Optimal Foraging Theory Flashcards
What is optimality theory?
describes which behavioural strategy, after weighing up the costs and benefits, maximises fitness
It aims to describe how traits are optimal for survival
What are the 3 factors involved in optimality?
- Decisions - selecting a behavioural option
- Currency - what is being maximized?
- Constraints - behaviour, morphology, physiology
What are the 2 main types of foragers
Generalists
Specialists
What are generalists?
Predators that have adapted to locate and consume various prey, likely to fluctuate in abundance during their lifetime
Eat variety of prey
What are specialists?
Predators that are adapted to exploit one or several specific food items that have stable populations and are predictably present
Eat one type of prey
What factors do generalist predators look for in prey?
Relative abundant or profitability (i.e: how much time/ energy is spent for energy reward)
Name a species that is a generalist predator?
Starfish
- Prefers mussels but will eat barnacles
Raccoon Cockroaches Crows Brown Bears Foxes Wolves House Fly Coyote Rats
What type of forager is a starfish?
Generalist
Why do generalists spend less time foraging?
So they have less predation risk
When would you find specialist predators?
When prey is abundant and predictable
If prey is abundant and predictable, what type of predator will be present?
Specialist
If prey fluctuates in abundance, which type of predator will feed on it?
Generalists
What are the richest food sources?
The species that are protected from other species the most (i.e: have the least predators)
Name a species that is a specialist
Monophagous koala (eats eucalyptus leaves)
Venus flytrap
Pandas (bamboo)
Nudubranchs/ sea slugs (eat sea aneomes)
Name a species that is a generalist
Racoons (berries, insects, eggs, small mammals)
Whitetail Deer (herbivore - variety of plants and trees)
Coyote (anything with meat)
How are nudibranchs specialists?
They can absorb the cnidocysts of sea aneomes and deposit them into their bodies for defence
The cnidocysts are poisonous and not eaten by anything else.
What do starlings show about optimal time spent foraging?
Time spent foraging does NOT equal the amount of food collected
In breeding starlings, what is the currency of foraging in optimal foraging theory?
The maximum rate of delivery of food to nestling
What is the marginal value theorem (MVT)?
The Marginal Value Theorem is an optimality model that describes the strategy that maximizes gain per unit time, in systems where resources, and thus rate of returns, decrease with time.
Why must there be an optimal foraging time limit?
Because the more time spent foraging = more energy used.
If there is more energy expended than gain from food it will be too costly.
What can the Marginal Value Theorem predict?
how much time an individual will spend searching a particular patch of habitat before moving on to a new one
In general, what are the 2 factors that will cause an individual to stay on a patch longer?
1) if patches are further apart (energy used to travel between)
2) Current patches are poor in resources
What is the MVT equation?
Slope = Food/ Total Time
What is the following equation for:
Slope = Food/ Total Time
Marginal Value Theorem
How do dung flies demonstrate optimality in copulation?
Longer time spent copulating = more eggs fertilised
BUT
Longer time spent copulating = more opportunities missed elsewhere
How do crows demonstrate optimality with whelks?
Crows hunt whelks at low tides
Smash shells on rocks to expose flesh by dropping from a certain height
Zach (1979) observed that crows choose largest whelks only and drop from ~5.2 meters on average
Shows optimal dropping height for energy gained was 5.2 meters
How do shore crabs demonstrate optimality?
They will pick mussel sizes based on which gives them the highest rate of energy vs time spent breaking shells
Larger mussels = lots of energy breaking shell - less profitable in energy yield
Smaller mussels = easy to crack, contain little energy
What are the 3 factors that affect optimal prey choice
- Energy values
- Handling time
- Search time
When hungry and non-hungry sticklebacks are placed in a small tank with different prey densities, what happens?
Very hungry stickleback chose high prey densities
Less hungry sticklebacks chose lower prey densities
Why do less hungry sticklebacks chose lower prey densities?
Because they need to look out for predators
how can larger groups increase individual benefit?
Improves foraging success
Predator protection
Parental care
Altruism
How can larger group sizes cause a cost to individuals?
Increased resource competition
Diseases
Stand out to predators
How do lions show the cost and benefit of group sizes?
larger lion prides increase capture success but means there are more mouths to share food with
What did Caraco et al (1980) find about flock sizes in yellow-eyed juncos? (3)
Flocks sizes change with costs of climate and predation
Fighting increases at higher temperatures in larger flock sizes
Extra scanning increases at large flock sizes in presence of a hawk
What did Wynne-Edwards (1962) suggest about offspring number in tits?
Offspring numbers were adjusted so populations didn’t overuse environmental resources
What is phenotypic plasticity?
the ability of a genotype to give a range of phenotypic expressions under different environmental conditions.
What is an example of phenotypic plasticity?
Physical:
- water fleas that develop a spiny helmet in the presence of predators
Behavioural phenotypic plasticity:
- Alternative mating strategies
Is animal behaviour considered to be phenotypic plasticity?
Yes
What can trigger phenotypic plasticity?
Environmental conditions
Food availability
Mate availability
What does Caraco et al (1980) suggest causes Yellow-Eyed Juncos flock size to change? (2)
- Climate
- Predation
At higher temperatures, what happens to Yellow-Eyed Juncos’ behaviour?
Dominants increase aggression
Means flocks size benefits from being smaller
What are the 3 main types of alternative mating tactics?
- Female mimicry (by males)
- Sneaking behaviours (in males)
- Force Copulation
What is the GUT in MVT
The Giving Up Time
= the interval of time between when the animal last feeds and when it leaves the patch
What is GUD in MVT?
Giving Up Density
= the food density within a patch when the animal chooses to move on to other food patches
If the travelling time decreases, what happens to the slope gradient?
It gets steeper
- Less time travelling = (less energy wasted) more time foraging = more food found
What does MVT describe?
It describes the behavioural strategy that optimizes gain per unit time
