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The Biodiversity Insurance Hypothesis in a Time of Climate Change
Bartomeus, I., Park, M.G., Gibbs, J., Danforth, B.N., Lakso, A.N. and Winfree, R. 2013. Biodiversity ensures plant-pollinator phenological synchrony against climate change. Ecology Letters 16: 1331-1338.

Many climate alarmists are greatly concerned about the harm that might possibly be caused to various ecosystems because of phenological mismatches that could occur between some of their mutually-dependent species if their essential interactive activities were to be made more difficult by rising air temperatures. One such situation that has been hypothesized to occur is the potential disturbance of the synchrony of the plant-pollinator relationship in a warming climate. But just how often is such a disturbance likely to occur in the real world of nature?

What was done
This question was recently examined by Bartomeus et al. (2013) in a study of how naturally existing biodiversity might possibly harm, stabilize, or enhance the phenological synchrony that originally existed between the trees of a commercial apple orchard and their native pollinator bees in the state of New York, USA, over a subsequent period of 46 years of what they called climate warming, wherein they employed a previously developed 46-year time-series data set on the bloom phenology of the apple trees along with an independent data set on the phenology of wild bee species that commonly visited the apple flowers and that had been collected over the same time period in a broad region centered on the apple orchard. And in addition to these data, they conducted their own survey of diversity and abundance of bees visiting the apple trees for three years, in the springs of 2009, 2010 and 2011, while also collecting 2730 specimens of the 82 bee species they observed visiting the apple trees during those three years, while temperature data for the full 46 years were obtained from a weather station located within 1 kilometer of the orchard.

What was learned
The six scientists found that "the phenologies of apple and its complete community of 26 key pollinator species had largely shifted at similar rates over 46 years of climate warming," which led them to conclude that asynchrony was "likely prevented by the varied rates of phenological change observed among different pollinator species," all of which observations support "the idea that biodiversity can buffer ecosystem functioning against the loss of individual species," which concept is referred to as the biodiversity insurance hypothesis, which has been described in detail by Lawton and Brown (1993), Naeem and Li (1997) and Loreau et al. (2001).

What it means
Bartomeus et al. thus brought their study to an end by writing that "overall, our results suggest that pollination systems, especially for generalized species such as apple, may be buffered against climate change," while adding that their study also "supports the biodiversity insurance hypothesis" and saying that it "adds to several recent lines of evidence indicating that high levels of biodiversity are needed to sustain ecosystem function in real-world ecosystems," citing the investigations of Isbell et al. (2011) and Reich et al. (2012).

Isbell, F., Calcagno, V., Hector, A., Connolly, J., Harpole, W.S., Reich, P.B., Scherer-Lorenzen, M., Schmid, B., Tilman, D., van Ruijven, J., Weigel, A., Wilsey, B.J., Zavaleta, E.S. and Loreau, M. 2011. High plant diversity is needed to maintain ecosystem services. Nature 477: 199-202.

Lawton, J.H. and Brown, V.K. 1993. Redundancy in Ecosystems. Springer, Berlin, Germany, pp. 255-270.

Loreau, M., Naeem, S., Inchausti, P., Bengtsson, J., Grime, J.P., Hector, A., Hooper, D.J., Huston, M.A., Raffaelli, D., Schmid, B., Tilman, D. and Wardle, D.A. 2001. Biodiversity and ecosystem functioning: Current knowledge and future challenges. Science 294: 804-808.

Naeem, S. and Li, S. 1997. Biodiversity enhances ecosystem reliability. Nature 390: 507-509.

Reich, P.B., Tilman, D., Isbell, F., Mueller, K., Hobbie, S.E., Flynn, D.F. and Eisenhauer, N. 2012. Impacts of biodiversity loss escalate through time as redundancy fades. Science 336: 589-592.

Reviewed 15 January 2014