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 and abiotic factors

Answer 3

• Biotic: living features of an ecosystem e.g. predators, disease
• Abiotic: non-living features of an ecosystem e.g. light, temperature

Question 4

Define habitat

Answer 4

The place where an organism lives within an ecosystem

Question 5

Define a niche

Answer 5

The role of a species within its habitat, consisting of both biotic interactions e.g. what it eats, and abiotic interactions, e.g. time of day it is active

Question 6

What is meant by carrying capacity?

Answer 6

The maximum size of population an ecosystem can support

Question 7

Name 4 abiotic factors that affect population growth

Answer 7

• Temperature
• Light
• pH
• Water/humidity

Question 8

What is meant by intraspecific and interspecific competition?

Answer 8

• Intraspecific: competition between organisms of the same species
• Interspecific: competition between organisms of different species

Question 9

What resources might organisms compete for?

Answer 9

• Food
• Water
• Shelter
• Light
• Minerals
• Mates (intraspecific only)

Question 10

Describe the pattern of a typical predator-prey relationship in terms of population change

Answer 10

• 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 11

How are quadrats used for estimating population size?

Answer 11

• 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 12

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

Answer 12

• 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 organisms is captured, and the number of marked organisms are counted

Question 13

Equation for mark-release-recapture

Answer 13

Question 14

What assumptions does mark-release-recapture make?

Answer 14

• Marked individuals distribute evenly
• No migration in or out of the population
• Few births or deaths
• Method of marking does not affect survival

Question 15

Why are ecosystems described as being dynamic?

Answer 15

• 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 16

What is meant by primary succession?

Answer 16

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

Question 17

Summarise the process of primary succession

Answer 17

• Pioneer species can survive harsh conditions and 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 18

What is the climax community and how is it reached?

Answer 18

• 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 19

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

Answer 19

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 20

Define conservation

Answer 20

The protection and management of species and habitats, in order to maintain biodiversity

Question 21

How might succession be managed in order to aid conservation?

Answer 21

• 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

Question 22

Succession occurs in natural ecosystems. Describe and explain how succession occurs

Answer 22

1. Colonisation of pioneer species
2. Change in environment due to the species present e.g. species makes environment less hostile
3. Enables other species to colonise - are better competitors than previous pioneer species
4. Change in biodiversity
5. Conditions become more stable
6. Climax community is reached