Unit 1 - life histories Flashcards
chapter 8 concepts
- life history traits represent the schedule of an organism’s life.
- life history traits are shaped by trade offs
- organisms differ in the number of times that they reproduce, but they all eventually become senescent
- life histories are sensitive to environmental conditions
life history terms:
life history: the schedule of an organism’s growth, development, and survival
fecundity: the number of offspring produced by an organism per reproductive episode
parity: the number of reproductive episodes and organism experiences
parental investment: the time and energy given to an offspring by its parents
longevity (life expectancy): the life span of an organism
slow to fast continuum
life history traits often vary consistently with life form, habitat, or environmental conditions
“slow” life history:
-long time to sexual maturity
-long life spans
-low numbers of offspring
-high parental investment
ex. elephants, oak trees
“fast” life history:
-short time to sexual maturity
-short life spans
-high numbers of offspring
-little parental investment
ex. fruit flies, weeds
r versus K selection
K species tend to spend most of their evolutionary history at or near their carrying capacities, K.
r species tend to spend most of their evolutionary history away from their carrying capacities, usually lower than their Ks.
selection is thought to favor different suites of life history traits for these 2 kinds of species
life history traits in plants
Grime proposed that plant life history depends on stress, competition, and the frequency of disturbances
plants functioning at the extremes of these environmental axes could be categorized as stress tolerators, competitors, or reuderals
stress tolerators vs competitors vs ruderals
stress tolerators: typically small herbs with a long life span, slow growth, and long time to sexual maturity, rely on vegetative reproduction (reproducing from roots and stems)
competitors: grow fast, achieve early sexual maturity, and devote little energy to see production
ruderals: grow fast and devote high proportion of their energy to reproduction
semelparity vs iteroparity
semelparity: when organisms reproduce only once during their life; relatively rare in vertebrates, but common in insects and plants
iteroparity: when organsims reproduce multiple times during their life; common among birds, reptiles, mammals, and amphibians
annual: an organism that has a life span of one year
perennial: an organism that has a life span of more than one year
a semelparous life history
2 fitness components:
-survival to become an adult
-reproduction as an adult
total expectation of lifetime R of a propagule is the product of the probability it survives to become an adult and the average adult reproduction
R = s * m
ex. pacific salmon, giant octopus, annual plants, biennial plants
an iteroparous life history
many fitness components:
-survival to become adult aged 1
-reproduction at age 1
-survival from age 1 to age 2
-reproduction at age 2
-etc
R = s0,1 * m1 + (s0,1 * s1,2) * ms + (s0,1 * s1,2 * s2,3) * m3 +…
ex. atlantic salmon, elephants, perennial plants
principle of allocation
the observation that when resources are devoted to one body structure, physiological function, or behavior, they cannot be allotted to another
natural selection will favor individuals that allocate their resources ina way that achieves maximum fitness
there is a TRADEOFF between offspring number and offspring survival
evolution of life history traits
- life history traits involved in tradeoffs
~ limited amount of energy to invest in survival, maintenance, and reproduction - natural selection is expected to optimize in light of tradeoffs
~ max number of offspring surviving to maturity
~ depends on the likelihood of survival to different age classes
major life history tradeoffs
- present v future reproduction (Williams)
- within present reproduction (Lack)
~ offspring size )quality) v offspring number (quantity) - Juvenile survival versus adult reproduction (Gilliam)
- when ecological conditions constrain return on investment into one fitness component, natural selection favors redirecting investment into other fitness components
Lack’s Tradeoff
offspring number vs parental care
-As the number of offspring increases, the amount of parental care per offspring decreases (and reduces offspring survival).
offspring number vs size of offspring
- the expected trade-off is often not observed. The number of offspring is variable, but the size remains relatively constant. This indicated that selection favors a uniform offspring size.
William’s Tradeoff
- tradeoff between present and future reproduction
- individuals maximize lifetime reproductive success
- laid foundation for life history theory
- senescence is favored by natural selection if there is a tradeoff between present and future reproduction, and if gains early in life are great than costs expressed later in life
parental care vs parental survival
- having more offspring can stimulate parents to hunt harder for food to feed their offspring. This additional effort can affect the parent’s fitness.
Gilliam’s Tradeoff
growth rate vs fitness
- allocation of energy to increased fecundity during one year occurs at the cost of further growth that year.
determinate growth: growth pattern where an individual does not grow anymore once it initiates reproduction (favored by long life span organisms)
indeterminate growth: growth pattern in which an individual continues to grow after it initiates reproduction (favored by short life span organisms)
