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📝 Adaptive radiation (12 MCQs)

📖 From Campbell Biology • 1. Evolution and the theme of Biology and Scientific Inquiry • 12 questions available

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What is Adaptive radiation?

Definition:
Adaptive radiation is the rapid evolutionary diversification of a single ancestral lineage into many new species, each adapted to exploit different ecological niches, often occurring when a population colonizes a new environment with diverse habitats or when new adaptive zones become available, leading to the emergence of a variety of forms specialized for specific roles, such as Darwin's finches or Hawaiian honeycreepers.

Working:
Adaptive radiation works through a combination of ecological opportunity (e.g., new islands or mass extinctions) and natural selection, where isolated populations adapt to different resources, leading to reproductive isolation and speciation, and the diversification rate can be described by the equation $\frac{dS}{dt} = \lambda S - \mu S$ , where $S$ is the number of species, $\lambda$ is the speciation rate, and $\mu$ is the extinction rate, and this leads to a burst of speciation events with relatively short divergence times.

Example:
A classic example is the adaptive radiation of Darwin's finches on the Galápagos Islands, where a single ancestral finch species diversified into about 18 species with different beak shapes and sizes, adapted to different food sources such as seeds, insects, and cactus flowers, demonstrating how rapid speciation fills available ecological niches.

Reason:
Adaptive radiation is important because it illustrates the power of natural selection in generating biodiversity, provides insight into the process of speciation, and is key to understanding the origin of species and the filling of ecological roles, with implications for conservation, evolutionary studies, and understanding the impact of environmental changes on species diversity.

Easy

Medium

Hard

📝 All Adaptive radiation MCQs

Q1. A population of finches reaches an island with abundant seeds, insects, and cactus flowers. After many generations, descendant populations specialize on these different resources. Which process best explains this pattern?

A.Independent mutations producing identical species

B.One ancestral population diversifying into multiple ecological niches ✅

C.Random movement of individuals without reproductive consequences

D.Individuals changing traits because they need new foods

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: The pattern represents adaptive radiation because descendants of a common ancestral population diversify into several forms that exploit different ecological resources. Natural selection can favor different heritable traits in separate environments, eventually producing distinct populations.

Q2. Why can several closely related finch species coexist on the same island without all competing for exactly the same food?

A.They necessarily have identical feeding behaviors

B.Each species may occupy a different ecological niche and use different resources ✅

C.Natural selection prevents any competition between species

D.All species reproduce at completely different times

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: Closely related species can coexist when they use resources differently. Differences in beak structure, feeding behavior, or habitat can reduce direct competition, allowing populations to specialize on distinct ecological opportunities.

Q3. Two finch populations descended from the same ancestral population. Population X mainly eats hard seeds, while population Y mainly eats insects. Which conclusion is best supported if their beak shapes also differ consistently?

A.The beak differences must have developed because individual birds consciously adapted

B.The populations may have experienced different selection pressures favoring different heritable beak traits ✅

C.The populations cannot share a common ancestor

D.Different diets always produce immediate genetic changes in individuals

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: Different diets can impose different selection pressures. If beak differences are heritable and associated with feeding success, natural selection can cause the populations to diverge as different beak forms become more common.

Q4. Researchers observe that finches on two islands have similar beak shapes, although genetic evidence indicates they are not especially close relatives. Which explanation is most reasonable?

A.Similar environments may have independently favored similar feeding adaptations ✅

B.The birds must have recently descended from the same individual

C.Beak shape cannot be affected by natural selection

D.Genetic differences always prevent similar adaptations

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Similar environmental conditions can produce similar selective pressures in unrelated or distantly related populations. This is an example of convergent adaptation and does not require recent common ancestry for the traits.

Q5. An ancestral finch population enters an island containing several underused food resources. Generation after generation, individuals with different heritable feeding traits leave more offspring in different habitats. What is the most likely long-term outcome?

A.All descendants become genetically identical

B.The population may diversify into specialized forms adapted to different resources ✅

C.Natural selection stops because resources are abundant

D.Every descendant develops every feeding trait equally

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: When different heritable traits provide advantages in different ecological settings, selection can favor divergent characteristics. Over many generations, this can produce multiple specialized lineages from one ancestral population.

