Most models of how climate change affects species apply projected climate conditions to the species’ assumed preferred climate conditions based on its current range. Move the climate envelope, and it follows that the species will have to track that to survive. But our understanding of species adaptive capacity, or their ability to change and respond to new climate conditions, is virtually nil for the vast majority of life on earth.
Two recent studies shed some light on this important issue. Both report on phenotypic changes of plants in response to climate change. However, they both point to future challenges in planning and adapting to climate change.
The first study, by Nicotra et al. (2010) brings attention to the importance of phenotypic plasticity in the ability of plants to respond to climate change. Phenotypic plasticity is the mechanism that allows plants to respond to environmental changes, and depends on the genetic arsenal of the plant species. The paper evaluates current molecular and genetic mechanisms underlying a species’ ability to change relevant to climate change, and the authors argue that, in the context of rapid climate change, phenotypic plasticity can be a crucial determinant of plant responses, both in the short- and long-term. High levels of genetic variation within natural populations improve the potential to withstand and adapt to environmental changes related to climatic change.
According to the authors, because it is hard to predict patterns of plasticity in key traits in response to climate change, it is important to identify the traits more likely to show relevant responses to changing environmental conditions, and predict what species would likely exhibit those plastic responses. The traits could then be tested under various climate conditions to determine the actual outcome and extent of plasticity. Among the various functional traits listed for assessment of plant response to climate change is altering of plant stoma, the little pores in plant leaves that allow gas exchange.
That leads to the second study of this post, by Lammertsma et al. (2011). The authors describes how nine common plant species found in Florida respond to increased CO2 in the atmosphere by altering the number, structure, and functioning of their stomata. Plant metabolism and water content is mediated through stomata, and when CO2 concentration in the atmosphere increases, a main response is to change stomata in various ways in order to decrease transpiration and loss of water. This response has been observed in short term studies in greenhouses and controlled environments, where plants were submitted to increased levels of CO2 and responded in that manner. However, in this study, the authors show that this type of response can be enhanced by growing leaves with reduced stomatal density and altered stomatal structure. Furthermore (and more importantly), the response is species specific, and individual plants species alter the number, structure, and functioning of their stomata in different ways to obtain similar metabolic results. This strongly suggests that plants can and do adapt to changing conditions to optimize their individual survival. In fact, an accompanying paper by De Boer et al. (2011) states that although the process is likely to be eventually limited by species-specific limits to phenotypic plasticity, their model predicts that adaptation will continue beyond double current CO2 concentrations.
These two papers together describe a scenario where (1) plants will adapt to climate change as much as their plasticity allows them; (2) their plasticity allows them to respond to increased atmospheric CO2 in different ways that lead to the same result, i.e., reduced transpiration; and (3) as a result of increased CO2, plants will be releasing less water vapor in the atmosphere.
The next logic step – if one is thinking in terms of climate change and of global hydrological balance – is that, if transpiration decreases, plants retain more water, and therefore there may be more moisture in the ground. However, there will also be less plant-released moisture in the atmosphere. And depending on the location, if there are more drought events and/or less rainfall, that may mean less moisture in the ground eventually. That in turn can affect the hydrologic cycle and ecosystems in complex and innumerable ways.
What does that mean in terms of conservation and climate adaptation planning? That one needs to look beyond projections of Global Circulation Models (GCMs), vulnerability assessments, and predicted effects on habitats and species. Understanding phenotypic plasticity in the context of adaptive capacity is extremely important in climate adaptation planning, and having more scientific resources geared towards species responses to specific climate-related changes might be a wise investment. The more comprehensive the approach, evaluation, and analysis conducted before the development of adaptation strategies, the more effective they are likely to be. Incorporating a climate change component in any conservation plan is an important step to ensure comprehensiveness. Granted, there is a lot of “what ifs”, and it is practically impossible to imagine and address all of them, but if we address as many as we possibly can, we greatly increase the probability of a positive outcome.
These studies provide some hope that climate change is not all doom and gloom, and that given the chance, some species may be able to locally adapt to climate change successfully. However, as stated in the second study, the adaptive capacity of species will eventually be limited by their available genotypic “tool box”. And at current rates of change, and without global curbs on greenhouse gas emissions, any adaptive capacity is likely to be exhausted.