Individual Ecology - Life History

Question 1

Life History Theory

Answer 1

Questions regarding the nature and evolution of life history traits:
What are these traits?
How do these traits vary?
Why do these traits vary?
How are different life history traits interrelated?
How does variation in life history traits influence the distribution and abundance of organisms?

Question 2

Life History Traits

Answer 2

Biological traits that influence the schedule of survival or reproduction
Examples:
- Size at birth
- Rate and pattern of growth
- Age/size at sexual maturity
- Length of life
- Number, size, and sex of offspring
- Age and sex-specific reproductive investment
- Mortality schedules

Question 3

Principle of Allocation

Answer 3

If an organism can acquire a limited amount of resources/energy for which two different processes compete, then an increase in resources to one must result in an equal decrease in resources for the other.

Finite energy budget!

Question 4

Optimization

Answer 4

Natural selection favours those individuals with the greatest fitness

• All life-history traits affect fitness (survival or fecundity/fertility)
• Define an appropriate fitness “currency”
• > analyze life-history traits in terms of costs and benefits
• > balance between costs and benefits determines the optimal value of a trait!!

Question 5

Currencies for Life History Traits

Answer 5

1. Intrinsic Rate of Increase of a genotype (r): how fast the number of individuals of that genotype increases over time
2. Reproductive value (R0): the number of descendants that a female of a given age (specific cohort) is expected to have the rest of its life

Question 6

Can measure these currencies and compare which life history strategy is:

Answer 6

“optimal” given the conditions

Question 7

Natural selection will favour the life history strategy with the:

Answer 7

HIGHEST total reproductive value or intrinsic rate of increase

Question 8

Different traits cannot vary independently because:

Answer 8

of the Principle of Allocation

• Resource allocation = competing processes
• Results in “trade-offs”

Question 9

2 Major Types of Trade-offs

Answer 9

1. Allocation of reproductive effort (size vs. number):
   - How should resources devoted to reproduction be divided among individual offspring?
   - Many small or few large?
2. Production effort (growth vs. reproduction):
   - What proportion of resources should be devoted to reproduction vs. growth?
   - When and how often to reproduce?

Question 10

Allocation of Reproductive Effort

Answer 10

The trade-off between number of offspring and fitness of offspring (survival)

• As the number of offspring increases, the amount of paternal energy or care given to each offspring must decrease
• Larger or better provision offspring often have a higher probability of survival

Question 11

Costs of Reproduction

Answer 11

Current costs: reproduction uses energy and other reserves

Future costs: may reduce future fecundity, may reduce probability of parental survival

Question 12

Trade-off: Number vs. Size

Answer 12

Because an organism has limited resources, when reproducing there are two scenarios for reproducing:

• few large offspring
• many small offspring

The same TOTAL amount of energy is invested in reproduction, but it is done in different ways

Question 13

Growth vs. Reproduction

Answer 13

If resources are allocated to reproduction, there will be fewer resources available for growth. This may potentially decrease future reproduction.

Question 14

The benefits of maturing earlier and at a smaller size include:

Answer 14

1. A higher probability of survival to maturity because of a shorter duration of the risky developmental juvenile period
2. A shorter generation time which allows parents to produce offspring that are born earlier and that start to reproduce sooner
   * Thus high adult mortality should favour the evolution of early maturation

Question 15

The benefits of maturing later and at a larger size include:

Answer 15

1. Larger size at maturity = increased fecundity
2. Lower adult mortality due to larger size
3. Higher quality offspring (increased investment per offspring) which increases the probability of survival

Question 16

Life History – “Rules of Thumb”

Answer 16

1. If mortality increases in all age classes, reproductive effort increases early in life and age (or size) at maturity decreases
2. if mortality increases after a particular age, reproductive effort increases before and decreases after that age

Question 17

Because organisms have finite resources, fundamental trade-offs arise. Two important ones are:

Answer 17

1. Growth vs. Reproduction

2. Size vs. Number

Question 18

The optimal life history strategy depends on:

Answer 18

the local conditions