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Climate Change and Amphibian Population Declines in Spain
Bosch, J., Carrascal, L.M., Duran, L., Walker, S. and Fisher, M.C. 2006. Climate change and outbreaks of amphibian chytridiomycosis in a montane area of Central Spain; is there a link? Proceedings of the Royal Society B:10.1098/rspb.2006.3713.

Chytridiomycosis, in the words of the authors, "is an emerging infectious disease of amphibians that is causing mass mortality and population declines worldwide." The causative agent of the disease is Batrachochytrium dendrobatidis, a non-hyphal zoosporic fungus that is known to infect nearly a hundred different species; and because of the fungus' recent increase in virulence, Pounds et al. (2006) and Parmesan (2006) have striven to attribute its increasingly devastating effects on amphibians to concomitant global warming.

What was done
Working within the Penalara Natural Park in the Sierra de Guadarrama of Central Spain, Bosch et al. looked for relationships between 20 different meteorological variables and the development of chytridiomycosis infection in the area's amphibian populations, focusing on "two time periods according to the lack (1976-1996) or presence (1997-2003) of observed chytrid-related mortalities."

What was learned
The five researchers report that their analysis showed "a significant association between change in local climatic variables and the occurrence of chytridiomycosis" within the region of their study. More specifically, they conclude that "rising temperature is linked to the occurrence of chytrid-related disease."

What it means
Being careful not to be too adamant about what their data imply, Bosch et al. note that "associations between climate and disease do not necessarily imply causation." They also state that "chytrid-related declines are probably the result of a complex web of interaction, and the effects of climate will be conditional on other factors such as host density, amphibian community composition, microbial competitors and zooplankton predators, to name but a few [our italics]," and in order to disentangle this network into its key compartments, they say it will be necessary "to collect seasonal data on amphibian densities, contemporary and historical measurements of the prevalence and intensity of infection, seasonal mortalities, and fine-scale meteorological conditions from a range of sites that represent altitudinal clines," as well as to employ "molecular epidemiological analyses." Consequently, as we conclude in our Editorial of 29 Nov 2006, "the last word on this subject has yet to be written."

Parmesan, C. 2006. Ecological and evolutionary responses to recent climate change. Annual Review of Ecology, Evolution, and Systematics 37: 637-669.

Pounds, J.A., Bustamante, M.R., Coloma, L.A., Consuegra, J.A., Fogden, M.P.L., Foster, P.N., La Marca, E., Masters, K.L., Merino-Viteri, A., Puschendorf, R., Ron, S.R., Sanchez-Azofeifa, G.A., Still, C.J. and Young, B.E. 2006. Widespread amphibian extinctions from epidemic disease driven by global warming. Nature 439: 161-167.

Reviewed 29 November 2006