Behavioural Ecology Flashcards
Behavioural Ecology
Focuses on individual behaviours and how they influence fitness and the interactions with the environment
- Genetic basis
- Two aspects of behaviour: foraging and sexual selection
What decisions does an organism need to make to capture nutrients/energy?
- What and how much to eat?
- How long to forage?
- When to move to a new area?
Needs energy with limited time = trade-offs.
Allocate time and energy to eat AND reproduce
Optimal Foraging Theory
Based on the idea that natural selection will influence how organisms feed and behave while foraging
Assumes that natural selection is likely to favour individuals within a population that are more effective at acquiring limited resources.
Maximize gains: energy/nutrients
Minimize loss: time, risk (predation), and energy spent on foraging
Optimal Foraging Models
Models how an organism feed as an optimizing process which maximizes the net energy gained per unit feeding time
2 models:
- Charnov’s Marginal Value Theorem (patch model)
- Optimal Diet Composition Model
Eating in a patch (graph)
Why does it have this shape?
Cumulative max of food/energy to gain -> there is limited food in a given area so it must flatten out at some point
Eating in a patch (with travel time)
The slope of the line is the rate of energy gain (steeper slope = better energy gain in less time)
Time searching for or travelling to a patch: reduces energy gain the more time spent on travel/search = negative energy gain
If travel time increases, there will be less energy gain overall (diminishing returns)
How does patch quality influence time spent in a patch?
High quality = more time in patch but much higher energy gain
Low quality = less time in patch but low energy gain. Not worth spending much time in low quality patch.
Predictions From the Patch Model
- Foragers should abandon a patch when the rate of energy gain is at a maximal
- Foragers should stay in a rich patch longer than a poor patch
- For patches of the same quality, time spent foraging should increase with time spent travelling to a patch
Diet: Selection of Food Factors
- Abundance: quantity of different food types vary in time and space
- Handling time: how long it takes to handle and consume an item
- Maximum rate of energy intake: how can an organism choose which food to eat to maximize the rate of energy intake
Optimal Diet Model
Foraging Time (T): divided into Searching (Ts) and Handling (Th)
Suppose there are different prey items (Pi)
- Each has different energy value (Ei)
- Each has different handling time (Th)
- i indicates the prey item
Optimal Diet Model: Profitability
(Ei)/(Thi)
Individuals should always choose to eat the most profitable food type if they encounter it.
If encounter a less profitable item, should they eat it?
- Eat it if the energy gain is higher than going elsewhere and wasting energy searching
- Do not eat if energy gain going elsewhere is better despite more searching
Whether an individual should include the less profitable item in its diet depends on:
The search time of the most profitable prey item.
Specialist:
If the most profitable item is common (less search time), then it is more likely to just eat the more profitable item
Generalist:
If the most profitable item is rare (high search time), then it is more likely to eat other items
Food choice depends on a number of factors:
- Net energy gain by eating a food
- How long it takes to handle a food
- How long individuals search for a food
- Relative abundance of each food type
Organisms only include a food source in their diet if their rate of energy intake increases by doing so
Type I Functional Response
Linear graph
Does this graph tell us about the feeding rate of the predator as a function of prey density?
As prey density increases, feed rate increases linearly
What does the slope of the line represent? What would a change in slope signify?
- Efficiency of the predator at capturing prey
- Proportion of prey density consumed
Type I Functional Response: If you know the slope of the relationship and density, how would you calculate attack rate (i.e. number of prey captured per individual per time)?
Slope is the attack rate, it is the predator’s efficiency
Y = mx + b
Feeding rate = attack rate*prey density (NO INTERCEPT, not possible to eat nothing)
What type of organisms would be expected to have a Type I Functional Response?
No handling time like filter feeders (zooplankton, blue whales)
Type II Functional Response
What does the graph say about the feeding rate of the predator as a function of prey density?
Feeding rate will initially increase with prey density but will reach a maximal feeding rate
What might cause the curve to level off at high prey densities?
Predators cannot handle the prey any faster
What type of organisms would be expected to have a Type II Functional Response?
