How To BE FiT 283
year. But many other species, such as bristlecone pines and tortoises, and humans
for that matter, do not fit this pattern. Perennial herbs, most trees, most familiar ver-
tebrates, and many other species are iteroparous. Some of them, such as albatrosses
and humans, delay reproduction. And some species are semelparous but reproduce
at an advanced age (FIGURE 11.8). How have these life histories evolved?
Under some circumstances, the cost of early reproduction may exceed its benefit,
and fitness may be lower than it would be if reproduction were deferred. Several
factors may make deferred reproduction advantageous. For one, fecundity is often
correlated with body mass in species that grow throughout life, such as many plants
and fishes. In such species, allocating resources to growth, self-
maintenance, and self-defense rather than to immediate repro-
duction is an investment in the much greater fecundity that
may be attained later in life (see Figure 11.12A). In this vein, a
very important factor is that many species suffer much higher
mortality from predation and other ecological factors when
they are young and small than when they are older and larger.
The vast majority of seedlings of forest trees, for example, die
before they reach even modest size; furthermore, the fecundity
of trees increases greatly with size and their ability to compete
for light and other resources [20]. Mammals do not grow in
size very much after they reach reproductive age, but they
might provide better parental care, and enhance the survival of
their offspring, if they grow in strength or experience with age.
We might expect, then, that in species with high rates
of adult survival, especially if young age classes have high
mortality, selection favors delayed reproduction and higher
reproductive effort later in life. As predicted, species that
have low mortality rates as adults also reach reproductive
maturity at a later age (FIGURE 11.9) [47, 53].
Experiments have also provided strong support for life
history theory. David Reznick and colleagues have studiedFutuyma Kirkpatrick Evolution, 4e
Sinauer Associates
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Evolution4e_1108.ai Date 11-02-2016(A) (B)FIGURE 11.8 Some semelparous plants reproduce once, after many years, and then
die. (A) The cabbage palm Corypha utan, of southeastern Asia, may produce up to
a million flowers. (B) Bamboos engage in highly synchronous reproduction and then
die, resulting in years of great food scarcity for animals that eat the shoots (such as
specialized insects and giant pandas) and great food abundance for those that eat the
seeds (such as finches). (Photos by D. J. Futuyma.)FIGURE 11.9 Among species of snakes (e.g., the worm snake,
Carphophis amoenus) and lizards (e.g., the collared lizard, Cro-
taphytus collaris), the lower the annual mortality rate of adults,
the later they reach reproductive maturity. This pattern conforms
to the prediction that delayed onset of reproduction is most likely
to evolve in species with high rates of adult survival. (After [53].)Futuyma Kirkpatrick Evolution, 4e
Sinauer Associates
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Evolution4e_11.10.ai Date 11-21-201612480.125 0.25 0.5 1 2
Mortality rate of adultsAge at maturity (years)Snake species
Lizard species11_EVOL4E_CH11.indd 283 3/22/17 1:11 PM