Lecture 6: Life Histories Flashcards
Define life history
the lifetime pattern of growth, development, reproduction and survival of an organism that is characteristic of its species
Describe the principle of allocation
individuals have limited resources (energy) and resources allocated to one thing cannot also be allocated to another
What are the 3 things energy is allocated to?
Growth
maintenance
reproduction
These are considered for both the present and the future
What trade-offs are organisms faced with as a result of finite energy resources?
Trade-offs between life history traits related to growth and reproduction because maintenance ‘costs’ are relatively stable throughout an individual’s life
When does maintenance take up more energy in an individuals life history?
During early development and growth, once an individual reaches sexual maturity, the energy allocation for maintenance is stable
What is included in maintenance?
the basic functions that keep an organism alive such as cellular respiration, metabolism, heart rate, etc.
What does growth refer to? (in terms of energy allocation)
adding biomass to oneself
What does reproduction refer to? (in terms of energy allocation)
investing biomass in offspring
What kind of growth do most endothermic animals (mammals and birds) have?
determinate growth
What kind of growth do many plants and ectothermic animals (invertebrates, fish, non-bird reptiles, and amphibians) have?
indeterminate growth
Describe determinate growth
Individual grows until they reach a typical size for the species before reproduction and stops growing after reproduction
After reproduction, all energy is allocated to producing offspring and maintenance
Describe indeterminate growth
Growth slows down at sexual maturity but does not stop
Define fecundity
an individual’s reproductive capacity over a period of time
Typically measured by the number of offspring produced per reproductive episode
What is fecundity of female typically strongly correlated with?
their body size
Usually, the larger the female is, the more offspring she will have
When is an organism considered mature?
At the age of their first reproduction
What is the risk to delaying maturity until the organism is large enough to maximize fecundity?
Death
There is an optimal reproductive age for all organisms and if reproduction is delayed, there are less reproductively fit days left in that organism’s life
How is the optimal age for maturity determined?
by potential reproductive output and probability of survival to a given age
Why is earlier reproduction not an optimal life history strategy?
lower fecundity because the body size will be too small to maximize number of offspring
Why is delayed reproduction not an optimal life history strategy?
Organisms have a limited lifespan, if reproduction is delayed then there are fewer years left to reproduce
If predation risk is high, hypothetically, the age of maturity should be ___?
Younger
T or F: maturation is not affected by the environment of the individual
FALSE
Environment effects chances of survival
Explain the Trinidadian guppie example of how environment effects maturation and survival
Guppies in an environment with high predation reached maturity at an earlier age (86 days) and smaller size (162 mg)
Whereas guppies in an environment with low predation matured at a later age (94 days) and larger size (190 mg)
Explain the Coho salmon example and how there is an optimal age for maturation
Male Coho salmon can be either of 2 morpho-types:
- Hooknoses: return to natal stream after 3 years to reproduce
- significantly larger
- have hooked lower jaw and enlarged teeth - Jacks: return to natal stream after 2 years to reproduce
- much smaller, no hook
While the hooknoses are more prepared to fight each other for first access (and higher success) to the female’s eggs, the smaller jacks hide and sneak in when they can (much earlier than if they had to wait their turn)
This balances out the disadvantages of being smaller.
The disadvantage of waiting until they are larger for the hooknoses is that they spend more time in the open ocean and have less chance of returning to natal stream
Give an example of how offspring survival depends on the environment
When small-large seeds were put into a) wet environment and b) dry environment
Wet: both small and large seeds had higher chance of survival = size had little do with survival
Dry: smaller seeds had very low chances of survival
larger seeds come packed with more resources = higher chance of survival
Give an example of how life history strategies for producing number of offspring can change in response to the environment
Dry environment: reproductive success increased with offspring size so it’s better to make only a few, large offspring
Wet: reproductive success decreases with offspring size so an individual can produce many small offspring
What is a trade-off in the life history of parental care?
between offspring number and parental care
give an example of an optimized trade-off between parental care and offspring number
Magpies and other birds have optimized their egg number and adding/removing eggs reduces reproductive success
If there are too many eggs, the parents cannot care for them all
If there are too few eggs, they will be fledging less birds/reproducing less offspring (fitness is based on how many offspring are produced and survive)
Define parity
The number of reproductive episodes in an individual’s lifetime
What are the 2 kinds of parities?
- iteroparity
2. semelparity
Define semelparity and give an example
organisms reproduce once and typically die shortly after reproduction
ex. Salmon, Agave, Sunflower
Define iteroparity and give an example
Organisms reproduce more than once and gradually decline in physiology afterwards
ex. tapeworms, voles, oak trees
T or F: Semelparity and iteroparity help predict if a lifespan is annual or perennial
FALSE
In what kind of environments is semelparity favoured?
Environments where adult survival after reproduction is uncertain
In what kind of environments is iteroparity favoured?
Environments with variable resources in which individuals can reproduce fewer (or no) offspring in years with low resource availability or more in years with plentiful resources
