Lecture 6: Life Histories

Question 1

Define life history

Answer 1

the lifetime pattern of growth, development, reproduction and survival of an organism that is characteristic of its species

Question 2

Describe the principle of allocation

Answer 2

individuals have limited resources (energy) and resources allocated to one thing cannot also be allocated to another

Question 3

What are the 3 things energy is allocated to?

Answer 3

Growth
maintenance
reproduction

These are considered for both the present and the future

Question 4

What trade-offs are organisms faced with as a result of finite energy resources?

Answer 4

Trade-offs between life history traits related to growth and reproduction because maintenance ‘costs’ are relatively stable throughout an individual’s life

Question 5

When does maintenance take up more energy in an individuals life history?

Answer 5

During early development and growth, once an individual reaches sexual maturity, the energy allocation for maintenance is stable

Question 6

What is included in maintenance?

Answer 6

the basic functions that keep an organism alive such as cellular respiration, metabolism, heart rate, etc.

Question 7

What does growth refer to? (in terms of energy allocation)

Answer 7

adding biomass to oneself

Question 8

What does reproduction refer to? (in terms of energy allocation)

Answer 8

investing biomass in offspring

Question 9

What kind of growth do most endothermic animals (mammals and birds) have?

Answer 9

determinate growth

Question 10

What kind of growth do many plants and ectothermic animals (invertebrates, fish, non-bird reptiles, and amphibians) have?

Answer 10

indeterminate growth

Question 11

Describe determinate growth

Answer 11

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

Question 12

Describe indeterminate growth

Answer 12

Growth slows down at sexual maturity but does not stop

Question 13

Define fecundity

Answer 13

an individual’s reproductive capacity over a period of time

Typically measured by the number of offspring produced per reproductive episode

Question 14

What is fecundity of female typically strongly correlated with?

Answer 14

their body size

Usually, the larger the female is, the more offspring she will have

Question 15

When is an organism considered mature?

Answer 15

At the age of their first reproduction

Question 16

What is the risk to delaying maturity until the organism is large enough to maximize fecundity?

Answer 16

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

Question 17

How is the optimal age for maturity determined?

Answer 17

by potential reproductive output and probability of survival to a given age

Question 18

Why is earlier reproduction not an optimal life history strategy?

Answer 18

lower fecundity because the body size will be too small to maximize number of offspring

Question 19

Why is delayed reproduction not an optimal life history strategy?

Answer 19

Organisms have a limited lifespan, if reproduction is delayed then there are fewer years left to reproduce

Question 20

If predation risk is high, hypothetically, the age of maturity should be ___?

Answer 20

Younger

Question 21

T or F: maturation is not affected by the environment of the individual

Answer 21

FALSE

Environment effects chances of survival

Question 22

Explain the Trinidadian guppie example of how environment effects maturation and survival

Answer 22

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)

Question 23

Explain the Coho salmon example and how there is an optimal age for maturation

Answer 23

Male Coho salmon can be either of 2 morpho-types:

1. Hooknoses: return to natal stream after 3 years to reproduce
   - significantly larger
   - have hooked lower jaw and enlarged teeth
2. 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

Question 24

Give an example of how offspring survival depends on the environment

Answer 24

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

Question 25

Give an example of how life history strategies for producing number of offspring can change in response to the environment

Answer 25

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

Question 26

What is a trade-off in the life history of parental care?

Answer 26

between offspring number and parental care

Question 27

give an example of an optimized trade-off between parental care and offspring number

Answer 27

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)

Question 28

Define parity

Answer 28

The number of reproductive episodes in an individual’s lifetime

Question 29

What are the 2 kinds of parities?

Answer 29

1. iteroparity

2. semelparity

Question 30

Define semelparity and give an example

Answer 30

organisms reproduce once and typically die shortly after reproduction

ex. Salmon, Agave, Sunflower

Question 31

Define iteroparity and give an example

Answer 31

Organisms reproduce more than once and gradually decline in physiology afterwards

ex. tapeworms, voles, oak trees

Question 32

T or F: Semelparity and iteroparity help predict if a lifespan is annual or perennial

Answer 32

FALSE

Question 33

In what kind of environments is semelparity favoured?

Answer 33

Environments where adult survival after reproduction is uncertain

Question 34

In what kind of environments is iteroparity favoured?

Answer 34

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