Lynne Forster (1) and Simon Grove (2)
(1) University of Tasmania, Private Bag 98, Hobart, Tasmania, 7001, Lynette.Forster@utas.edu.au
(2) Tasmanian Museum and Art Gallery, GPO Box 1164, Hobart, Tasmania, 7001, Simon.Grove@tmag.tas.gov.au
Altitudinal shifts in the distribution and/or composition of species communities or assemblages are often portrayed as demonstrating early signals of climate change. Mountain-top assemblages are often suggested as being particularly good indicators, as well as being potentially among the most vulnerable since they may have nowhere to go if the climate warms. Yet it is conceivable that not all component species found at high altitudes are indeed high-altitude specialists. If we are to use these assemblages as indicators, we had better be sure that their compositions are driven, directly or indirectly, by climate and not by other aspects of the environment that are independent of a climate signal. A decadal study of beetle assemblages along an altitudinal transect on Mount Weld in southern Tasmania provides an opportunity to explore some of these assumptions. We found that beetle assemblages on Mount Weld vary by altitude and over time. Higher-altitude assemblages are largely a nested subset of those of lower altitudes, but the data-set also contains some putative high-altitude indicators. The study-area is embedded in a wider landscape, the Warra Supersite, whose beetle assemblages have also been subject to long-term research, including annual monitoring. Employing this contextual data, we explore some methodological issues that help to overcome limitations of assemblage data that contain many rare species and that are incomplete in both space and time. We use these findings to throw some light on the role of climate, vicariance, and habitat specialism in determining species distributions and variability in assemblage composition.