Soil food web
At the end of the food chain, decomposers such as bacteria and fungi break down dead plant and animal material into simple nutrients.
Larger macrofauna such as earthworms and insect larva can be removed by hand, but this is impossible for smaller nematodes and soil arthropods.
Early food webs were topological; they were descriptive and provided a nonquantitative picture of consumers, resources and the links between them.
The earliest topological food web, made in 1912, examined the predators and parasites of cotton boll weevil (reviewed by Pimm et al. 1991).
By convention, the dead material flowing back to detritus is not shown, as it would complicate the figure, but it is taken account in any calculations.
[6] Miosis build on interconnected food chains , adding quantitative information on the movement of carbon or other nutrients from producers to consumers.
Hunt et al. (1987) published the first flow web for soil, describing the short grass prairie in Colorado, USA.
In another landmark study, researchers from the Lovinkhoeve Experimental Farm in the Netherlands examined the flow of carbon and illustrated transfer rates with arrows of different thicknesses.
An increase in primary productivity will result in a larger influx of leaf litter into the soil ecosystem, which will provide more resources for bacterial and fungal populations to grow.
The soil environment is also a matrix of different temperatures, moistures and nutrient levels, and many organisms are able to become dormant to withstand difficult times.
[10] For example, aboveground herbivores can overgraze an area and decrease the grass population, but decomposers cannot directly influence the rate of falling plant litter.
They can only indirectly influence the rate of input into their system through nutrient recycling which, by helping plants to grow, eventually creates more litter and detritus to fall.
[18] If the entire soil food web were completely donor controlled, however, bacterivores and fungivores would never greatly affect the bacteria and fungi they consume.
Certain predators or parasites, when added to the soil, can have a large effect on root herbivores and thereby indirectly affect plant fitness.
These results implied that the nematode, as a natural enemy of the ghost moth caterpillar, protected the plant from damage.
While wasps and ladybugs are commonly associated with biological control, parasitic nematodes and predatory mites are also added to the soil to suppress pest populations and preserve crop plants.
In order to use such biological control agents effectively, a knowledge of the local soil food web is important.
Until the last decade, it was believed that soil food webs were relatively simple, with low degrees of connectance and omnivory.
In other areas of ecology, it was realized that the food webs used to make these models were grossly oversimplified[23] and did not represent the complexity of real ecosystems.
[21] Donor controlled food webs may be inherently more stable, because it is difficult for primary consumers to overtax their resources.
[12] Many soil organisms, for example bacteria, can remain dormant through difficult times and reproduce quickly once conditions improve, making them resilient to disturbance.
Litter transformers, mutualists, and ecosystem engineers all have strong impacts on their communities that cannot be characterized as either top-down or bottom-up.
While on the surface this may not seem impressive, the fecal pellets are moister and higher in nutrients than the surrounding soil, which favors colonization by bacteria and fungi.
While the bacterial symbionts of cows live inside the rumen of their stomach, isopods depend on microbes outside their body.
[12] This knowledge is critical to understanding how food webs affect important qualities such as soil fertility.
