Lecture 9 Flashcards
(22 cards)
First 5 biological traits that influence the schedule of survival or reproduction
- Size at birth (how well an organism is able to survive)
- Rate and pattern of growth –> survive
- Age at sexual maturity –> reproductive success
- Size at sexual maturity –> reproductive success
Second 5 biological traits that influence the schedule of survival or reproduction
- Length of life
- Number, size and sex of offspring
- Age and sex specific reproductive investment
- Mortality schedules –> Individuals die
Principle of allocation
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 of resources to another (finite energy budget
Optimisation
- Natural selection favours those individuals with greatest fitness
- All life history traits affect fitness (survival or fecundity)
Define an appropriate fitness “currency”
- Analyze life history traits in terms of costs
and benefits (see the costs and benefits - Balance between costs and benefits determines the optimal value of a trait
Two currencies for life history traits
- Intrinsic rate of increase of a genotype (r)
- Reproductive value (R0)
Intrinsic rate of a genotype (r)
How fast the number of individuals of that genotype increases over time
Reproductive value (R0)
The number of descendants that a female of a given age (specific cohort) is expected to have over the rest of its life
Currencies for life history traits
- We can measure and and compare which life history strategy is ‘optimal’ given the conditions.
- Natural selection will favour life history strategy with the highest TOTAL reproductive value or intrinsic rate of increase
Why can’t different life history traits vary independently
- Due to principle of allocation
- Resource allocation is a competing processes
- Results in “trade-offs”
2 major types of trade offs
- Allocation of reproductive effort (size vs number)
- Production effort (growth vs reproduction)
Allocation of reproductive effort
- Trade-off between number of offspring and fitness of offspring (survival)
- As the number of offspring increase, the amount of parental energy or care given to each offspring must decrease.
- Larger or better provisioned offspring often have a higher probability of survival
- Tiny offspring could survive better as they don’t need to spend as much energy compared to bigger offspring
Production effort
- What proportion of resources should be devoted to reproduction vs growth?
- When and how often to reproduce?
Number vs size
- Because an organism has limited resources, there are two scenarios for reproducing (Few large offspring, and Many small offspring)
- The same TOTAL amount of energy is invested in reproduction, but done in different ways.
- More babies = smaller babies
Current costs of reproduction
Reproduction uses energy and other reserves
Future costs of reproduction
- May reduce future fecundity
- May reduce probability of parental survival.
Growth vs reproduction
If you allocate resources to reproduction you will have less resources available for growth, potentially decreasing future reproduction
Benefits of maturing earlier and at a smaller size
- A higher probability of survival to maturity because of a shorter duration of the risky developmental juvenile period
- 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 earlier maturation
The benefits of maturing later and at a larger size include
- Larger size at maturity –> increased fecundity
- Lower adult mortality due to larger size
- Higher quality offspring (increased investment per offspring), which increases the probability of survival (reduces mortality rate)
Life history rules of thumb
- If mortality increases in all age classes, reproductive effort increases early in life and age (or size) at maturity decreases
- If mortality increases after a particular age, reproductive effort increases before and decreases after that age
Life history traits are characteristics of:
a. individuals that influence their ability to evolve
b. individuals that influence their schedule of survival and reproduction
c. a species that influence its ability to evolve
d. a species that influence carrying capacity
e. a species that influenced its evolutionary past
b. individuals that influence their schedule of survival and reproduction
he more seeds an individual plant produces in a single reproductive episode, the ________ of each seed.
a. greater the probability of survival
b. smaller the size
c. greater the size
d. more irregular the shape
b. smaller the size
