Evolutionary ecology
Lecture 1: Introduction (28/02)
Ecological perspective
Beak shapes are adapted to eat different things; different morphology (in beak and jaw) in fish that
suck and bite; unrelated species in different lakes that are very similar (convergent evolution)
Evolutionary perspective
Light conditions cause that fish cannot recognize other species; high transmission in blue
wavelength; the wider the spectrum (see more colors, less turbid water), the more species
→ Understanding of interactions with other organisms and environment (ecology) critical for
understanding evolution; species and interactions are the outcome of evolution → ecology and
evolution go hand in hand
Lecture 2: Optimality (28/02)
Tinbergen’s four questions:
- Ultimate questions (why?): natural selection
1. Function (adaptation)
2. Evolutionary history (phylogeny)
- Proximate questions (how?):
1. Causation (mechanisms)
2. Individual development (ontogeny)
Why did butterflies migrate and how did migration evolve → ultimate
How do butterflies navigate and how do they know when to migrate → proximate
Ultimate question is what sets evolutionary biology apart from all other sciences; in other sciences,
proximate questions most important
Ultimate (why) questions: natural selection
- Intraspecific competition (struggle for existence)
- Differences in fitness (capacity to survive and reproduce; contribution of genes to gene pool;
Darwinian fitness);
- Fitness differences must be heritable
Expectation: population composition changes toward
improved fitness
X and Y are traits → different combinations of these traits
yield different fitness → optimal combination is highest peak
(highest fitness)
Optimality paradigm: explain adaptations in terms of fitness
maximization; proxy used (measuring fitness is difficult);
offspring produced
Example: optimal flight speed in birds
Power (BMR) per unit time: basal metabolic rate: y axis
Velocity: x axis
→ the higher the velocity, the higher the power (except for very low velocity)
, - Hypothesis 1: birds minimize
power needed to fly → flight
speed is at lowest point of
power
→ true flight speed is higher
→ hypothesis rejected
- Hypothesis 2: birds minimize
energy per distance
Minimize the slope (find
tangent)
Optimality approach:
1. Specify available options
(strategies); what is option
set
- Information: What is
known?
- Constraints: What is possible? → include all possible velocities of an animal
2. Derive fitness consequences
- Currency: proxy for fitness (in example: fitness currency is energy tradeoff)
- Trade-offs (some animals invest more in reproduction; survival vs reproduction)
- Cost-benefit analysis (first be aware of currency and trade-offs)
3. Determine optimal solution
4. Compare observed behavior with optimal behavior
5. Improve optimality model
Research process: verbal/formal model is based on a lot of assumptions → data can match or not
match expectations, causing hypothesis to be or not to be rejected
Copulation duration in dungflies
- Dungflies copulate for 40 minutes; 5 minutes would be sufficient
- What are the options → all possible copulation times
- What are benefits/costs or
longer copulations?
1. Benefits: higher
fertilization success
(diminishing returns)
2. Costs: time lost for
finding and fertilizing
other females
(opportunity costs);
average search time is 160
min
- How do we define fitness?
, Hypothesis: fitness = eggs fertilized per time invested (time copulating + time searching)
→ make graph in excel → optimal copulation time indeed t = 40 min
Good fit between predictions and observations
Time required to find new opportunity (time in patch): time on negative axis
Yield per time corresponds to the slope of green line → find maximal slope
Marginal value theorem: whenever “yield per time” is maximized, the optimal time can be found
graphically
Foraging behavior of honeybees
Flight becomes more expensive when bees carry pollen
- How many flowers to visit before returning to hive? (how much energy is contributed to the
hive net); cost becomes more important the longer the flight time between flowers
- Currency: maximizing delivery rate to the hive?
