The Core Principles

• Immigration Rate: Highest for islands closest to the mainland (near islands), as more species can easily reach them. Immigration rate decreases for distant (far) islands.

• Extinction Rate: Lowest on large islands, which offer more resources and habitats, reducing competition and supporting larger populations. Extinction rate is higher on small islands due to limited resources and higher vulnerability to random events.

Understanding the Curves

• Immigration Curves:

  • Near islands have higher immigration rates at any given number of species, so their curve is positioned higher on the graph.

  • Far islands have lower immigration rates, so their curve is lower.

• Extinction Curves:

  • Large islands have lower extinction rates, so their curve is lower.

  • Small islands have higher extinction rates, so their curve is higher.

Matching Labels to Graph Features

Given the options and the logic above, here’s how the labels typically map:

• A (Immigration curve for near or far): Higher immigration = near; lower immigration = far.

• B (Immigration curve for the other): The opposite of A.

• C (Extinction curve for small or large): Higher extinction = small; lower extinction = large.

• D (Extinction curve for the other): The opposite of C.

Applying the Theory to the Options

From the search results and established theory:

• Large islands have lower extinction rates (extinction curve is lower).

• Small islands have higher extinction rates (extinction curve is higher).

• Near islands have higher immigration rates (immigration curve is higher).

• Far islands have lower immigration rates (immigration curve is lower)12346.

Now, match the options:

1. A-large, B-small, C-near, D-far

2. A-small, B-large, C-far, D-near

3. A-near, B-far, C-small, D-large

4. A-far, B-near, C-large, D-small

The correct mapping, based on the classic model, is:

• A: Near (higher immigration)

• B: Far (lower immigration)

• C: Small (higher extinction)

• D: Large (lower extinction)

This matches Option 3: A-near, B-far, C-small, D-large.

Conclusion

According to MacArthur and Wilson’s equilibrium theory of island biogeography, the correct identification of A, B, C, and D in the model is:

A – near, B – far, C – small, D – large
(Option 3)