Understanding Food Webs

Though all of these statements are true, the fact that species can occupy different trophic levels depending on what they're eating is not a consequence of the fact that only 10% of all stored energy can ascend from one trophic level to the next. These facts are related, but one does not cause the other.

Food chains only have four or five trophic levels at maximum because the food chain is rapidly depleted of stored energy after each trophic level increase. Logically, producers always have the most biomass of any trophic level because they must produce all of the energy that will sustain the trophic levels above them. Finally, it makes sense that fluctuating population sizes threaten the stability of longer food chains because if even one trophic level suffers a population decrease, then all of the trophic levels above it are potentially jeopardized.

Herbivores are organisms that eat plant material. They are considered as the primary consumers in an ecosystem. An example of an herbivore is a deer, which feeds on flowers and grass.

Biodiversity refers to the different types of life present on Earth. This can refer to the variety of species in an ecosystem, the genetic variation across the planet, and ecosystem variation.

Because energy transfer between trophic levels is only about 10% efficient, it takes several organisms at a lower trophic level to support one organism at a higher trophic level. If each fish (lower level organism) has 10 toxin molecules in its body, and each eagle (higher level organism) eats 10 fish, the eagle now has 100 toxin molecules in its body. Molecules stored in an organism accumulate at higher trophic levels; this accumulation is known as biological magnification.

Saprotrophs are decomposers that are capable of breaking down dead or dying organisms. Because of this, saprotrophs can obtain energy directly from any other organisms in an ecosystem.

Producers are autotrophs, and do not require organic input to create energy. Carnivores, herbivores, and omnivores are loose classifications of organisms based on diet. Carnivores typically feed on heterotrophs, while herbivores generally feed on autotrophs. Omnivores typically feed on both autotrophs and heterotrophs.

Secondary production is defined as the generation of biomass by heterotrophs, mainly through the transfer of organic compounds among trophic levels. Organisms that are primarily responsible for secondary production include animals, protists, and fungi.

Primary production is defined as the synthesis of organic compounds from atmospheric carbon. The main process through which this synthesis occurs is photosynthesis. Primary production is characterized as the generation of biomass in autotrophs. On the other hand, secondary production is described as the generation of biomass in heterotrophs.

Animals are a type of heterotrophs. Heterotrophs are unable to make their own organic materials and so they must consume other organic materials in the form of autotrophs and other heterotrophs.

The energetic hypothesis states that the length of a food chain is limited by the inefficiency of energy transfer along the chain. Only ten percent of energy stored in organic matter at each trophic level is actually converted to organic matter at the next trophic level. This keeps trophic structures in check and limits the abundance of predatory organisms at the top of the trophic structure.

The cascade model, or top-down model, states that there is a unidirectional influence from higher to lower trophic levels. This model follows the idea that predation controls community organization. Predators limit the number of herbivores, and herbivores limit plants, and plants limit the amount of nutrients available in the soil.