Understanding the impacts of climate change on organisms and ecosystems: contributions from Experimental Biology

Hans-O. Pörtner

Alfred-Wegener Institute, Germany

Physiological studies in animals, from whole organism to molecular levels, are contributing to unravelling the impacts of climate change. At the same time, physiological work needs to connect to ecological principles and observations in order to support meaningful conclusions. Across most habitats this requires analyzing animal responses to warming, often combined with other drivers such as water loss in the terrestrial realm, or acidification and oxygen loss in aquatic environments. Temperature plays a key role in setting the geographical range of a species as well as shaping ongoing biogeographical shifts. Few studies provide such an integrative view. Early work in marine invertebrate populations across a latitudinal cline provided evidence that both low and high thermal tolerance limits involve mismatch phenomena in oxygen supply and demand due to limitations in oxygen supply capacity. These findings, verified across animal groups, led to the hypothesis that constraints in aerobic power budget are involved in shaping thermal performance curves, with related ecological implications. Such insight also provides the foundation for identifying the borders of both the fundamental and then the realized niche, the latter also considering the functional capacity of species to interact with others at ecosystem level. Assessing niche limits and constraints across life stages explains differences between ecological patterns during the life cycle of a species. Such studies would need to be complemented by investigations of differences and associated tradeoffs in functional properties of organisms adapted to various climate zones. From a macro-ecological and -physiological perspective, uncertainty is currently high as to whether organisms are sufficiently able to acclimatize and finally adapt to a changing climate in situ (through extent and rate of functional change and, finally, related genetic shifts). Current biogeographical shifts elicited by climate change suggest that limits to functional adaptation set in early, possibly eliciting behavioral responses. Overall, for relevant contributions to the societal and policy debate, the experimental community may benefit from establishing a forward-looking consensus building mechanism that would build on the available evidence and assess confidence and gaps of knowledge concerning climate change impacts and risks. Finally, a mechanism-based understanding allows scrutinizing the confidence in often simplified modeling approaches used to project future climate impacts and shifts in biogeographies as well as the associated risks for marine and terrestrial ecosystems.