Abiotic factors affecting the abundance & distribution of organisms

The abundance is the number of organisms in an ecosystem and their distribution is affected by abiotic factors. These are factors that are non-living. They include:

Light intensity

Some plants have evolved for optimum growth in bright sunlight. An example of this is a cactus houseplant. Cacti originally come from deserts where they grow in bright sunlight. Other plants have evolved to grow in shade.

Many orchids, which are also kept as houseplants, grow on trees in the rainforest and have evolved for optimum growth in darker conditions. If you were to put an orchid on a bright windowsill and a cactus in a dark corner of your room neither plant would grow well.


Both animals and plants have evolved to grow healthily at their optimum temperatures. If you planted either your cactus or orchid houseplants outside in cold temperatures, they would die. Similarly, animals that have evolved to live at the North Pole, such as the polar bear, could not survive in warmer conditions.

Moisture levels

More people kill houseplants by overwatering than by under-watering them. Many plants cannot survive in waterlogged soils. Their roots are unable to respire, they rot and the plant dies. Other plants, such as pitcher plants, grow best in bogs where the moisture levels are high. Soil moisture meters can accurately determine how wet an area is.

Soil pH content

The pH of soils can have a huge effect on the plants that are able to grow in them. Some plants, like azaleas, grow best in acidic soils and will quickly die if planted in alkaline soils. Others, like clematis, prefer alkaline soils. Some, like the hydrangea, can grow in both. These plants are unusual in that their flower colour changes in different soils. Just like universal indicator paper, hydrangea flowers are pink in acidic soils and blue in alkaline soils.

A pH metre reader
pH meters can accurately determine the pH of soils.

The pH of water can also affect the aquatic organisms that are found there. Different species have evolved to survive at different pH levels found within water.

A bar chart that shows the varying tolerance levels of pH in animalsThe graph highlights the various pH tolerances of different species found in water.

Soil mineral content

Many plants require high levels of soil minerals to grow well. An example of this is magnesium, which is required to produce chlorophyll. Plants with unnaturally yellow leaves may have a magnesium deficiency. Carnivorous plants, such as pitcher plants, have evolved to catch insects to supplement the low levels of minerals found in the soils in which they grow.

Wind intensity and direction

The strength of the wind and its direction has a huge impact on where organisms are found within ecosystems. Many organisms prefer more sheltered locations. Plant seeds are more likely to settle and germinate there, and animals which depend upon these are more likely to live close to where they grow. The strength of the wind can also affect the growth of individual organisms.

Carbon dioxide levels for plants

Carbon dioxide is a reactant in photosynthesis which means plants need it to survive. Areas with higher levels of carbon dioxide are more likely to have healthy plants growing. Farmers often release carbon dioxide within their greenhouses to maximise their crop yield. Woodlands often have higher carbon dioxide levels than open grassland, so many plants living in open areas have evolved mechanisms to overcome a shortage of carbon dioxide.

Oxygen levels for aquatic animals

Oxygen from the air and oxygen produced by aquatic plants dissolves in water. Without this, aquatic animals would suffocate and die. Healthy lakes and rivers have high levels of oxygen, and polluted waters often have low levels of oxygen. This pollution means that only certain species can survive there such as sludgeworms. These are bioindicator species because their presence or absence informs us about the condition of the habitat.

These are bioindicators of oxygen levels within water.

Clean: stonefly nymph, mayfly larva. Some pollution: freshwater shrimp, caddis fly larva. Moderate: bloodworm, water louse. High: sludgeworm, red-tailed maggot.  Very high: no living insects.

Levels of pollutants

Air pollutants such as sulfur dioxide are released from the burning of coal. Lichens cannot survive if the concentration of sulfur dioxide is too high. So lichens are considered to be indicator species for air pollution. If the air is clean there will be lots of lichens so that if the city and countryside are compared, there will be more lichen species further away from the city centre.