<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> <P> Food webs are necessarily aggregated and only illustrate a tiny portion of the complexity of real ecosystems . For example, the number of species on the planet are likely in the general order of 10, over 95% of these species consist of microbes and invertebrates, and relatively few have been named or classified by taxonomists . It is explicitly understood that natural systems are' sloppy' and that food web trophic positions simplify the complexity of real systems that sometimes overemphasize many rare interactions . Most studies focus on the larger influences where the bulk of energy transfer occurs . "These omissions and problems are causes for concern, but on present evidence do not present insurmountable difficulties ." </P> <P> There are different kinds or categories of food webs: </P> <Ul> <Li> Source web - one or more node (s), all of their predators, all the food these predators eat, and so on . </Li> <Li> Sink web - one or more node (s), all of their prey, all the food that these prey eat, and so on . </Li> <Li> Community (or connectedness) web - a group of nodes and all the connections of who eats whom . </Li> <Li> Energy flow web - quantified fluxes of energy between nodes along links between a resource and a consumer . </Li> <Li> Paleoecological web - a web that reconstructs ecosystems from the fossil record . </Li> <Li> Functional web - emphasizes the functional significance of certain connections having strong interaction strength and greater bearing on community organization, more so than energy flow pathways . Functional webs have compartments, which are sub-groups in the larger network where there are different densities and strengths of interaction . Functional webs emphasize that "the importance of each population in maintaining the integrity of a community is reflected in its influence on the growth rates of other populations ." </Li> </Ul>

Which organism is the producer in this food web