chapter 13 trade offs in life histories

Life history

A description of the major characteristics of an organism from its birth to its death

Adaptations of an organism that influence aspects of its biology

• # of offspring

• Survival

• Size and age at reproductive maturity

Key life history traits

• body size

• Fecundity

• Parity

• Maturity

• aging/senescence

Body size

Length, height, weight

• influenced how you interact with the environment

• Ex. How much energy…

Fecundity

Number of offspring per reproductive episode

Parity

number of reproductive episodes over lifetime

Maturity

Age at first reproduction

Aging/senescence

Lifespan/survival

Parity in animals

Semelparity/semelparous and iteroparity/iteroparous

Semelparity/semelparous

One reproductive event in their lifetime

• means only once, give birth

Iteroparity/iteroparous

Multiple reproductive events during their lifetime

Parity in plants

Monocarpic and policarpic

Monocarpic plant

Flowers and sets seeds only once and then dies

• ex. Canola and agave

Policarpic plant

Flowers and sets seeds only once multiple times in their lifetime

• ex. Apple tree

Related terms for life span in plants

Annual plant and perennial plant

Annual plant

Completes life cycle in one growing season

Perennial plant

Completes life cycle in multiple growing seasons

Allometry

Study of the relationship between body size and various biological traits/functions (shape, anatomy, physiology, behavior, etc.)

Why body size?

It determines how organisms use energy and interact with their environment (temperature, water, nutrients).

Principle of allocation

The amount of energy available to each organism is limited

• when energy is allocated to one function, it reduces the energy available for other functions

Energy budgets

Need to allocate energy between all parts of:

• growth

• Reproduction (trade offs within reproductive budget offspring number vs size)

• Activity

• Maintenance (trade offs between reproduction and other activities (with survival and growth)

Life history - trade off examples

• offspring size vs number

• Seed size vs dispersal distance

• Offspring size vs gene flow

• Survival vs age at maturity

• Size vs maturity and behavior

Gene flow

Transfer of genetic material from one population to another.

• ex. Darter fish that lay smaller eggs, lay more eggs (higher fecundity)

Reproductive effort

The allocation of energy, time and other resources to produce and care for offspring rather than grow and survival

• When adult survival is lower

• When adult survival is higher

When adult survival is lower

Early reproduction is favoured → less energy for growth and future survival

When adult survival is higher

Delayed reproduction is favoured → more energy for growth and survival

Why do both the hooknose and jack exist?

Two groups represent alternative, but successful, evolutionary strategies: fighter and sneaky

Hooknose

Fight others to establish territory where females will lay eggs.

• pro: best territory

• Con: be predated

Jacks

Hide and sneak in to fertilize eggs while hooknoses are fighting.

• pro: not predated as fast

• Con: sneaky

Simplified life history categories

• traits measured quantitatively vary immensely across species and species groups (ex. # of offspring vs size of offspring)

• Trait variation can be summarized into general life history categories that are selected for