Food chains can be either very simple or very complex but they serve the purpose of showing the flow of energy in various ecosystems and habitat types.

Food webs can be separated into either terrestrial or aquatic, but they can also be separated into brown or soil based or detritus based food webs or "green" or producer based food webs. Green food webs have been fairly well described with plants as the starting point, followed by the herbivores that feed on them and then carnivores that feed on the herbivores and so on.

However; little attention has been given to brown food webs which are the aim of this article.

Basically, in brown food webs, the starting point is with the detritus which is referred to by different names depending on what type of ecosystem one is dealing with.

For instance, in terrestrial systems, it is in the form of leaf litter on the forest floor, while in other terrestrial ecosystems when it is mixed with soil it is referred to as humus. In aquatic ecosystems when it is suspended in water it is called "marine snow".

The organisms that feed on detritus are referred to as decomposers, forming the first trophic level. The consumers of detritus include organisms like fungi and bacteria. Then those organisms become food for others.

These are fed upon by microbivores, which are mainly insects thus making up the next trophic level. The following trophic level is made up of the predators of insects, such as reptiles, birds and mammals, as well as other insect species.

An example of a brown food web is freshwater lakes where the detritus at the bottom is formed from the bodies of dead aquatic organisms and plants that sink to the bottom when they die and then decay.

In these ecosystems, the predators are heavily subsidised by benthic prey. However, brown food webs can also be of a terrestrial nature, where the detritus includes necromass, which consists of frass (insect droppings) and insect carcasses.

In aquatic ecosystems detritus feeders have developed special structures to help them in feeding such as tentacles in order to increase the surface area available to catch the detritus that settles down the water column.

This is known as filter feeding. By using such structures, it acts as a filter. Organisms that are rooted or do not move around much use this method. Another method used is referred to as mucus feeding, where the detritus collects in lumps in the mucus secreted by the organism. Then the lumps of detritus are carried to its mouth using slender finger-like projections called cilla.

Of course many factors, both physical and chemical in nature influence the amount of energy and nutrients that are passed along this type of food web. The physical structure of the area also influences the efficiency of the flow of nutrients in brown food webs.

For example, in an area of closed canopy forest, the forest floor is so sheltered that little moisture reaches it and thus assists in the decomposition process. Also the closed canopy prevents a percentage of sunlight from reaching the forest floor and therefore the temperature stable. Temperature itself also affects this type of food web by influencing the rate of decay of organic material and thus its availability in the food web. The topography of the area is another factor that can be taken into consideration, for instance, if the area is situated on top of a hill, less moisture will be available than in the valley.

Chemical parameters are another type of factor that influence brown food webs. One factor is the amount of nitrogen present in the soil, which is an important nutrient needed for plant growth. Low levels of that in a region mean that less plants or stunted vegetation will grow.

In either case less organic matter will be available to decay and release and make available nutrients to organisms higher up in the food web.

Brown food webs can be considered "dirty" as it deals with dead material and the decomposers that feed on it. But the organisms involved in this type of food web play a very important function by releasing the nutrients locked in the organic matter of dead organisms into the environment for use by plants which are the starting point of green food webs. Just as green food webs, brown food webs are complex and influenced by a variety of physical and chemical parameters, and therefore and require just as much attention as green food webs.