#optimal foraging

Predator Prey Model

According to MVT, a forager should leave a patch when:

The marginal value theorem states that a forager should leave a patch when its instantaneous capture or energy-gain rate has declined to the average rate attainable across the environment, including travel time between patches. Early in a patch visit, profitable items are readily found and marginal return is high. Continued exploitation depletes the patch, so each additional unit of time yields less. Once the marginal return equals the habitat-wide average, staying longer would lower long-term intake; departing for a new patch raises it. Maximum total energy within the current patch is not the

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 14

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PREDATOR

Patch residence time is maximized when:

When travel between patches takes a long time, leaving the current patch imposes a large period with no resource intake. The marginal value theorem therefore predicts that a forager should exploit each reached patch more thoroughly and remain there longer before departing. With short travel, frequent movement is less costly and earlier departure can be optimal. Resource-poor patches generally support shorter visits unless travel costs are extreme, and low energetic rewards do not by themselves maximize residence. The relationship arises because the optimal departure tangent is calculated over

Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 10

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The term 'marginal value' in foraging refers to:

The marginal value theorem evaluates the rate at which a forager gains energy while exploiting a depleting patch. Early in a visit, abundant accessible resources produce rapid gains; as the patch is depleted, the instantaneous gain rate falls. Departure is favored when that marginal rate declines to the average rate obtainable across the environment after accounting for travel time between patches. Thus the relevant quantity is energy gained per unit time, not energy per bite or the identity of a least-preferred prey. The theory predicts longer residence in richer patches and when travel is co

Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 10

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What reduces profitability of a prey item?

Prey profitability is commonly measured as energetic value E divided by handling time h. A long handling interval lowers E/h because the predator spends more time capturing, subduing, opening, or consuming the same energy package. High energy raises profitability, while rapid capture tends to shorten handling and increase it. Search time affects the habitat-wide rate of intake and whether lower-ranked prey should be accepted, but it is not part of the basic post-encounter profitability ratio. Natural defenses such as shells, spines, toxins requiring careful processing, or difficult body size c

Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 10

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In OFT, if prey2 is more abundant but less profitable, predator should:

A lower-ranked prey should not be accepted merely because it is abundant. In the classic optimal diet model, acceptance depends on whether its energy per handling time exceeds the average return expected from rejecting it and searching for more profitable prey. If prey 1 remains sufficiently available, consuming prey 2 would occupy handling time that could be spent obtaining a better item, so prey 2 is rejected. The density of prey 2 itself has little effect on this encounter decision because the choice is made after prey 2 has already been found. However, the statement is conditional: if pref

Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 10

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Which model component represents handling time?

In optimal foraging notation, h denotes handling time: the interval required to pursue, subdue, process, and consume a prey item after encounter. Profitability is often expressed as E/h, so the same energetic reward becomes less attractive as handling time increases. S conventionally denotes search time, E the energetic return, and P may represent encounter probability, prey density, or another model-specific parameter. Distinguishing search from handling is important because a predator can change diet breadth when preferred prey become difficult to find even if their handling profitability re

Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 10

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Search time S1 affects decision to eat:

Search time S1 is the expected time needed to locate the more profitable prey type. It affects whether rejecting a lower-ranked prey 2 is worthwhile. When S1 is short, the predator can bypass prey 2 and soon obtain a better return from prey 1. When S1 becomes long because prey 1 is scarce, waiting is costly and prey 2 may enter the optimal diet. By contrast, prey 1 remains worth accepting on encounter because it already has the higher profitability E1/h1. Thus S1 changes the acceptance threshold for prey 2 rather than the decision to consume the preferred prey type itself. The alternatives can

Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 10

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