In the section "Investigating Life: Birds Do It,Bees Do It",bumblebees pollinated M.lewisii,whereas hummingbirds preferred the red-flowered M.cardinalis.If a hummingbird carries M.cardinalis pollen to M.lewisii,the resulting hybrid offspring are viable.M.lewisii and M.cardinalis are different species because of

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M.lewisii and M.cardinalis are different species because they have pre-zygotic barriers to reproduction, meaning they do not mate or fertilize each other's gametes due to factors such as differences in mating behavior, timing of reproduction, or physical incompatibility. The fact that hybrid offspring can result from pollen transfer by hummingbirds suggests that the two species can produce viable offspring, but they do not do so in their natural habitats because of these barriers. A and E are incorrect because there is no indication that post-zygotic barriers (such as infertility or inviability of hybrids) or asexual reproduction (which would not involve gamete exchange) are involved in defining these species. C and D are also irrelevant because they describe patterns of evolutionary change, not the reproductive isolation that defines species.

In the Section "Investigating Life: Birds Do It,Bees Do It",bumblebees