7.4 POPULATION IN ECOSYSTEMS

Question 1

What is an ecosystem?

Answer 1

A community that includes all the biotic and abiotic factors.

Question 2

What is the carrying capacity?

Answer 2

The size of the population that the ecosystem can support.

Question 3

What is the community?

Answer 3

All populations of different species live in the same place at the same time.

Question 4

What is a habitat?

Answer 4

A place where an organism normally lives and is characterised by its physical features.

Question 5

What is a niche?

Answer 5

The organism’s role in the environment, ie where it lives / what it does, etc.

Question 6

What abiotic factors affect the population size & variation?

Answer 6

• Temperature: each species has a different optimum temperature, the further away from this the fewer individuals that are able to survive.
• pH: this can have an impact on the action of enzymes with each enzyme having an optimum pH that it can work at.
• Light: this is a basic necessity of light, with the rate of photosynthesis increases as light intensity increases.
• Water: in instances where water is scarce only small populations of adapted species will exist.
• Humidity: affects transportation in plants and therefore only those that are adapted to environments where transpiration is high will survive.

Question 7

What is intraspecific competition?

Answer 7

Competition between members of the same species.

Question 8

What are some examples of things that are competed over?

Answer 8

• Food
• Water
• Mates
• Shelter
• Niches

Question 9

What is interspecific competition?

Answer 9

Competition between members of different species.

Question 10

What is predation?

Answer 10

When numbers of predators and prey fluctuate due to feeding and death.

Question 11

Outline the predator-prey cycle

Answer 11

1. Prey gets eaten so numbers fall.
2. Therefore predator number grows and prey keeps going down.
3. Lack of prey means predator population falls.
4. Therefore prey population can recover with fewer predators.
5. The cycle starts again.

Question 12

How do you sample non-motile organisms? (2)

Answer 12

1. Random sampling

2. Systematic sampling

Question 13

What is a point quadrat?

Answer 13

• Horizontal bars with 10 holes and a long pin that can be dropped through any hole.
• Each species the pin touches is recorded.

Question 14

What is a frame quadrat?

Answer 14

• A square is divided into equal divisions by a wire.
• Placed at different locations to measure abundance.
• The abundance found by one quadrat can be scaled up to find the abundance of the whole area.

Question 15

How do you measure the abundance of a species? (2)

Answer 15

1. Frequency by counting the actual number.
2. Percentage cover, used when the frequency is hard to count so you can roughly eyeball the percentage cover of a quadrat.

Question 16

How do you sample motile organisms?

Answer 16

The mark-release-recapture system (MRR)

Question 17

Outline MRR.

Answer 17

1. Animals are caught and marked.
2. Animals are released back into the community.
3. Sometime later animals are recaptured, and the marked no. from this group are recorded.

Question 18

What is the equation used after carrying out MRR?

Answer 18

(no. in sample 1 x no. in sample 2) / marked individuals recaptured.

Question 19

What must you do when carrying out MRR?

Answer 19

• Make sure the mark is inconspicuous, non-toxic, and durable.
• Give time for the first population to evenly redistribute back into the ecosystem.

Question 20

What assumptions does MRR rely on?

Answer 20

• Proportion of marked individuals in the second sample is indicative of their proportion of the whole population.
• There must be definitive boundaries to the population. (no immigration/emigration)
• No net deaths or births.

Question 21

What is succession?

Answer 21

Changes in the ecosystems over time in terms of the species that inhabit that area. It is what makes the ecosystem dynamic and ever-changing.

Question 22

Outline the stages of succession.

Answer 22

1. Barren, hostile land is colonised by pioneer species.
2. As pioneers die, they decompose to form soil. They are broken down to form nutrients and allow secondary colonisers to grow and inhabit.
3. Over time, the soil gets richer and allows for more colonisers to inhabit.
4. Once the environment has stayed stable for a long time, it has reached the climax community.

Question 23

How does succession increase biodiversity?

Answer 23

• More nutrients over time
• More habitats
• More niches
• More competition so the most advantageous organism live on.
• Abiotic features get less hostile
• More biomass
• More complex food webs

Question 24

Why are climax communities cleared and secondary succession begins?

Answer 24

Allows original species to come back to their habitats and makes it possible to conserve these rather than let them die out during succession.