zoology biology benno meyer rochow science blog food pyramid Florian Nock

Food Pyramid

It’s not the same as the “food web” or “food chain”

Even well-seasoned biologists, as has happened once at a conference that I attended in Makarska (Croatia), can make mistakes and confuse the two terms “food pyramid” and “food web”. Food webs can be inextricably complicated and contain all possible interactions between various plant and animal species. They not only involve which kinds of food the individuals of a species accept, but also how the food species interact with each other, what roles the enemies, parasites and disease causing organisms play, whether immature and adult individuals have different food preferences and face attacks from different organisms. Even what happens to the dead organisms enters into a food web. Such extraordinarily complex relationships are extremely hard to model, unless one focuses on a food web with very few “players” in it, for example Antarctic springtails (tiny arthropods, which co-exist with less than a handful of other species on the southern continent).

A food pyramid, on the other hand, is surprisingly simple to grasp. As virtually all life depends on green plants, whether they be tiny marine phytoplanktonic algae or gigantic eucalypt red wood trees, these “primary producers” form the basis, the foundation of the food pyramid. It is the green plants that with the aid of their chlorophyll and the light of the sun turn water and carbon-dioxide gas into organic molecules like sugar, starch, and even lipids. Thus, plants constitute the first trophic (feeding) level and provide food directly for the primary consumers, the herbivores, which make up the next trophic level. If the first consumer is a sheep and that is eaten by a wolf, then the wolf is at the third trophic level of the food pyramid (or you could also say the third rung of the food ladder or link of a food chain).

With the so-called top predator at the apex, food pyramids are rarely reaching higher than to the fourth “storey”. And there is a good reason for that. At each trophic level, which basically represents energy availability, only approximately 10% of the ingested biomass is used to build up new body tissue. The rest of 90% is partially for body maintenance and partially lost as waste. To put it differently: to gain 1 kg in weight, a fox would have to consume 10 kg of shrews, which would have eaten 100 kg of field crickets, which would have fed on 1 ton of herbage. Astonishing figures were also obtained by Norwegian researchers, who calculated that per day 2,000 sea-gulls gobble up approximately 6 million krill shrimps – day after day. And now consider the 40 million guano-producing sea birds off the coast of Peru …. You got the answer? Try to work it out without a calculator.

However, what this also shows is that the shorter the food chain, the less energy is wasted. The huge Baleen whales (Blue whales, Humpbacks, Right whales, Fin whales and the like) feed on small shrimp-like crustaceans known as krill and the latter consume nothing but tiny floating phytoplankton: an amazingly low food pyramid, i.e. short food chain with as little as possibly wasted energy initially captured by the plants. And what are the biggest terrestrial animals on Earth again? What were elephants, rhinos, hippopotamuses (and the closest relatives to humans, i.e., the gorillas) feeding on? Plants, at the bottom of the food pyramid.

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Back to the roots!

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2017.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.

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