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

Describe biotic factors, giving examples

Answer 3

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

Question 4

Describe abiotic factors, giving factors

Answer 4

Abiotic = 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 its 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

• Temperature
• Light
• pH
• Water

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 (intraspecifc 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 populations 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 is captured, and the number of marked organisms are counted

Question 15

What is the equation for mark-release-recapture?

Answer 15

Estimated population size = total no. of individuals in 1st sample x total no. of individuals in 2nd sample / no. 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 and colonise the area
• They change abiotic factors of their environment
• Over time, this allows more complex organisms to survive

Question 20

What is the climax community?

Answer 20

The final stage of succession, where the ecosystem is balanced and stable

Question 21

How is the climax community reached?

Answer 21

It is reached when the soil is rich enough to support large trees or shrubs, and the environment is no longer changing

Question 22

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

Answer 22

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 23

Define conservation

Answer 23

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

Question 24

How might succession be managed in order to aid conservation?

Answer 24

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