Abundance thresholds and ecological processes in a fragmented landscape: field voles, parasites and predators

• Main Author: Renwick, Anna R
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2009
• Subjects: Ecology

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 (Microtus agrestis), their predator, the common weasel (Mustela nivalis vulgaris), 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.