Chapter 9 Flashcards
What are life histories?
- The attributes of the life cycle through which an individual passes, with particular reference to survival and reproduction.
- Expressed through behaviour, physiology, anatomy
- Genetic variation and phenotypic plasticity
What are life history traits?
- Age of maturity
- Size at maturity
- Fecundity (#of offspring)
- Size of offspring
- Frequency of reproduction
How does the age at maturity varies
across different timescales?
- Minutes (e.g. many bacteria)
- Months (e.g. small mammals)
- Decades (e.g. many sharks, whales)
How does maturity and age at
maturity correlate?
Large bodied animals have a later age at maturity
What is fecundity?
- Annual fecundity is the number of offspring
produced by an individual during a breeding season - Annual fecundity is influenced both by the
number of reproductive events and the number of offspring per event - The number of reproductive events
varies from once in a lifetime to repeatedly
over centuries (iteroparous vs semelparous)
What is the relation between size and # of offspring?
- Across species, there is a negative correlation
between size and number of offspring. - Organisms produce numerous small offspring, or few large offspring
What is reproductive effort
- Proportion of total energy devoted to reproduction, including:
– Physiological effort (e.g. energy demands)
– Anatomical effort (e.g. gonad development)
– Behavioural effort (e.g. migration)
Fecundity and age
In some cases, fecundity is consistent across the lifespan
In others, fecundity increases with female body size (when the female is older)
Parental care
- Parental care that follows reproductive events determines how many kids an individual has
- Some organisms (cod) spend lots of energy on # of offspring and none on parental care
Others have few offspring but lots of parental care (grey seal)
Reproductive efforts
- Proportion of total energy devoted to reproducing, including:
1.) Physiological efforts (energy demand)
2.) Anatomical efforts (gonad development)
3.) Behavioural efforts (migration/ finding food)
Life history traits vary
Among species
Among populations
Within populations
ex.
Brook trout, Freshwater river:
- Smaller size of maturity
- more eggs
- Larger eggs
- Probably faced with more predators
Brook trout creek
- Focused on semantic growth
Constraints
Age at maturity increases with adult body size
Population growth decreses with body size
(small animals reproduce more faster)
Bet-hedging strategies
Multiple reproductive events (maybe at different spots)
to assure that at least some of your kids will survive
Increased fitness in suboptimal conditions
Lower in optimal
ex. cod laying eggs over longer intervals because it doesn’t know when it will get the nutrients it needs for it’s ofspring to survive
Cost of reproduction
An increase in one life history trait often causes a decrease in another
- Organisms only have so much energy, they can’t maximize everything
ex. Brightest male guppies have the highest reproductive success, but are more visible to predators
Selection on life histories
Natural selection favours genotypes where survival and fecundity result in the highest fitness relative to other genotypes
Must survive and reproduce
