Biotic factors

Overview

Food availability, new predators, new pathogens and competition as biotic factors, with red and grey squirrels, poor acorn crops, island prey, lost plant species and diseased ash trees, and interpreting population data on introduced species and disease.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Name four biotic factors that can affect a community.

   Model answer

   Availability of food, new predators arriving, new pathogens, and one species outcompeting another.

2. 2

   Why is the arrival of a new predator described as a biotic factor rather than an abiotic one?

   Model answer

   It is a change caused by another living organism rather than by a physical or chemical condition of the environment.

3. 3

   Explain how a new pathogen can change a community.

   Model answer

   Species with no resistance to it die in large numbers, and species that depended on them for food or shelter are affected too.

4. 4

   Explain how one species outcompeting another can end a population altogether.

   Model answer

   The losing species obtains too little food or space, so its numbers fall until too few individuals remain to breed.

5. 5

   Grey squirrels are introduced into a wood containing red squirrels. Explain what may happen to the red squirrel population.

   Model answer

   Grey squirrels compete for the same food and shelter and carry a disease the reds cannot resist, so red squirrel numbers fall.

6. 6

   A cold spring is followed by a very poor acorn crop. Explain the effect on the mice that feed on acorns.

   Model answer

   Less food is available, so more mice starve and the mouse population falls.

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