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B7 C) Abiotic & Biotic Factors
B7 C) Abiotic & Biotic Factors
The population and distribution of organisms in an ecosystem is affected by biotic and abiotic factors. Biotic factors are living factors, and abiotic factors are non-living factors. Let’s look at abiotic factors first.
Abiotic Factors
These are non-living factors in an ecosystem. Here are some abiotic factors:
We are going to look at each of these factors in a little bit more detail.
Light Intensity
Plants need light so that they can undertake photosynthesis. Larger plants (such as trees) may grow taller and block out light for the plants living underneath the tree. This will decrease the light intensity for the plants underneath the tree, which will decrease the rate of photosynthesis and growth of the plants underneath the tree. The population of plants underneath the tree may decrease as a result of the reduction in light intensity.
Plants have evolved to live in the conditions that they grow in. For example, cacti have evolved to grow in bright sunlight. Other plants have evolved to grow in the shade; for example, orchids grow on trees in rainforests and they have evolved to grow best in shadier/ darker conditions.
These are non-living factors in an ecosystem. Here are some abiotic factors:
- Light intensity
- Temperature
- Moisture levels
- Soil pH and mineral content
- Wind intensity and direction
- Carbon dioxide levels for plants
- Oxygen levels for aquatic animals
We are going to look at each of these factors in a little bit more detail.
Light Intensity
Plants need light so that they can undertake photosynthesis. Larger plants (such as trees) may grow taller and block out light for the plants living underneath the tree. This will decrease the light intensity for the plants underneath the tree, which will decrease the rate of photosynthesis and growth of the plants underneath the tree. The population of plants underneath the tree may decrease as a result of the reduction in light intensity.
Plants have evolved to live in the conditions that they grow in. For example, cacti have evolved to grow in bright sunlight. Other plants have evolved to grow in the shade; for example, orchids grow on trees in rainforests and they have evolved to grow best in shadier/ darker conditions.
Temperature
Plants and animals have evolved to live in warmer and colder regions. For example, artic foxes and camels have evolved to live in the conditions where they live (we will look at the adaptations of artic foxes and camels in the next section).
Climate change is causing temperatures and conditions of ecosystems to change. This may result in animals becoming less suited to their climate changed environment, which will likely result in a decrease in their populations. For example, the ice caps are melting, which reduces the habitats for polar bears. Polar bears are less suited to warmer climates, so their populations will decline (one study predicts that polar bears will become extinct by 2100).
Plants and animals have evolved to live in warmer and colder regions. For example, artic foxes and camels have evolved to live in the conditions where they live (we will look at the adaptations of artic foxes and camels in the next section).
Climate change is causing temperatures and conditions of ecosystems to change. This may result in animals becoming less suited to their climate changed environment, which will likely result in a decrease in their populations. For example, the ice caps are melting, which reduces the habitats for polar bears. Polar bears are less suited to warmer climates, so their populations will decline (one study predicts that polar bears will become extinct by 2100).
Moisture Levels
Different plants have evolved to live in conditions with different moisture levels. For example, some plants grow well in extremely dry conditions (cacti) and other plants grow well in waterlogged conditions (water lilies).
Soil pH & Mineral Content
The growth of plants is affected by the pH of the soil. Acid rain causes whatever it falls on to become acidic (the acid rain may fall on soil or in lakes). Most plants and animals are very sensitive to pH and a small change in the pH of the soil or a lake can kill organisms. For example, if acid rain falls on a forest, the soil in the forest will become acidic. If the soil becomes too acidic, the trees and plants in the forest will die. Trees and plants are producers in ecosystems. So, a reduction in the number of trees and plants will cause a reduction in the populations of other organisms in the forest; the populations of the primary, secondary and tertiary consumers will decrease. All of the organisms in an ecosystem are interdependent; a change in the population of one organism will result in changes in the populations of other organisms. The image below shows what a forest looks like after acid rain has fallen on it for many years.
Different plants have evolved to live in conditions with different moisture levels. For example, some plants grow well in extremely dry conditions (cacti) and other plants grow well in waterlogged conditions (water lilies).
Soil pH & Mineral Content
The growth of plants is affected by the pH of the soil. Acid rain causes whatever it falls on to become acidic (the acid rain may fall on soil or in lakes). Most plants and animals are very sensitive to pH and a small change in the pH of the soil or a lake can kill organisms. For example, if acid rain falls on a forest, the soil in the forest will become acidic. If the soil becomes too acidic, the trees and plants in the forest will die. Trees and plants are producers in ecosystems. So, a reduction in the number of trees and plants will cause a reduction in the populations of other organisms in the forest; the populations of the primary, secondary and tertiary consumers will decrease. All of the organisms in an ecosystem are interdependent; a change in the population of one organism will result in changes in the populations of other organisms. The image below shows what a forest looks like after acid rain has fallen on it for many years.
The mineral content of the soil influences how well plants grow. If a plant does not get enough minerals, it may grow with deficiencies, which can result in the plant dying. The recycling of minerals and nutrients from organisms is vital for an ecosystem to be stable.
Wind Intensity & Direction
Many plants and animals prefer sheltered conditions. Seeds are more likely to germinate in sheltered conditions. Also, some plants use the wind to distribute their seeds.
Wind Intensity & Direction
Many plants and animals prefer sheltered conditions. Seeds are more likely to germinate in sheltered conditions. Also, some plants use the wind to distribute their seeds.
