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霊長類行動学4. 生活環(Life history)


Life history(生活環)

  • life history
    • birth, growth, reproduction, life span, mortality, and etc.
    • explains the evolution of changes during the life course by analyzing demography, genetics, behavior, and morphology in a developmental and, typically, quantitative context.
    • most broadly includes "not only the age-specific fecundity and mortality rates, but the entire sequence of changes through which an organism passes in its development from conception to death"
  • risk
    • statistical function.
    • i.e., does not guarantee the result
    • natural selection operates on the same principle

  • Morbidity rate: ill
  • Mortality rate: death

  • Development
    • growth and maintenance of the body
    • gestation (妊娠) rate - speed of mature offspring grows
      • (gestation time) / (neonatal mass)
      • impact both on offspring and mother
        • the faster rate, the more energy required
        • but gestation does not take a lot of energy compare to lactation (10-12% of diet)
    • postnatal growth rate - speed of the growth


      • (weaning age) / (weaning weight)
      • weaning (離乳)
        • time when they become independent by catching food by themselves
          • about 4 years old in human
        • NOT same to the age they can survive by themselves
      • impact both on offspring and mother
        • lactation for kids of mom takes a lot of energy
        • and support herself at the same time.
  • Reproductive effort
    • include number of offspring you can have per year, per cycle, per age, etc)
    • age at 1st reproduction
      • 19 years old is the average for human in natural
    • female need to be fat
    • reproductive rate:
      • (litter size (産子数)) / (inter-birth interval)
      • inter-birth interval
        • Pan: about 6 years
        • Human: about 4 years
      • litter size:
        • human: 1
  • intrinsic of natural increase
    • how fast the population grows, fill up the habitat.
  • mortality rate
    • major link to life history
    • animals try to minimize mortality, maximize reproducibility
    • extrinsic mortality
      • predation
    • intrinsic mortality
      • starvation & disease
    • allocare
      • care given by other than parent, usually kin like brother, father, and etc.
      • minimizes the mortality by having multiple people taking care of children
      • but sometimes may become a problem by abusing
  • senescence (老化)


  • Body size
    • allometry (相対成長)
      • change in structure with size
      • e.g., 体重が重ければ重いほど足が出かかったり


    • Life-history is correlated with size


      • life-history gets slower with large size

Female life history

  1. Infancy
    • identical to male (same dev., mortality, and etc)
    • depend on mother
    • high mortality risk
    • physically immature
  2. Adolescence
    • period of learning and socialization
      • relatively short term
  3. Adulthood
    • reproductive span
      • all complicated things start
  4. Senescence
    • death, except in apes and humans

Adulthood (female)
  • all life of females can be either the following
    1. cycling - less time
    2. pregnant
    3. Lactating - most of the time

  • Cycling
    • "Estrus" (発情期)
      • when females are receptive to mating
      • ovulation (排卵)
        • females have a max receptiveness
        • occurs during estrus
      • Estrus can be signaled
        • pheromones - chemical signal (humans do not have)
          • when received, becomes receptive
        • Callitriehids - suppress ovulation of other females in the group
        • sex skins - perinatal swellings - signalling estrus


          • males taste vroue and vaginal secretions
    • Anestrus
      • when females are UNreceptive (completely dis-interested in sex)
      • humans are always estrus
  • to maximize reproductive output and minimize surviving offspring:
    • reproductive output = (life span) / (inter-birth interval)
    • e.g., 20 year life / 1.3 year → 15.4
    • infant mortality limits
  • need energy for SELF
    • low energy-poor health → mortality, infertility (不妊), lower fecundity (繁殖力)
    • female reproducibility is contingent with resources (food)
      • need energy for infant
        • low energy -> low birth rate - high mortality
        • longer infancy -> higher mortality risk
  • offspring
    • gestation: low energy for a female
    • infancy: high energy for a female
      • human: lactation: 1.3 x (normal metabolic requirement)
      • other mamas: 2〜5 x (normal metabolic requirement)
    • weaning ages
      • wean early
        • desirable
          • infant out high mortality phase quickly
          • lots of food available, more milk
      • wean late
        • undesirable
          • food is unreliable
          • slower growth
          • increase mortality
  • environment seasonality
    • food is season dependent
      • they have birth season
    • food is season independent
      • they do NOT have a birth season
    • food seasonality effects birth season

