502 CHAPTER 19Phylogenetic studies of Diversity
Zoologists and botanists who study living organisms have long recognized certain
conditions that appear to have fostered high diversity, which is often manifested as
adaptive radiations. For example, many clades have radiated in species richness and
ecological disparity where they found ecological opportunity, that is, many open
ecological niches [71]. Taxa on oceanic islands provide many examples. The Hawai-
ian honeycreepers, derived from an ancestor in the diverse finch family Fringillidae
(rosefinches, goldfinches, and others), are a spectacular example. About 60 species
(of which 18 survive) are almost the only songbirds native to the Hawaiian archipel-
ago, where they faced almost no competition and diversified greatly in diet and in
bill morphology (FIGURE 19.11) [38]. The diversification of many clades accelerated
when they expanded into new geographic regions [46].
Research on both extinct and living organisms has pointed to certain key
adaptations that have enhanced species diversity [3, 51]. These are features that
enable a lineage to interact with the environment in a new way and to use new
resources. During insect evolution, for example, rates of origination and extinction
of families were first accelerated when wings evolved, and later by the evolution of
complete metamorphosis: the distinct larval and pupal stages that characterize the
immensely diverse beetles (Coleoptera), wasps (Hymenoptera), true flies (Diptera),
and moths (Lepidoptera) (see Figure 17.18) [50]. Among the sea urchins (Echinoi-
dea), three orders increased greatly in diversity beginning in the early Mesozoic
(FIGURE 19.12). The order Echinacea evolved stronger jaws that enabled its mem-
bers to use a greater variety of foods. The heart urchins (Atelostomata) and sand
dollars (Gnathostomata) became specialized for burrowing in sand, where they
feed on fine particles of organic sediment. The key adaptations allowing this major
shift of habitat and diet include a flattened form and a variety of highly modified
tube feet that can capture fine particles and transfer them to the mouth.FIGURE 19.11 Adaptive radiation of Hawai-
ian honeycreepers (family Fringillidae). The
species vary greatly in diet, reflected in their
bill shapes. Some feed on insects (short, thin
bill), some on seeds and fruit (thick bill), and
some on nectar (slender, curved bill), match-
ing diverse unrelated birds that fill these
ecological niches on continents. This group
is descended from an Asian ancestor related
to the common rosefinch (Carpodacus
erythrinus), the bird in the center. The Hawai-
ian honeycreepers diversified as the several
islands in the archipelago were sequentially
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