Associated biodiversity and planned biodiversity are the two components of biodiversity. Associated biodiversity is the part of biodiversity that naturally colonizes an agroecosystem thanks to the surrounding environment. It includes all organisms (agriculturally beneficial, neutral and harmful organisms) that are present, whether punctually or continuously, in cultivated fields and adjacent semi-natural habitats.

Farming practices on the farm and neighbouring farms determine the quantity of available resources for associated biodiversity (sources of food and habitats). This part of biodiversity will therefore evolve in time and space. Associated biodiversity can be approached from two angles:

• Functional biodiversity (whether beneficial or harmful) refers to the diversity of the organisms and ecosystem services, or damage, generated;
• Reactive biodiversity is the diversity of responses from species to an environmental change, these responses make the ecosystem able to maintain itself.

Worms are a good illustration of these two angles: some worms decompose dead plant material while others are involved in soil structuration, and they therefore have different roles. Millipedes also participate in structuring the soil, but react differently to the environmental disturbances, thus enriching reactive biodiversity. An agroecosystem rich in functional and especially reactive biodiversity will be more resilient to disturbances than an agroecosystem with little biodiversity.

Taking biodiversity into account in agricultural practices optimizes ecosystem services in an agroecosystem. These alternative practices, acting as a substitute to the use of certain chemical inputs, comply with the principles of agroecology. Conversely, agro-industrial principles seek an optimal control of planned biodiversity and the reduction of associated biodiversity in the agroecosystem. Indeed, associated biodiversity management is complex and a potential source of hazards (possible damage).