Applying the concept of the ecological niche and a macroecological approach to understand how climate influences zooplankton: Advantages, assumptions, limitations and requirements

Ecosystem effects of climate change have been detected in all components of the Earth System. In the marine biosphere, climate-change responses have caused large and well-documented biogeographical and phenological shifts, which have in turn altered local dominance hierarchies, and also the structure, diversity and functional linkages within regional marine ecosystems. There is an urgent need to improve both our knowledge of the global-scale effects of climate change on marine biodiversity and our capacity to project future impacts. But extrapolation of previously estimated changes to additional places and to future conditions is complicated by non-linear responses to environmental variables, and also by complexities of multivariate interaction that can lead to tipping-points. In this paper, we show how observations from widely-spaced locations can be combined to characterise the ecological niche of a species, and how the concept of the niche can be used to understand and project how climate-induced changes in temperatures will alter marine zooplankton both locally and globally. As an example to illustrate our view, we apply this framework to the relatively well-known copepod Calanus finmarchicus. Our results suggest that climate change will strongly affect the local abundance of this species in the North Atlantic Ocean by the end of this century. Predicted changes are large (e.g. increase by +/- 6-10-fold of the temporal changes in the abundance of C. finmarchicus) and vary as a function of the magnitude of warming and the local sign and steepness of the thermal niche. Substantial rates of change hold even under optimistic climatic scenarii. After reviewing the main limitations of the niche concept in bioclimatological research, we argue that the application of this concept in ecology and bioclimatology might nevertheless represent the best tool currently available to scientists to discern and anticipate the effect of global climate change on species and ecosystems. The framework we proposed forces us however to think globally and to develop a worldwide coordinated macroecological approach, that includes global monitoring, new mathematical tools of detection and new types of modeling. (C) 2012 Elsevier Ltd. All rights reserved.