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FIGURE 6.2 Fit of Fisher’s logseries to the relative abundance data of Amazonian tree genera [(data from ter Steege et al. (2006)]. Fisher’s α (θ) is ≈71.

FIGURE 6.2 Fit of Fisher’s logseries to the relative abundance data of Amazonian tree genera [(data from ter Steege et al. (2006)]. Fisher’s α (θ) is ≈71.

a quarter million individual tree records has been assembled by many people from a large number of small plots over the Amazon Basin (ter Steege et al., 2006). The plots extend throughout the Brazilian Amazon into Amazonian Colombia, Ecuador, Peru, and Bolivia to the west and into the Guianan Shield to the northeast. The 288,973 trees have been classified into 514 genera.

The abundances of these genera are fit very well by Fisher’s logseries and not by Preston’s lognormal (Fig. 6.2). The data are well fit with a value of Fisher’s α (θ) of 71. The Preston-style histogram of species binned into doubling classes of abundance (Fig. 6.2 Inset graph) has no mode at intermediate abundances and exhibits a flat top as predicted by the logseries in species-rich assemblages but not by the lognormal. Given this result—although we do not yet know the species abundance distribution for the tree flora of the Amazon—it is highly unlikely that the species distribution will be a Preston canonical lognormal. This is different from the prevailing view, which is that tropical lowland forests have low β-diversity and are comprised of relatively widespread common species (Condit et al., 2002) although some dispute this view (Tuomisto et al., 1995).

ESTIMATING THE BIODIVERSITY NUMBER AND ABUNDANCE OF AMAZONIAN TREE SPECIES

Having established that Fisher’s logseries and neutral theory give a good fit to the diversity of genera of trees throughout Amazonia, we now need to estimate tree diversity and relative abundance at the species



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