How do we affect impact the Ecosystems ?
Natural resources are resources supplied by nature that are used by humans.Air, water, soil, wildlife and forests are renewable natural resources.They can be replaced in the ecosystem by natural cycles as long  as humans do not overuse them.On the other hand, fossil fuels take millions of years to form naturally.They cannot be replaced once they are used, hence they are called non-renewable natural resources.Human beings are continually using and depleting or reducing the Earth's natural resources, and upsetting the balance of nature in many areas.The Uncontrolled use of the Earth's natural resources, such as forests and wildlife , has caused lasting damage to the environment.The environmental damage is largely irreversible.
Human activities much be carefully monitored to preserve and conserve the environment for the future.
Deforestation
Before 1819, Singapore's population numbered about 250 villagers.There were very few houses and most of Singapore's land area was covered by swampy jungle.Almost 200 years later, the population has exploded to about 4 millions people! Tall buildings and roads have sprung up almost everywhere.Today , Singapore is often referred to as a concrete jungle.
Why are forests cleared?
The clearing of forests is known as deforestation.Forests are cleared to meet the increasing demands for land and materials such as wood
With modern technology, forests are being cleared at a much faster rate than they can be replaced.Deforestation leads to loss of habitats.
What are the effects of deforestation ?
1. Soil erosion
    Deforestation causes soil erosion.The leafy canopy of the trees in tropical rain forests protects the soil from the impact of the falling rain.Rainwater is retained and absorbed by the roots of trees and gradually released to the soil and to the nearby streams and lakes.With the trees removed , the soil is exposed directly to the force of the rain.Topsoil , the most fertile layer , gets washed away or eroded during heavy rain, especially when rain falls on steep slopes.
2. Flooding
Eroded soil may be deposited in rivers and streams , blocking the flow of water,The water levels in rivers rise rapidly , causing floods.
3. Desertification
Sunlight falls directly onto the soil, which then hardens.With the topsoil eroded, the land becomes barren.Plants cannot grow in the soil.
Other organisms which depend directly or indirectly upon plants for food also die off.The destruction of land leading to desert like condition is called desertification.Consequently, habitats are lost and many species of organisms become extinct.Overgrazing by animals also leads to desertification because the plants cannot regenerate fast enough.
4. Climate changes
Deforestation also causes climate changes.Rainwater that is retained and  absorbed by the roots of trees is lost as water vapour during transpiration.The water vapour eventually condenses and falls as rain.When trees are cleared , the area becomes dry and warm and annual rainfall decreases.
Uncontrolled fishing practices
How do uncontrolled fishing practices harm the ecosystems ?
Humans catch fish for food.As the human population increases , so does the demand for fish.Some species of fish have been caught in such large numbers that their populations have drastically decreased.We say that these species are over-fished.Also, most modern fishing gear used in commercial fishing catches marine life indiscriminately , that is, it does not distinguish between the targeted catch and immature organisms or unwanted species.For example , gigantic drift nets trap  almost everything in their path.Marine life such as turtles, sharks and dolphins are unintentionally caught.These accidental catches are dumped back into the sea, but they often die.
Some methods of fishing also destroy the seabed  and marine habitat.
1. Shrimp or prawn trawlers drag large fishing nets along the bottom of the sea.Many unwanted species are trapped in the process.
2. Scallop dredges scrap the seabed , destroying coral reefs and organisms that live on the seabed.
3. In cyanide fishing , cyanide, a poison , is squirted into the water around coral reefs.The cyanide stunds reef fish and makes them unable to swim property.Fisherman then captur the fish for the sale
as pets.Explosives such as dynamite are also used to stun and catch reef fish.Both cyanide and explosives kill corals and many other reef organisms.
Effects of uncontrolled fishing practices.
If fishing practices are not controlled, some species of fish will be caught faster than they can be replaced.Young fish that are caught will not have a chance
to grow and reproduce.Hence, fish populations will decrease.
Also, other marine organisms that are unintentionally caught often die.Eventually , some species may become endangered or event extinct.
Key Ideas
1. Human activities such as deforestation and uncontrolled fishing damage the environment.
2. Forests are cleared for land and materials such as wood.Deforestation leads to soil erosion, flooding , desertification and climate changes.
3. Over-fishing , use of indiscriminate fishing gear and destructive fishing have led to a decrease in fish populations and loss of marine habitats.