Food chain

Examples of terrestrial and marine trophic chains.

The trophic chain (from the Greek trophos, to feed, nourish) describes the process of transferring nutritive substances through the different species of a biological community, in which each one feeds on the previous one and is food for the next one. Also known as the food chain or food chain, it is the current of energy and nutrients that is established between the different species of an ecosystem in relation to their nutrition.

Links

In a trophic chain, each link (trophic level) obtains the energy necessary for life from the immediately previous level; and the producer obtains it through the process of photosynthesis by which light energy is transformed into chemical energy, thanks to the sun, water and mineral salts. In this way, energy flows through the chain in a linear and upward fashion.

In this flow of energy there is a great loss of it in each transfer from one link to another, for which a high level of consumer (example: tertiary consumer) will receive less energy than a low one (example: primary consumer).

Given this condition of energy flow, the length of a string does not go beyond tertiary or quaternary consumer.

Disappearance of a link

A food chain in the strict sense, has several disadvantages in case a link disappears:

1. The level will be overpopulated immediately before, because there are no more predators.
2. Lower levels and contiguous levels will be unbalanced by the lack of competition between that species and that which makes up the missing link.

Elements of the trophic chain

In a biocenosis or biological community there are:

• Primary producers, autotrophs, which using solar energy (photsynthesis) or mineral chemical reactions (quimiosynthesis), obtain the energy necessary to manufacture organic matter from inorganic nutrients that take from the air and soil.
• Consumers, heterotrophos, which produce their components from organic matter from other living beings. Consumer species can be, if we classify them by the mode of exploitation of the resource:
  • Predators and Singers. Agencies that ingest the body of their prey, whole or partly. This activity can be called and is sometimes called predation, but it is more common to see this term used only for carnivorous activity, that is, second order or higher consumers (see below).
  • Decomposers or degraders. The first are those saptrophic organisms, such as bacteria and fungi, which take advantage of waste through external digestion followed by absorption (osmotrophy). The detritivores are some protists and small animals, which devour (fagotrophy) the solid residues found in the soil or in the sediments of the bottom, as well as large animals that feed on corpses, which is to which you can call themselves carcasses.
  • Parasites. Parasites differ from predators who do not kill the animals they feed. They can be predated, in turn, as are the parasites of the great African herbivores, devoured by picabueyes and other birds. They can also have their own parasites, so that each primary parasite can be the basis of a special trophic chain of parasites of different orders. Parasitoids are a special type of parasites, which ends up killing your prey or guest.

Trophic chain.

• If we look at the highest level of the organisms exploited by a species, we will attribute to this an order in the transfer chain, according to the number of terms we have to count from the beginning of the chain:
  • Primary Consumers, phytophages or herbivores. They devour the autotrophic organisms, mainly plants or algae, feed on them in a parasitic way, such as the pulgones, are comensals or symbionts of plants, such as bees, or specialize in devouring their dead remains, such as the oribbean acaros or the milpiés.
  • Side consumers, zophages or carnivores, which feed directly from primary consumers, but also the parasites of herbivores, such as mites VarroaStop the honey bees.
  • Tertiary consumers, organisms that regularly include secondary consumers in their food source. In this link are the dominant animals in ecosystems, over which they influence a measure far greater than their contribution, always scarce, to total biomass. In the case of the great hunter animals, which consume even other predators, they must be called superpredators (or superpredators). In terrestrial environments, for example, birds of prey and large felines and canides. These have always been regarded as a threat to human beings, by directly suffering their predation or by competition for hunting resources, and have often been exterminated systematically and in many cases. In this chapter they would also enter, in addition to the predators, the parasites and eaters of carnivores.
  • There can actually be up to six or seven trophic levels of consumers, seldom more, forming as we have seen not only chains based on predation or direct capture, but on parasitism, mutualism, comensalism or decomposition.

It is noteworthy that in many different species, categories of individuals may have different ways of nourishing themselves, which in some cases would place them at different trophic levels. For example, the flies of the Sarcophagidae family are collectors of nectar and other sugary liquids during their adult life, but while they are cheres (larvae) their typical diet is from corpses (they are among the "worms" that develop during putrefaction). Adult anurans (frogs and toads) are carnivorous, but their larvae, the tadpoles, gnaw on stones to obtain algae. In mosquitoes (family Culicidae), horseflies (family Tabanidae), and others, females are blood-sucking parasites of animals, but males use their biting mouthparts to feed on plant matter, such as sap.

