Trophic Pyramids (Illustrated!)
A trophic pyramid, used in ecology, is basically a slightly more refined version of a food chain. However, it illustrates the way that energy is lost as it moves through a food chain--that is, as a producer, which gets its energy from sunlight, is eaten by a primary consumer (herbivore), which is in turn eaten by a secondary consumer, and so on up the "trophic levels." Therefore, producers and primary consumers are placed at the broader bottom of the pyramid, while higher-level consumers are placed at the narrower top. Even the pyramid illustration does not show how much energy is lost, though, as the general rule of thumb is that only ten percent of energy makes it from one level to the next. For example, there should be ten times as much volume of primary consumers as there is of secondary consumers. Nonetheless, the trophic pyramid is a useful illustration of the way Asian carp can damage an ecosystem.
An Ideal Trophic Pyramid
What you see on the right is a simplification of what a trophic pyramid in the Mississippi River Basin ought to look like. On the bottom are the phytoplankon, single-celled photosynthetic organisms like algae. They are in turn eaten by zooplankton, which provide food for small fish and invertebrates, which are eaten by panfish like crappie, bullhead and perch, which finally become prey to large game fish like blue catfish and walleye. This is, as I say a, a simplification, and there are small numbers of large filter feeders, like the paddlefish, that feed from the lower trophic levels. Still, the pyramid shows how all the lower levels are necessary to support the big, popular sport fish. (Drawing created and photographed by me, Joey Benevento) The Worst-Case Scenario Asian carp are incredibly specialized filter feeders. They lack stomachs, but constantly process the plankton they take in virtually every time they breathe. Their efficient feeding and large size makes it difficult for smaller plankton eaters to compete with them. Their large size also precludes them being forage for any higher-level consumers. Thus, when they feed on the phytoplankton and zooplankton on the lowest two levels of the trophic pyramid, they form a third level that allows for no further levels above it. Furthermore, since they are filter feeders, they will not take a bait or lure, and cannot be used as sport fish. This pyramid is even more simplified than the previous one, and it would be a gross exaggeration to claim carp are capable of eliminating all other fish in an ecosystem. Still, the diagram illustrates well the fact that Asian carp are not just in competition with other filter feeders. Their ravenous consumption of plankton affects all the organisms in the aquatic ecosystem, siphoning off the flow of nutrients at its source. (Drawing created and photographed by me, Joey Benevento.) |
This site was created by Joey Benevento in Emory University's Domain of One's Own Program as part of an English 212W class with Professor Marc Bousquet.