Ecosystem definitions
A: BIOTIC FACTORS AND ABIOTIC FACTORS
Ecosystems consist of biotic and abiotic factors i.e. living and non-living.
Organisms (plants, animals, algae, fungi and bacteria) are the living parts.
The physical environment (air, light, water, temperature, minerals, soil, climate) are
the non-living.
The biotic and abiotic interact to keep the ecosystem alive.
B: TROPHIC LEVELS
Certain organisms in an ecosystem convert the abiotic components of an ecosystem
into living matter. These are called producers. They produce new biological matter or
biomass. Consumers are organisms that cannot make their own food and eat other
organisms to obtain energy and matter. The position the organism is in the food
chain is called the trophic level. You can have primary consumer, secondary
consumer, tertiary consumer and even quaternary consumer.
C: FOOD WEBS
Interconnected food chains form a food web. Decomposers feed on dead biomass
created by the ecosystem. Herbivores eat only plant matter. Carnivores are
secondary or above consumers that eat animals. Omnivores eat both plant matter
and animals. Decomposers can be found at any level of the food chain.
D: PYRAMIDS OF NUMBER
If you count the number of producers and consumers in an ecosystem you can draw a
graphical representation called a pyramid of numbers. They are not always pyramid
shaped and may be partly upside down pyramids e.g. a tree with lots of insects and
then fewer birds feeding on them, or a typical pyramid e.g. grassland, caterpillars,
birds etc.
E: PYRAMID OF BIOMASS
This is a graph that shows the amount of biomass in each level of an ecosystem.
These are usually pyramid shaped as energy and biomass tend to decrease along the
food chain. Think about the trees in a rainforest, then the herbivores, then the
carnivores – each time there is less of a biomass store. However a field may have a
lower amount of biomass in grass than is in cows. This is measured in g/m2. It can be
measured as the amount of energy per metre squared i.e. J/m2.
F: PYRAMID OF PRODUCTIVITY
This is a graph showing the rate of production of a level of the ecosystem in an
amount of time. These are always pyramid shaped as there is always more energy in
the lower layers than in the higher ones. Because energy is lost through food chains
the animals at the top of the food chain are always most at risk from disturbance
lower down the chain. If there is a reduction in the number of plants then this will
affect the number of animals that eat those plants and so on… This is measured in
g/m2/year.
G: THE SNOW LEOPARD
This animal is found in the mountains of Central Asia. It eats wild sheep and goats.
Farms exist on the lower slopes and there are too many domesticated sheep and
goats, overgrazing the land. With little food to eat, the snow leopard starts to eat the
farmers’ sheep and goats. The farmers then try to kill the snow leopards. There are
less than 7000 snow leopards around now and they are designated an Endangered
Species.
H: BIOACCUMULATION
Animals at the top of the food chain are at rsik from what gets into the bottom of the
food chain. When DDT was used as a pesticide it accumulated in the plants. Then the
animals that ate the grass stored that DDT. Then the animals that ate those animals
stored it and so on until the animals at the top of the food chain had lots of DDT. This
is called bioaccumulation. The substance also becomes more concentrated in the
tissues. This is biomagnification. With a longer lifespan, animals at the top of the
chain accumulate more.