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The Marginal value theorem

 



The correct answer is:

Option 4: P = Optimum patch residence time; Q = Time taken to travel between patches

Explanation:

The Marginal Value Theorem (MVT) is an important concept in behavioral ecology, especially used to describe foraging behavior — how animals decide when to leave a resource patch (like a flower, tree, or field) and move to a new one.

Let’s go step by step 👇

🧠 Basic Idea

When an animal forages, it gains food (energy) from a “patch.”

  • At first, food is abundant — energy gain is high.

  • As time goes on, food becomes harder to find — rate of gain decreases.

So, the animal faces a decision:

“Should I keep searching here or move to another patch?”

⚖️ The Principle (Charnov, 1976)

The Marginal Value Theorem states:

A forager should leave the current patch when the marginal rate of resource gain (the slope of the gain curve at that moment) drops to equal the average rate of gain from the environment (including travel time).

 


According to the Marginal Value Theorem (MVT):

  • The animal gains energy at a decreasing rate while foraging in a patch (the curved line).

  • The straight dashed line represents the average rate of energy gain (total energy gained divided by total time spent, including travel).

  • The tangent point where this line touches the curve represents the optimal point — where the animal should leave the patch.

Thus:

  • Q (x-intercept of the tangent line) = Travel time between patches

  • P (point of tangency on the curve) = Optimum patch residence time

So the animal should stay in the patch until time P, which maximizes energy gain per unit time given travel time Q.


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