Theoretical studies have proposed that a critical threshold occurs below which a small change in the amount of habitat can cause an abrupt change in population persistence.  I tested the threshold concept using field voles (<i>Microtus agrestis</i>), their predator, the common weasel (<i>Mustela nivalis vulgaris</i>), and their ecto-parasites in a highly fragmented agro-ecosystem. I found strong support for a threshold in margin width, below which vole abundance was extremely low.  I also revealed that changes in the demography and behaviour of vole populations occurred in relation to the detected thresholds.  However, despite these responses, no effect was observed on their survival.  I found no evidence of a threshold response in either predator activity or parasite prevalence in relation to either prey/host abundance or habitat size.  Weasels may have been able to compensate for low vole abundances by consuming other rodents or by moving to areas with higher prey abundances.  The lack of any detectable effect of habitat loss on weasel activity may therefore be related to the scale of this study relative to their home range and their degree of diet specialisation.  The ecto-parasites observed infested all seven of the small mammal species trapped.  The high level of transiency and movement within this multi-host system may have facilitated the spread of parasites between margins.  The susceptibility of predators and parasites to habitat loss due to their trophic position may therefore have been offset by the high vagility of predators and the capability of both predators and parasites to predate/parasitise a range of host species.

No description available.

Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on Mar. 26, 2010). Includes bibliographical references.

No description available.

No description available.

No description available.

The research presented in this thesis concerns the diel activity rhythm of the meadow vole, Microtus Pennsylvanicus pennsylvanicus Ord, as shown under laboratory conditions. In the course of the investigations a general survey was made of rhythmic behaviour in the animal kingdom. / Thesis / Master of Science (MS)

Many lipophilic pesticides are known to be transferred to offspring via the mother's milk. The present study was conducted to determine how much endrin was transferred from endrin resistant and susceptible dams to their suckling pups and to further characterize the effects that endrin may have on the hepatic mixed function oxidase (MFO) system in the pups. Dosing of the dams with endrin began one day after birth with either (l) oral doses of endrin in corn oil or (2) a mixture of endrin in ground feed. The total amount of endrin in the pup was determined by gas chromatography. MFO activity was determined in 2-1/2 week old pups and for adult animals using maximal activities for the demethylation of ethylmorphine and hydroxylation of aniline. No difference in the amount of endrin present in the pups was observed between strains provided both received equal amounts of endrin. MFO activity for endrin dosed mature animals and for 2-1/2 week old pups from endrin dosed dams exhibited a significant decrease from control activities. There was no difference in MFO activities between age groups. A significantly higher ethylmorphine demethylase activity was observed in comparing the resistant to the susceptible strain but there was no significant difference in aniline hydroxylase activity. / Master of Science

No description available.

I monitored demography, movement, and reproductive behavior of gray-tailed voles, Microtus canicaudus, in experimental habitat patches with and without corridors. I tested the hypotheses that reproductive rate, juvenile recruitment, and population size and growth rate would be affected negatively by immigrants that were introduced to resident groups (+ male and + female treatments). I hypothesized that "strangers" would commit infanticide thus decreasing juvenile recruitment. Second, I determined if movement corridors facilitated dispersal among habitat patches, thus potentially increasing infanticide, but decreasing reproductive inhibition of opposite-sex relatives by allowing them to separate (corridor treatment). Experiments were conducted in 12 0.2 ha enclosures planted with alfalfa that was fragmented into four patches (each 156 m��) separated by 12.5 m of bare ground. Introduction of unfamiliar conspecifics did not adversely affect reproductive rate, juvenile recruitment, population size, density, or growth rate. Corridors facilitated dispersal movements with males moving more than did females; however, corridors did not result in an even distribution of animals in the four patches. Unconnected habitat patches resulted in female- rather than the typical male-biased dispersal and females dispersed at lower body mass than in controls. Males that did not disperse from their natal patch exhibited a slight delay in sexual maturation. I conclude that movement is deterred in patchy environments, enhanced with corridors, and differentially affects males and females. Behavioral factors that affect an individual's dispersal or reproductive pattern should be considered in landscape planning. / Graduation date: 1997