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 approximately 1 degrees C over the past 40 years, accompanied by a decline in precipitation. This ha's led to a reduction in the peat moisture content of mires and higher growing season ''warmth''. The temperature- and moisture-sensitive sedge, Uncinia compacta R. Pr. (Cyperaceae), has consequently increased its aerial cover on Prince Edward Island, but harvesting of seeds by feral house mice (up to 100% removed) has prevented this from happening on Marion Island. Such extensive use of resources suggests that prey switching may be taking place at Marion Island. Seat analyses revealed that mice are not only eating ectemnorhinine weevils 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 [Bothrometopus randi Jeannel and Ectemnorhinus similis C.O. Waterhouse (Coleoptera: Curculionidae)] has taken place on Marion Island (1986-1992), but not on Prince Edward Island. This appears to be a result of increased predation on weevils. In addition, adults of the prey species, E. similis are relatively more abundant on Prince Edward Island than adults of the smaller congener E. marioni Jeannel, and could not be found on Marion Island in the late austral summer of 1991. These results not only provide support for previous hypotheses of the effect of global warming on mouse-plant-invertebrate interactions on the Prince Edward Islands, but also provide limited evidence for the first recorded case of predator-mediated speciation. They also show that the interaction of human-induced changes operating at different scales may have profound consequences for local systems.