Earth Science: Ecosystems – Energy flow and food Chains
Food chains, or food networks, describe the feeding relationships between species within a certain ecosystem. The system illustrates the intricate interactions between organisms in terms of consumption and production.
The organisms of an ecosystem that are linked to each other by production and consumption of biomass form food chains that are generally interrelated within often very complex food networks. Simplified, trophic (food) relationships in all ecosystems can be depicted as follows: The sun is always the energy source. Its energy transforms autotrophic organisms, that is, mainly plants and cyanobacteria (primary producers) into chemical energy with the aid of photosynthesis.
This energy is stored very complex food networks. Simplified, trophic (food) relationships in all ecosystems can be depicted as follows: The sun is always the energy source. Its energy transforms autotrophic organisms, that is, mainly plants and cyanobacteria (primary producers) into chemical energy with the aid of photosynthesis. This energy is stored energy-rich sub- stances within their cells.
Subsequently, plant-eating animals feed on the producers. These are the consumers of the first order, which modify the energy taken in and store it in their cells. The next link in the chain are the meat-eaters, which feed on the plant- eaters and which are then designated as consumers of the second order. They are often eaten by other species (consumers of the second order, and so on).
Meat-eating animals that no longer have any natural enemies make up the end of the food chain (apex, or top-level predators). Upon their death other organisms, such as the decomposers, begin to break down these terminal links of the food chain. Decomposers are mainly bacteria and fungi, which disintegrate these dead organisms into low-molecular components.
Primary producers then utilize these particles so that the top predators’ organic substances are returned to the perpetual cycle of nature. Under natural conditions, such pure food chains can exist, however, only in biotopes that are deficient in species. In most ecosystems there is a net of interrelated food chains, called a trophic web. Typical of such trophic webs are numerous cross connections between different organisms.
This arises principally from the fact that animals usually do not feed on a single species alone, but rather have a far wider and richer food spectrum.
FOOD PYRAMID
Within food chains, the weight of consumers increases only by about one tenth of the amount of food consumed, since most of the food serves to generate energy and not to increase mass.
Part of the biomass is also lost as heat and via excretion. Thus, food chains rarely have more than five links, otherwise there would be little left for terminal consumers such as humans.
BASICS
INTERFERENCE If a food chain is interrupted, e.g., by pesticides entering water, the subsequent links in that chain also perish. Broader food webs are less sensitive.