Ecosystems, competition and environmental changes
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Explainer Video
Summary
Ecosystems, competition and environmental changes
In a nutshell
Ecosystems are communities of organisms along with abiotic conditions. Ecosystems can be affected by environmental changes that can cause their populations to increase or decrease, or cause changes in their distribution.
Ecosystems
Ecosystems are organised into different levels.
| 1 | Individual | A single organism. |
| 2 | Population | All the organisms of one species in a habitat. |
| 3 | Community | All the organisms across different species living in a habitat. |
| 4 | Ecosystem | A community of organisms along with all the non-living conditions. |
Competition between organisms
Organisms need things from their environment and other organisms to survive and reproduce. Each species depends on other species, this is called interdependence.
Examples
Plants | Light, space, water and minerals from the soil. |
Animals | Space (territory), food, water and mates. |
Organisms compete with members of their own species and other species for resources.
Example
Red and grey squirrels live in the same habitat and eat the same food. The competition between them means there is not enough food for the red squirrels so their population is decreasing.
Environmental changes
The environment in which organisms live in changes all of the time. The changes are caused by abiotic (non-living) and biotic (living) factors. Interdependence of all living things in an ecosystem means that any major change can have far-reaching effects.
Example
Stonefly larvae live in streams. If they are killed by pollution this could have effects on other organisms in the food web.
Organism | Effect | Population effect |
| Blackfly larvae | Less competition for algae which they share as a food source with stonefly larvae. | Increase |
| Blackfly larvae | More likely to be eaten by predators. | Decrease |
| Water spider | Less food. | Decrease |
| Stickleback (fish) | Less food if the water spider population decreases. | Decrease |
Abiotic factors
Temperature | The distribution of bird species in Germany is changing because the average temperature is rising. The European Bee-Eater bird is a Mediterranean species that is now present in some parts of Germany. |
Moisture level | Daisies grow best in slightly damp soils. If the soil becomes waterlogged (too wet) or too dry the population of daisies will decrease. |
Light intensity | As trees grow and provide more shade to the ground below, grasses may be replaced by fungi and mosses which are better suited to the low light intensity. |
Soil pH | Azalea shrubs grow best in acidic soil, if the pH becomes too alkaline the population of azaleas will decrease. |
Biotic factors
Food availability | If there is a high growth of berries one year, the population of blackbirds may increase as there will be enough food. |
Number of predators | If the number of a predator increases then the number of prey will decrease as more of them are eaten.
ExampleIf the number of foxes increases, the number of rabbits would decrease. |
Competition | One species may outcompete another so that numbers are too low to breed as seen with red and grey squirrels. |
New pathogens | A new pathogen could cause the population to quickly decrease if it spreads. |
In communities, all of the species and environmental factors are in balance so that the population sizes are roughly constant. These are called stable communities.
Predator-prey population cycles
The population of any species is limited by the amount of food available, if the population of prey increases, then the population of predators will also increase. If the population of predators increases, the number of prey will decrease. This is another example of interdependence.
Example
More grass means more rabbits and more rabbits means more foxes. More foxes lead to fewer rabbits which will eventually lead to fewer foxes again. This cycle continues.
Predator-prey cycles are always out of phase with each other as it takes a while for one population to respond to the other. This may be because one species like the foxes take time to reproduce.
Parasitic and mutualistic relationships
Parasitic and mutualistic relationships are more examples of interdependence.
Relationship | Description | Example |
| Parasites | Parasites live off the host and take what they need to survive without giving anything back. They often cause harm to the host. | Tapeworms absorb lots of nutrients from the host which can cause them to suffer from malnutrition. |
| Mutualism | Both organisms benefit from this type of relationship. | Clownfish live in the poisonous tentacles of sea anemones, they can survive the toxins and are protected from predators. The clownfish help protect the anemones by eating parasites that could cause them harm. |
Changes in distribution
Environmental changes can cause the distribution of organisms to change. This means a change in where an organism lives. These changes can be caused by seasonal factors, geographic factors or as a result of human interaction.
Examples
Environmental change | Description | Example |
| Water availability | The distribution of some animal and plant species in the tropic changes between wet and dry seasons. | In Africa, large numbers of giant wildebeests migrate north and then south as the rainfall pattern changes. |
| Atmospheric gases | The distribution of some species changes when there is more air pollution. | Some lichen species cannot grow in some areas where sulphur dioxide is given out by industrial processes. |
FAQs - Frequently Asked Questions
What is the difference between ecosystem and communities?
An ecosystem is a community of organisms along with all the non-living conditions. A community is all the organisms across different species living in a habitat.
What causes environmental changes?
Environmental changes are caused by abiotic (non-living) and biotic (living) factors.
What is an ecosystem?
An ecosystem is a community of organisms along with all the non-living conditions.