Animal temperature limits and ecological relevance: effects of size, activity and rates of change

1. Climate change is affecting species distributions and will increasingly do so. However, current understanding of which individuals and species are most likely to survive and why is poor. Knowledge of assemblage or community level effects is limited and the balance of mechanisms that are important over different time-scales is poorly described. Laboratory experiments on marine animals predominantly employ rates of change 10-100 000 times faster than climate induced oceanic warming. To address this failure we investigated differences in individual and species abilities to tolerate warming, and also how rate of warming affected survival. 2. This study identifies community level effects of thermal biology by applying a multi-species, multi-trophic level approach to the analysis of temperature limits. 3. Within species analyses of 14 species from 6 phyla showed smaller individuals survived to higher temperatures than large animals when temperatures were raised acutely. If this trend continues at slower warming rates, the early loss of larger individuals has marked consequences at the population level as larger individuals form the major reproductive component. 4. Between species comparisons showed active species survived to higher temperatures than sessile or low activity groups. Thus active groups (e.g. predators) and juvenile or immature individuals should fare better in rapid warming scenarios. This would be expected to produce short-term ecological imbalances in warming events. 5. The rate of warming markedly affected temperature limits in a wide range of Antarctic marine species. Different species survived to temperatures of 8.3-17.6 degrees C when temperatures were raised by around 1 degrees C day(-1). However they only survived to temperatures between 4.0 degrees C and 12.3 degrees C when temperatures were raised by around 1-2 degrees C week(-1), and temperatures of only 1.0-6.0 degrees C were tolerated for acclimations over periods of months. 6. Current models predicting range changes of species in response to climate change are either correlative or mechanistic. Mechanistic models offer the potential to incorporate the ecophysiological adaptation and evolutionary processes which determine future responses and go beyond simple correlative approaches. These models depend on the incorporation of data on species capacities to resist and adapt to change. This study is an important step in the provision of such data from experimental manipulations.

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