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than 70 phyla of all life from bacteria to vertebrates. Those that are exclusively marine number about 20; 18 are exclusively terrestrial. Twenty-three other phyla contain marine species, whereas only 10 more contain terrestrial species. In short, diversity of the oceans is about double the land’s if it is phyla that we consider. What can we make of this? Looking further, we see that protists and invertebrates predominate in oceans and higher plants predominate on land. That is to say, these environments are vastly different in community composition, making biologically dubious any attempt to compare diversity among them simply by counting taxa. This same difficulty exists on the level of species. The tropics contain more species than do polar regions, but there are hardly any walruses in the Amazon, nor parrots in Antarctica. The species and phylum content of environments is an essential fact of ecology, but simply knowing which environments have more or fewer may be misleading and must be subject to further interpretation.
This leads to an examination of life form, that is, distinguishing species by means of verbs (describing what they do) instead of nouns (indicating what they are); this approach gathers life into functional, ecological groupings not necessarily related to their taxonomy. It is instructive to compare the aquatic and terrestrial realms from this viewpoint. I cannot think of a terrestrial life form that does not have an aquatic equivalent, but counterparts of several marine life forms are so rare on land that cartoonists have to invent them; see, for example, the sit-and-wait, deception-bait gulper-predator in Figure 4–2. The goosefish (Figure 4–3) is one example of this life form that is common in the sea. A life-style that is totally absent from land is filter feeding—an activity practiced by numerous aquatic life forms, from sponges to whales. There may be some distant terrestrial equivalents of filter feeding. I have been reminded by Dr. Eugene Morton of the Smithsonian Institution that swallows and swifts are analogs of filter feeders because they scoop high-flying “planktonic” insects from the air. But these isolated examples do not
FIGURE 4–2 A predatory life form. Cartoon by Gary Larson. This Far Side cartoon is reprinted by permission of Chronicle Features, San Francisco.