BIOL2102 Life History Stratigies

What is life history?

The set of traits that affect an organism’s survival and reproduction (timing, frequency, number, size of offspring, lifespan)

List four traits used to describe life history

Age at first reproduction; number of offspring; size of offspring; lifespan

Why do organisms face evolutionary trade-offs?

Because resources (energy, time, nutrients) are limited, so investing in one trait reduces investment in another

Trade-off: number of offspring vs offspring survival

More offspring leads to lower survival per offspring; fewer offspring leads to higher survival

Trade-off: parental care vs parental survival

More parental care increases offspring survival but decreases parent survival

What is r-selection?

Selection for traits that maximize reproduction at low population density

What is K-selection?

Selection for traits that maximize success near carrying capacity (high population density)

Population density in r-selection

Low density (far below carrying capacity)

Population density in K-selection

High density (near carrying capacity, K)

How does r-selection relate to the logistic growth model?

It maximizes r (intrinsic growth rate) when population size is low

How does K-selection relate to the logistic growth model?

It occurs when populations are near K (carrying capacity)

Two traits of r-selected species

Many small offspring; little or no parental care

Two traits of K-selected species

Few large offspring; high parental care

Example of an r-selected organism

Weeds, insects, or rodents

Example of a K-selected organism

Elephants, humans, or large mammals

What is a density-independent factor?

A factor that affects population size regardless of population density

What is a density-dependent factor?

A factor whose effect changes with population density

How does competition regulate population growth?

Higher density increases competition, reducing resources and lowering survival/reproduction

How does disease regulate population growth?

Higher density allows disease to spread more easily, increasing mortality

How do intrinsic factors regulate population growth?

High density causes stress or physiological changes that reduce reproduction

How does territoriality regulate population growth?

Individuals defend space, limiting population size and reducing overcrowding