Environment

In the 1850s , Charles Darwin described the struggle for life.The plains of the serengeti in Africa provide an excellent example of this.Living things interact and compete together.The fittest ones survive.Over time a species gradually changes and improves its chances of survival.The fiercest predators eat well but the fastest prey escape and live to reproduce.If a species fails to adapt and improve it becomes extinct, like the dinosaurs.

All special interact with each othere and with their environment. Humans are upsetting the Earth`s balance but we can now reverse some of these changes. Sustainable development and conservation programmes
show that we need not destroy hold the key to restoring this delicate balance.

In this topic you will learn that

• animals and plants depend upon each othere
• all organism are adapted to their environment
• there is often competition between organisms for resources
• natural selection is a long process over many genertions. 

Chain, webs and pyramids

By the end of this page you will know:

• what a food chain is
• that many food chains link together to make a food web
• that pyramids can show the numbers , biomass or energy at different stages in a food chain.

The diagram show a food chain in the east African Serengeti. Food chain are examples of energy-transfer chains.The arrows show the flow of energy through the food chain. Because green plants use photosynthesis to make their own food they are called producers. Almost every food chain in the world begins with a green plant.

The Serengeti-Mara is the 26,000 km 2  home to more than 3 million large animals.After the rains, over 2 million grazers move into the area, feeding on grasses and acacia bushes.Large predators use the area as a hunting ground to find food.The savannah ecosystem has lots of different food chains. When food chains are linked together, they make a food web.The top carnivores have few predators.When top carnivores die, scavengers eat their bodies.

The Serengeti-Mara plains are not endless.Every lion needs about 350 grazers to feed it.Each grazer needs enough grass to survive. About 2000 lions live in the Serengeti-Mara.This gives each lion about 13 km of hunting ground.The same area contains about 350 grazers, mainly Thomson's gazelle,wildebeest and zebra.

Food chains tell you how energy is transferred from one organism to another but not much more.A food pyramid is a numerical (quantitative) way of showing the organism in a food chain.There are two kind of food pyramid:pyramids of number and pyramids of biomass.Biomass is the dry mass of living matter.Pyramids of number show how many of each organism are found at each level of a food chain.Pyramids of biomass show the amount of living matter at each level of  the pyramid.

Our influence on the environment

 By the end of this page you will know:

• how economic, industrial and population changes affect the environment.

The human population has dramatically increased in size over the last 100 years ( see graph A).  All of these extra people need food, water and somewhere to live.Everyone wants a good standard of living which means higher demand for things like electricity and cars. Generating more electricity, burning forest to clear land for farming and burning fuel in cars all produces more carbon dioxide. All of this puts pressure on the environment.The environment is the place where an organism lives and is made up of many different features such as air, water , soil and other living things.

A

Carbon dioxide is a`greenhouse gas'. This means that it traps heat in the Earth's atmosphere.If there is more heat trapped in the atmosphere then the earth could become warmer. This could lead to melting of polar ice and rising sea levels.Many places in Britain and across the world would be at risk from flooding if sea levels rose.

B                                                                                                               C

The satellite photograph shows Timbuktu in Mali , West Africa .The area around Timbuktu is the sahel, which means`the edgeof the desert`.Nomads used to graze animals in this area until farmers began planting peanuts to sell. This change in land use together with local climate changes, has resulted in the loss of soil fertility. This is called desertification.                                                                                                              

Recently an area of South American rainforest the size of Belgium was cleared to grow crops and to graze animals- the trees were sold as timber.This is deforestation.This can lead to soil washing away and increased flooding.

Here are some of the things that you can do to help the environment. Use less energy-make sure you turn off lights when you leave a room. Don`t leave your TV or computer on standly.Try not to use the car for ever journey - walk to school if you can. Glass , aluminium and paper are just a few of the things that you can recycle.

Competition for resources

By the end of this page you should know:

• that living things compete with each other for the things they need
• that predators compete with each other for prey
• that animal population are affected by numbers of predators and by competition for resources.

A

Charles Darwin described life as a struggle for survival.Animals compete with each other for resorces. The savannah is a hot, grassy plan in africa.There are very few trees and many of them have sharp thorns.The grass provides food for huge herds of zebras, wildebeest, gazelles and many other species.Because they all eat the same food, these animal compete for the best grass.Competition between different species,such as zebra and wildebeest, is called inter-species competition. competition within a single species competition.

As a general rule the strongest, best-adapted animals get to eat most of the food.These animals survive and breed so their population increases at the expense of other weaker,less adapted species. Sometimes species adapt so that they can live comfortable side by side.In addition to food, animals compete for water, shelter, a suitable mate and places to breed.


B

Predators are hunters which kill and eat other animals.The animal which is hunted is called the prey.Scavengers are animals which eat the `left-overs` of animals killed by predators.The large herbivores on the savannah are prey to animals like lions and cheetahs.Other predators and scavengers eat smaller herbivores such as gazelles and dik-diks.The plants and animals on the savannah are interdependent.Changes in the numbers of one organism affect the numbers of other organisms.


How populations of a predator and its prey change over time.

Have you ever wondered:
Does the numbers of foxes control the number of rabbits or does the number of rabbits control the number of foxes?

In years when there is plenty of grass, competition between the herbivores is reduced.The number of herbivores will increase.Young herbivores are easy prey for predators.This extra source of meat allows predators to successfully raise more young.When the grass fails to grow, or if there are too many predators, the herbivore population will drop. Figure C shows how the populations change over a long period of time.