For Ecologists, Is Climate Change Research Sufficiently Complex?

Adam Rosenblatt

Climate change will alter myriad natural processes as precipitation patterns shift and oceanic and atmospheric temperatures and CO2 concentrations rise. Modern ecology and environmental science has already examined the potential effects of climate change on species and ecosystems, allowing us to elucidate the mechanisms and pathways through which it may operate (Tylianakis et al. 2008).

Most of this research, however, has focused on the effects of single climate change variables on single species in isolation or simplified food webs and ecosystems (Norby and Luo 2004). Out of 268 articles on the effects of climate change on multitrophic interactions (e.g., predator-prey, herbivore-plant, parasitoid-host) 87% manipulated only one climate change variable. The variable most frequently manipulated in these studies was temperature (50%) followed by carbon dioxide (28%). Also, 65% of the studies only used two trophic levels in their experiments.

Research this narrowly focused poorly approximates what may happen in reality.  First, food webs and ecosystems are usually highly complex with many interacting species, trophic levels, and processes.  Second, individual climate change variables rarely exert their effects in isolation, instead acting in concert with many other variables (Crain et al. 2008). Exploring the potential interactive effects of multiple climate change variables on species and ecosystems is therefore imperative for accurately predicting how climate change will affect nature. Indeed, some reviews report that multiple stressors (such as climate change variables and pollution) can interact synergistically, producing much larger effects in combination than either would in isolation (Crain et al. 2008). Furthermore, “ecological surprises” (i.e. unpredicted outcomes) may be quite common in the future as interacting abiotic forces change rapidly (Darling and Cote 2008).

In my literature review, I also examined the types of interactive effects that multiple climate change variables can have on multitrophic systems.  In most cases, the variables interacted multiplicatively (54%) or antagonistically (38%). In contrast, synergistic effects were rare (8%). These results suggest that the effects of climate change may be difficult to detect in simple experimental systems, and that different climate change variables affect species performance through different mechanistic pathways. For example, increased temperature may increase the metabolism of an insect herbivore, while carbon dioxide may alter the nutritional composition of its host plant in a way that counteracts the increase in consumer metabolism.

It is important to note that many of the interactive effects of multiple climate change variables on multitrophic interactions can be dependent on non-climate factors as well. For example, multitrophic interactions can additionally be affected by intraspecific genetic differences (Kopper and Lindroth 2003), variability in available nutrients (Burnell et al. 2013), and species identity (Blake and Duffy 2010). Thus, the responses of food webs and ecosystems to climate change will likely be highly context-dependent. Regardless, the results of my literature review, though preliminary, suggest that in some cases the projected effects of climate change on food webs and ecosystems may be weaker than currently expected. However, the potential for the occurrence of ecological surprises (Darling and Cote 2008) remains high given the substantial uncertainties associated with almost every facet of climate change-related predictions. Our ability to anticipate some of these surprises will greatly depend on climate change studies that successfully incorporate more realistic complexity.

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Citations:

Blake R, JE Duffy (2010) Grazer diversity affects resistance to multiple stressors in an experimental seagrass ecosystem. Oikos 119:1625-1635

Burnell O, BD Russell, AD Irving, SD Connell (2013) Eutrophication offsets increased sea urchin grazing on seagrass caused by ocean warming and acidification. Marine Ecology Progress Series 485:37-46

Crain C, K Kroeker, BS Halpern (2008) Interactive and cumulative effects of multiple human stressors in marine systems. Ecology Letters 11:1304-1315

Darling E, IM Cote (2008) Quantifying the evidence for ecological synergies. Ecology Letters 11:1278-1286

Kopper B, RL Lindroth (2003) Effects of elevated carbon dioxide and ozone on the phytochemistry of aspen and performance of an herbivore. Oecologia 134:95-103

Norby R, Y Luo (2004) Evaluating ecosystem responses to rising atmospheric CO2 and global warming in a multi-factor world. New Phytologist 162:281-293

Tylianakis J, RK Didham, J Bascompte, DA Wardle (2008) Global change and species interactions in terrestrial ecosystems. Ecology Letters 11:1351-1363