Summary Ecology of Animal Life Histories

Content:

1. Course information
2. Lectures
3. Discussion papers
4. Formulas



Course information
Grade:

70% exam

25% review paper

5% presentation paper discussion



Learning outcomes:

1. Discuss the basic principles of life history theory
2. Provide examples of individual decision making with respect to reproduction and adaptation
and explain how natural selection acts on these decisions
3. Explain how genetics and physiology affect and constrain life history decisions and how
natural selection acts on these underlying mechanisms
4. Explain the link between individual decision making and population dynamics
5. Analyse life history ‘dilemmas’ using the tools provided in the course
6. Develop a coherent review on a specific facet of life history evolution in a specific animal
group



Exam:

- Lectures & papers
- 10 open questions



Lectures
Introduction lecture
Darwinion demon

 Reproduce at birth
Unlimited reproduction
Live forever
 Does not exist => constraints



Life history

,  Study of evolution of fitness components
 Unite & explain diversity of living things
 Framework to understand action of natural selection
 Evolution of life history traits + plasticity -> determine population dynamics


Life history theory => allocation of finite time & energy to fitness components

 Trade-offs
 Optimize combinations of traits -> maximize fitness
 Life history strategy => age and/or specific pattern in timing of events (decisions that have to
be made at each stage)


Life history trait (exam) => any aspect of organism that affects it’s life table & ultimately it’s fitness

o Growth rate
o Size at maturity
o Age at 1st repro
o #offspring
o Size offspring
o (Repro) lifespan



 Extrinsic factors (constraints)
- Ecological constraints
- Predation
- Resources
- Climate
 Intrinsic factors => trade-offs (relationship between traits that constrain other traits)
- Physiological constraints
- Reprodcutive schedule
- Anatomic constraints
- Longevity



Life history pace

o Life history traits covary along fast/slow pace
o Not always clear division/covariance (turtle)
o Lot of variation in traits

,Trade-offs

 Causal – relationship between 2 traits with effects on fitness -> increased investment in 1
trait results in less investment in another trait
 Larger body size -> lower fertility (less offspring/year)
 Larger offspring size -> lower fertility
 Variation most of the times consistent for individual & population level
 Trade-offs across life cycle
- When to reproduce & grow



Phenotypic plasticity => ability of 1 genotype (G) to produce different phenotypes (P) across
different environments (E)

 Clutch size
- Always 2 eggs -> no plasticity (fixed)
- 4-8 eggs -> plasticity
 Reaction norms => range of expression for phenotypic trait across different environments
within 1 genotype (red line)
- Describes plasticity of genotype
- Curve represents range of phenotypes produced by genotype in response to
environment
 Not always adaptive (not always selection for plasticity)
- Not always beneficial
- Can be costly if environment is misread
 Example:
- Poor breeding conditions -> small reproductive effort can result in dramatically
decreased survival
- Good breeding conditions -> effort plays little role in survival




Birth & early development
Offspring => measure of (reproductive) fitness

 Reproductive investment => investment by parent that increases offspring chances of
surviving, at cost of parent’s future survival or reproduction
- Cost of future survival/reproduction = cost of reproduction
- Investment by parent = parental care



Clutch/litter size variation
 Variable across & within species
- Optimization of individual fitness (within species; most offspring at least cost)
- Adjustment to environmental conditions (plasticity)
 Optimal clutch size => produces highest #viable offspring

, - Offspring survival curves can be related to clutch size
- Trade off offspring quantity vs quality -> more investment in offspring reduces quantity
- Survival curves can be related to clutch size: mostly asymmetrical -> low survival rate in
small clutches (thermoregulation), sharp decline survival rate larger clutch sizes
 Lack’s principle (exam) => clutch size of each species is product of natural selection which
favours largest #offspring that parents can provide for
 William’s principle => effort spent on reproduction must be worth the cost, compared to
long-term reproductive fitness of individual
- Refines Lack’s principle
- Given amount of reproductive effort at certain age should make parent’s future
reproductive effort smaller than it would have been without current reproduction
- Difference in future reproductive effort = cost of reproduction
 Litter size affected by:
- Intrinsic factors
- Extrinsic factors
- Parent-offspring conflict & sibling rivalry

↓

Reproductive effort model

 Profit of having numerous offspring 😊 VS costs of reproduction ☹
 Optimum?



Reproductive strategies and predation
Strategies

 Semelparous => death immediately after 1st reproduction
Iteroparous => multiple reproductions in 1 lifetime
 Capital breeders => reproductive event financed with stored capital (whales; fast during
lactation)
- Fast during lactation
- High food availability favours capital breeding (accumulation of capital)
Income breeders => reproductive event financed with current income (humans, dogs)
- Replenish energy stores in between
- High seasonality favours income breeding