Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Effects of varying habitats on competition between endangered San Joaquin kit foxes (Vulpes macrotis mutica) and Coyotes (Canis latrans)(Montana State University - Bozeman, College of Letters & Science, 2005) Nelson, Julia Lynn; Chairperson, Graduate Committee: Scott CreelCoyotes (Canis latrans) are the primary predator of endangered San Joaquin kit foxes (Vulpes macrotis mutica). Coyotes often associate with coverrich habitats while kit foxes use grasslands, alkali shrublands, and urban environments. Effects of varying habitats on coyote and kit fox competition are relatively unknown. I assessed exploitation and interference competition between coyotes and kit foxes in grassland and shrubland habitats to determine if kit foxes are niche displaced by coyotes. I evaluated habitat and spatial partitioning, diet, and prey abundance of kit foxes and coyotes, as well as survival and fecal glucocorticoid levels (GC) of kit foxes at the Lokern Natural Area in central California from January 2003 through June 2004. Kit foxes partitioned habitat, space, and diet with coyotes. Coyotes primarily used shrubland habitats while kit foxes selected for burned grasslands that coyotes avoided. Kit foxes and coyotes had high dietary overlap, though coyotes had higher dietary breadth than kit foxes, creating significant differences in their diets. Kit fox scats recovered in grasslands showed preference for the larger kangaroo rat, Dipodomys heermanni, which was closely tied to shrub habitats. Predation was the primary source of mortality for kit foxes and was greater in the shrublands than grasslands. As a result of increased predation in shrublands, kit foxes with home ranges containing greater proportions of shrub had lower survival rates than foxes residing in grasslands. Despite increased predation risk in shrublands, I detected no difference in kit fox GC levels in shrubland versus grassland habitats, indicating that use of shrub habitats did not produce a physiological stress response in kit foxes. Results suggest that a heterogeneous landscape may allow for the parsimonious coexistence of San Joaquin kit foxes and coyotes. I also analyzed fecal glucocorticoid levels of kit foxes in rural and urban environments to assess the effect of various environments on kit fox stress responses. I detected no difference in glucocorticoid levels in kit foxes residing in urban compared to rural environments, suggesting that the niche shift from traditional rural habitats to the urban setting does not carry physiological costs due to chronic stress responses.Item Competition between the threatened Bliss Rapids snail, Taylorconcha serpenticola (Hershler et al.) and the invasive, aquatic snail, Potamopyrgus antipodarum (Gray)(Montana State University - Bozeman, College of Letters & Science, 2004) Richards, David Charles; Chairperson, Graduate Committee: Billie L. Kerans; David Weaver (co-chair)Due primarily to habitat loss and invasive species, extinction rates for North American mollusk taxa are among the highest for any taxonomic group in the world. Competition between invasive and native species often leads to decreases in native populations. For example, a primary reason for listing the Bliss Rapids snail, Taylorconcha serpenticola as threatened in the Snake River drainage was the perceived impacts of the highly invasive New Zealand mudsnail, Potamopyrgus antipodarum. Despite federal protection of T. serpenticola and the known presence of P. antipodarum in the Snake River drainage for almost 20 years, almost nothing is known about their ecology and competitive interactions. For this dissertation I conducted both field and laboratory studies to determine niche overlaps, spatial patterns, and some life history characteristics of both species. I compared optimal growth temperatures and estimated temperature tolerances for each species, under laboratory conditions; 2) examined stage (size) class fecundity rates and growth rates; and 3) examined photophobic tendencies of both species. I then explored environmental conditions and spatial patterns of both species in Banbury Springs, a tributary of the Snake River, near Hagerman, Idaho, that may have affected their distribution and abundance using regression tree analysis and geostatistical methods. I then conducted several competition experiments between both species under controlled conditions at Banbury Springs, developed competition coefficients, and related their growth rates and competitive outcomes to periphyton abundance and diversity. Finally, I monitored and then modeled seasonal and yearly population density trends of both species in a section of Banbury Springs, where both coexist, using time series analysis. Results of this study show that that both species have niche overlaps (i.e. temperature overlaps, photophobic tendencies, and somewhat similar habitat requirements) and can compete for limited food resources, but may have just enough niche separation or their occupied habitat is heterogeneous enough for them to coexist, at present. It is possible however that not enough time has elapsed for the effects of competition with P. antipodarum to push T. serpenticola to extinction.