Carbon Dioxide Levels for Plants
The levels of carbon dioxide are important for plants because carbon dioxide is one of the reactants in photosynthesis – the equation for photosynthesis is: carbon dioxide + water –> glucose + oxygen. Areas that have high levels of carbon dioxide often have lots of plants compared with areas that have low levels of carbon dioxide.
Oxygen Levels for Aquatic Animals
Oxygen levels in lakes and rivers is important for aquatic animals as they need the oxygen for respiration – the equation for respiration is: glucose + oxygen –> carbon dioxide + water. Aquatic animals would die if there was not sufficient oxygen in rivers and lakes.
The levels of carbon dioxide are important for plants because carbon dioxide is one of the reactants in photosynthesis – the equation for photosynthesis is: carbon dioxide + water –> glucose + oxygen. Areas that have high levels of carbon dioxide often have lots of plants compared with areas that have low levels of carbon dioxide.
Oxygen Levels for Aquatic Animals
Oxygen levels in lakes and rivers is important for aquatic animals as they need the oxygen for respiration – the equation for respiration is: glucose + oxygen –> carbon dioxide + water. Aquatic animals would die if there was not sufficient oxygen in rivers and lakes.
Sometimes sewage or fertilisers can run into lakes (or rivers). This can lead to an algae boom as there is extra nutrients for the algae, so it grows quickly. The algae grows across the surface of the lake, which blocks out light for the plants at the bottom of the lake underneath the algae. A lack of light causes these plants underneath the algae to die. Decomposers break down the dead plant material and respire. The decomposers respiring uses oxygen, which decreases oxygen levels in the lake. A reduction in oxygen means that other organisms like fish cannot respire and therefore die, which decreases their populations. This process is known as eutrophication.
Biotic Factors
These are living factors in an ecosystem. Here are some biotic factors:
We are going to look at each of these factors in a little bit more detail.
Availability of Food
All animals require food to live. An increase in the supply of food usually results in an increase in the populations of organisms that eat that food. For example, foxes eat rabbits. If there was an increase in the population of rabbits, there would be more food available for the foxes, which will result in the population of foxes increasing. We will look at this in a bit more detail in the predator-prey cycle section.
These are living factors in an ecosystem. Here are some biotic factors:
- Availability of food
- New predators arriving
- New pathogens
- One species outcompeting another species
We are going to look at each of these factors in a little bit more detail.
Availability of Food
All animals require food to live. An increase in the supply of food usually results in an increase in the populations of organisms that eat that food. For example, foxes eat rabbits. If there was an increase in the population of rabbits, there would be more food available for the foxes, which will result in the population of foxes increasing. We will look at this in a bit more detail in the predator-prey cycle section.
New Predators
The arrival of new predators can disrupt the balance between predators and prey in an ecosystem. In a stable/ balanced ecosystem, the predators catch enough of the prey to survive, but they do not catch so much that they kill all of their food; this results in the populations of both prey and predators remaining roughly constant.
The arrival of a new species/ predator will disrupt this predator-prey balance. For example, the introduction of the red fox in Australia has affected the populations of birds and small mammals.
New Pathogen
The introduction of a new pathogen to an ecosystem can result in a dramatic drop in the population of a particular organism if the new pathogen kills some of the organism. The graph below shows how the population of one organism can be affected by the introduction of a new pathogen.
The arrival of new predators can disrupt the balance between predators and prey in an ecosystem. In a stable/ balanced ecosystem, the predators catch enough of the prey to survive, but they do not catch so much that they kill all of their food; this results in the populations of both prey and predators remaining roughly constant.
The arrival of a new species/ predator will disrupt this predator-prey balance. For example, the introduction of the red fox in Australia has affected the populations of birds and small mammals.
New Pathogen
The introduction of a new pathogen to an ecosystem can result in a dramatic drop in the population of a particular organism if the new pathogen kills some of the organism. The graph below shows how the population of one organism can be affected by the introduction of a new pathogen.
The new pathogen came into the ecosystem in 1950 and as soon as it was introduced, the population of this organism fell dramatically. Usually the population will then increase a few years after the introduction of the new pathogen because some of the population of the organism will develop immunity to the pathogen. The population of this organism starts to increase from around 1953.
An example of a new pathogen entering an ecosystem is ash dieback which has killed many ash trees in the UK since 2012.
Out-Competition
Out-competition is where the introduction of a new species in an ecosystem out-competes an existing organism in an ecosystem for food, space and other resources. This results in the population of the new species increasing and the population of the existing species decreasing.
An example of this is the introduction of grey squirrels to the UK from America. The introduction of grey squirrels to the UK resulted in the native red squirrels and grey squirrels being in competition with each other. Grey squirrels are better suited to the UK than the native red squirrels because the grey squirrels are larger so can store more fat to last the winter. This meant that grey squirrels outcompeted red squirrels for resources, which caused the population of red squirrels to decline; it is very rare to see a red squirrel in the UK and extremely common to see grey squirrels.
An example of a new pathogen entering an ecosystem is ash dieback which has killed many ash trees in the UK since 2012.
Out-Competition
Out-competition is where the introduction of a new species in an ecosystem out-competes an existing organism in an ecosystem for food, space and other resources. This results in the population of the new species increasing and the population of the existing species decreasing.
An example of this is the introduction of grey squirrels to the UK from America. The introduction of grey squirrels to the UK resulted in the native red squirrels and grey squirrels being in competition with each other. Grey squirrels are better suited to the UK than the native red squirrels because the grey squirrels are larger so can store more fat to last the winter. This meant that grey squirrels outcompeted red squirrels for resources, which caused the population of red squirrels to decline; it is very rare to see a red squirrel in the UK and extremely common to see grey squirrels.