CLIMATE AND MODERN NEOTROPICAL PLANT DISTRIBUTIONS: MACROECOLOGICAL AND PALEOECOLOGICAL IMPLICATIONS

The climatic correlates of extant plant family and genus distributions have macroecological and macroevolutionary significance. Environmental preferences shared by individuals of a given family or genera reveal inherited ecophysiological characters. These characters provide the basis for interpreting compositional changes in fossil pollen and fossil plant records. They also provide the basis for predicting ecosystem response to ongoing climate change.

We investigate the role that spatial differences in local climate play in governing the occurrence and abundance of plant families and genera in one model system – modern South American tropical forests. We use published data from vegetation surveys of 121 forest transects and seasonal climate data that include temperature, precipitation, and insolation variables. The data include 161 families and 1038 genera. The results identify: (1) tropical families and genera that demonstrate the greatest sensitivity to variations in climate and (2) the climate parameters which most affect modern plant distributions.

The relationship between climate and taxonomic distributions is explained by a small number of variables. First-order variation in abundances among families in this dataset is governed, surprisingly, by temperature, accounting for 40% of the variation observed. Second-order variation is governed by precipitation – particularly the number of wet days during the growing season. This accounted for 17% of the variation observed. However, among genera, the nature of the relationship between climate and abundance is family-specific.

Our results run counter to patterns in species richness, number of individuals, and vegetation type, all of which correlate most strongly with water availability. In contrast, the results suggest that although richness may be most strongly affected by precipitation, the taxonomic composition of tropical forests is governed by temperature. Abundance patterns of taxa most sensitive to climatic variation, including large families such as Fabaceae and Bignoneaceae, can also be used in paleoclimatic interpretation of floras with no modern analogue.