Lecture 18 - Age-structured populations and life history

What are factors of age-structured populations?

fecundity (giving birth) and survivorship (us dying) depend on age

What do exponential and logistic models do?

they treat all individuals the same but not all individuals have same probability of dying and giving birth

What are life history strategies?

species have different life history strategies
- fecundity and survivorship are dependant on species

What are key components of life history strategy?

- lifespan
- timing of reproduction
- number of offspring
- parental investment in offspring

What is the typical life history of plants and animals?

- start at small size
- grow without reproducing
- become mature w enough resources and reproduce by spending resources; some all at once, some spread
- consider age structures to predict trajectories

What is the population rate difference of individuals with high mortality in reproductive age compare to individuals in post-reproductive age?

in reproductive age, will slow down rate of population growth

Is there variation in age of reproductive maturity, fecundity, and lifespan?

yes look at example of elephants, humans, pikas, and salmon

What are age-structured population growth important implications of?

- evolution of life histoires
- conservation of populations
- understanding changing structure of human populations
(human demography)

What are age-structured population growths taking into consideration?

- single population
- fecundity and survivorship with age

What is this graph of age-sex pyramid showing us?

- went from pyramid shape (bc of rise of babies after WW2) to stable amounts of each age
- used to me mean of 17 but now it is 40

What does it mean by ∑nx?

that there are stages of life in ages and that the sum of them are 24
- pictures include females because females are the ones who invest the most in reproduction
- they limit population growth

Why do females invest more in reproduction?

eggs are more energy costly than sperm
- gestation and lactation in female mammals

What are age-class intervals?

- units of time to give number of age classes for organism
- show variation on how fecundity and survivorship depend on age

What are life tables? What are the variables that fall under this?

- summarizes life events that are expected of individual at a certain age
- age of death
- age and timing of birth
- consider females only
- treated as constants

According to the interactive web app, what should survivors always do?

survivors should always decline in age
- lx (probability of being alive) declines with x (age)

What are survivorship schedules? What are the variables? What do they mean? What is a survivorship curve?

- subscript x is age classes
- lx is the probability of being alive
- lo =1 (only count individuals alive)
- lx (probability of being alive) declines with x (age)

- graph of lx vs x

What are the different types of survivorship curves as depicted in this photo? What are the explanations of each of the types based on the graphs? What are examples of each to these types?

- if mortality is constant with age you get an exponential decline
- graph in log (lx), u get a negative straight line

Type 1: early life survival is high but declines rapidly in old age
- parental investment in offspring
- ex. humans and elephants

Type 2: individuals die w/o dependance on age
- same chance of getting eaten at young or adult get

Type 3: high mortality in early-age classes
- ex. trees and invertebrates
- ex. offspring of seeds are likely to die before they germinate BUT if they germinate, they survive and live long lives

What does this graph show about human lx?

- infant morality is high
- increasing mortality with age
- senescence in late age; old and dying
- death

What do these graphs of real data show?

there is high survivorship of females than males

What does this graph of real data including income show?

there is high survivorship in age classes with higher income than lower income even with a good medical system

What are fecundity schedules?

- subscript x represents age classes
- mx (bx) is # of daughters born to female of x age during interval x to x+1
- reproductive period is preceded by resource-accumulation phase
- fecundity-survivourship trade offs = cost of reproduction

What is the cost of reproduction equation?

= fecundity - survivorship

What does this graph of Canadian women data depict?

there is high fecundity in women in age classes of 30 to 34

What does this graph of fecundity between Saskatchewan and Ontario tell us?

- women in Saskatchewan have babies earlier than women in Ontario
- having babies earlier leads to faster population growth

What is the net reproductive rate, Ro?

its the average number of daughters a female has in her lifetime

What is the equation of the net reproductive rate? How does it work?

Ro = ∑lxmx

- ∑mx is total number of daughters produced by mother that doesn't die early
- times lx accounts for mothers that die early

What is the variable Ro similar to and how?

similar to lamda because it determines if populations will grow or shrink, depending on <>1of one generation than one interval

How is Ro in epidemiology related to Ro in biology?

- average number of something based off one single thing
- they are both factors that describe how a population is growing
-

What was the goal of Ro in terms of the corona virus?

drive Ro

What is the generation time equation?

T = ∑x lx mx / Ro

- formula for weighted average
- weights x by how many offspring are produced at that age
- dividing gives weight average that specifics when a female gives birth

What is the relationship between Ro, lamda, and r? How are they related mathematically?

- factor by which a population changes during discrete interval of time
- individuals are different

r = ln(Ro)/T = ln(lamda)

What is general about organisms with higher growth rates?

they have higher fitness

Why are all animals have higher growth rates?

constraints and trade offs
- reproduction is costly
- long reproductive periods allow time to accumulate resources

What does semelparous mean?

species have all their reproductives in the last year of life
- spend early years gathering resources to reproduce
- ex. salmon

What does iteroparous mean?

- producing reproductives over multiple years/age classes
- ex. humans, elephants, pikas

What are plant life history categories?

seasons of growth, semelparous, iteroparous

- one annual not applicable
- two biennial. not applicable
more than two. monocarpic perennial. perennial

- annual - all offspring in one year
- biennial - grow and accumulate resources
- flower and set seed
- monocarpic perennial - single bout at end of life

- perennial - few reproductive in many consecutive years

Why does natural selection favour semelparity? What about in plants?

- reproductive output is increased by accumulating resources for longer
- depends on the size

- big fruit and flowers attract more beneficial animals
- massive seed crops satiate seed predator populations which all more seeds to go uneaten

What does this graph of semelparous fish show us?

- in semelparous fish produced eggs of bigger size when they were larger in size and this improved their fitness

- in iteroparous fish, slightly bigger fish produced larger eggs but nothing compared to semelparous fish

What is an example of synchronized semelparity?

- bamboo plants

What is an advantage of synchronized semelparity? Hint: rat flood

- predator satiation tactic
- produce a lot of seeds and predators can't eat all of them so some escape and germinate and create new patches

- predictable events where whole populations come to into flower and set seeds

What is masting? In what types of plants does it occur in?

itereoparity - produce reproductives many times a year
- produce a lot of acorns at once to avoid predator satiation

What is the different between K strategy and r strategy?

K strategy:
- slower growth
- long generation time
- large body size
- investment in somatic growth
- lower reproductive rate
- better competitive ability
- poor at dispersal
- investment in individual offspring
- iteropratiy is likely
- shade tolerant

R strategy:

- faster growth
- short generation time
- small body size
- more investment in gonad
- high reproductive rate
- poor competitors
- good at dispersal
- produce more but light seeds
- semelpparity more likely
- shade intolerant, seed dormancy
- born to run

Why does selection select for early reproduction?

good for fitness
- more gene copies into populations faster

What overrides the effect of early reproductive selection? What does it produce?

accumulating resources and size-dependant mating success

produces delayed reproduction or semelparity

What selects on synchrony and why?

semelparity and predator satiation

- others are available to mate at the same time
- production of a lot of seeds at once

What other statistics can you calculate from life tables?

- life expectancy ex:
- expected years of life left

- reproductive value vx:
- number of future daughters left to individuals
- males prefer females with high reproductive value
- conservation and releasing of animals with high reproductive value

What does this graph of reproductive value in humans depict?

- lower at birth:
- chance they won't live long to reproduce

- maximum at late teens and entering reproductive years

- lower in late years as fecundity declines