How do changes affect the balance of an ecosystem?
How do physical and human forces affect ecosystem balance?
Natural events, such as extreme weather, flooding and natural hazards can disturb the balance of ecosystems. For example, in 1987, a great storm resulted in the felling of 15 million trees in England. This led to a considerable decline in primary and secondary consumers in the food chain. Consumer species have since returned following secondary forest growth. This is an example of ecosystem resilience.
Human actions can also significantly upset the natural balance in an ecosystem. A range of human activities in the Amazon rainforest has had a detrimental effect on the ecosystem. The removal of forest exposes the topsoil, which is then eroded, making it impossible for the rainforest to recover.
Human-induced climate change has the potential to threaten the balance of ecosystems in many places. Changes in rainfall and temperature in the south of England could lead to a significant change in ecosystems such as Epping Forest.
How does the loss or gain of one species affect a food web?
The diagram below shows the food web for Epping Forest. A decline in insects due to disease could lead to a reduction in the number of rabbits, mice and small birds. Also, more primary consumers, such as caterpillars are consumed as there are fewer insects, reducing butterfly numbers. However, deciduous trees may thrive due to the lower number of insects feeding on them. As well as these direct impacts, there will also be indirect impacts caused by the reduction of insects. There could be fewer secondary consumers such as foxes, owls and sparrow hawks as there are few secondary consumers.
How can ecosystem balance be restored through management?
In the past bears and wolves were removed from ecosystems in Europe and North America as they were a hazard to people and their cattle. However, the removal of these carnivores led to a population explosion of rabbits and deers who removed vegetation, stipping the soil bare, which led to soil erosion. This disrupted the natural balance of the ecosystem.
‘Rewilding’ or ‘ecosystem restoration’ has been used to restore balance in ecosystems. In 1995 grey wolves were re-introduced to Yellowstone National Park in the USA as a way of returning balance to the ecosystem. Since the removal of wolves from the ecosystem in the 1920s, the elk population boomed along with other large prey animals. The number of elk and other large prey animals increased to the point that they gathered in large herds along valley bottoms and meadows overgrazing new-growth vegetation. This caused a significant change in the ecosystem as deciduous woody plant species such as upland aspen and riparian cottonwood became severely diminished.
Other changes also occurred within the ecosystem. There was significant growth in the number of coyotes who replaced the niche left by wolves. However, they were unable to control the large populations of primary consumers. The reintroduction of the wolves has restored balance to the ecosystem and landscape.
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