FIGURE 6.7 Predicted extinction rates of tree species in the Brazilian Amazon under the optimistic and nonoptimistic scenarios of Laurance et al. (2001) as a function of population size. The abundance bins (histogram bars) are labeled with the logarithm to the base 10 of the lower bound of abundance in the respective bin. (a) Extinction scenario 1: Species go extinct only if their entire geographic range is in heavy-impact areas (in Fig. 6.6) on either the optimistic or the nonoptimistic scenarios of Laurance et al. (2001). (b) Comparison of extinction scenarios 1 and 3. In extinction scenario 3, species manage to survive in heavy-impact areas if at least one occupied cell survives, with probability 0.05 per cell. Extinction scenario 2 (data not shown), in which species can go extinct if they have some portion of their range in areas other than heavy-impact, gave results very similar to extinction scenario 1
(19.9%) are predicted to go extinct, of which 36 species have population sizes of >105 individuals. However, for the 3,248 species (29.0%) with >106 individuals apiece, there are no forecast extinctions under the optimistic scenario.
Extinction scenario 2 (results not shown) gave qualitatively similar results to scenario 1 because we made it hard to go extinct in moderate-to light-impact areas (all occupied cells in these areas had to go extinct, with fairly low probability of extinction in each cell: 15% and 5% per-cell extinction probability in moderate- and light-impact areas, respectively).