Trophic pyramids

The trophic pyramid or ecological pyramid is a particularly abstract way of describing the circulation of energy in the biocenosis and its composition. It is based on the unequal representation of the different trophic levels in the biological community, because the energy mobilized and the biomass produced per unit of time is always more, the lower the trophic level is.

Pyramid of energy in an aquatic community. In ocher, net production of each level; in blue, breathing; the sum, to the left, is the assimilated energy.

• Energy pyramid: In theory, nothing limits the amount of trophic levels that can sustain a food chain however, there is a problem. Only a part of the energy stored at a trophic level passes to the next level. This is because organisms use much of the energy they consume to carry out their vital processes, such as breathing, movement and reproduction. The rest of the energy is released into the environment in the form of heat: Only 10% of the energy available within a trophic level is transferred to the organisms of the next trophic level. For example a tenth of the solar energy captured by the grass ends up stored in the tissues of the cows and other pasture animals. And only a tenth of that energy, i.e. 10 %, or 1 % in total, is transferred to people who eat cow meat. Therefore the more levels exist between the producer and the consumer of the highest level in the ecosystem, the less the energy left of the original amount.
• Biomass pyramid: the total amount of living tissue within a trophic level is called biomass. Biomass is often expressed in terms of organic matter grams by unitary area. A biomass pyramid represents the amount of potential food available for each trophic level in an ecosystem.
• Number pyramids: ecological pyramids can also be based on the number of individual organisms of each trophic level. In some ecosystems, such as the meadow, the form of the pyramid of numbers is equal to the pyramids of energy and biomass. However, it is not always so. For example, in almost all forests there are less producers than consumers. A tree has a lot of energy and biomass, but it is a single organism. Many insects live in the tree, but have less energy and biomass. For them, the pyramid of numbers of the forest ecosystem, is nothing like a normal pyramid.

This phenomenon is also usually manifested indirectly when the individuals of each level are censused or counted, but here the exceptions are more frequent and have to do with the large differences in size between the organisms and with the different generation times, giving rise to inverted pyramids. Thus, in some ecosystems, the members of a trophic level can be much larger and/or have a longer life cycle than those that depend on them. This is the case that we observe, for example, in many equatorial forests where the primary producers are large trees and the main phytophagous are ants. In such a case the smallest number is presented by the lowest trophic level. The pyramid of numbers is also inverted when the biomasses of consecutive members are similar, but the generation time is much shorter at the lower trophic level; Such a case can occur in aquatic ecosystems where the primary producers are cyanobacteria or nanoprotists.

Relationship between energy and trophic levels

In this succession of stages in which an organism feeds and is eaten, energy flows from one trophic level to another. Green plants or other photosynthesising organisms use solar energy to make carbohydrates for their own needs. Most of this chemical energy is processed in metabolism and lost as heat in respiration. Plants convert the remaining energy into biomass, above ground as woody and herbaceous tissue and below ground as roots. Finally, this material, which is stored energy, is transferred to the second trophic level that comprises grazing herbivores, decomposers, and detritus feeders.

Although most of the energy assimilated in the second trophic level is lost again as heat in respiration, a portion is converted to biomass. At each trophic level, organisms convert less energy into biomass than they receive. Therefore, the more steps that take place between the producer and the final consumer, the less energy that remains available.

There are rarely more than four links, or five levels, in a food web. Over time, all the energy that flows through the trophic levels is lost as heat. The process by which energy loses its ability to do useful work is called entropy.

Plants get their energy directly from the sun through photosynthesis. Animals obtain energy from the food they eat, be it vegetable or animal. Through respiration, both plants and animals take advantage of energy, but dissipate part of it in the form of heat, which passes into the external environment. Therefore, the flow of energy through an ecosystem is unidirectional.

Some microorganisms transform dead organic matter into mineral salts. The salts are used by autotrophs, and autotrophs are eaten by heterotrophs. Afterwards, both the autotrophic and heterotrophic organisms die and their remains are transformed by microorganisms, starting the cycle all over again. Thus, matter circulates in the ecosystem in a cyclical way.