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Fig. 9. Scaling of population growth rates in the BBS data set. (A) Distribution of
population growth rates
s
log[N(t+1)/N(t)]
across all species in the data set. The growth rate
s is calculated by log
transforming the ratio of species abundances in successive years. Abundances
are taken as the total number of individuals of a particular species counted
within each survey route. (After Keitt
and Stanley, 1998.) (B) Probability density
p(s|N) of
the growth rate s for all
bird species in the BBS database for different initial population size
classes. The distribution represents all annual growth rates observed in the
31 year period 1966-1996. Data are shown for three different bins of initial
sizes (circles, 100<N(t)<101; squares,
101<N(t)<102.4; diamonds,
102.4<N(t)<,103.8). The solid lines are
exponential fits to the empirical data close to the peak. (C) Scaled
probability density
pscal
p(s|N)
as a function of the scaled growth rate
s
scal[s-<s>]/
for all species and years in the survey. The values were re-scaled using the
measured values of
<s> and .
Notice that all the data collapse upon the universal curve pscal
(-|r scal|). (After
Keitt et al., 2002.)
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