3.7.4 Populations in ecosystems (A-level only)

what is a community

populations of different species

what forms an ecosystem

a community and the non-living components of its environment together form an ecosystem.

what changes biodiversity

Changes that organisms produce in their abiotic environment can result in a less hostile environment and change biodiversity.

what is conservation

the protection and management of species and habitats in a sustainable way.

describe the management of succession

conservation frequently involves preventing succession in order to preserve an ecosystem in its current stages of succession.

what happens within a habitat

a species occupies a niche governed by adaptation to both abiotic and biotic conditions.

what is a niche

the role of a species within its habitat, for example, what it eats, and where and when it feeds.

what is an abiotic factor

are the non-living features of an ecosystem, such as the temperature and soil.

what is a biotic factor

are the living features of an ecosystem, for example,
the presence of predators or food.

what is the carrying capacity

a certain size of a population of species that an ecosystem can support.

how can an ecosystems population size vary

• the effect of abiotic factors
• interactions between organisms: interspecific and
intraspecific competition and predation.

what is the meaning of interspecific

Interspecific competition is when organisms of different species compete with each other for the same resources. This can mean that the resources available to both populations are reduced, e.g. if they share the same source of food, there will be less available to both of them. This means both populations' will be limited by a lower amount of food. They’ll have less energy for growth and reproduction, so both species' population sizes will be lower. If two species are competing but one is better adapted to its surroundings than the other, the less well-adapted species is likely to be out-competed — it won’t be able to exist alongside the better-adapted species.

what is the meaning of intraspecific

Intraspecific competition is when organisms of the same species compete with each other for the same resources. It can cause a cyclical change in population size around the ecosystem’s carrying capacity — where the population grows, shrinks, grows, and so on. This is because the population of a species increases when resources are plentiful. As the population increases, more organisms will compete for the same amount of space and food. Eventually, these resources become limiting. If the population grows beyond the carrying capacity, there won’t be enough resources for all the organisms and the population will begin to decline.
A smaller population then means that there’s less competition for space and food, which is better for growth and reproduction — so the population starts to grow again.

how can the size of a population be estimated

• randomly placed quadrats, or quadrats along a belt transect, for slow-moving or non-motile organisms
• the mark-release-recapture method for motile organisms. The assumptions made when using the mark-release-recapture method.

what is the mark-release-capture method

Mark-release-recapture is a method used to measure the abundance of more mobile species. Here’s how it’s done:

1. Capture a sample of a species using an appropriate technique and count them.
2. Mark them in a harmless way, e.g. by putting a spot of paint on them or by using an identification tag.
3. Release them back into their habitat.
4. Wait a week, then take a second sample from the same population.
5. Count how many of the second samples are marked.
6. You can then use this equation to estimate the total population size

Total population =
size
Number caught in 1st sample x Number caught in 2nd sample/
Number marked in 2nd sample

what is succession

is the process by which an ecosystem changes over time.