#prey selection

Predator Prey Model

If a predator prefers prey1 regardless of prey2 abundance, it is due to:

In the optimal diet model, prey are ranked by expected energetic return per unit handling time, E/h. If E1/h1 exceeds E2/h2, prey 1 is the higher-ranked item and should be accepted whenever encountered. This profitability difference explains a persistent preference, but the phrase “regardless of prey2 abundance” reflects an additional prediction: acceptance of a lower-ranked prey generally depends on encounter rates with the more profitable prey, not on how abundant the lower-ranked prey itself is. When prey 1 is sufficiently common, a predator can reject prey 2 and spend search time seeking prey 1; when prey 1 becomes rare, including prey 2 may increase average gain. A long handling time for prey 2 could contribute to its lower ratio but is not the complete criterion because energy content also matters. Equal profitability would not predict a consistent ranking. Thus, the inequality correctly identifies prey 1 as more profitable, while prey 1 encounter rate determines whether strict specialization remains advantageous.

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

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Predator Prey Model

A predator will prefer prey type P1 over P2 if:

Optimal diet theory ranks prey by profitability, usually E_i/h_i, where E_i is usable energy from prey type i and h_i is handling time. Prey type P1 ranks above P2 when E1/th1 exceeds E2/th2, because each unit of post-encounter time devoted to P1 yields more energy. The ratio, not the sum or product of energy and handling time, captures energetic return rate. A predator encountering the higher-ranked type should accept it under the basic model. Whether it also accepts the lower-ranked type depends mainly on the encounter rate with higher-ranked prey: abundant P1 can make rejecting P2 worthwhile, whereas rare P1 raises search costs and favors a broader diet. Abundance of P2 itself does not directly determine acceptance after encounter in the classic contingency model. Real choices can incorporate nutrients, capture probability, toxins, and risk, but these can be represented by adjusting expected gain or effective handling cost. The inequality therefore states a ranking rule rather than a complete prediction of diet composition.

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

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PREDATOR

Predators prefer prey with:

Energy gained per handling time, E/h, is the standard measure of prey profitability after encounter. A high value means the predator obtains a large energetic return while spending relatively little time pursuing, subduing, or processing the item. Optimal diet theory ranks such prey above items with low E/h and predicts their acceptance whenever encountered, assuming capture risk and nutritional constraints are comparable. High search time concerns how frequently prey are found rather than their handling profitability. Equal profitability provides no preference without other differences. Selection for high E/h increases the predator's potential long-term intake rate and leaves more time for additional foraging or other activities. At population level, this mechanism can influence abundance, coexistence, and evolutionary selection. Separating immediate individual effects from longer-term community outcomes gives the selected concept a clearer ecological meaning and avoids relying only on memorized terminology. The relevant evidence concerns process rather than wording alone. Linking the described pattern to energetic returns, fitness consequences, or receiver responses makes the inference biologically coherent and distinguishes it from the competing alternatives.

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

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PREDATOR

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 be separated by asking what changes for each participant and which process causes that change. That approach is more reliable than treating familiar examples as fixed labels, because many interactions shift with environmental context. From an evolutionary perspective, traits persist when their net effects improve inclusive or direct fitness under prevailing conditions. The ecological terminology therefore summarizes both an immediate mechanism and its likely consequences across generations.

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

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PREDATOR

According to OFT, prey1 with E1/h1 > E2/h2 means:

A prey type with larger E/h provides more energy for each unit of handling time and is ranked above a lower-profitability type. On encounter, prey 1 should therefore be accepted because rejecting it to search for prey 2 would replace a superior immediate opportunity with an inferior one. The abundance of prey 1 influences whether the predator should broaden its diet to include prey 2, but it does not normally make the predator reject prey 1. Saying prey 2 is always ignored is too strong: when preferred prey become rare and search time rises, including the lower-ranked type may increase total intake rate. The ranking guarantees acceptance of prey 1, not permanent exclusion of prey 2. This reasoning connects organismal behavior with broader ecological consequences. A mechanism that changes encounter rates, resource use, or reproductive success can scale up to alter population trajectories and the structure of species interactions. The alternatives can be separated by asking what changes for each participant and which process causes that change. That approach is more reliable than treating familiar examples as fixed labels, because many interactions shift with environmental context.

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

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