Food pyramid
In ecology, the food pyramid (also called ecological pyramid) is a schematic, graphic representation of the quantitative relationships between the trophic levels of a biocenosis (community) in an ecosystem . The food pyramid is a step pyramid, the steps of which correspond to a trophic level.
The basis of the pyramid are the producers , the autotrophic organisms that build organic substances from inorganic substances. Consumers ( heterotrophic organisms), who are dependent on the intake of organic substances for their nutrition, occupy the following levels : first the first-order consumers ( herbivores ), followed by the various trophic levels of carnivores .
Depending on the ecosystem, there are food chains of different lengths, which is why the food pyramid can have a different number of levels for the respective ecosystem, so there may be no second-order consumers or there may be second, third and fourth-order consumers, i.e. animals that are not only herbivorous , but also feed on other carnivores. The consumers of the top level are referred to as top predators or (derived from English) as top predators, sometimes also referred to as end consumers. The term top predator does not refer to the number of animals captured, but to the position at the top of the food pyramid.
The qualitative basis of a food pyramid is a food chain , i.e. a section of the food web of an ecosystem. The assignment of a certain species to a trophic level is an abstraction that somewhat simplifies the real situation.
When setting up the food pyramid, saprobionts (including scavengers ) and destructors are not included. The most important reason for this is that, unlike herbivores, they have no direct influence on their food base. Even parasites may be disregarded in the rule. The food pyramid does not represent the entire ecosystem, but only a section of it.
Types of food pyramids
Depending on the measured parameter, one can differentiate between different food pyramids ( eltonian number pyramids ):
Biomass
 |
1 common buzzard with an average body weight of 1 kg eats 3000 field mice with a total body weight of 90 kg in one year , which in turn eat 1 ton of cereal grains . |
Here you can see how the biomass decreases from trophic level to trophic level. This is due to the fact that a consumer has to eat many times his body weight in food in the course of his life, as some cannot be used and is excreted again and a large part is breathed in to generate energy , so that less biomass is passed on to the next Trophy level can be passed on.
| Trophy level | Biomass transfer to the next higher level (%) | Detritus loss of biomass (%) | Respiratory losses (%) |
|---|---|---|---|
| Primary producers | 16 | 26th | 58 |
| Primary consumers | 1.8 | 5.2 | 9 |
| Secondary consumers | 0.1 | 0.2 | 1.5 |
| End consumers | 0 | 0.04 | 0.06 |
| Total: | 31.44 | 68.56 |
Note: The figures refer to the biomass of the producers (100%). The detritus biomass can be quickly and completely degraded in a closed ecosystem by the destructive elements ( tropical rainforest ). In an open system, the biomass is deposited in the long term (as digested sludge , peat , coal or petroleum ).
Territory size
In order not to limit the number of prey in an area so much in the long term that it cannot find enough food, a predator must have a large area at a high trophic level with high food requirements. However, the size of the territory for food specialists depends primarily on the density of their prey. Example: area sizes of birds
| Art | Territory size (ha) |
|---|---|
| Eagle | 14,000 |
| Eagle owl | 8,000 |
| hawk | 4,000 |
| Sparrowhawk | 1,000 |
| jay | 25th |
| Great tit | 0.25 |
Note: eagles, eagle owls, hawks and sparrowhawks are usually end users of various food chains.
Offspring number
Due to enemy pressure, the species of lower trophic levels produce more offspring in an ecosystem in equilibrium. Species of higher levels, on the other hand, raise fewer offspring because the size of the territory makes it more difficult to obtain food. However, the number of offspring also depends on other factors such as the intensity of brood care and the development time of the young.
Number of individuals
In some ecosystems the pyramid of the number of individuals corresponds to the biomass pyramid. Example waters: phytoplankton - zooplankton - plankton eater - fish - birds. However, other conditions are also possible: If trees are the basis of the food pyramid, a few individuals are sufficient to feed a large number of insects.
Individual size
As a rule, in predator-prey relationships, the predator is larger than the prey. This results in a pyramid standing on top.
Example: phytoplankton 0.01–0.1 mm - zooplankton 0.8–2 mm - herring 30 cm - tuna 1.5–2.5 m - killer whale 9 m
Remarks
- Food pyramids can change their shape over the course of a year or during the development of an ecosystem ( succession ). In the northern hemisphere, for example, the level of primary producers in the biomass pyramid is greatly reduced in winter, while the level of consumers remains essentially the same, apart from the reductions due to migration in autumn ( migratory birds , reindeer ).
- The quantitative relationships between trophies provide an understanding of the accumulation of substances in the food chain ( biomagnification ) that are not degradable and are hardly excreted by the organisms.
Example: The enrichment of DDT after combating mosquitos in Clear Lake ( California , USA) led to an almost complete destruction of the original 1000 breeding pairs of racing divers . In the 20 years following the actions, the brood population sank to 25 pairs, only one young was raised. After 2 weeks the DDT was no longer detectable in the water. The accumulation in plankton was 250 times that of water - 2000 times for small fish - 10,000 times for whitefish and catfish - 12,000 times for sun bass - 80,000 times for small divers. - Food pyramid: The food pyramid of ecology should not be confused with the food pyramid of nutritional science ( ecotrophology ), as it was published, for example, by the US Department of Agriculture in 1992. It indicates which foods and how much should be consumed per day in order to avoid damage from a poor diet.
- The biomanipulation tries through the control of the food chain, for example, with the trimming of top predators such as pike eutrophic to rehabilitate lakes.
literature
- Frank A. Klötzli: Ecosystems . 3. Edition. Spectrum, Gustav Fischer, Stuttgart / Jena 1993, ISBN 3-8274-0734-6 , pp. 244-249.
Individual evidence
- ↑ Lutz Hafner et al .: Ecology . Schroedel-Verlag, 1978, p. 60
- ^ Robert L. Rudd: Pesticides and the living landscape . University of Wisconsin Press, Madison 1964.
- ^ TH Suchanek et al .: Evaluating and managing a multiply-stressed ecosystem at Clear Lake, California: A holistic ecosystem approach . In: Managing For Healthy Ecosystems: Case Studies . CRC / Lewis Press 2002, pp. 1233-1265.