User:Clean Demeanor/Food chain

A common metric used to quantify food web trophic structure is food chain length. In its simplest form, the length of a chain is the number of links between a trophic consumer and the base of the web. The mean chain length of an entire web is the arithmetic average of the lengths of all chains in the food web. The food chain is an energy source diagram. The food chain begins with a producer, which is eaten by a primary consumer. The primary consumer may be eaten by a secondary consumer, which in turn may be consumed by a tertiary consumer. The tertiary consumers may sometimes become prey to the top predators known as the quaternary consumers. For example, a food chain might start with a green plant as the producer, which is eaten by a snail, the primary consumer. The snail might then be the prey of a secondary consumer such as a frog, which itself may be eaten by a tertiary consumer such as a snake which in turn may be consumed by an eagle.

Length[edit]
The length of a food chain is a continuous variable providing a measure of the passage of energy and an index of ecological structure that increases through the linkages from the lowest to the highest trophic (feeding) levels."Food chains are directional paths of trophic energy or, equivalently, sequences of links that start with basal species, such as producers or fine organic matter, and end with consumer organisms."Food chains are often used in ecological modeling (such as a three-species food chain). They are simplified abstractions of real food webs, but complex in their dynamics and mathematical implications.

Ecologists have formulated and tested hypotheses regarding the nature of ecological patterns associated with food chain length, such as length increasing with ecosystem volume, limited by the reduction of energy at each successive level, or reflecting habitat type.

Producers, such as plants, are organisms that utilize solar or chemical energy to synthesize starch. All food chains must start with a producer. In the deep sea, food chains centered on hydrothermal vents and cold seeps exist in the absence of sunlight. Chemosynthetic bacteria and archaea use hydrogen sulfide and methane from hydrothermal vents and cold seeps as an energy source (just as plants use sunlight) to produce carbohydrates; they form the base of the food chain. Consumers are organisms that eat other organisms. All organisms in a food chain, except the first organism, are consumers.[citation needed]

Food chain length is important because the amount of energy transferred decreases as trophic level increases; generally only ten percent of the total energy at one trophic level is passed to the next, as the remainder is used in the metabolic process. There are usually no more than five tropic levels in a food chain. Humans are able to receive more energy by going back a level in the chain and consuming the food before, for example getting more energy per pound from consuming a salad than an animal which ate lettuce.

Keystone Species
A keystone species is a singular species within an ecosystem that other species within the same ecosystem, or the entire ecosystem itself, rely upon. Keystone species' are so vital for an ecosystem that without their presence, an ecosystem could transform or stop existing entirely.

One way keystone species impact an ecosystem is through their presence in an ecosystem's food web and by extension, a food chain within said ecosystem. For instance, sea otters, a keystone species in pacific coastal regions, prey on sea urchins. Without the presence of sea otters, sea urchins practice destructive grazing on kelp populations which contributes to declines in coastal ecosystems within the northern pacific regions. The presence of sea otters in turn, controls sea urchin populations and helps maintain kelp forests, which are vital for other species within the ecosystem.

A keystone species can appear at any trophic level within a food chain.