Life History
Population growth is linked to life history traits:
Some animals live for a short period of time but reproduce profusely –
large r
Whereas other animals live for a long period of time but produce only few
offspring – smaller r
Life history = the pattern of allocation to growth, development,
reproduction, survival etc.
Age and size at reproduction
Number of reproductive seasons: semelparous (once) vs. iteroparous
(many)
Life span (e.g. annual vs. perennial)
Number and size of offspring
The “perfect” life history - predictions:
mature at birth
continuously produce high-quality offspring in large numbers
live forever
Why does it not exist? Amount of resources available to an organism is
finite – generates trade-offs
Different ways to slice a pie – evolution of life history strategies:
Some commonly studied trade-offs, shaped by natural selection but
with profound consequences in ecology:
Life span vs. reproductive output
Note: life span and senescence are not the same thing: senescence =
physiological ageing, life span = ecological product of the environment
you live in. Fission organisms do not senesce, but they are not immortal.
Even if an organism could live forever, it wouldn’t – random chance,
predators, parasites.
Life span will be the result of an organism’s genetics and its environment
Therefore probability of reproducing decreases with age
Population growth is linked to life history traits:
Some animals live for a short period of time but reproduce profusely –
large r
Whereas other animals live for a long period of time but produce only few
offspring – smaller r
Life history = the pattern of allocation to growth, development,
reproduction, survival etc.
Age and size at reproduction
Number of reproductive seasons: semelparous (once) vs. iteroparous
(many)
Life span (e.g. annual vs. perennial)
Number and size of offspring
The “perfect” life history - predictions:
mature at birth
continuously produce high-quality offspring in large numbers
live forever
Why does it not exist? Amount of resources available to an organism is
finite – generates trade-offs
Different ways to slice a pie – evolution of life history strategies:
Some commonly studied trade-offs, shaped by natural selection but
with profound consequences in ecology:
Life span vs. reproductive output
Note: life span and senescence are not the same thing: senescence =
physiological ageing, life span = ecological product of the environment
you live in. Fission organisms do not senesce, but they are not immortal.
Even if an organism could live forever, it wouldn’t – random chance,
predators, parasites.
Life span will be the result of an organism’s genetics and its environment
Therefore probability of reproducing decreases with age
