Biotic Factors (AQA GCSE Biology): Revision Note
Exam code: 8461
Types of biotic factors
In biology, ‘biotic’ means living. A biotic factor is a living factor
Biotic factors that can affect a community
Availability of food:
More food means organisms have a higher chance of surviving and reproducing, so their populations can increase
Example:
Rainforest ecosystems have a rich food supply and this allows many species to live there.
Deserts have a poor food supply and this allows fewer species to live there
New predators:
In balanced ecosystems, predators catch enough prey to survive but not so many that they wipe out the prey population.
If a new predator is introduced to the ecosystem, it may become unbalanced
Example:
Red foxes were introduced for recreational hunting in Australia in the 1800s but have since caused the decline of many native species that they feed on, such as small mammals and birds.
This has also reduced the food supply for native predators
New pathogens:
If a new pathogen enters an ecosystem, the populations living there will have no immunity or resistance to it and the population may decline or be wiped out
Example:
Coronavirus caused a global pandemic and a decline in many human populations around the world because it was a new pathogen
Competition:
If two species compete for the same resource(s) and one is better adapted to take advantage of these resources, then that species will outcompete the other.
This may continue until there are too few members of the lesser adapted species to breed successfully
Example:
North American grey squirrels were introduced to the UK in the 1800s and have since caused the decline in our native red squirrel population
Grey squirrels have outcompeted red squirrels for resources such as food and nest-sites
They also carry a virus (a new pathogen) that red squirrels have no resistance to
Effect of biotic factors
Exam questions often ask students to extract and interpret information from charts, graphs and tables relating to the effect of biotic factors on organisms within a community
Worked Example
A study recorded the number of red and grey squirrels in a particular woodland habitat for 20 years. Grey squirrels were introduced to the habitat in year 6 of the study.
This ia a graph of their results:
What conclusion can you draw from this graph about the effect of introducing grey squirrels to a habitat that is occupied by red squirrels?
Explain why this might have occurred.
[3 marks]
Answer
As the number of grey squirrels increases, the number of red squirrels decreases. This might have occurred because the two squirrel species are competing for one or more of the same resources. Grey squirrels are better adapted to use these resources and have outcompeted the red squirrels until eventually there are too few red squirrels left to breed successfully and there are none left in the habitat.
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