Date of Award
Master of Science
The golden mouse (Ochrotomys nuttalli), a state-threatened species in Illinois, is sympatric throughout most of its geographic range with the ubiquitous white-footed mouse (Peromyscus leucopus). The degree of interspecific competitive interaction between these species has been investigated by previous researchers, with often conflicting results. I live trapped and marked both species on two grids from 21 May 2008 through 8 May 2009. One grid was the control area; from the second grid I removed white-footed mice. Habitat on the grids was very similar for six measured habitat variables. My objectives were to document the extent of competition between the two species as indicated by a population density or behavioral response of golden mice to removal of white-footed mice on the experimental grid, and to determine if white-footed mouse presence or habitat variables affected the capture of golden mice. During 6,528 trap nights per grid, I captured a total of 22 individual O. nuttalli and 66 P. leucopus on the control grid, and 48 O. nuttalli and 202 P. leucopus on the removal grid. Compared to previous studies (Rose, 2008), the number of individual golden mice captured on my two sites (n = 70) was very large. Whereas I expected an increase in numbers and space use of golden mice upon removal of Peromyscus, the only statistically significant change was an apparent decrease in space use--there was no population density change. These results, which may indicate a lack of interspecific competition, are more likely the result of experimental design flaws, especially considering the following results. The likelihood of trapping a golden mouse at any given station on the control site was unaffected by any of the six habitat variables. White-footed mouse presence significantly decreased the likelihood of capturing golden mice on both sites. These results were the same for both elevated and ground traps. On the experimental site, golden mice changed from predominantly arboreal space use before Peromyscus removal to equal space use between arboreal and ground habitat after Peromyscusremoval. These results illustrate a spatially segregated habitat with competitively superior white-footed mice dominating the ground level microhabitat and golden mice staying predominantly in elevated microhabitat. My study, and others, demonstrate that golden mice in southern Illinois are likely habitat generalists (Morzillo et al., 2003), competitively inferior to Peromyscus(Feldhamer and Maycroft, 1992), and excluded from certain microhabitat; although it may be they actually prefer different microhabitats.
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