Ecolocgy Chapter 9: Life Histories

Life history

A lifetime strategy; includes things like how many young to have, when, how often, how much parental care, and life expectancy

Fecundity

Number of offspring produced per reproductive episode

Parity

Number of reproductive episodes

Parental investment

How much parental care to give, including time and energy

Longevity

Life expectancy of an organism

R-selected species

Species that have high levels of reproduction whose populations spike and then decline rapidly

R-selected traits

Rapid development, early age of reproduction, semelparity, large clutches, small eggs, short life spans, small organisms, and no parental care

Semelparity

Organisms breed once and then die

K-selected species

Species that tend to occur near carrying capacity in resource scarce environments

K-selected traits

Slow development, delayed reproduction, iteroparity, small clutches, large eggs or young, long life spans, and parental care

R and K continuum

Not all species are extremely R or K selected, but rather somewhere in the middle

Plant life history

Depends on stress, competition, and frequency of disturbances

Ruderals

Plants that have increase disturbance and r-selected traits

Stress tolerators

Plants that have increasing stress and have k-selected traits; tend to be small herbs that rely on vegetative reproduction

Competitors

Plants that have increasing competition and are somewhere in between r and k characteristics; usually grow fast, mature early, and devote little energy to seed production

Principle of allocation

When resources are devoted to one trait, they cannot be devoted to another trait; natural selection favors individuals that devote resources to reproductive fitness

Offspring number vs size

The larger the offspring, the less that can be produced, and vice versa

Offspring number vs parental care

As the number of offspring increases, the amount of parental care per offspring decreases, and offspring survival decreases as well

Offspring number vs parental survival

More offspring can stimulate the parents to work harder, which can decrease their own survival

Determinate growth

Growth pattern in which an individual does not grow anymore once it initiates reproduction; typical in organisms with long life spans

Indeterminate growth

Growth pattern in which an individual continues to grow after it initiates reproduction; typical in organisms with short life spans

Cole’s paradox

An idea that, mathematically, semelparity produces the same fitness as iteroparity, if not better, so why does iteroparity even exist? (C = P)

C

Proportion of offspring that survive to breed

P

Proportion of adults living to breed again

C>P

Environment in which adult survival is low and offspring survival is high; favors semelparous reproduction

P>C

Environment in which adult survival is high and offspring survival is low; favors iteroparous reproduciton

Senescence

Gradual decrease in fecundity and increase in the probability of mortality as age of the individual increases

Photoperiod

Amount of light that occurs each day

Stimuli for change

The right timing of life history events is critical; often includes photoperiod, the effects of resources, and the effects of predation

Effects of resources

Fluctuations in resource abundance often determines the timing of life history events, as individuals with more resources can metamorphosize early and healthily

Effects of predation

Predation can trigger early hatching or sexual maturity, which can have tradeoffs