Changes in ecosystems
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Explainer Video
Summary
Changes in ecosystems
In a nutshell
Organisms have specific roles within an ecosystem and both living and non-living factors impact these roles. Over time, these ecosystems can change and lead to the development of new ecosystems with new organisms that have different roles.
Definitions
Keyword | Definition |
| Habitat | The area where an organism lives. |
| Population | All the organisms of one species within a habitat. |
| Community | Populations of different species in a habitat. |
| Ecosystem | A community and all of the non-living conditions in the area it lives. |
| Abiotic conditions | Non-living features of an ecosystem. |
| Biotic conditions | Living features of an ecosystem. |
| Niche | The role of a species within its habitat. |
Niche
A niche includes all the biotic and abiotic conditions to which an organism is adapted in order to survive and reproduce. No two species occupy the exact same niche: this is known as the competitive exclusion principle.
Example
Koalas are specialist species as they have a specific niche. They only feed on the leaves of eucalyptus trees in Australia.
Population size
Definition
The total number of organisms of one species in a habitat.
An ecosystem can support a certain size of population in which it is stable: this is known as the carrying capacity. The carrying capacity is impacted by both biotic and abiotic factors.
Abiotic factors
Abiotic factors include water, temperature, humidity, light and pH. If the abiotic conditions are ideal for a species, they will grow fast and reproduce successfully.
Example
If the temperature of the surroundings is ideal for the metabolic reactions of a mammal, they will not have to use as much energy to maintain their body temperature. This means more energy can be used for growth and reproduction. This will increase their population size.
If the abiotic conditions are not ideal, the organism will not be able to grow fast or reproduce.
Example
If the temperature of the surroundings is lower or higher than the mammal needs for metabolic reactions, then they will use a lot of energy trying to maintain the correct body temperature. There will be less energy used on growth and reproduction. This leads to a decrease in population size.
Biotic
Biotic factors such as competition and predation also impact population size.
Interspecific competition
This is competition between different species for the same resources. This can cause changes in population size as it could mean there are less resources (e.g. food available to both populations). Both populations will therefore be limited by the amount of resources, so they'll have less energy for growth and reproduction.
However, if one of the two species is better adapted to the surroundings, it is less likely to be out-competed and will have more of the available resources. This means it can spend more energy on growth and repair so the population size will grow.
Intraspecific competition
This is competition for the same resources between members of the same species.
| 1. | The population of a species will increase when resources are in high supply. As the population increases, there will be more organisms competing for the same food and space. |
| 2. | These resources will then become limiting as there will not be enough for all the organisms. This causes the population to decline. |
| 3. | The population is now smaller so there is less competition for resources. This means there is more growth and reproduction and the population size increases again. The cycle then repeats. |
Predation
Predator and prey populations go in cycles. Consumers that hunt and kill other animals are called predators. The animals that predators eat are called prey. In a stable community, the population size of a species is limited by the amount of food it has. This means the population size of predators is directly affected by the population size of prey.
| 1. | Foxes are predators, rabbits are prey. |
| 2. | If the number of rabbits increases, the number of foxes will also increase as they have more food. |
| 3. | As the number of foxes increases, the number of rabbits will decrease as more rabbits are eaten by the foxes. |
Succession
Definition
The process by which an ecosystem changes over time, succession allows the formation of complex ecosystems and results in a climax community. There are two types of succession.
Primary succession
This occurs on newly formed land where there is no soil or organic material. The abiotic conditions are hostile.
Example
| 1. | Lichen are the pioneer species, which are the first species to colonise the area, and will land on the rocks. This breaks down the rocks and releases minerals. |
| 2. | The lichen will die and decompose to form a thin soil. As more organic matter is formed, the soil will thicken which allows other species such as mosses to grow. |
| 3. | As the soil deepens, larger plants that need more water can move in. This includes grasses and small flowering plants. |
| 4. | As the larger plants die and decompose, the soil continues to deepen. |
| 5. | Shrubs, ferns and small trees begin to grow. They out-compete the grasses and smaller plants and become the dominant species. This leads to an increase in diversity. |
| 6. | The soil is now deep and rich in nutrients. This will support large trees who will then become the dominant species. A climax community has now been formed. |
Secondary succession
This occurs on land that has been cleared of all the plants but soil still remains.
Example
Secondary succession can occur on land where there was a forest fire.
The pioneer species in secondary succession are normally larger plants such as shrubs. As with primary succession, each stage brings different organisms that are better adapted to the improved conditions. This allows them to out-compete existing species and become the dominant species. It also ends in a stable climax community.
Climax communities
Climax communities are the final stage of succession where the ecosystem is supporting the larges and most complex organisms. It will not change much more from this point onwards as it is stable. The species in a climax community depend on the climate of an ecosystem. The climax community for a particular climate is known as its climatic climax.
Climate | Conditions | Species |
| Temperate | Plenty of water, mild temperatures and limited change between seasons. | Large trees can grow once the soil has deepened. |
| Polar | Not much water, low temperatures and massive fluctuations between seasons. | Large trees cannot grow, only shrubs and herbs; but it is still a climax community. |
Conservation
The activities of humans can prevent succession and stop a climax community from developing. This climax community, when succession is stopped artificially, is known as a plagioclimax.
Example
A regularly mown lawn won't be able to grown shrubs and trees, even if the climate is suitable
Sometimes this is done on purpose to protect and preserve (conserve) an ecosystem in its current stage of succession.
Examples
| 1. | Animals are allowed to graze on fields, this stops trees and shrubs from establishing and ensures vegetation is low. This is ideal as it provides a food source to the animals. |
| 2. | Managed fires allow secondary succession to occur. The pioneer species is the species being conserved. |
FAQs - Frequently Asked Questions
What is intraspecific competition?
Intraspecific competition is competition for the same resources between members of the same species.
What is a niche in an ecosystem?
A niche in an ecosystem is the role of a species within its habitat.
What is succession?
Succession is the process by which an ecosystem changes over time.