Q6. A drought causes large, hard seeds to become much more common while soft seeds become scarce. In a finch population, birds with deeper, stronger beaks obtain more food and produce more offspring. If the trait is heritable, what should researchers expect after several generations?

A.Average beak depth is likely to increase ✅

B.Average beak depth must decrease because drought is stressful

C.All birds immediately grow deeper beaks during their lifetime

D.Beak depth will remain unchanged because food does not affect fitness

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: The drought changes the selective environment by altering food availability. If deeper beaks are heritable and improve survival or reproduction under these conditions, their frequency should increase over generations.

Q7. Suppose three finch populations occupy different habitats. Population A feeds mainly on hard seeds, B feeds mainly on insects, and C feeds mainly on cactus flowers. Which evidence would provide the strongest support for adaptive radiation?

A.The populations have different body colors only

B.The populations share ancestry but show heritable adaptations associated with their different ecological niches ✅

C.All populations live on the same island

D.The populations have identical feeding structures

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: Adaptive radiation predicts diversification from a common ancestral lineage in response to different ecological opportunities. Evidence linking heritable differences to distinct niches provides stronger support than differences unrelated to resource use.

Q8. A student claims, Finches developed different beaks because each bird needed a particular food source, and the birds intentionally changed their beaks." What is the main error in this reasoning?"

A.It ignores that beaks are involved in feeding

B.It treats adaptation as an intentional response rather than a population-level change in heritable variation across generations ✅

C.It assumes food resources can influence survival

D.It correctly describes how natural selection works

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: Individuals do not intentionally redesign their inherited traits in response to need. Natural selection acts on existing heritable variation, causing advantageous variants to become more common in populations over successive generations.

Q9. Another student argues, If two finch species have different beaks, they cannot have evolved from the same ancestor." Why is this reasoning incorrect?"

A.Common ancestry requires descendants to remain identical

B.Evolution can modify descendant populations differently when they experience different environments and selection pressures ✅

C.Species with common ancestry must always occupy the same niche

D.Natural selection only produces identical traits in related species

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: Common ancestry does not imply identical descendants. Divergent evolution can cause related populations to accumulate different heritable characteristics when ecological conditions favor different traits.

Q10. A graph shows that as generations increase from 0 to 100, the proportion of deep-beaked finches rises from 20% to 70%, while shallow-beaked finches fall from 80% to 30%. During the same period, hard seeds become increasingly abundant. Which interpretation is strongest?

A.Hard seeds probably favored deeper beaks, increasing their representation over generations ✅

B.Hard seeds directly transformed every shallow beak into a deep beak

C.The graph proves that beak depth is never heritable

D.The decline of shallow beaks proves that all shallow-beaked birds died

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: The parallel increase in hard seeds and deep-beaked finches is consistent with selection favoring deeper beaks when hard seeds are abundant. The graph alone does not prove every individual changed or that all shallow-beaked birds died.

Q11. Two finch populations begin with similar beak variation. Island 1 becomes dominated by hard seeds, whereas Island 2 becomes dominated by insects. After many generations, Island 1 has mostly deep-beaked birds and Island 2 mostly narrow-beaked birds. Which combination best explains the result?

A.Different selection pressures acted on heritable variation in separate environments ✅

B.Random mutations guaranteed identical adaptations on both islands

C.Individuals changed beaks according to personal preference and passed those changes directly to offspring

D.Different food resources eliminate the role of reproduction in evolution

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: The two environments impose contrasting selection pressures. If beak variation is heritable and affects feeding success, different variants can increase in frequency on each island, producing divergent adaptations.

Q12. Imagine two isolated finch populations experiencing different food conditions for many generations. Population A contains heritable variation in beak depth, while Population B has almost no heritable beak variation. Which population is more likely to show rapid adaptive divergence in beak depth?

A.Population A, because natural selection requires heritable variation on which selection can act ✅

B.Population B, because lack of variation makes selection stronger

C.Both populations must evolve at exactly the same rate

D.Neither population can respond to environmental differences

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: Population A has the essential raw material for evolutionary change: heritable variation. If different beak forms affect survival or reproduction under changing food conditions, selection can shift trait frequencies and promote divergence.

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