Latitudinal and longitudinal differences in thermal habitat for fishes influenced by climate warming: expectations from simulations
Lakes vary considerably from region to region in morphometry, chemistry, and origin (HuTCHINSON 1957). These obvious differences may disguise a regional pattern related to gradients of climatic factors. LEWIS (19g3) further developed the idea that lake dynamics, and thus mixis classification, could be predicted from lake size and latitude. Larger lakes are more exposed to wind than are smaller lakes, while latitude relates to the amount of heat available to the lake. Lakes tend to be cold monomictic at high latitudes and warm monomictic at low latitudes; in intermediate locations they are generally dimictic. Thermal properties of lakes are major determinants of the fish populations that can occupy them. Most aspects of fish fitness, but particularly growth, are strongly dependent on temperature (FRY 1971, KITCHELL 19g3). Earlier analyses (MAGNUSON, MEISNER \& HILL 1990, HILL \& MAGNUSON 1990) have considered the responses of fish in the Laurentian Great Lakes to climate change simulated by general circulation models (GCM). Here we present the results of moving one standard lake in North America along both a north-south transect (latitudinal change) and a west-east transect (altitudinal change), by simulating thermal structure of that lake with weather appropriate to locations along the transects. Our objectives were to: 1) determine whether the differences in air temperatures that result from simulated greenhouse warming is comparable with those that occur with changes in latitude and altitude; 2) compare the influence of simulated climate warming on air and water temperatures across latitudinal and altitudinal transects; and 3) evaluai:e the potential responses of fish to simulated climate warming along latitudinal and altitudinal transects.