Optimal Foraging Theory Flashcards by Emilia Cole

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

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What are the 3 factors involved in optimality?

Decisions - selecting a behavioural option
Currency - what is being maximized?
Constraints - behaviour, morphology, physiology

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What are the 2 main types of foragers

Generalists

Specialists

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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

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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

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What factors do generalist predators look for in prey?

Relative abundant or profitability (i.e: how much time/ energy is spent for energy reward)

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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

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What type of forager is a starfish?

Generalist

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Why do generalists spend less time foraging?

So they have less predation risk

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When would you find specialist predators?

When prey is abundant and predictable

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If prey is abundant and predictable, what type of predator will be present?

Specialist

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If prey fluctuates in abundance, which type of predator will feed on it?

Generalists

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What are the richest food sources?

The species that are protected from other species the most (i.e: have the least predators)

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Name a species that is a specialist

Monophagous koala (eats eucalyptus leaves)
Venus flytrap
Pandas (bamboo)
Nudubranchs/ sea slugs (eat sea aneomes)

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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)

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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.

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What do starlings show about optimal time spent foraging?

Time spent foraging does NOT equal the amount of food collected

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In breeding starlings, what is the currency of foraging in optimal foraging theory?

The maximum rate of delivery of food to nestling

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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