Many songbirds breed in North America in the spring and summer, and then migrate to Central and South America in the fall. They spend the winter in these warmer areas where they feed and prepare for the spring migration north and another breeding season. Two hypothetical species of sparrow, A and B, overwinter together in mixed flocks in Costa Rica. In spring, species A goes to the east coast of North America, and species B goes to the west coast. What can you say about the isolating mechanisms of these two species?
A. One of the species is probably polyploid, so they are reproductively isolated by genetic incompatibility.
B. Reinforcement must be occurring when they winter together.
C. The two species do not breed in the same area, so they are reproductively isolated by allopatry.
D. They must have strong prezygotic or postzygotic isolating mechanisms in order to spend winter in such close proximity.

Which type of organism is missing from the food web seen in the illustration? primary consumers decomposers primary producers secondary consumers

Where do the respiratory and circulatory systems meet? a. in the heart b. in the muscles c. in the lungs d. in the brain

The accompanying figure shows the percent of selected dna sequences that match between a chimpanzee and other primates. these data support the hypothesis that the figure shows the percentage of selected d n a sequences that match between the chimpanzee and other primates. the human has an almost 98 percent match, the gorilla has an almost 97 percent match, the orangutan has a 96 percent match, the gibbon has an almost 95 percent match, and the old world monkey has an almost 92 percent match. the accompanying figure shows the percent of selected dna sequences that match between a chimpanzee and other primates. these data support the hypothesis that the figure shows the percentage of selected d n a sequences that match between the chimpanzee and other primates. the human has an almost 98 percent match, the gorilla has an almost 97 percent match, the orangutan has a 96 percent match, the gibbon has an almost 95 percent match, and the old world monkey has an almost 92 percent match. chimpanzees and gibbons are the most closely related the chimpanzee's closest surviving relative is humans orangutans are the primates least closely related to chimpanzees old world monkeys and gibbons are the most closely related