A removal experiment with sympatric populations of Apodemus sylvaticus (L.) and A. flavicollis (Melchior) (Rodentia: Muridae)

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Abstract
This study examines the role of competition in the relationship between sympatric populations of Apodemus sylvaticus and A. flavicollis at Woodchester Park, Gloucestershire, England. Three grids were trapped for twelve months to monitor changes in population size, survival, reproduction, body weight, spatial segregation and microhabitat associations. The A. flavicollis was removed from one grid, A. sylvaticus from another while the rodent community on the third was left intact as a control. Subsequent changes in ecological parameters were observed over a further period of 7 months. Isolated populations of both species entered reproductive condition earlier than on the control grid. This resulted in a rapid increase of the A. flavicollis population but the dynamics of A. sylvaticus were unaffected. In the absence of their congener both species made greater use of areas of woodland once frequented by the absent species. However specific microhabitat associations observed in two species communities remained after experimental manipulation. It is concluded that although A. sylvaticus and A. flavicollis do compete for space, this is a comparatively weak interaction which does not lead to habitat exclusion. Competition is probably ameliorated by intrinsic differences in the biology of these Apodemus species.