<P> The base or basal species in a food web are those species without prey and can include autotrophs or saprophytic detritivores (i.e., the community of decomposers in soil, biofilms, and periphyton). Feeding connections in the web are called trophic links . The number of trophic links per consumer is a measure of food web connectance . Food chains are nested within the trophic links of food webs . Food chains are linear (noncyclic) feeding pathways that trace monophagous consumers from a base species up to the top consumer, which is usually a larger predatory carnivore . </P> <P> Linkages connect to nodes in a food web, which are aggregates of biological taxa called trophic species . Trophic species are functional groups that have the same predators and prey in a food web . Common examples of an aggregated node in a food web might include parasites, microbes, decomposers, saprotrophs, consumers, or predators, each containing many species in a web that can otherwise be connected to other trophic species . </P> <P> Food webs have trophic levels and positions . Basal species, such as plants, form the first level and are the resource limited species that feed on no other living creature in the web . Basal species can be autotrophs or detritivores, including "decomposing organic material and its associated microorganisms which we defined as detritus, micro-inorganic material and associated microorganisms (MIP), and vascular plant material ." Most autotrophs capture the sun's energy in chlorophyll, but some autotrophs (the chemolithotrophs) obtain energy by the chemical oxidation of inorganic compounds and can grow in dark environments, such as the sulfur bacterium Thiobacillus, which lives in hot sulfur springs . The top level has top (or apex) predators which no other species kills directly for its food resource needs . The intermediate levels are filled with omnivores that feed on more than one trophic level and cause energy to flow through a number of food pathways starting from a basal species . </P> <P> In the simplest scheme, the first trophic level (level 1) is plants, then herbivores (level 2), and then carnivores (level 3). The trophic level is equal to one more than the chain length, which is the number of links connecting to the base . The base of the food chain (primary producers or detritivores) is set at zero . Ecologists identify feeding relations and organize species into trophic species through extensive gut content analysis of different species . The technique has been improved through the use of stable isotopes to better trace energy flow through the web . It was once thought that omnivory was rare, but recent evidence suggests otherwise . This realization has made trophic classifications more complex . </P>

What is another name for plants in the food web