Climate sensitivity of species ranges

There is great concern that changes in climate will have substantial impacts on biological systems, including extinctions due to limitations on species distributions (Thomas et al. 2004). Many reports suggest that climate changes are already impacting organisms and ecosystems (Walther et al. 2002; Parmesan and Yohe 2003). A common prediction in this literature is that, as the climate changes, organisms will need to migrate to follow their climate "niche" or face extinction (Laurie et al. 2009). Indeed, the climate envelope models used by Thomas et al. (2004) are based on this assumption.

Are species really that sensitive to changes in the environment? This is a complex question that will require much more work than a blog post. But, we might be able to learn a little bit about this question by reviewing how species ranges have changed in the past.

There are a few examples of studies that have examined changes in species' entire ranges (as opposed to the plethora of studies that only examine changes at a single site, or along a single range margin), which I've summarized below in a table indicating how many species' ranges shifted, expanded, contracted, or saw no discernible change:

Table 1. Analysis of species range responses to environmental change.

An interesting finding from this analysis is that, even though nearly half of the species have followed this "shift or contract" pattern, almost a quarter of species have not changed their distribution at all. In fact, a large chunk of species have expanded their ranges. These findings are consistent with other results suggesting that similar fractions of species are either non-responsive to climate change or have responded in a direction opposite to that predicted (Parmesan et al. 2005).

There are multiple hypotheses for why this pattern might happen, ranging from a simple lag between when the environment changes to when the species responds (e.g., maybe the species who are not responding or are expanding will shift or contract in the future) to complex responses including physiological plasticity and stronger sensitivity to local habitat conditions (Crimmins et al. 2011) or species interactions (Clark et al. 2011) than to broad climatic patterns. As I've discussed previously on the blog, climate envelope models are less than ideal for predicting species responses to climate change. A major reason for this shortcoming is that these models assume that species will track large-scale changes in climate conditions. The fact that many species do not track their climate "niche" emphasizes the important limitation of this approach to understanding the responses of ecosystems to environmental change.

A basic conclusion from this analysis is that species are not equally sensitive to changes in climate. This conclusion certainly complicates predictions of species extinctions that are based on assumptions about how species respond to large-scale environmental change (à la Thomas et al. 2004) and justifies efforts to 1.) assess which species are more or less sensitive to changes in climate, and 2.) identify why these differential responses exist.

Brief literature cited

• Loarie, S., Duffy, P., Hamilton, H., Asner, G., Field, C., & Ackerly, D. (2009). The velocity of climate change Nature, 462 (7276), 1052-1055 DOI: 10.1038/nature08649
• Parmesan, C., & Yohe, G. (2003). A globally coherent fingerprint of climate change impacts across natural systems Nature, 421 (6918), 37-42 DOI: 10.1038/nature01286
• Parmesan, C., Gaines, S., Gonzalez, L., Kaufman, D., Kingsolver, J., Townsend Peterson, A., & Sagarin, R. (2005). Empirical perspectives on species borders: from traditional biogeography to global change Oikos, 108 (1), 58-75 DOI: 10.1111/j.0030-1299.2005.13150.x
• Thomas, C., Cameron, A., Green, R., Bakkenes, M., Beaumont, L., Collingham, Y., Erasmus, B., de Siqueira, M., Grainger, A., Hannah, L., Hughes, L., Huntley, B., van Jaarsveld, A., Midgley, G., Miles, L., Ortega-Huerta, M., Townsend Peterson, A., Phillips, O., & Williams, S. (2004). Extinction risk from climate change Nature, 427 (6970), 145-148 DOI: 10.1038/nature02121
• Walther, G., Post, E., Convey, P., Menzel, A., Parmesan, C., Beebee, T., Fromentin, J., Hoegh-Guldberg, O., & Bairlein, F. (2002). Ecological responses to recent climate change Nature, 416 (6879), 389-395 DOI: 10.1038/416389a