3.7.4 Populations in 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

Define biotic factors.

Answer 3

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

Question 4

Define abiotic factors.

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.

Question 7

What is meant by carrying capacity?

Answer 7

The maximum size of population an ecosystem can support.

Question 8

State 4 abiotic factors affecting 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 a predator, resulting in the predator population increasing and the 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

What is mark-release-recapture?

Answer 14

A method used for estimating population size.

Question 15

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

Answer 15

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

For motile organisms.

Question 16

Mark-Release-Recapture Equation

Answer 16

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 17

5 Assumptions of Mark-Release-Recapture

Answer 17

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

Question 18

Why are ecosystems described as being dynamic?

Answer 18

• Populations constantly rise and fall.
• Small changes can have large effects.
• Biotic and abiotic factors may alter the conditions.

Question 19

What is meant by primary succession?

Answer 19

The process where an area previously devoid of life is colonised by a community of organisms.

Question 20

What are pioneer species?

Answer 20

Pioneer species are organisms that can survive harsh conditions and colonize an area.

Question 21

How do pioneer species affect abiotic factors?

Answer 21

Pioneer species change abiotic factors like decomposition, which adds nutrients to the ground.

Question 22

What is the result of nutrient addition in primary succession?

Answer 22

The addition of nutrients allows more complex organisms to survive over time.

Question 23

What is a climax community?

Answer 23

The final stage of succession in an ecosystem.

Question 24

What characterises a climax community?

Answer 24

It is balanced and stable.

Question 25

What conditions are necessary for a climax community to be reached?

Answer 25

The soil must be rich enough to support large trees or shrubs.

Question 26

What happens to the environment in a climax community?

Answer 26

The environment is no longer changing.

Question 27

How might a species alter the environment that develops during succession?

Answer 27

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

Question 28

Define conservation.

Answer 28

The protection and management of species and habitats, in order to maintain biodiversity, with methods adapted to the ecosystem in question.

Question 29

How might succession be managed in order to aid conservation?

Answer 29

Sometimes succession needs to be prevented to preserve an ecosystem at a certain point, e.g., stopping moorland from progressing into spruce forest, known as a plagioclimax.