Environmental Engineering Reference
In-Depth Information
10
Other orders
1
0.1
Primates
0.01
0.01
0.1
1
10
100
1000
Body mass (kg)
Fig. 2.10
An allometric relationship between body mass,
M
, and intrinsic rate of
increase for mammals. Note the log scales. For primates,
r
max
0.31
M
0.41
; for
other mammals,
r
max
0.94
M
0.27
(Rowcliffe
et al
. 2003).
Finally, in the absence of specific information, a possible alternative is to esti-
mate
r
max
by
comparison
with a similar but better known species. In vertebrates,
intrinsic growth rate is related to size, with larger species generally having lower
rates. This allows the comparative approach to be generalised, using allometric
equations to predict
r
max
(Figure 2.10). However, this approach is limited by the
low precision of its predictions—among the 127 species represented in
Figure 2.10, fitted values differed from actual estimates up to three-fold.
Survival is one component of population growth, and as we saw in the previous
section, it can be used to estimate growth rate. It can also be used in predictive
models (Chapter 5), and is itself affected by harvest mortality, which can be an
important indicator of sustainability. Survival rate expresses the probability that a
given individual will survive over a given period of time, and for most practical
purposes, it can be expressed as a finite rate. Thus, if the annual survival rate in a
population is 0.6, on average 60% are expected to survive each year. Survival can
be estimated either from population count data (Section 2.4.2.1), or from a sam-
ple of known individuals (Section 2.4.2.2).
2.4.2.1 Using count data
Population ratios
In principle, survival rates can be estimated as ratios from repeated estimates of
population size split by age (Box 2.9). For example, if it is known that a population
numbered 100 individuals of all ages (aged 0 and older) in one year, and the next
year there were 80 adults, the survival rate would be estimated as 80/100
0.8.
