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578 TEACHING RESOURCES SEE EDUCATION AND OUTREACH TEMPERATURE CHANGE LAUREN SZATHMARY AND BRIAN HELMUTH University of South Carolina Global climate change encompasses many indirect and direct impacts on the physiology and ecology of plants and animals. Changes in precipitation, sea level rise, nutrient availability, and rates of erosion are all predicted to occur in the coming decades over a range of spatial and temporal scales. One of the most direct and damaging effects of climate change, however, is the impact of global warming on the body temperatures of organisms, and the subsequent impacts of changes in organism temperature on survival, physiological performance, and patterns of species distribution. Understanding how climate drives patterns of body temperature and how changes in global climate are likely to alter spatial and temporal patterns of organism temperature, is therefore key for forecasting the likely impact of climate change on species distribution patterns. A MODEL SYSTEM TO STUDY EFFECTS OF TEMPERATURE CHANGE Patterns of both environmental parameters and organism body temperatures in the rocky intertidal are quite complex and vary considerably spatially and temporally; thus, examining how changing climate will affect this ecosystem is a complex undertaking. Additionally, different ectothermic species achieve different body temperatures under identical sets of environmental conditions because of the species’ distinct physical properties. The complex interaction of climate with the characteristics of an organism and its habitat in driving patterns of body temperature therefore calls for a systematic, thorough approach to determining where and when to look for the direct impacts of climate change in the rocky intertidal. The rocky intertidal zone is a model system for exploring how climate change will affect species distributions in nature. Organisms in rocky intertidal zones are thought to live very close to their thermal tolerance limits, resulting in regular patterns of zonation. Several studies have demonstrated strong correlations between temperature and the distribution of intertidal species and populations over a range of spatial and temporal scales. Therefore, changes in the body temperatures of these organisms are expected to have large effects on the patterns of zonation and geographic distribution of species in this ecosystem. Specifically, if rocky intertidal species are already living at the limits of their physiological tolerances, then any significant change in the physical environment should be reflected by shifts in upper zonation limits. Namely, in the face of warming we should see a downward shift in the upper zonation limits of species wherever this limit is set by some aspect of climatic stress. Second, if some aspect of physiological stress related to body temperature sets species range boundaries , then we should similarly observe a geographic shift in the distribution of warm- and cold-acclimated species . Such shifts have been observed at geographic range boundaries. Recent evidence, however, suggests that we should be looking at the centers of species distributions in addition, because environmental conditions in the middle of range boundaries can in some cases be as extreme as they are at range edges. T DRIVERS OF INTERTIDAL TEMPERATURE CHANGE Intertidal ecosystems exist at the interface of the marine and terrestrial environments (Fig. ). Because organisms in these ecosystems are alternately submerged during high tide and aerially exposed during low tide, they must contend with stresses imposed by both environments. These species are therefore affected by changes in both water temperature and terrestrial climatic parameters (e.g., air temperature or solar radiation). Thus, both aquatic and terrestrial climatic influences are ecologically important and will result in complex patterns of ecosystem change. Only by examining the effects of both changing water temperature and changing aerial conditions will we be able to gain a clear understanding of how temperature change as a whole will affect the rocky intertidal. of organisms prior to aerial exposure and by serving as a heat source or sink to the substratum. In fact, some recent models have suggested that in some parts of the intertidal, water temperature can contribute as much to the heat budgets of some intertidal organisms as air temperature. Aerial Temperatures The body temperatures of intertidal organisms are generally much higher during aerial exposure than they are during immersion. While exposed to aerial conditions, body temperatures are the result of many interacting environmental variables, such as solar radiation, wind speed, air temperature, relative humidity, and cloud cover. Air temperature is often used as a proxy for intertidal organisms ’ body temperature, but there is often a very poor correlation between air temperature and body temperatures on any given day. For example, an animal’s...
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