An opportunity for an entirely gratuitous quote: 

"May I ask what you were hoping to see from a Torquay hotel bedroom window? Sydney Opera House perhaps? The Hanging Gardens of Babylon? Herds of wildebeest sweeping majestically across the plain?"

Ecosystems

Basic Definitions

Biosphere

• that part of the Earth and its atmosphere inhabited by living organisms
• is made up of many different ecosystems

Ecosystem

2 definitions:

• is a network of habitats and communities linked by flows of energy and nutrients between them
• an ecological unit which consists of several habitats and their associated communities. It therefore includes both biotic and abiotic components

So ecosystems describe the links between organisms and their environment

Ecosystems can be nested: with small ecosystems within larger ecosystems e.g. a British woodland would be a woodland ecosystem within the larger terrestrial ecosystem which is part of the island ecosystem of Britain

Habitat

• the place where an organism lives - its geographical "address"
• the habitat takes into account the biotic factors (other organisms) and abiotic factors (physico-chemical features) of the area

Niche

• a description of the physical, chemical and biological factors required by a species to survive and reproduce

Community

• a collection of plants and animals which occupy a particular habitat
• so community only takes into account the biotic factors of the habitat

Population

• the group of individuals of a particular species which occupy a particular habitat

Biotic factors

• describes the effects of the living things within a habitat on other living things within that habitat
• these effects include:
  • availability of food
  • competition - for food, space, water
    • this can be between members of the same species or between organisms occupying similar niches 
  • predation
  • parasitism

Abiotic factors

• the non-living components of an organism's habitat
• these include:
  • physical factors
    • sunlight
    • rainfall
    • temperature
    • wind
    • water currents
  • chemical factors

Producers

• organisms that use the sun's energy to make food which becomes available to other organisms in the ecosystem
• autotrophs
• plants basically!

Consumers

• organisms that have to consume other organisms to obtain their nutrients
• heterotrophs
• every except plants basically!

Decomposers

• a special type of consumer
• decomposers break down the organic remains of dead organisms and make it available as either decomposer biomass (for consumption) or as carbon dioxide (for photosynthesis)
• includes worms, some bacteria and some fungi

Food Chains

• a food chain shows a simple series of feeding relationships within an ecosystem
• an arrow is used to indicate "is eaten by"

rose bush --> caterpillars --> robin --> sparrowhawk

In this example the rose bush is consumed by the caterpillars which are consumed by the robin which, in turn, is consumed by the sparrowhawk

• there is a flow of energy through the food chain with:

  • some of the energy contained in the rose bush being consumed by the caterpillars

  • and some of the energy contained in the caterpillars being consumed by the robin

  • and some of the energy contained in the robin being consumed by the sparrowhawk 

• note that, although it is not shown on the diagrams on this page all food chains begin with an input of energy from the sun

Food Webs

• food chains show one series of feeding relationships but there are many species in an ecosystem and most consume more than one other species. 
• taking all of the feeding relationships into account results in a complex network called a food web

Image from http://www.communitiesonline.org.uk/science/ks4_topic_Biology_Energy_Transfers/food_chains_page_2.htm

Trophic Levels

• Each stage in a food chain represents a different trophic level
• these are called:
  • primary producers (the plants)
  • herbivores (first consumer)
  • first carnivore (second consumer)
  • second carnivore (third consumer)
  • etc
• because there is a loss of energy at each trophic level it is very unusual to find food chains with more than 5 member

The diagram below shows a food web arranged so that species at a particular trophic level are grouped together. 

But the difficulties with doing this are illustrated: fish and insects are classified as first consumers because they eat the photosynthetic species - but they also eat each other

Image from http://www.geographyjim.org/food.htm

The salt marsh diagram also includes the decomposer level - these are the fungi and bacteria that break down dead organic matter making it available for use by the other species in the ecosystem

Revision Questions

Adapted from Biology by Martin Rowland (1992, pub. Nelson)

Fill in each of the blanks in the following sentences using the appropriate term: community, ecosystem(s), habitat(s), or population(s).

1. A moorland ........................... contains grassland, scrub and stream .......................
2. Highland streams are a ......................... for trout and salmon
3. A cat harbours a ......................... of fleas in its fur
4. Ladybirds are members of the predator ......................... that feeds upon ..................... of greenfly, reducing their number
5. The grassland ........................... of the Serengeti in Africa, is grazed by a ....................... of large herbivores including wildebeest, zebra, topi and buffalo

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