Most common - any organism that requires time to handle prey/food resource
Type III Functional Response
What does the graph say about the feeding rate of the predators as a function of prey density?
Low prey density: feeding rate increase slowly
Medium prey density: feeding rate get faster
High prey density: feeding rate reaches a plateau
At what prey density is the predator feeding rate at a maximum?
High prey density
Type III Functional Response Cont.
What causes this curve to level off at high prey densities?
Handling time
What causes the feeding rate to be lower than the type II functional response at low prey densities?
Prey spatial refuge, predator learning/search image, prey switching
What type of organisms would be expected to have a Type III Functional Response?
Similar to Type II but when prey spatial refuge, predator learning/search image, or prey switching applies
Which functional response type for predators is ideal for prey?
Type III
Chances of survival:
High survival = low prey density
Low survival = high prey density
Ideal Free Distribution
Describes how individuals will distribute themselves among patches
States that:
1. The number of individuals that will aggregate in various patches is proportional to the number of resources in the patch
2. Therefore the payoff for an individual will be equal in all patches
- Assumes that individuals can accurately judge the quality of different habitats and are free to move between patches
Sexual Selection
Selection that depends on the advantage that certain individuals have over others of the same sex and species solely in the respect of reproduction.
Deals with characteristics or behaviours that increase an organism’s ability to reproduce
Sources of fitness differences:
- Survival (viability selection)
- Gamete production (fecundity)
- Mating ability (gamete exchange)
- Fertilizing ability (gamete fusion)
Darwin and Sexual Selection
- Viewed natural selection as operating via phenotypic differences in survival and gamete production
- Introduced sexual selection for phenotypic selection based on differences in mating and fertilizing ability
Sexual selection is used to explain the existence of:
- Secondary sexual characteristics: characteristics of males/females not directly involved in process of reproduction
- Sexual dimorphism: differences b/w male and female i.e antlers vs no antlers
Sexual selection is particularly important under 2 conditions:
- When individuals of one sex compete among themselves for mates (INTRAsexual selection)
- When individuals choose mates of the opposite sex on basis of some particular trait (INTERsexual selection)
Intrasexual Selection
Results from competition among members of the same sex for opportunities to mate or to fertilize gametes
Example: combat/fighting
Intersexual Selection
Results from individuals choosing mates of the opposite sex based on some characteristics
Examples: plumages, showy displays, songs, nest buildings, etc.
Why might individuals make choices based on these characteristics?
“honest signal of good genes”
Males vs. Females
- Reproductive investment
2. Reproductive success
Reproductive Investment
The time and resources expended on each offspring
- Females produce larger gametes
- Typically, females have higher reproductive investment than males
Reproductive Success
Typically, one sex shows much more variation in the reproductive success among individuals then the other does (variation around # of offspring produced per cycle)
Main factor limiting reproductive output differs between sexes:
- High investment sex (usually female): limited primarily by availability of resources for the production of gametes or offspring = low variability
- Low investment sex (usually male): limited primarily by mating opportunities = high variability
If a female is the high investment sex with lower variability in the reproductive output, what strategy should the female take with regard to mate choice?
Invest in high quality mate to obtain high quality offspring
What type of sexual selection is going to be particularly important for high investment females?
Intersexual selection, males must impress the females
If the male is the low investment sex with high variability in reproductive output, what strategy should the males take?
Indiscriminate - increase the quantity of mating opportunities
What type of sexual selection is going to be particularly important for low investment males?
Intrasexual selection to gain access to mates, there is competition between males
Bateman’s Principle
- Reduced investment in gametes and parental care by males increases their potential rate of reproducing, biasing the relative numbers of sexually active males to receptive females at any one time
- This leads to increased intensity of intrasexual competition, greater variance in breeding success, and stronger selection for traits affecting competitive ability in males than in females
- This leads to greater selectivity in the choice of mating partners by females
- Which generates selection pressure in males for traits that display their quality as breeding partners (secondary sexual characteristics)
Some exceptions!
Females can be promiscuous
- Genetic compatibility
- Reduced risk of inbreeding
- Protection against infanticide
Males can be choosey
- Sperm is not always cheap
- Copulation can be demanding
- Sex-role reversal
