<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> <P> Pyramid structure can vary across ecosystems and across time . In some instances biomass pyramids can be inverted . This pattern is often identified in aquatic and coral reef ecosystems . The pattern of biomass inversion is attributed to different sizes of producers . Aquatic communities are often dominated by producers that are smaller than the consumers that have high growth rates . Aquatic producers, such as planktonic algae or aquatic plants, lack the large accumulation of secondary growth as exists in the woody trees of terrestrial ecosystems . However, they are able to reproduce quickly enough to support a larger biomass of grazers . This inverts the pyramid . Primary consumers have longer lifespans and slower growth rates that accumulates more biomass than the producers they consume . Phytoplankton live just a few days, whereas the zooplankton eating the phytoplankton live for several weeks and the fish eating the zooplankton live for several consecutive years . Aquatic predators also tend to have a lower death rate than the smaller consumers, which contributes to the inverted pyramidal pattern . Population structure, migration rates, and environmental refuge for prey are other possible causes for pyramids with biomass inverted . Energy pyramids, however, will always have an upright pyramid shape if all sources of food energy are included and this is dictated by the second law of thermodynamics . </P> <P> Many of the Earth's elements and minerals (or mineral nutrients) are contained within the tissues and diets of organisms . Hence, mineral and nutrient cycles trace food web energy pathways . Ecologists employ stoichiometry to analyze the ratios of the main elements found in all organisms: carbon (C), nitrogen (N), phosphorus (P). There is a large transitional difference between many terrestrial and aquatic systems as C:P and C: N ratios are much higher in terrestrial systems while N:P ratios are equal between the two systems . Mineral nutrients are the material resources that organisms need for growth, development, and vitality . Food webs depict the pathways of mineral nutrient cycling as they flow through organisms . Most of the primary production in an ecosystem is not consumed, but is recycled by detritus back into useful nutrients . Many of the Earth's microorganisms are involved in the formation of minerals in a process called biomineralization . Bacteria that live in detrital sediments create and cycle nutrients and biominerals . Food web models and nutrient cycles have traditionally been treated separately, but there is a strong functional connection between the two in terms of stability, flux, sources, sinks, and recycling of mineral nutrients . </P>

In a food web what organism must be in greatest abundance in order for the food web to be stable