CLIMATE-CHANGE AND THE SHORT-TERM IMPACT OF FERAL HOUSE MICE AT THE SUB-ANTARCTIC PRINCE-EDWARD-ISLANDS

At the Prince Edward Islands, temperatures have increased by approxima tely 1 degrees C over the past 40 years, accompanied by a decline in p recipitation. This ha's led to a reduction in the peat moisture conten t of mires and higher growing season ''warmth''. The temperature- and moisture-sensitive sedge, Uncinia compacta R. Pr. (Cyperaceae), has co nsequently increased its aerial cover on Prince Edward Island, but har vesting of seeds by feral house mice (up to 100% removed) has prevente d this from happening on Marion Island. Such extensive use of resource s suggests that prey switching may be taking place at Marion Island. S eat analyses revealed that mice are not only eating ectemnorhinine wee vils to a greater extent than found in previous studies of populations at Marion Island, but that they also prefer larger weevils (+/- 6 mm) . A decrease in body size of preferred weevil prey species [Bothrometo pus randi Jeannel and Ectemnorhinus similis C.O. Waterhouse (Coleopter a: Curculionidae)] has taken place on Marion Island (1986-1992), but n ot on Prince Edward Island. This appears to be a result of increased p redation on weevils. In addition, adults of the prey species, E. simil is are relatively more abundant on Prince Edward Island than adults of the smaller congener E. marioni Jeannel, and could not be found on Ma rion Island in the late austral summer of 1991. These results not only provide support for previous hypotheses of the effect of global warmi ng on mouse-plant-invertebrate interactions on the Prince Edward Islan ds, but also provide limited evidence for the first recorded case of p redator-mediated speciation. They also show that the interaction of hu man-induced changes operating at different scales may have profound co nsequences for local systems.