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. Example If 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

Biology; Ecosystems and material cycles; KS4 Year 10; Ecosystems, competition and environmental changes — *1. Rabbits, 2. Foxes, A. Time, B. Population size.*

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.