Ecology and ecosystems

Ecology – from the Greek oikos meaning “home”

An organisms home or habitat lies in the biosphere. The scale varies:

• small micro-habitats e.g. under a leaf or stone

• Specific locations e.g. pond

• Zones e.g. layers in the tropical rainforest

• Biomes – large areas cutting across whole continents

How an ecosystem works

Definition

An ecosystem is all the living organisms of a defined area together with their inter-relationships with the environment

Ecosystems are often represented as having a number of parts or components. The living parts are described as belonging to different trophic levels (see diagram)

The whole system is powered by the sun, but successive levels of the ecosystem obtain their energy in different ways:

• Trophic level 1 – energy is obtained from inorganic sources. The representatives of this group are called producers (autotrophs). It includes green plants capable of producing their own food by photosynthesis.

• All other levels are occupied by consumers or heterotrophs

• Trophic level 2 – animals that graze on plants are called herbivores, they feed on the producers.

• Trophic level 3 – smaller carnivores act as secondary consumers feeding on the herbivores

• Trophic level 4 – larger carnivores feed on herbivores and the smaller carnivores

• Omnivores (a group which includes humans) eats both plants and animals

• Detrivores/decomposers e.g. bacteria and fungi, operate at all levels

Food chains

Food chains arise when energy is transferred through an ecosystem.

The table contains examples of three food chains

Level

1

Level

2

Level

3

Level

4

Grass Worm

Hawk

Cater-pillar

Shrew Badger

Photo-

plankton

Zoo-

planktonFish