(2) Life history

Sept 17 - 26

Life history

The schedule of an organism’s growth, development, reproduction, and survival. Represents an allocation of limited time and resources to achieve maximum reproductive success

Fecundity

The number of offspring produced by an organism per reproductive event

Parity

The number of reproductive episodes an organism experiences

Parental investment

The resources (time and energy) given to an offspring by its parents

Longevity

The life span of an organism

Slow life history

• long time to sexual maturity

• long life span

• low numbers of offspring

  • high parental investment

Fast life history

• short time to sexual maturity

• short life span

• high numbers of offspring

• little parental investment

Plant life history depends on:

Stress, Competition, and frequency of disturbances

Life history in plants plotted as three axes:

• Increasing competition → competitors

• Increasing stress → stress tolerators

• Increasing disturbances → ruderals

Life history traits for stress tolerators

• Potential growth rate → slow

• Age of sexual maturity → late

• Proportion of energy used to make seeds → low

• Importance of vegetative reproduction → frequently important

Life history traits for competitors

• Potential growth rate → fast

• Age of sexual maturity → early

• Proportion of energy used to make seeds → low

• Importance of vegetative reproduction → often important

Life history traits for Ruderals

• Potential growth rate → fast

• Age of sexual maturity → early

• Proportion of energy used to make seeds → high

• Importance of vegetative reproduction → rarely important

Principle of allocation

• no such thing as a perfect organism

• life history trait exist as tradeoffs

• when resources are devoted to one body structure, physiological function, or behaviour, they cannot be allotted to another

• general tradeoff between offspring number and offspring survival

Offspring number vs size

a negative correlation - a general trade-off between the number of offspring and the size of those offspring is predicted

Parental care vs. parental survival

offspring

• more offspring = less food, less parental effort

  • as the number of offspring produced increases, the mount of parental care per off spring will decrease

Parental care vs. parental survival: tropical birds

tropical birds law fewer eggs, greater parental effort, more provision per offspring

Parental care vs. parental survival: Temperate birds

Temperate birds law more eggs, less parental effort but more offspring

Determinate growth

A growth pattern in which an individual does not grow any more once it initiates reproduction; occurs in many species of birds and mammals

• Growth stops at sexual maturity

• Slow life history

Indeterminate growth

A growth pattern in which an individual continues to grow after initiating reproduction

• Fast life history

Tradeoffs of Trinidadian guppies

• lower streams = short life expectancy, more and smaller offspring, high predation, fast life history

• Higher streams = long life expectancy, fewer and larger offspring, low predation, slow life history

Semelparity

When organisms reproduce only once during heir life

• Indeterminate growth

• Fast life history

Iteroparity

When organisms reproduce multiple times during their life

• Determinate growth

• Slow life history

Senescence

A decrease in fecundity and an increase in the probability of mortality

Why does senescence exist?

• An inevitable consequence of natural wear and tear

• Reflect the accumulation of molecular defects that fail to be repaired

• Rate of wear can be medicated by physiological mechanisms that prevent or repair damage

The effects of resources

Fluctuations in resource availability can determine the timing of life history events

• e.g. barking treefrog, those with high food resources can metamorphose at a younger age

• Lower food resource creates a smaller frog, therefor they’re easier to kill

The effects of predation

Predation affects many life history traits (e.g. time to and size at hatching, metamorphosis, and sexual maturity)

• e.g. the red-eyed tree frog lays eggs om leaves that ever hang water, these eggs can sense vibrations and will hatch early if they sense a predator approaching

• Makes them smaller and more susceptible to predators

The effects of climate change

Small temperature can have large impacts on an organisms physiology

• The general increase in global temperature gas changed the breeding patters of many animals and plants

• e.g. the North American tree swallows have been laying eggs earlier in the season due to the increase in temperature in spring

• e.g. plants have been found to be flowering earlier in the season in recent years

Consequences of altered breeding

Problems arise when a species depend in the environment to provide the necessary resources when the breeding season is altered

Impact of humans

In addition to global warming, human activities can impose a string selection and have substantial impacts in organisms life histories

• e.g. commercial fisheries imposing selection pressure on fish size by harvesting the larger fish

• un-natural selection

Models of population

• Age: individuals cannot reproduce until they have achieved reproductive maturity; reproductive rate may decline with age

Survivorship curve: type 1

population that experiences low mortality early in live and high mortality later in life

Survivorship curves: type 2

Populations that experience constant mortality throughout its life span

Survivorship curve: type 3

Populations with high mortality early in life and high survival later in life

Life tables

tables that contain class-specific survival and fecundity data