Question:
Ecologists have studied the distributions of birds on archipelagos. Some studies found an interesting "checkerboard" pattern within island groups. Sister species were never present on the same island, even when the islands were very close to each other. Which one of the following processes best explains this checkerboard pattern?
Ecologists have studied the distributions of birds on archipelagos. Some studies found an interesting "checkerboard" pattern within island groups. Sister species were never present on the same island, even when the islands were very close to each other. Which one of the following processes best explains this checkerboard pattern?
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Sister species share very similar resource needs, so placing two of them on one island triggers competitive exclusion.
Updated On: Jul 20, 2026
- Mutualism
- Competition
- Predation
- Commensalism
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The Correct Option is B
Solution and Explanation
Step 1: Understand the checkerboard pattern.
Across an island group, ecologists found that sister species (very closely related species that use similar resources) are never found together on the same island, even when islands sit right next to each other. Instead, each island tends to hold only one of the two related species at a time.
Step 2: Ask what process would produce this kind of mutual exclusion.
Sister species usually have very similar ecological needs, food, nesting sites, and habitat structure, because they evolved from a shared ancestor only recently. When two such similar species end up on the same island, they are forced to fight over the same limited resources.
Step 3: Apply the principle of competitive exclusion.
The competitive exclusion principle states that two species with near-identical ecological requirements cannot coexist indefinitely in the same place; one will eventually outcompete and displace the other. Over time, this leads to islands being occupied by only one of the two competing sister species, exactly the checkerboard pattern observed, first documented in detail by Jared Diamond in his studies of New Guinea bird communities.
Step 4: Rule out the other options.
Mutualism is a relationship where both species benefit from each other's presence, which would tend to bring species together, not keep them apart.
Predation involves one species eating another; sister species living similar lifestyles are rarely each other's predators.
Commensalism benefits one species while the other is unaffected, and again does not explain a strict, mutual absence from the same island.
Final Answer:
Only strong competition between ecologically similar sister species, leading to competitive exclusion, explains why they never share an island.
\[ \boxed{\text{Competition}} \]
Across an island group, ecologists found that sister species (very closely related species that use similar resources) are never found together on the same island, even when islands sit right next to each other. Instead, each island tends to hold only one of the two related species at a time.
Step 2: Ask what process would produce this kind of mutual exclusion.
Sister species usually have very similar ecological needs, food, nesting sites, and habitat structure, because they evolved from a shared ancestor only recently. When two such similar species end up on the same island, they are forced to fight over the same limited resources.
Step 3: Apply the principle of competitive exclusion.
The competitive exclusion principle states that two species with near-identical ecological requirements cannot coexist indefinitely in the same place; one will eventually outcompete and displace the other. Over time, this leads to islands being occupied by only one of the two competing sister species, exactly the checkerboard pattern observed, first documented in detail by Jared Diamond in his studies of New Guinea bird communities.
Step 4: Rule out the other options.
Mutualism is a relationship where both species benefit from each other's presence, which would tend to bring species together, not keep them apart.
Predation involves one species eating another; sister species living similar lifestyles are rarely each other's predators.
Commensalism benefits one species while the other is unaffected, and again does not explain a strict, mutual absence from the same island.
Final Answer:
Only strong competition between ecologically similar sister species, leading to competitive exclusion, explains why they never share an island.
\[ \boxed{\text{Competition}} \]
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