Trophic level - Definition


Trophic level - Definition

In ecology, the trophic level is the position that an organism occupies in a food chain - what it eats, and what eats it.

Contents

1 Energy economy

1.1 Components of ecosystems
1.2 Biomass production

2 Trophic levels and biodiversity

3 See also

Energy economy

Wildlife biologists look at a natural "economy of energy" that ultimately rests upon solar power. When they look at an ecosystem there is always some foundational species that directly harvests energy from the sun, for example grass. Next comes along some sort of herbivore that eats the grass, such as the rabbit. Then comes along a carnivore that eats the rabbit, such as a bobcat.

There can be several intermediate links, which means that we can have another layer of predators on top, in this case we have mountain lions which sometimes eat bobcats. Very often this top predator is a keystone species since it affects most of the balances beneath. Since each layer of this system relates to the one below it by absorbing a fraction of the energy it consumed, each one can be understood as resting on the one below---which is called a lower trophic level.

"Every time there is an exchange of energy between one trophic level and another, there is a quite significant loss due to the fundamental laws of thermodynamics. This means so many units of grass can only support a much smaller number of units of rabbits, who can only support a smaller group of bobcats, who can only support a smaller group of cougars. This is why trophic levels are usually portrayed as a triangle, one that places grass on the bottom and cougars on top---the top is always much smaller than the bottom." Each level implies a loss of energy and efficiency and less life that can be supported by the sun. [1]

Components of ecosystems

Ecosystems have four basic components:

The abiotic environment
Producers
Consumers
Decomposers

Producers utilise energy from the sun and nutrients from the abiotic environment (carbon dioxide from the atmosphere or water, other nutrients from the soil or water) to develop by means of photosynthesis. Examples of producers are green plants (those with chlorophyll) and phytoplankton. Since they get their carbon from carbon dioxide rather than from organic carbon, they are called autotrophic organisms. See carbon cycle for more on carbon's role. That's bacteria management!!!

Consumers feed on protoplasm produced from photosynthesis or on other organisms from higher levels. Consumers depend on producers for their energy and synthesis needs. For example, herbivores are primary consumers (and secondary producers). A carnivore that eats only herbivores is a secondary consumer and a tertiary producer.

Decomposers utilise energy from wastes or dead organisms, and so complete the cycle by returning nutrients to the soil or water, and carbon dioxide to the air and water. See water cycle for more on water's role.

Biomass production

Primary production is generation of biomass through photosynthesis. The highest producers of biomass are

tropical rain forests, 2000 g/m²/yr of biomass
swamps and marshes, 2500 g/m²/yr of biomass
algal beds and reefs, 2000 g/m²/yr of biomass
river estuaries, 1800 g/m²/yr of biomass

Others include

Temperate forests, 1200 g/m²/yr of biomass
Cultivated lands; 600 g/m²/yr of biomass

while lowest producers are deserts and frozen areas (less than 200 g/m²/yr of biomass).

In the ocean, phytoplankton is the primary producer (the first level in the food chain or the first trophic level).Phytoplankton converts inorganic carbon into protoplasm.
Phytoplankton is consumed by microscopic animals called zooplankton (these are the second level in the food chain).
Zooplankton is consumed by Crustaceans (the third level in the food chain).
Fish eating crustaceans could constitute the fourth trophic level, while seals consuming the fishes are the fifth.
Trophic levels are very similar on land, with plants being the first trophic level, cows eating the grass being the second, and humans eating the cows being the third.

The amount of biomass produced for a given amount of solar energy is highest at the first level. Less biomass is produced at the second level, for some energy is lost during the conversion. The more trophic levels there are, the more energy is lost through conversion.

Humans are generally primary and secondary consumers, and thus represent usually second and third trophic levels. Most humans are omnivores, which means they consume both plants and animals. Less energy is required to support vegetarian humans than omnivores ones, for there is a significant energy loss during the conversion of grain and vegetables in animal matter.

Trophic levels and biodiversity

Each species in an ecosystem is affected by the other species in that ecosystem. There are very few single prey-single predator relationship. Most preys are consumed by more than one predator, and most predators have more than one prey. Their relationships are also influenced by other environmental factors.
biodiversity (seen along the specific diversity point of view) gives ecosystems stability. When consumers have several differents producers available for food, the disappearance of one is not likely to have a lot of impact. However, for a consumer which has only one or a few producer, a decrease in the producer population is likely to affected it strongly.

Reduction of habitat, hunting and fishing of some species to extinction or near extinction, eradication of insects and pollution, tend to tip the balance of biodiversity. Similarly, in-situ conservation areas need to be carefully designed to maintain a diverse and stable environnement for the extinct species to thrive.

For a systematic treatment of biodiversity within a trophic level, see unified neutral theory of biodiversity.