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As we know, there are unequal numbers of organisms on earth, and
these differences are often related to position in a food chain or food weh.
The most numerous, or voluminous (it is more practical to measure the total
volume of a group of organisms than their individual numbers), are those or-
ganisms that capture and incorporate the primary energy source; they may be
plants or bacteria. This volume is often teferred to as biomass, and in most
communities the biomass of plants is the largest in the system. Because the
transfer of energy from plants to those animals that eat plants is never com-
plete (most energy is lost), the biomass of herbivores is normally only a frac-
tion of the autotroph biomass. In many ecological systems, herbivores ac-
count for only about 10% as much biomass as the autotroph. The same ratio
obtains for the carnivores that eat the herbivores; they add up to perhaps
10% as much biomass as the herbivores.
If we arrange these biomass measures in tabular form, we quickly see
that the trophic groups make up a pyramid. This trophic pyramid explains
why large carnivores are so rare compared to herbivores and why plants are
so abundant compared with any of the animals that eat them.
These and other simple principles are the rules that enable ecologists to
organize their understanding of living organisms. They have been applied
(with less success) to the ancient world as well, in the discipline of paleo-
ecology. The main problem, as noted earlier, is that we can see only the ani-
mals that have left fossils, and thus we have a very biased view of the ancient
world and its ecosystems.
These simple rules are the guiding principles of paleoecology. Just as
particular mixtures of animals and plants in our world define living associa-
tions, or communities, so too should fossils found in recurring associations be
considered ancient communities. The relative abundance of the fossils
should similarly be clues to ancient trophic structure. And most important,
the types of organisms should be clues to ancient environments if we accept
the principle of uniformitarianism, which states that the present is a clue
to the past. In our world, coral reefs are found in tropical latitudes in warm,
clear, shallow seas. Coral reefs of the deep past may have occupied deep, cold
watet, but this is very unlikely, and much information suggests that reefs of
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