Result: bees go past way less flowers → optimality model failed
Options for failing model
- Behavior not yet optimal; evolution has not caught up yet
- Evolutionary problem not adequately represented (flight time also affects chances to be
caught by predators, not only energy expenditure)
- Currency chosen no adequate representation of fitness
- Constraints are not adequately represented; option set is different from what we assumed
Plausible proxies for fitness
Maximization of energetic efficiency does
correspond to foraging behavior in bees → do not maximize delivery
rate but energy efficiency; currency chosen was not an adequate
representation of fitness
Physiological and ecological constraints
Duration of low-water period is of effect on the food consumption;
- There is a maximum food intake
- There is a maximum on how much food can be digested per
unit time; increases when amount of time they have to eat
increases
Lecture 1: Introduction (28/02)
Ecological perspective
Beak shapes are adapted to eat different things; different morphology (in beak and jaw) in fish that
suck and bite; unrelated species in different lakes that are very similar (convergent evolution)
Evolutionary perspective
Light conditions cause that fish cannot recognize other species; high transmission in blue
wavelength; the wider the spectrum (see more colors, less turbid water), the more species
→ Understanding of interactions with other organisms and environment (ecology) critical for
understanding evolution; species and interactions are the outcome of evolution → ecology and
evolution go hand in hand
Lecture 2: Optimality (28/02)
Tinbergen’s four questions:
- Ultimate questions (why?): natural selection
1. Function (adaptation)
2. Evolutionary history (phylogeny)
- Proximate questions (how?):
1. Causation (mechanisms)
2. Individual development (ontogeny)
Why did butterflies migrate and how did migration evolve → ultimate
How do butterflies navigate and how do they know when to migrate → proximate
Ultimate question is what sets evolutionary biology apart from all other sciences; in other sciences,
proximate questions most important
Ultimate (why) questions: natural selection
- Intraspecific competition (struggle for existence)
- Differences in fitness (capacity to survive and reproduce; contribution of genes to gene pool;
Darwinian fitness);
- Fitness differences must be heritable
Expectation: population composition changes toward
improved fitness
X and Y are traits → different combinations of these traits
yield different fitness → optimal combination is highest peak
(highest fitness)
Optimality paradigm: explain adaptations in terms of fitness
maximization; proxy used (measuring fitness is difficult);
offspring produced
Example: optimal flight speed in birds
Power (BMR) per unit time: basal metabolic rate: y axis
Velocity: x axis
→ the higher the velocity, the higher the power (except for very low velocity)
, - Hypothesis 1: birds minimize
power needed to fly → flight
speed is at lowest point of
power
→ true flight speed is higher
→ hypothesis rejected
- Hypothesis 2: birds minimize
energy per distance
Minimize the slope (find
tangent)
Optimality approach:
1. Specify available options
(strategies); what is option
set
- Information: What is
known?
- Constraints: What is possible? → include all possible velocities of an animal
2. Derive fitness consequences
- Currency: proxy for fitness (in example: fitness currency is energy tradeoff)
- Trade-offs (some animals invest more in reproduction; survival vs reproduction)
- Cost-benefit analysis (first be aware of currency and trade-offs)
3. Determine optimal solution
4. Compare observed behavior with optimal behavior
5. Improve optimality model
Research process: verbal/formal model is based on a lot of assumptions → data can match or not
match expectations, causing hypothesis to be or not to be rejected
Copulation duration in dungflies
- Dungflies copulate for 40 minutes; 5 minutes would be sufficient
- What are the options → all possible copulation times
- What are benefits/costs or
longer copulations?
1. Benefits: higher
fertilization success
(diminishing returns)
2. Costs: time lost for
finding and fertilizing
other females
(opportunity costs);
average search time is 160
min
- How do we define fitness?
, Hypothesis: fitness = eggs fertilized per time invested (time copulating + time searching)
→ make graph in excel → optimal copulation time indeed t = 40 min
Good fit between predictions and observations
Time required to find new opportunity (time in patch): time on negative axis
Yield per time corresponds to the slope of green line → find maximal slope
Marginal value theorem: whenever “yield per time” is maximized, the optimal time can be found
graphically
Foraging behavior of honeybees
Flight becomes more expensive when bees carry pollen
- How many flowers to visit before returning to hive? (how much energy is contributed to the
hive net); cost becomes more important the longer the flight time between flowers
- Currency: maximizing delivery rate to the hive?
Result: bees go past way less flowers → optimality model failed
Options for failing model
- Behavior not yet optimal; evolution has not caught up yet
- Evolutionary problem not adequately represented (flight time also affects chances to be
caught by predators, not only energy expenditure)
- Currency chosen no adequate representation of fitness
- Constraints are not adequately represented; option set is different from what we assumed
Plausible proxies for fitness
Maximization of energetic efficiency does
correspond to foraging behavior in bees → do not maximize delivery
rate but energy efficiency; currency chosen was not an adequate
representation of fitness
Physiological and ecological constraints
Duration of low-water period is of effect on the food consumption;
- There is a maximum food intake
- There is a maximum on how much food can be digested per
unit time; increases when amount of time they have to eat
increases
