As natural ecosystems develop over time, they become complex communities with many individuals of a large number of different species (large number of different species)
Agricultural ecosystems are controlled by humans
Farmers select species for particular qualities that make them more productive; as a result the number of species, and the genetic variety of alleles they possess, is reduced to the few that exhibit the desired features
To be economic, the numbers of these desirable species need to be large
Any particular area can only support a certain amount of biomass
If most area is taken up by the one species the farmer considers to be desireable, it follows that there is a smaller area available for all the other species
These other species have to compete for space and resources
Many will not survive this competition
In addition, pesticides are used, resulting in a reduction in species diversity
The species diversity index is therefore low in agricultural ecosystems
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Impact of deforestation
Forests are the natural vegetation over much of the Earth, homing many habitats
Many species are adapted to living in these different habitats, so species diversity is high
Tropical rainforests have the highest species diversity
Deforestation is due to accidental fires, but mainly human activity
Deforestation is the permanent clearing of forests and the conversion of the land to other uses (e.g. agriculture, grazing, housing and reservoirs)
Some forests have been destroyed as a result of man-made pollutants producing acid rain
Biodiversity is lost due to deforestation, as many as 50,000 species are lost each year
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