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Biological response to climate change on a tropical mountain



Recent warming has caused changes in species distribution and abundance1,2,3, but the extent of the effects is unclear. Here we investigate whether such changes in highland forests at Monteverde, Costa Rica, are related to the increase in air temperatures that followed a step-like warming of tropical oceans in 1976 (refs4, 5). Twenty of 50 species of anurans (frogs and toads) in a 30-km2 study area, including the locally endemic golden toad (Bufo periglenes), disappeared following synchronous population crashes in 1987 (68). Our results indicate that these crashes probably belong to a constellation of demographic changes that have altered communities of birds, reptiles and amphibians in the area and are linked to recent warming. The changes are all associated with patterns of dry-season mist frequency, which is negatively correlated with sea surface temperatures in the equatorial Pacific and has declined dramatically since the mid-1970s. The biological and climatic patterns suggest that atmospheric warming has raised the average altitude at the base of the orographic cloud bank, as predicted by the lifting-cloud-base hypothesis9,10.

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We thank C. J. Still, P. N. Foster and S. H. Schneider for sharing their GCM simulations and for their comments on the manuscript; we also thank M. Brenes, R. W. Carlson, P.M.Fogden, G. R. Graves, J. F. Jackson, F. J. Joyce, K. L. Masters, J. M. Savage and N. T. Wheelwright for comments that improved the final version. J.A.P. acknowledges partial support from the MacArthur Foundation, Stanford University's Center for Conservation Biology, the Brookfield Zoo, the University of Miami, the US NSF, the Jessie Smith Noyes Foundation, the Organization for Tropical Studies, the Tropical Science Center and the University of Florida.

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Correspondence to J. Alan Pounds.

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Further reading

Figure 1: Trends and fluctuations in dry-season precipitation and stream flow.
Figure 2: Trends and fluctuations in dry-season air temperatures.
Figure 3: Changes in the bird community of the 1,540-m plot.
Figure 4: Declines in populations of anoline lizards and anurans.


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