Male life history

  1. infant - same as female
    • immature, high mortality risk
    • dependent on mother
    • vulnerable (脆弱な) to predators - easy prey, don't fight back, tenure
  2. Adolescent - period of learning and growth
    • depending on social situation, different paths
  3. adult - reproductive period

male faces two major challenges in Adolescence and Adulthood

Mating (male)
  • juvenile mortality is often a minor concern.
    • they think they can overcome loss of infants by gaining more mates
    • i.e., if offspring dies, then they can just mate again.
      • out-produce females and other males; maximize output relative to other male
    • variance in reproductive success = reproductive skew (females do not have)
      • dictate life history
        • competition with other males
        • your reproduction success is other male's failure
    • thus, male should not care about offspring
  • Primates are odd because males DO care for offspring because ..
    • 1. protect limited investment when reproductive potential falls off
    • 2. act nice to the kids to gain favor with female
    • 3. male parental care in necessary (polyandry)

  • Mating potential is contingent on female distribution
    • Female dispersal determines whether males are forced into proximity
      • if females are clumped, males group together
      • if females are dispersed, males disperse
    • this is because, amount of female and males has is dependent on how many men can guards them.

Adolescence (males)
  • Male grows up in group
    • at some point, he becomes a threat to adult males, then he will be forced to leave group
    • puberty -> threat -> kicked out
  • Male living on own is faced with higher mortality
    • 1. Poor access to resources
      • because groups are centered around best resources
      • shortage
    • 2. Susceptibility to predators
    • 3. Harassment by other males
      • leads to motality and death
      • sick all time so susceptible to disease

Options for males at transfer stage

  1. find group as fast as possible
    • outside but safety; start with being a peripheral males
  2. become cryptic - hide
    • only possible in dense forest - rain forest
  3. join an all male bond = bachelor band
    • open country
    • if gets in, will be at the bottom so harassed.
      • stressful which leads to disease
        • disearse risk and predation
      • nutritional risk

life-history choice (grow fast or grow long?) (male)

  • three concerns
    1. can't be threat to other adults
    2. need to learn
    3. need to grow
  • Male decision based on grouping pattern of females


  • 1. single-male group
    • grow fast
      • have rate-hyper morphosis
        • オスは勢いよく成長する。
      • get out of juvenile stage
    • groups often associated with abundant resources, so starvation not an issue
      • many folivores (leaves) = not resource limiting
        • no shortage in leaves
      • (problem only for multi-male group) higher risk of mortality from starvation and disease
    • little social learning required
      • single male is brute who takes group
      • only need to be able to kill and reproduce
      • (problem only for multi-male group) sudden growth makes male and early threat, forcing him out of group
  • 2. multi-male group
    • grow slow
      • have bimaturism
        • ♂♀共に時間をかけて同じように成長するが、オスの方が長い期間成長し続ける
      • reduce metabolic requirements
      • tend to eat restricted resources like fruit
        • significant risk for starvation
    • provide long time for social learning
      • dominant hierarchy
      • associate with females and males
      • alternative strategies to get around dominance
        • relations with females (socialization)
          • make friends with females
      • make friends with males to make tenantry alliance to over throw dominant males.

      • give time to work into new group without being a threat
    • overcome higher risk of mortality due to immaturity by parental care.
    • problem may be the lower reproductive output (shorter time for reproduction)

Adulthood (male)
  • male maximizes reproductive output
  • compete for access to females
  • metabolic requirements of secondary importance
  • in multi-male group
    • dominant male tolerant of offspring (don't actively kill them)
    • when lose dominance, his reproductive success is limited, so turn to parental care (guard children from other males)
    • i.e., Take care of infants only after reproductive potential declines even though male reproductive potential is almost lifelong




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