Usually ecosystems increase in the number of different species as they develop and increase the index of diversity.Agricultural ecosystems have reduced biodiversity and a reduced gene pool. Most of the area is taken up by few species so other species compete for less of space and many do not survive. In addition, pesticides and herbicides artificially exclude other species, so the index of diversity is low.Practices that reduce species diversity include:
- removal of hedgerows
- filling in ponds
- creating monocultures
- overgrazing of land
- use of pesticides and fertilisers
- pollution with effluent silage stores and slurry tanks
- absence of crop rotation
- lack of intercropping and undersowing