Populations and ecosystems

Question 1

Define community.

Answer 1

All the different species that live in one area and interact with each other.

Question 2

Define ecosystem.

Answer 2

All the living organisms found in one area, combined with non-living aspects of their environment. Can vary from very large to very small.

Question 3

What is meant by the term ‘biotic factor’?

Answer 3

living features of an ecosystem e.g. predators, disease.

Question 4

What is meant by the term ‘abiotic factor’?

Answer 4

non-living features of an

ecosystem e.g. light, temperature.

Question 5

Define habitat.

Answer 5

The place where an organism lives within an ecosystem.

Question 6

Define a niche.

Answer 6

The role of a species within its habitat, consisting of both its biotic interactions

e. g. what it eats, and abiotic interactions
e. g. time of day it is active.

Question 7

What is meant by carrying capacity?

Answer 7

The maximum size of population an ecosystem can support.

Question 8

Name four abiotic factors that affect population growth.

Answer 8

1. Temperature
2. Light
3. pH
4. Water/humidity

Question 9

What is meant by intraspecific competition?

Answer 9

competition between

organisms of the same species.

Question 10

What is meant by interspecific competition?

Answer 10

competition between

organisms of different species.

Question 11

What resources might organisms compete for?

Answer 11

Food, water, shelter, minerals, light, mates (intraspecific only).

Question 12

Describe the pattern of a typical predator-prey

relationship in terms of population change.

Answer 12

● Prey is eaten by predator, resulting in predator
population increasing and prey population decreasing.
● Fewer prey means increased competition for food, so predator population decreases.
● Fewer predators means more prey survives, and the cycle begins again.

Question 13

How are quadrats used for estimating population size?

Answer 13

Can be placed on grid coordinates, or at intervals along a belt transect. Results reported as either percentage cover or
frequency. For slow-moving or non-motile organisms

Question 14

How is mark-release-recapture used for estimating population size?

Answer 14

● A sample of a species is captured, marked, then
released back into the same area they were caught.
● After a certain period of time another sample of the
is captured, and the number of marked organisms are counted.
For motile organisms

Question 15

What is the equation for mark-release-recapture?

Answer 15

Estimated population size =
total number of individuals in the first sample X
total number of individuals in the second sample
/number of marked individuals recaptured

Question 16

What assumptions does the

mark-release-recapture method make?

Answer 16

● Marked individuals distribute evenly.
● No migration in or out of the population.
● Few births or deaths.
● Method of marking does not affect survival.
● Mark does not come off.

Question 17

Why are ecosystems described as being dynamic?

Answer 17

● Populations constantly rise and fall.
● Any small change can have a large effect.
● Biotic and abiotic factors may alter the conditions of the ecosystem

Question 18

What is meant by primary succession?

Answer 18

Where an area previously devoid of life is colonised by a community of organisms.

Question 19

Summarise the process of primary succession.

Answer 19

● Pioneer species can survive harsh conditions &
colonise the area.
● They change abiotic factors of their environment
e.g. decomposition adds nutrients to ground.
● Over time, this allows more complex organisms to
survive.

Question 20

What is the climax community and how is it reached?

Answer 20

The final stage of succession, where the ecosystem is balanced and stable.
It is reached when the soil is rich enough to support large trees or shrubs, and the environment is no longer changing.

Question 21

How might a species alter the environment that

develops during succession?

Answer 21

A species may improve the environment to make it more suitable for other species. Alternatively, a species may worsen the
environment by making it less suitable for other species

Question 22

Define conservation.

Answer 22

The protection and management of species and habitats, in order to maintain biodiversity. Methods need to be adapted to the ecosystem in question.

Question 23

How might succession be managed in order to aid conservation?

Answer 23

Sometimes succession needs to be prevented in order to preserve an
ecosystem at a certain point, e.g. stopping
moorland from progressing into spruce forest. This is called a plagioclimax