What was done
Working in Switzerland along an elevation gradient stretching from 210 to 2760 meters above sea level, the authors identified 55 colline ponds with an overlying mean annual air temperature of more than 8°C, 27 montane ponds with mean annual air temperatures of 5-8°C, 15 subalpine ponds in the 2.5-5°C temperature range, and 16 alpine ponds with temperatures less than 2.5°C; and for all of these ponds, they evaluated species richness for five taxonomic groups: aquatic vascular plants, aquatic Gastropoda, aquatic Coleoptera (larvae and adults), Odonata adults, and Amphibia. Then, utilizing 15 environmental variables -- including mean annual air temperature, which they found to be "the best climatic variable to characterize pond thermal conditions" -- they developed Generalized Additive Models of species richness and used them to predict species richness for the end of the next century (2090-2100) based on the temperature increase predicted to occur in conjunction with the A2 emission scenario of the IPCC.

What was learned
Rosset et al. found, in their words, that "temperature rise could significantly increase pond species richness," noting that "for the five taxonomic groups pooled, species richness would potentially increase from 41 to 75 (+83%) in lowland ponds," and that "in presently species-poor high altitude ponds, the potential increase would be particularly marked, with a proportional increase (+150%; from 14-35 species) almost double that in lowland areas."

What it means
Previously, little attention had been focused on global warming effects on the biodiversity of small ecosystems. At the regional scale, however, species richness, as Rosset et al. report, had "been shown to increase under the influence of climate warming in Europe and North America (e.g. Iverson and Prasad, 2001; Daufresne and Boet, 2007; Buisson et al., 2008)." And they write that "it is also well-known and well-described in almost every ecology textbook, that terrestrial and freshwater species richness tends to be lower in colder areas, i.e., at higher altitude or latitude (e.g. Gaston and Spicer, 2004; Nagy and Grabherr, 2009)," noting that "this trend has also been well-described at the local scale for plants, invertebrates, and vertebrates (reviewed in Rahbek, 1995)," while noting still further that "among the few existing studies, Henderson (2007) and Hiddink and ter Hofstede (2008), using time series, report an increase in fish species richness in marine ecosystems in response to climate warming," and that "long-term monitoring of vegetation plots in terrestrial environments indicates an increase in local species richness (Pauli et al., 2007; Vittoz et al., 2009)." Clearly, therefore, the findings of Rosset et al. harmonize well with a vast body of other research conducted at many scales and across many different environments, all of which demonstrate that warming tends to significantly increase ecosystem species richness.

References
Buisson, L., Thuiller, W., Lek, S., Lim, P. and Grenouillet, G. 2008. Climate change hastens the turnover of stream fish assemblages. Global Change Biology 14: 2232-2248.

Daufresne, M. and Boet, P. 2007. Climate change impacts on structure and diversity of fish communities in rivers. Global Change Biology 13: 2467-2478.

Gaston, K.J. and Spicer, J.I. 2004. Biodiversity. An Introduction. Blackwell Science Ltd., Malden, Oxford, United Kingdom.

Henderson, P.A. 2007. Discrete and continuous change in the fish community of the Bristol Channel in response to climate change. Journal of the Marine Biological Association of the United Kingdom 87: 589-598.

Hiddink, J.G. and ter Hofstede, R. 2008. Climate induced increases in species richness of marine fishes. Global Change Biology 14: 453-460.

Iverson, L.R. and Prasad, A.M. 2001. Potential changes in tree species richness and forest community types following climate change. Ecosystems 4: 186-199.

Nagy, L. and Grabherr, G. 2009. The Biology of Alpine Habitats. Oxford University Press, Oxford, United Kingdom.

Pauli, H., Gottfried, M., Reier, K., Klettner, C. and Grabherr, G. 2007. Signals of range expansions and contractions of vascular plants in the high Alps: observations (1994-2000) at the GLORIA master site Schrankogel, Tyrol, Austria. Global Change Biology 13: 147-156.

Rahbek, C. 1995. The elevational gradient of species richness -- a uniform pattern. Ecography 18: 200-205.

Vittoz, P., Dussex, N., Wassef, J. and Guisan, A. 2009. Diaspore traits discriminate good from weak colonizers on high-elevation summits. Basic and Applied Ecology 10: 508-515.