The dynamics of wild woodland rodents

This thesis investigates the variation of life history traits within species, how they underpin population dynamics in woodland rodent populations and how they are effected by interactions between species. We ask how do life history traits differ between populations of the same species in similar habitats? We then go on to ask how two different species living in sympatry differ and the possible effects of interactions. We used data collected against three populations of Columbian ground squirrels (Urocitellus columbianus) in Canada and two species of woodland rodents from a site in the UK. Integral Projection Models or IPMs were used to compare the three populations of Columbain ground squirrels and identify differences between them. By using a form of perturbation analysis on the IPMs it was possible to identify the driving demographic and trait transition functions for the differences between the three populations. We then looked at interactions between wood mice (Apodemus sylvaticus) and the bank vole (Myodes glareolus) in the UK, and the possible effect on trapping bias. As data was limited for the two UK species, we could not construct a full IPM, but instead looked at the differences in growth rates of both species to determine what was the most important factors. Comparing the population level estimates from the IPMs for the Columbian ground squirrels, revealed significant differences between the populations. In particular the populations differed in growth rate (λ), generation length and R0. Perturbation analysis of the three IPMs revealed the adult survival function to be the major contributor to the differences between the three population. The inheritance function also had a large impact on the offspring estimates. For the two UK rodent species we found a large impact on the trapping bias due to interactions between the two species. With a significant increase in the chance of the same species being caught within a trap as previously caught. When analysing growth rates, we found that environmental factors only impacted growth for some groups, and we suggest that this may be due to the mitigation by the woodland of impacts of the environmental conditions. We did find that the density of a third species, the yellow necked mouse (Apodemus flavicollis), did have a large negative impact on growth rates on the other two species. In summary species population dynamics can very considerably between populations, even when the populations exist in potentially similar habitats. It is also possible for species living in sympatry to also have an impact on each otherâs population dynamics. Extreme care should then be taken when making comparisons between species based solely on single population data.