Scientists studying a group of related bird species on an island archipelago discover that these species are always more closely related to each other within an island than they are between any two islands. The most likely explanation for this result is that

Question

A.  each bird species evolved different adaptations in allopatry and then colonized the other islands.
B.  one bird species colonized each island and then evolved into distinct species on that island through character displacement.
C.  each bird species became reproductively isolated by living on a different island, then later colonized the other islands and acquired new adaptations.
D.  many ancestral bird species colonized each island.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
 
Gather Content
· What do you already know about adaptive radiation?
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
 
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

B.  one bird species colonized each island and then evolved into distinct species on that island through character displacement.

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses adaptive radiation.
· What type of thinking is required?
        o This question is asking you to weigh and judge evidence, or evaluate, to choose the best of the possible answers.
 
Gather Content
· What do you already know about adaptive radiation?
        o Adaptive radiation can occur different ways.
        o In the classic model of adaptive radiation, a species colonizes several islands, and speciates allopatrically while the populations are separated. Later, the species may colonize the other islands as well.
        o The species may evolve different adaptations while separated (allopatric) or after sharing the same island (sympatric).
        o Two species sharing an island creates pressure to minimize their competition for resources. In the process of character displacement, natural selection favors those individuals that can use resources not used by the other species. Thus the two species will diverge in their favored resources and habitat.
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o The question states that the bird species are always more closely related to each other within an island than they are between any two islands.
        o Therefore, does it make sense that each bird species evolved different adaptations in allopatry and then colonized the other islands? No, because then the closest related species would be found on different islands.
        o Therefore, does it make sense that each bird species became reproductively isolated by living on a different island, then later colonized the other islands and acquired new adaptations? No, because then the closest related species would be found on different islands.
        o Therefore, does it make sense that many ancestral bird species colonized each island? No, because then the species on the same island would not be closely related.
        o Therefore, does it make sense that one bird species colonized each island and then evolved into distinct species on that island through character displacement? Yes. That would fit with the finding that species within an island are most closely related. Character displacement is a mechanism by which species acquires different adaptations when living sympatrically.
 
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o The question required you to weigh and judge evidence, or evaluate, to choose the best of the possible answers.
        o Did you recognize that if species on the same island are most closely related, they likely radiated from a progenitor on that island?