1. Biotic Factors
Noadswood Science, 2016

2. Saturday, June 16, 2018
Biotic Factors
To be able to identify biotic factors and how these impact ecosystems

3. Precise Learning
Students should be able to explain how a change in a biotic factor might affect a given community given appropriate data or context.
Biotic (living) factors which can affect a community are:
availability of food
new predators arriving
new pathogens
one species outcompeting another so the numbers are no longer sufficient to breed
Students should be able to extract and interpret information from charts, graphs and tables relating to the effect of biotic factors on organisms within a community.

4. Biotic Factors Biotic factors are the living factors in an ecosystem
Biotic factors include:
New predators arriving
Competition (one species may outcompete another so that numbers are too low to breed)
New pathogens
Availability of food

5. Biotic Factors
Biotic factors can also vary in an ecosystem – a change in the environment could be the introduction of a new biotic factor, e.g. a new predator or pathogen
These changes can also affect the size of populations in a community which can have knock-on effects because of interdependence
E.g. a new predator could cause a decrease in the prey population such as grey squirrels which out-compete the native red squirrel populations

6. Abiotic and Biotic Data
In an investigation into the effects of fertiliser on the environment it was added to a field which contained a pond. The plants and wildlife in and around the pond were then studied for 40 days. The table shows the size of the fish population in the pond and the graph shows the percentage cover of the pond by algae over time
A higher percentage cover means that less light is able to reach the plants below the surface of the water

7. Abiotic and Biotic Data
The amount of algae increased because the fertiliser increased the amount of nutrients in the water. Explain whether the increase in algae was caused by a biotic or abiotic factor…
Abiotic – nutrients in the water is a non-living factor

8. Abiotic and Biotic Data
Describe the relationship between the percentage cover of algae and the size of the fish population
Between 0-10 days the percentage cover of algae increases, but the fish population barely changes. Between days the percentage covers continues to increase and the size of the fish population decreases rapidly

9. Abiotic and Biotic Data
Suggest an abiotic factor that could be responsible for the change in the size of the fish population and explain why this is the case
A reduced oxygen level – the algae cover reduces the amount of light reaching the plants below the surface of the water, so the plants cannot carry out photosynthesis and die off
One of the products of photosynthesis is oxygen, so if there are fewer plants carrying out photosynthesis less oxygen is released
The lack of oxygen means that the fish cannot survive, so the population decreases

10. Abiotic and Biotic Data
The graph below shows how the size of the fish population and a population of fish-eating birds changed over the 40days of observation
Suggest a biotic factor that could be responsible for the trend in the size of the fish-eating bird population between day 10 and 40

11. Abiotic and Biotic Data
A shortage of food for the birds – the size of the bird population starts to decrease shortly after the size of the fish population starts to decrease
As the size of the fish population decreases, there is less food available to the birds, so the birds either die or move elsewhere in search of food