Edexcel: Topic 5, what is an ecosystem?


The part of the earth inhabited by living organisms is knows as the biosphere.  Within a biosphere there are different ecosystems with features that effect the organisms living there.  There are abiotic components (physical and chemical factors) and biotic components (determined by organisms such as predation and competition).  Ecosystems tend to be fairly self-sustaining.


There can be many habitats (the place with a distinct set of conditions where an organism lives) within an ecosystem. Within a habitat there may be many microhabitats again each with a distinct set of conditions.


Within a habitat there will be several populations (a group of individuals of the same species found in an area) of organisms.  The populations in a habitat make up a community.  If 2 species live in the same habitat and have the same niche they will compete with each other and eventually the better adapted will out-compete the other and exclude it from the habitat.  Two species can share a habitat only if they occupy different niches.

What determines which species occur in a habitat?

The conditions in which species fight for survival are defined by the ecological factors in their habitat.

Abiotic factors

These are non-living or physical factors such as Solar energy input (affected by latitude, season, cloud cover and changes to the earths orbit) Climate (rainfall, wind exposure and temperature) Topography (altitude, slope, aspect and drainage) Oxygen availability (particularly important in an aquatic environment)  Edaphic (factors connected with the soil such as pH and mineral salt availability) Pollution (can be of air, water or land) Catastrophes (infrequent events which disturb conditions considerably)

Biotic factors

These are 'living' factors such as competition (for resources such as food, light, water, space.  These can be Interspecific (between species) or intraspecific (within species)) Grazing, predation or parasitism (in all, one organism benefits at another's expense) Mutualism (a relationship where both partners benefit).  These are usually density dependent: effects are related to to the size of the population relative to the area available.  The greater the population density the greater the competition.  There is a greater diversity of organisms as the environment becomes more




This is so close to being the textbook copied out



This set of notes contains detailed, clearly written information on populations, ecosystems and succession which would be useful for any student needing to study this topic at GCE level. The highlighting of the key terms is useful and perhaps this could be used to create a set of revision flashcards which could be downloaded and used as a self  test.