Environmental Factors Affecting the Distribution and Abundance of Richardson’s Ground Squirrels

Date
2013-10
Authors
Fortney, Ashley Nicole
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Faculty of Graduate Studies and Research, University of Regina
Abstract

Richardson's ground squirrels (RGS) (Urocitellus richardsonii) are an important species for the grassland ecosystem on the Northern Great Plains of North America. They are a main source of prey and burrows for many prairie species including several Species at Risk (SAR) of extinction. RGS are also maligned as agricultural pests and managed extensively via poisoning. Control programs have negative consequences for RGS and non-target species, including some SAR. Despite their ecological importance and agricultural pest status, little is actually known about their distribution on the landscape and habitat variables that influence their distribution and abundance. This lack of knowledge is a major impediment to development of conservation strategies for SAR that are significantly impacted by the management of RGS, and a key limitation for forecasting conflicts with agricultural producers. The objective of my research was to provide information on the distribution of RGS and determine how habitat variables influence their presence and abundance. I surveyed for the presence (detected at a site) and abundance (number of individuals) across a large area (130,000 km2) of RGS range on the Canadian prairies during 2011 and 2012 using an alarm call-playback method. I found that RGS were not distributed evenly on the landscape. RGS were only detected at 157 (8%) of 1,900 systematic survey points across Saskatchewan, with an average of 3.3 ± 0.4 individuals per used location. In 2012, additional searches to locate larger colonies in the high-conflict (between RGS and agricultural producers) area of southwestern Saskatchewan resulted in 31 colony locations with an average of 10.1 ± 1 RGS per colony. The systematic broad-scale surveys and more random colony searches revealed fewer and more patchily distributed RGS than expected given their pest status. I used multivariate Resource Selection Function (RSF) modeling to examine RGS habitat selection. Habitat variables included in the analysis were vegetation height, land cover types, land use, and proximity to water, shrubs, trees, and buildings/structures. Vegetation height was the top predictor of RGS presence and abundance; vegetation height above 15-30 cm was associated with a drastic decrease in the probability of habitat use. RGS presence was positively influenced by the percentage cover of grass in an area and bare ground when greater than 10% of the land cover. The proximity to trees within 400 m had a negative effect on RGS presence, as did proximity to shrubs and water on RSG abundance. Lastly, RGS abundance was positively influenced by finely textured soils and tilled crops, while negatively affected by increasing percent shrub cover. My data on RGS distribution and habitat selection can be used to implement integrated pest management strategies, such as through the inclusion of habitat modification, and will also provide valuable information to aid conservation planning for SAR that rely on RGS.

Description
A Thesis Submitted to the Faculty of Graduate Studies and Research In Partial Fulfillment of the Requirements for the Degree of Master of Science in Biology, University of Regina. xi, 78 p.
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