Human influence on biodiversity


The burning of fossil fuels leads to an increase in sulphur dioxide in the atmosphere, which causes acid rain. Acid rain has devastating consequences on biodiversity as many plants and animal species cannot survive these conditions. As the rain becomes more acidic, biodiversity decreases.


Sewage must be treated before it is released into the environment. If untreated sewage is released into rivers it provides food for bacteria, which will increase in numbers and use up the oxygen supply of the water. This results in a decrease in species diversity since only species that can live in areas with low oxygen concentrations will survive.


Deforestation describes the removal of vast areas of natural forest for the benefit of humans. This can result in habitat destruction, a reduction in soil fertility and poor soil structure leading to a decrease in biodiversity.


Desertification describes the conversion of large areas of land to desert as a result of human activity. This decreases biodiversity as only species that can survive in a dry habitat will remain in these areas.


Grazing is carried out by animals such as deer and sheep that feed on a variety of plant species. At low grazing intensities the biodiversity of grassland is low because a few species of plants such as grasses are able to outcompete the others and dominate the ecosystem. As the grazing intensity increases the biodiversity increases as the dominant plant species are kept in check by grazers and the weaker competitors are therefore also able to grow. At very high grazing intensities the biodiversity decreases because only plants with adaptations to tolerate the effects of grazing are able to survive.

Only plants with adaptations can survive a very high grazing intensity. Bar chart with number of plant species on the y axis and grazing intensity on the x axis. Bar one is low grazing intensity, it goes one third of the way up the y axis.  The second is high intensity it goes two thirds of the way up the y axis and third is very high intensity, it goes halfway up the y axis.


Chemical pesticides are substances that are sprayed onto crop plants to kill organisms such as weeds, insects and fungi that can reduce crop growth.

Weeds compete with the crop plants for resources, fungi can cause plant diseases and insects may consume the plants and damage them.

Pesticides can have adverse effects on the environment if they are not biodegradable and they can accumulate in the bodies of organisms over time. Due to the animals at each level in a food chain eating large numbers of the organisms from the level below in the food chain, the concentration of pesticide in the bodies of organisms increases at higher levels of food chains. This can result in the toxicity of the pollutant reaching fatal levels in the organisms at the top of the food chain.

Pyramid showing how the concentration of pesticide rises during a food chain. 5 tiers, widest at bottom.  Tier 1: pesticide in water 0.000003 ppm. Tier 2: pesticide in algae 0.04ppm. Tier 3: pesticide in mayfly nymph 0.5ppm. Tier 4: pesticide in sunfish 2ppm and finally tier 5: pesticide in great blue heron 25ppm.