Biotic factors — AQA GCSE Biology
Test yourself on Biotic factors with AQA GCSE practice questions.
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Biotic factors explained
Biotic factors are the living influences on a community, including food availability, competition between species, predation and the availability of mates.
Read the full explanation
To explain an effect, identify the biotic factor that has changed, state the direction of change, then trace the consequence through the community. For example, if a new predator arrives, the population of its prey may fall, which reduces competition for the prey's food, so some plant or invertebrate populations may increase, while the predator's own numbers may later fall as prey becomes scarce. If a competitor is removed, the remaining species may expand its niche and increase in number. Always link the changed factor to survival, reproduction and population size, and use the data or context to support each step.
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.
Biotic factors are living influences on a community. Food availability sets the energy supply: if a plant's pollinators decline, seed set falls and the whole food web is affected. A new predator can reduce prey numbers directly, and may also alter prey behaviour, such as feeding less or hiding more. A new pathogen can spread rapidly if the population has little immunity, reducing numbers before resistance builds. Competition matters because if one species outcompetes another for food, light, space or mates, the weaker population may fall below the number needed to breed successfully. For example, grey squirrels outcompeting red squirrels for food and habitat can leave red squirrel numbers too low to sustain breeding. These factors interact, so a community's size and diversity depend on the balance between births, deaths, immigration and emigration.
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.
This skill requires reading data displays about biotic factors and turning them into biological conclusions. A chart, graph or table might show how predator numbers change over time, how a disease outbreak affects population size, or how two competing species change in abundance. To extract information, read the axes, units, labels and key carefully, then identify the relevant data points. To interpret, describe the trend, compare values between species or time periods, and link the pattern to a biotic factor such as predation, disease, food supply or competition. For example, if a graph shows prey numbers falling after predator numbers rise, you can explain this as increased predation. Always quote figures from the display to support your answer.
Your focus
- Identify the biotic factor that has changed and state the direction of change
- Explain the effect on survival and reproduction of named organisms in the community
- Trace knock-on effects through the community using the data or context provided
Show all 9 objectives
- Identify biotic factors from a given scenario and distinguish them from abiotic factors.
- Explain how a named biotic factor can change the size or diversity of a community.
- Apply the concept of outcompetition to explain why a population may fall below the level needed for successful breeding.
- Read and extract relevant data from charts, graphs and tables about biotic factors.
- Interpret trends and comparisons in data to explain effects on organisms in a community.
- Support conclusions with specific figures and units from the data display.
Biotic factors exam tips
Marking Points
- Identifies the specific biotic factor that has changed, such as food supply, competition, predation or mate availability
- States the direction of change and the organism or population affected
- Explains the consequence for survival or reproduction of the named organism
- Traces the effect through the community, including at least one further species where the context allows
- Uses the data or context provided, quoting values or trends, rather than giving a generic answer
- Uses correct ecological terminology, including community, population, competition, predator and prey
- Define biotic factors as living influences on a community, distinguishing them from abiotic factors such as temperature or light intensity.
- Explain that food availability controls the energy available to consumers, affecting growth, survival and reproductive success.
- Describe how a new predator can reduce prey numbers by direct predation and can also change prey behaviour, for example reducing feeding time.
- Explain that a new pathogen can cause disease and reduce population size, especially where the population has little immunity.
- Explain that interspecific competition can lead to one species outcompeting another for resources such as food, light, space or mates.
- State that if numbers fall too low, individuals may not find mates or may not breed successfully, so the population may decline further or disappear.
- Use a named example, such as grey squirrels outcompeting red squirrels, to show how a biotic factor affects a community.
- Read the axes, units, labels and key of a chart, graph or table accurately before selecting data.
- Identify the trend shown, such as an increase, decrease, plateau or fluctuation, and describe it using data values.
- Compare data for different species or time periods, quoting specific figures from the display.
- Link the pattern in the data to a named biotic factor, such as predation, disease, food availability or competition.
- Use the data to support a conclusion about the effect on organisms within the community, rather than describing the display alone.
Examiner Tips
- 💡Identify the biotic factor and the direction of change before writing your chain of reasoning.
- 💡Use because, so and therefore to link each step from factor to population change.
- 💡Refer to the data or context explicitly, quoting a value or trend to support your explanation.
- 💡When asked to identify a biotic factor, name a living factor and then state its effect on the community, for example 'a new predator reduces prey numbers'.
- 💡Use the phrase 'numbers are no longer sufficient to breed' when explaining the final consequence of outcompetition, as this directly matches the specification.
- 💡If a question gives a scenario, link each factor to a specific organism and a measurable change, such as a fall in population size or breeding success.
- 💡Avoid listing factors without explanation; marks are usually awarded for the effect on the community, not just the name of the factor.
- 💡Quote figures with units when describing a trend, for example 'the population fell from 500 to 200 between year 1 and year 5'.
- 💡Use comparative connectives such as 'whereas', 'compared with' and 'over the same period' when comparing two data sets.
- 💡Finish interpretation questions by naming the biotic factor and stating its effect on the organism or community.
- 💡Check whether the question asks you to extract information, interpret it, or both, and make sure your answer does what is asked.
Common Mistakes
- Classifying a non-living factor such as temperature as biotic; the correction is to check whether the factor is living or was produced by living organisms.
- Stopping the explanation after one species; the correction is to continue the chain to at least one other population in the community.
- Assuming a change always affects only one species; the correction is to consider knock-on effects on competitors, prey and predators.
- Classifying temperature or rainfall as a biotic factor. Correction: these are abiotic; biotic factors are living, such as predators, pathogens and competitors.
- Thinking a new predator only kills prey. Correction: it can also alter prey behaviour, for example causing prey to spend more time hiding and less time feeding.
- Assuming a new pathogen always wipes out a population. Correction: some individuals may have resistance, so the population may survive and recover.
- Believing competition always kills the weaker species immediately. Correction: it may reduce its numbers until breeding is no longer successful, leading to local extinction over time.
- Describing a factor without linking it to the community. Correction: always state the effect on population numbers, breeding or community diversity.
- Describing the shape of a graph without quoting any data; correct this by including specific values or ranges from the axes.
- Mixing up the axes or misreading the scale, for example treating a logarithmic or non-linear scale as linear; correct this by checking the intervals and units before reading values.
- Giving a conclusion that is not supported by the data shown; correct this by linking every statement to a specific data point or trend in the display.