Lecture 16: Life History Flashcards
What is life history, from a biological perspective?
Defined as the sequence of anatomical, physiological, and behavioral changes and events that an organism experiences over the course of its lifetime
What are the 6 primary stages that the life of a mammal can be divided into?
1) fetal (gestation)
2) infancy
3) juvenile
4) subadult
5) adult
6) post-reproductive (female)
How does the variation of the 6 primary stages of life define a life history?
Variation in the length of these stages along with the way a species allocates resources to each phase defines a life history
How did the phases of life history change with primates (especially apes and humans)?
In general, we have extended each phase of life history
There is a relationship between the amount of energy that a species invests in growth and development and what?
The number of offspring produced
What is an R strategist?
Minimal investment in individual growth with a high reproductive output
What does “R” in R strategist stand for?
Rate of increase in population
What is a K strategist?
Maximum investment in individual growth and low reproductive output
What does “K” in K strategist stand for?
Carrying capacity of environment (max sustainable population size)
What is the logistical population growth model?
- When N (population size) is very small, effect of limited resources is negligible
- As N approaches K (carrying capacity), rate of population increase declines
- When N=K, there is no population growth
- When N>K, the population Celine’s because demand exceeds available resources
R strategy populations tend to have what type of enervironment? What about K strategy pops?
R=highly variable and unpredictable
K=stable, predictable environments
Which strategy (R or K or both) has a density dependent mortality rate?
K strategy= density dependent mortality
R=density independent
Does K or R strategy show faster growing populations?
R
Which strategy (R or K) has a variable population size and where do they fall in relation to carrying capacitys?
R= variable population size and below carrying capacity K= stable population and near K
How do R strategy populations compete vs K strategy?
R= compete by having high reproductive output and colonizing of new areas
K=compete by exploiting available resources
What does the species success for both R and K strategy populations rely on?
R= habitat change and chance
K=quality of offspring
What does high resource allocation go to in R strategy vs K strategy?
R=to reproduction
K= to growth and maintenance
What is the parental investment in offspring for R strategy vs K strategy?
R= low parental investment
K=large parental investment
How does the offspring birthweight and development compare between R and K strategy?
R= small/low birth weight and rapidly developing K= offspring large/high birth weight, slow developing
How does offspring mortality, life span and gestation compare between R and K strategy?
R= high offspring mortality, short life span, short gestation K= low offspring mortality, long life span, long gestation
How does weaning occur in R strategy vs K?
R= early weaning K= Late weaning
Why are oysters a good example of a very r-strategy?
They produce 500 million fertilized eggs per year and provide no parental care
Why are great apes a good example of a very k-strategy?
They produce one infant every 5 or 6 years and provide extensive parental care
What are indicators of K selection?
Increase in animal body size and complexity over time. Larger size and great complexity=K
What is the “scala naturae” trend?
- Marine invertebrates release huge numbers of eggs or larvae –>
- Lower invertebrates show more parental investment–>
- tetrapods (and lower vertebrates) then encountered more variable environments, requiring slower developmental rates and reduction in # of offspring, greater parental investment –>
- Mammals increased metabolism to tolerate greater environmental fluctuations, eating to larger brain size, more complex behavior, higher calorie requirements, high level of parental investment, slow growth, fewer young
What is the general pattern for primates for first reproduction, fertility rate and life spans?
- relatively late ages at first reproduction
- low fertility (few offspring)
- Long life spans
What does the general primate life history point toward?
A pattern of relatively reduced reproductive effort, but high parental investments
The following describes which stage of human life history:
- gestation period (maternal investment)
- total dependence on mother
- maternal energy allocated to fetal growth
- the more time and energy allocated, the better the chances of survival to birth
- maternal trade offs include vulnerability to predators and cost of delaying the next offspring
Fetal period in general
Is the length of human gestation comparable to other primates?
Yes, chimps=216-260 days; orangutan=240-270 days; humans=266 days; gorilla=270 days
Why is human gestation thought to be unusually short? How is this possible?
Unusually short for our large brain size (which is extreme for our body size). Humans are unique in that our brains continue to grow significantly after birth
What percent of the adult size are newborn human brains? Newborn chimps?
Human newborns=25% of adult size
Chimps=47% of adult size
The following describes which stage of human life history:
- period of continued dependence on mother
- high energetic demands on mother
Infancy
What is the average age for humans of weaning, taking into account data from 64 traditional human societies?
Just<3 years old
The following describes which stage of human life history:
- Association with dental eruption
- not reproductively mature
Juvenile period
When does infancy end by definition?
Infancy ends with weaning, when young are able to forage independently and ingest solid food
Do humans have a long juvenile period?
Compared to other primates, we have a relatively long one
The following describes which stage of human life history:
- puberty, the process of becoming sexually mature
- Once an individual passes through puberty and is sexually mature, they are biologically an adult
- Species specific body mass associations
Subadult (adolescent)
The following describes which stage of human life history:
- Reproductive decline associated with old age
- males experience a more gradual long-term decline
- female humans are unique in experiencing menopause; total and permanent cessation of ovulation
Post-reproductive stage
What age does menopause in human females occur around?
50
What is it thought that menopause is a consequence of?
The compromise between early intensive investment in offspring and individual longevity
What are two reasons (hypotheses) as to why females live past the age of reproduction in humans?
“Grandmother” hypothesis and extended kin selection
What is the human life expectancy?
Now exceeds 80 years of age and continues to increase
Is longevity and life expectancy the same thing?
No, under “ideal” conditions the human life span can exceed 120 years
What plays into human longevity?
Environmental factors play a huge role but there is a significant underlying genetic factor. Longevity is subject to selection and has evolved over the years
How does higher investment in growth and reproduction alter life span?
It can reduce it. It has been observed in many species that lower calorie intake, which reduces growth and potentially reproduction, is also associated with longevity
How is brain size correlated to longevity?
High brains are associated with slower development, which in turn is associated with long lifespan
