In the Light of Evolution Volume II: Biodiversity and Extinction (2008) / Chapter Skim
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6 How Many Tree Species Are There in the Amazon and How Many of Them Will Go Extinct?--STEPHEN P. HUBBELL, FANGLIANG HE, RICHARD CONDIT, LUIS BORDA-DE-ÁGUA, JAMES KELLNER, and HANS TER STEEGE
6 How Many Tree Species Are There in the Amazon and How Many of Them Will Go Extinct?--STEPHEN P. HUBBELL, FANGLIANG HE, RICHARD CONDIT, LUIS BORDA-DE-ÁGUA, JAMES KELLNER, and HANS TER STEEGE
Pages 107-126
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From page 107... ...
We estimate that the Brazilian portion of the Amazon Basin has (or had) 11,210 tree species that reach sizes >10 cm DBH (stem diameter at breast height)
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From page 108... ...
als each that are expected to suffer nearly a 50% extinction rate under the nonoptimistic deforestation scenario and an ≈37% loss rate even under the optimistic scenario. Most of these species have small range sizes and are highly vulnerable to local habitat loss.
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From page 109... ...
The question therefore arises: Which of these two distributions is a better fit to the distribution of relative tree species abundance in tropical tree communities in general and, more specifically, to relative tree species abundances in the entirety of the Amazon Basin? zpq9990837710001.c.eps FIGURE 6.1 Fit of Fisher's logseries to the Amazonian relative tree species abundance data of Pires et al.
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From page 110... ...
APPLYING NEUTRAL THEORY: FISHER'S LOGSERIES OR PRESTON'S LOGNORMAL? How do we estimate Amazonian tree-species richness and extinction risk due to habitat loss?
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From page 111... ...
Metacommunity size is simply the sum of the population sizes of all species in the metacommunity. An important discovery from neutral theory is that the expected distribution of metacommunity relative species abundance is Fisher's logseries (Hubbell, 2001; Volkov et al., 2003)
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From page 112... ...
. 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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From page 113... ...
Large numbers of tree FIGURE 6.3 The predicted logseries rank abundance curve for tree species in the Brazilian Amazon. The size of the metacommunity for this calculation was taken as 4,648,400 km2 times 60,000 stems >10 cm DBH km−2.
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From page 114... ...
The remaining quarter of tree species in the Brazilian Amazon have estimated abundances between 103 and 105 individuals >10 cm DBH. ESTIMATING THE RANGE SIZES OF AMAZONIAN TREE SPECIES Many common Amazonian tree species must have extremely large range sizes.
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From page 115... ...
6.4a and c) and for canopy adult trees >20 cm DBH (Fig.
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From page 116... ...
, stems >1 cm DBH; Y = 0.7472 + 0.5608X, R2 = 0.99951.
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From page 117... ...
Species with >108 individuals occupy the entire Amazon Basin. These population and range size calculations are based on the power-law formulae for all individuals TABLE 6.1 Estimated Tropical Tree Species' Ranges as a Function of Species Abundance in the Brazilian Amazon (total area: 4,652,400 km2)
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From page 118... ...
with a stem diameter of >1 cm DBH, with slope and intercept adjusted for species abundance n (Fig.
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From page 119... ...
With regard to the first problem, the best we can currently do is to perform a large ensemble of stochastic simulations in which we assign locations of all species in the metacommunity randomly throughout the Brazilian Amazon and then average the extinction results over these simulations. In each stochastic simulation, we assigned the centroids of the species ranges at random locations and then calculated the number of pixels of each land-use category that lay within the calculated range size for the species of a given abundance.
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From page 120... ...
The first scenario obeys a middle-of-theroad conservative rule of the three extinction scenarios -- conservative in the magnitude of predicted extinction rates. The rule is that a species goes extinct if, and only if, its range lies entirely in heavy-impact areas.
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From page 121... ...
Below population sizes of ≈104 individuals, the mean probability of extinction is close to the proportion of heavy-impact areas under Laurance et al.'s (2001) optimistic and nonoptimistic deforestation scenarios.
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From page 122... ...
FIGURE 6.7 Predicted extinction rates of tree species in the Brazilian Amazon under the optimistic and nonoptimistic scenarios of Laurance et al.
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From page 123... ...
This fact is reflected by the scant change in heavy-impact areas in the eastern Amazon between the maps for the optimistic and nonoptimistic deforestation scenarios. Thus, our estimates of extinction rates due to future deforestation are likely to be overestimates because they include species that have already gone extinct.
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From page 124... ...
We urgently need information on the biogeography, population sizes, comparative life histories, and environmental requirements of tropical tree species. As such data accumulate, we can not only make more accurate assessments of extinction risks, but also have more informed and intelligent suggestions for how to save tropical tree species and forests from extinction.
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From page 125... ...
von Hildebrand, and R Vásquez for use of their unpublished plot data on the abundances of Amazonian tree genera.
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