9.2 - Abiotic & Biotic Factors
Abiotic and biotic factors
- The organisms in a community are shaped by two kinds of environmental factor.
- Abiotic factors are the non-living parts of the environment - the physical and chemical conditions.
- Biotic factors are the living parts of the environment - the effects that organisms have on one another.
Abiotic factors
- Light intensity
- Temperature
- Moisture (water) level
- pH and mineral content of the soil
- Wind intensity and direction
- Carbon dioxide level (matters for plants)
- Dissolved oxygen level (matters for aquatic animals)
- Pollutants, such as toxic chemicals
Biotic factors
- Availability of food
- New predators arriving
- New pathogens (disease) arriving
- Competition - One species outcompetes another for a shared resource such as food or space
Effects on distribution and abundance
- Both abiotic and biotic factors affect the distribution of organisms (where they're found in a habitat) and their abundance (the size of a population).
- A change in a single factor can change a population's size. Because organisms in a community depend on one another, this can have knock-on effects on other populations.
- An organism is usually more common where the factors suit it - e.g. daisies are more common in the open parts of a field, where there's more light than under the shade of trees.
Abiotic changes
- A fall in light intensity, temperature or carbon dioxide level lowers the rate of photosynthesis, so plants grow less and the plant population can fall.
- A drop in soil minerals such as nitrates has the same effect through poorer plant growth.
- The animals that feed on those plants are then affected in turn.
Biotic changes
- New predator - Can cut a prey population.
- New pathogen - Can cause a sharp drop in the species it infects.
- Stronger competitor - Can drive a weaker species' numbers down, e.g. grey squirrels outcompeting red squirrels for the same food.
Measuring abiotic factors
- Abiotic factors are measured directly in the field, giving a number for the condition an organism actually experiences.
- These numbers can then be compared between places or over time.
Equipment for each factor
- Light intensity - Measured with a light meter
- Soil moisture - Measured with a moisture meter
- pH - Measured with a pH meter or indicator
- Temperature - Measured with a thermometer
Reducing errors in readings
- Readings can carry errors - for example accidentally shading a light sensor, or taking a single reading that doesn't represent the whole area.
- To reduce these errors:
- Take measurements carefully and the same way each time - e.g. holding the sensor identically for every reading.
- Repeat readings and take several across the area, then average them so the values give a fair picture of the conditions.
TermDefinition
Abiotic factorA non-living part of the environment that affects organisms, such as temperature or light intensity.
Biotic factorA living part of the environment that affects organisms, such as predators or competition.
DistributionThe places within a habitat where organisms of a species are found.
AbundanceThe size of a population or the number of organisms in an area.
Key points to remember
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