lined ground squirrels (Spermophilus tridecemlineatus) in Colorado Shortgrass Steppe




Stapp, Paul, author
Hanni, David, author
Lindquist, Mark, author
SGS-LTER, Colorado State University, publisher

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We live-trapped thirteen-lined ground squirrels (Spermophilus tridecemlineatus) on three grassland and three saltbush-dominated sites in June and July 1999 to estimate population densities in representative vegetation types in shortgrass steppe, and to describe changes in population structure and body weight during their summer active period. We also compared population densities in 1999 to estimates from 1995, the last time that ground squirrel populations were surveyed on the SGS-LTER site in north-central Colorado. As in 1995, most squirrels captured in June 1999 were adults; the near absence of juveniles in June 1999 compared to the earlier study suggested that reproduction was delayed this year. Juveniles comprised > 70% of individuals captured in both habitats in July 1999, and were especially numerous on grassland sites. However, in contrast to 1995, when squirrels much more common in saltbush habitats, squirrels were significantly (2-3X) more abundant on grassland webs in 1999. The difference in population densities between habitats in 1995 vs. 1999 was unexpected because both years had similarly high early-season precipitation, and presumably, similar vegetation. Moreover, there were no consistent differences in the abundance of arthropod prey between years that could readily explain the differences in squirrel abundance. Additional long-term studies of ecology and population dynamics of thirteen-lined ground squirrels in shortgrass steppe will be necessary to identify the factors that determine patterns of abundance of this critical species over time.


The SGS-LTER research site was established in 1980 by researchers at Colorado State University as part of a network of long-term research sites within the US LTER Network, supported by the National Science Foundation. Scientists within the Natural Resource Ecology Lab, Department of Forest and Rangeland Stewardship, Department of Soil and Crop Sciences, and Biology Department at CSU, California State Fullerton, USDA Agricultural Research Service, University of Northern Colorado, and the University of Wyoming, among others, have contributed to our understanding of the structure and functions of the shortgrass steppe and other diverse ecosystems across the network while maintaining a common mission and sharing expertise, data and infrastructure.
Colorado State University. Natural Resource Ecology Laboratory; Colorado State University. Department of Forest and Rangeland Stewardship; Colorado State University. Department of Soil and Crop Sciences; Colorado State University. Department of Biology; California State University, Fullerton; United States. Agricultural Research Service; University of Northern Colorado.

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grassland ecology
shortgrass steppe
Central Plains Experimental Range
Pawnee National Grassland
long term ecological research


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