Answers to Section XVII. Species Selection and Adaptive Radiation

1. Speciation and extinction
2. Flowering plants undergo higher rates of speciation than do non-flowering plants.  Flowering plants undergo lower rates of extinction than do non-flowering plants.  A non-species selection answer would require that flowers had evolved independently in all the different species that have them; this could be hypothesized to occur through natural selection, but is unlikely
3. A trait such as wings (in bats) or evergrowing incisors (in rodents) could have resulted in species using the environment in a distinctive new way, and provided the basis for a high level of speciation. Alternative hypothesis: small size results in l ow extinction or high speciation.
4. On islands, there are typically few existing species (because of the difficulty in getting to the islands in the first place), so there may be more ecological "opportunities" for species -- that is, the environment is not already being used in all the ways that it could. So if ancestral species disperse to these islands, the result could be that descendent species will evolve to use the environment in many diverse ways, based on the evolution of structural diversity.
5. 1. On islands. 2. After a mass extinction. For both 1. and 2., there are relatively few species, so there are more ecological "opportunities", ancestral species can evolve into a variety of species that use the environment in different ways -- ther e aren't other species present to outcompete them and prevent such evolution from occurring. 3. If a species evolves a "key adaptation" or "key innovation", this means it has evolved a trait that results in it using the environment in a very different w ay from its ancestors and from what other species do; the result is that few other species use the environment in the same way, so there are few competitors, and evolution of a variety of species using the environment in different ways can occur because t here aren't other species using the environment in a way that would outcompete them and prevent such evolution from occurring.
6. mass extinction: many species from many diverse phylogenetic groups die out in a relatively short period of time, leaving no descendents. Adaptive radiation can occur after a mass extinction because there are relatively few species, so there are more ecological "opportunities", ancestral species can evolve into a variety of species that use the environment in different ways -- there aren't other species present to outcompete them and prevent such evolution from occurring.
7. A key innovation is a characteristic whose evolution results in adaptive radiation because the characteristic permits species to use the environment in a new, distinctive way so that it will have few competitors and many ecological "opportunities", or provides the basis for the evolution of more traits that allow such new uses of the environment. Examples include wings, jaw structure in cichlid fish.
8. A phylogenetic test would compare number of species in the group descended from the species that evolved the key innovation with number of species in the most closely related group; the group with the key innovation should have undergone more speciation and therefore should have many more species than the closest relative.
9. 
10. Phylogeny 1 supports the hypothesis best; it shows that venom is derived (since there is an outgroup without venom and an ingroup in which some members are venomous and some are not), and it shows that the group with venom has evolved many more species within the same time that the most related group with non-venom has evolved few (two) species.
11. character y.  Descendents from this ancestor with character y have had high rates of speciation; descendents from the most closely related group (the group within which char z evolved) have had much lower speciation within the same amount of time.  Key innovations lead to high speciation through adaptive radiation, so this fits the pattern predicted if z is a key innovation.  (Note: z is better than x because for the species with x there is one group -- the ones with z -- that have low speciation.  That wouldn't be predicted for a key innovation.  ALL descendents of the ancestor that evolved z have had high speciation).

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