<Li> the total number of species and food - chain length (including many weak interactors) and </Li> <Li> how community structure, function and stability is determined . </Li> <P> In a pyramid of numbers, the number of consumers at each level decreases significantly, so that a single top consumer, (e.g., a polar bear or a human), will be supported by a much larger number of separate producers . There is usually a maximum of four or five links in a food chain, although food chains in aquatic ecosystems are more often longer than those on land . Eventually, all the energy in a food chain is dispersed as heat . </P> <P> Ecological pyramids place the primary producers at the base . They can depict different numerical properties of ecosystems, including numbers of individuals per unit of area, biomass (g / m), and energy (k cal m yr). The emergent pyramidal arrangement of trophic levels with amounts of energy transfer decreasing as species become further removed from the source of production is one of several patterns that is repeated amongst the planets ecosystems. \ The size of each level in the pyramid generally represents biomass, which can be measured as the dry weight of an organism . Autotrophs may have the highest global proportion of biomass, but they are closely rivaled or surpassed by microbes . </P>

Why do food chains only have 4-5 levels
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