Populations in Ecosystems

Question 1

Define abiotic factor

Answer 1

A non-living / physical / chemical factor

Question 2

Examples of abiotic factors

Answer 2

soil pH
temperature
salinity (concentration of salt)
carbon dioxide concentration
humidity
light intensity

Question 3

Define biotic factor

Answer 3

predator
prey / food
disease
presence of opposite sex

Question 4

Define population

Answer 4

Groups of organisms of the same species living in the same habitat / ecosystem at the same time;

They have the potential to interbreed;

Question 5

TRUE OR FALSE

Organisisms of the same species that make up a population have the potential to interbreed

Answer 5

TRUE

They will produce fertile offspring

Question 6

Define community

Answer 6

All the populations of the different species in the same habitat / ecosystem at the same time

Question 7

Define ecological niche

Answer 7

The role played by an organism in a
habitat/ecosystem governed by adaptations to biotic/abiotic factors

Question 8

Explain the advantage of different species occupying different niches (1 mark)

Answer 8

Reduced (interspecific) competition for food/resources

Question 9

Define carrying capacity

Answer 9

Certain size of population of a species that can be supported by the ecosystem

Question 10

What can reduce carrying capacity?

Answer 10

Habitat loss;

Reductions in food availability;

Increases in the number of predators;

Disease

Question 11

Ecosystem definition

Answer 11

The interaction between a community and the abiotic components of the environment

Question 12

Competition between organisms of the same species is known as _________________ competition

Answer 12

intraspecific

Question 13

Competition between organisms of different species is known as _________________ competition

Answer 13

interspecific

Question 14

What term describes populations of different species living in the same habitat?

Answer 14

Community

Question 15

Describe and explain what typical patterns emerge when plotting the population sizes of predators and their prey over time (3 marks).

Answer 15

As prey populations increase, there is an increased availability of food for the predator population;

This causes a (delayed) increase in predator population;

Due to the increase in predators, the prey population
will decline;

A decline in prey populations leads to a shortage of food for the predators, and over time their population will also decline;

This decline reduces the predation on the prey population, allowing for interbreeding and an increase in the population size

(and repeat)

Question 16

Why use percentage cover rather than frequency / number of individuals to count algae.

Answer 16

Difficult / too many to count / individual organisms not identifiable / too small to identify/count / grows in clumps;

Question 17

The sundew is a small flowering plant, growing in wet habitats such as bogs and marshes.

Describe how you could estimate the size of a population of sundews in a small marsh (4 marks).

Answer 17

1. Use a grid;
2. Use random number generator for random coordinates (for quadrats);
3. Large sample of quadarts (10 or more);
4. Calculate mean by adding the total number / frequency in a quadrat and divide by number of quadrats;
5. Valid method of calculating total number of sundews, e.g. mean number of plants per m^2 multiplied by number of m^2 in marsh;

Question 18

Describe how you would determine the mean percentage cover for beach grass on a sand dune (3 marks).

Answer 18

1. Use random number generator for random coordinates (for quadrats);
2. Large number of quadrats (20 or more);
3. Divide total percentage by number of quadrats;

Question 19

Precautions needed when marking pine martens (during mark, release & recapture) to make sure the estimate of population size is valid (1 marks).

Answer 19

Marking does not affect survival e.g. make visible to predators (of the pine marten);

OR Marking not toxic so does not affect survival;

OR Marking does not rub off so recaptured pine martens are identified;

Question 20

What are the assumptions made when using the the mark-release-recapture method to make valid estimates of population size?

Answer 20

1. The population size does not change between the two capture times.
   * There should be no increase in predation of the marked organism
   * There should be no migration
2. The marked organisms have enough time to (randomly) disperse/distribute into the rest of the population
3. The marking should not rub off or be lost
4. Sample population is large enough

Question 21

Describe and explain two precautions required to estimate a valid population size for stream tree frogs (2 marks).

Answer 21

1. Marking does not affect survival e.g. make visible to predators;

OR Marking not toxic so does not affect survival;

OR Marking does not rub off so recaptured stream tree frogs are identified;

2. Time delay after release / before recapture so stream tree frogs are spread back into the population;

Question 22

Hostile environments such as rock and sand are colonised by ______________

Answer 22

pioneer species

Question 23

Characteristics of pioneer species

Answer 23

Photosynthesise;

Fix nitrogen;

Asexual reproduction;

Tolerance to hostile environments;

Question 24

At each stage in [1], certain species may be recognised which change the [2] so that it becomes more suitable for other species with different adaptations. The new [3] may change the environment in such a way that it becomes less suitable for the previous species.

Answer 24

[1] succession
[2] environment
[3] species

Question 25

Succession occurs in natural ecosystems.

Describe and explain how succession occurs (5 marks).

Answer 25

1. (Colonisation by) pioneer (species);
2. Change in environment / example of change caused by organisms present e.g. adds more humus;
   (humus = is the formation of a thin / basic layer of soil)
3. Enables other species to colonise / survive;
4. Increase in biodiversity;
5. Stability increases / less hostile environment;
6. Climax community;

Question 26

Final stage of primary succession

Answer 26

Climax community

Question 27

Features of a climax community

Answer 27

1. Same species present (over long time) / stable community (over long time);
2. Abiotic factors (more or less) constant (over time)
3. Populations stable (around carrying capacity)

Question 28

Reasons for conserving rainforests

Answer 28

1. Conserve / protect
   species / plants / animals / organisms

OR For (bio)diversity;

2. Conserve / protect habitats

OR Provides / many habitats ;

3. Reduces climate change;
4. Source of medicines/drugs/wood;
5. Reduces erosion/eutrophication;
6. (For) tourism;