Comparing niche- and process-based models to reduce prediction uncertainty in species range shifts under climate change. Morin, X.; Thuiller, W..
Obtaining reliable predictions of species range shifts under climate change is a crucial challenge for ecologists and stakeholders. At the continental scale, niche-based models have been widely used in the last 10 years to predict the potential impacts of climate change on species distributions all over the world, although these models do not include any mechanistic relationships. In contrast, species-specific, process-based predictions remain scarce at the continental scale. This is regrettable because to secure relevant and accurate predictions it is always desirable to compare predictions derived from different kinds of models applied independently to the same set of species and using the same raw data. Here we compare predictions of range shifts under climate change scenarios for 2100 derived from niche-based models with those of a process-based model for 15 North American boreal and temperate tree species. A general pattern emerged from our comparisons: niche-based models tend to predict a stronger level of extinction and a greater proportion of colonization than the process-based model. This result likely arises because niche-based models do not take phenotypic plasticity and local adaptation into account. Nevertheless, as the two kinds of models rely on different assumptions, their complementarity is revealed by common findings. Both modeling approaches highlight a major potential limitation on species tracking their climatic niche because of migration constraints and identify similar zones where species extirpation is likely. Such convergent predictions from models built on very different principles provide a useful way to offset uncertainties at the continental scale. This study shows that the use in concert of both approaches with their own caveats and advantages is crucial to obtain more robust results and that comparisons among models are needed in the near future to gain accuracy regarding predictions of range shifts under climate change.
Influences of temperature history, water stress, and needle age on methylbutenol emissions. Gray, Dennis W; Lerdau, Manuel T; Goldstein, Allen H.
Volatile organic compounds emitted by plants have long been recognized as having important influences on tropospheric chemistry, most notably in contributing to the production of tropospheric ozone and aerosols. One such compound, methylbutenol (MBO), was recently identified as a major component of the volatiles emitted by ponderosa pine and several other species of pine in western North America. On short time scales, MBO emissions increase with light intensity in parallel with photosynthetic responses, but emissions and photosynthesis show opposite responses to increases in temperature. We investigate the response of MBO emission to water stress, ambient temperature, and the aging of needles in field grown Pinus ponderosa (ponderosa pine). Photosynthetic rates and MBO production capacities of P. ponderosa were measured over the course of a season on saplings at a site that experienced summer drought and at a site that received supplementary water. In addition, a water-stress alleviation experiment was performed in which drought-stressed P. ponderosa seedlings were re-watered at the end of the season and pre-/post-alleviation photosynthetic rates and MBO production capacities were compared. Over the season photosynthesis declined while MBO production capacity tracked changes in ambient temperature linearly both over the entire season and on a day-to-day basis. Although severe water stress reduced photosynthetic rates, there was no difference in the response of MBO production capacity to ambient temperature under either drought-stressed or well-watered conditions, and there was no change in MBO production capacity following water stress alleviation. MBO emission declined with needle age. The correlation between MBO production capacity and ambient temperature is consistent with the view that MBO may provide a protection against high temperature stress similar to that suggested for isoprene.
Ten Years of Induced Ocean Warming Causes Comprehensive Changes in Marine Benthic Communities. David R. Schiel; John R. Steinbeck; Michael S. Foster.
One of the most commonly predicted effects of global ocean warming on marine communities is a poleward shift in the distributional boundaries of species with an associated replacement of cold-water species by warm-water species. However, these types of predictions are imprecise and based largely on broad correlations in uncontrolled studies that examine changes in the distribution or abundances of species in relation to seawater temperature. Our study used an 18-year sampling program in intertidal and subtidal habitats and before-after, control-impact analysis. We show that 3.5 degree rise in seawater temperature, induced by the thermal outfall of a power-generating station, over 10 years along 2 km of rocky coastline in California resulted in significant community-wide changes in150 species of algae and invertebrates relative to adjacent control areas experiencing natural temperatures. Contrary to predictions based on current biogeographic models, there was no trend toward warmer-water species with southern geographic affinities replacing colder-water species with northern affinities. Instead, the communities were greatly altered in apparently cascading responses to changes in abundance of several key taxa, particularly habitat-forming subtidal kelps and intertidal foliose red algae. Many temperature-sensitive algae decreased greatly in abundance, whereas many invertebrate grazers increased. The responses of these benthic communities to ocean warming were mostly unpredicted and strongly coupled to direct effects of temperature on key taxa and indirect effects operating through ecological interactions.