Eco Chapter 10: Life History

life history

the lifetime pattern of growth, development, and reproduction for an organism

life history trade-offs

allocating resources to one aspect of life history (like reproduction) can reduce the resources available to another aspect (growing).

Examples of life-history trade-offs:

• mode of reproduction

• age of first reproduction

• allocation to reproduction

• number/size of offspring (eggs, young, seeds)

• timing of reproduction

Factors that affect life-history trade-offs:

1. intrinsic: the evolutionary history of the species (developmental patterns, genetics, physiology)

2. extrinsic: the physical environment, presence of predators or competitors

dioecious plants

separate male and female individuals

hermaphroditic plants

individuals have both male and female reproductive organs in the same flower, perfect flowers; may be able to self-fertilize depending on the timing differences, structural separation, self-incompatibility, and pollinator dependence of the species

monoecious plants

individuals have both male and female reproductive organs but have separate male and female flowers, imperfect flowers

simultaneous hermaphrodites

the male organ of one individual is mated to the female organ of another, and vice versa, at the same time

sequential hermaphrodites

the individual will be a male for one part of its life and female during another

Benefits of asexual reproduction:

1. offspring are genetically identical to parent and thus adapted to local environment

2. all individuals are able to reproduce so there is a potential for high population growth

Cost of asexual reproduction:

loss of genetic recombination introduces no variation among offspring, less ability to adapt to changing environment

Benefits of sexual reproduction:

recombination leads to a population in which each individual is genetically unique, leads to an increased potential for population to evolve with environmental changes

Costs of sexual reproduction:

• it requires specialized reproductive organs

• energetically expensive

Age of Maturity

the transition from juvenile to adult, or the age of first reproduction

Natural selection (favors or doesn’t favor) individuals whose age at first reproduction results in the greatest number of offspring over a lifetime

favors

Larger body sizes means an (increase or decrease) in fecundity

increase

Cost of maturing later in life:

risk of dying before reproducing

Adult survival rate (increases or decreases) as a brood size increases due to…

decreases; an increased cost of energy (such as for foraging)

The individual body mass is (higher or lower) for chicks in large brood sizes and their survival rate is (higher or lower) when compared to smaller broods

lower; lower

Small egg strategy

• small investment in each egg (very little parental care, such as with turtles)

• many eggs produced to increase chance that some survive

• common in disturbed or unpredictable environments

large egg strategy

• large parental investment per egg

• few eggs produced

• increased chance of survival for young

• common in predictable or competitive environments

Altricial

young are born helpless, less energy exerted before birth and more after birth (ex: rodents, humans, songbirds)

Precocial

young born in an advanced stage of development, can forage independently shortly after birth, more energy exerted before birth and less after birth (ex: ducks, horses, whales)

Iteroparous organisms and iteroparity

• reproduce more than once (ex: trees)

• less maximum effort is optimal on the first attempt so that the organism survives to produce again

Semelparous organisms and semelparity

• produce only once (ex: mosquitoes)

• one large reproductive event followed by death is optimal

Mating system

the pattern of mating between males and females in a population, typically the social framework involving the selection of mates; influenced by resource availability

Outcrossing Mating System

cross-fertilization between two individuals, dioecious plants must outcross, possible for hermaphroditic and monoecious plants 

Autogamy Mating System

self-fertilization, possible for hermaphroditic and monoecious plants

Monogamy

pair bond between one male and one female

Seasonal monogamy

pair bond is formed for the duration of a breeding season

Lifetime monogamy

pair bond lasts multiple seasons or a lifetime

Cheating increases fitness because…

• genetic variation increases among offspring

• it increases the number of offspring

polygamy

the acquisition of two or more mates by one individual

polyandry

female with 2+ mates

polygyny

male has 2+ mates

intrasexual selection

male/male or female/female competition for mates (often exaggerated by secondary sexual characteristics such as large size, aggressiveness, threatening antlers)

intersexual selection

differential attractiveness of one sex to another (females select mates based on phenotype like how female birds like males with large bright feathers or elaborate sexual displays like dancing)

r-strategists

species that are short-lived, develop rapidly; influenced by unstable habitats such as temporary ponds; selection favors species that have a small body size, reproduce rapidly, produce many offspring with low survival, and invest little parental care (ex: mosquitoes or frogs)

k-strategists

species are long-lived and develop slowly; habitats are stable over time; selection favors species that have bigger body size, reproduce slowly, produce fewer offspring with high survival, and invest in heavy parental care (ex: bears, lions, elephants, primates)

2 Life History Classifications for Plants:

1. stress

2. disturbance

Plants: Stress

restricts plant growth and productivity, typically when plant does not receive adequate light or water or is in a non-optimal temperature

Plants: Disturbance

partial or total destruction of biomass due to herbivores, pathogens, or natural disasters

Ruderal Plants

low stress, high disturbance; typically, small and short-lived but has good dispersal abilities (like weeds that grow in cracks in the sidewalk, foot traffic is a disturbance)

Competitive Plants

low stress, low disturbance; found in predictable habitats with an abundance of resources

Stress-tolerant plants

high-stress, low disturbance; resources are limited and go towards maintenance (ex: tall grass on a mountain with cold temperatures and high winds)