Topic 7C: Populations in Ecosystems

Question 1

Definition: Ecosystem

Answer 1

All of the living organisms in a community, plus all the non-living conditions in the area in which they live.

Question 2

Definition: Biotic conditions

Answer 2

The living-features of an ecosystem.

Question 3

Definition: Abiotic factors

Answer 3

The non-living features of an ecosystem.

Question 4

Definition: Habitat

Answer 4

The place where an organism lives within an ecosystem.

Question 5

Definition: Niche

Answer 5

The role of a species within its habitat, which can be explained in two categories - it’s biotic interactions, and it’s abiotic interactions.

Question 6

Niche: Biotic interactions

Answer 6

What the organism eats, or is eaten by etc.

Question 7

Niche: Abiotic interactions

Answer 7

The temperature range an organism lives in, the time of day it eats etc.

Question 8

What are the features of a niche?

Answer 8

• Every species has a unique niche.
• If two species try to occupy the same niche, one species will outcompete the other meaning the other species won’t be able to survive.

Question 9

Definition: Adaptation

Answer 9

A feature which members of a species have that increase their chances of survival and reproduction.

Question 10

What are the different types of adaptations?

Answer 10

• Physiological:
Processes inside the organisms body.

• Behavioural:
The way the organism acts.

• Anatomical:
Structural features of the organisms body.

Question 11

Definition: Population

Answer 11

All of the organisms of one species in a habitat.

Question 12

Definition: Community

Answer 12

Made up of the different populations in a habitat.

Question 13

Definition: Carrying capacity

Answer 13

The maximum stable population size of a species that an ecosystem can support.

Question 14

How do abiotic factors affect population size?

Answer 14

• If abiotic conditions are ideal for a species, organisms can grow quicker and reproduce more successfully.
• If abiotic conditions are not ideal for a species, organisms cannot grow as fast or reproduce as successfully.

Question 15

How do biotic factors affect population size: Interspecific competition

Answer 15

1) Organisms of a different species compete for the same resources.
2) Resource availability for each population is reduced.
3) Therefore, organisms have less energy for growth and reproduction, so the population size of each species decrease.
4) One species will be better adapted to the environment and so outcompete the other.

Question 16

How do biotic factors affect population size: Intraspecific competition

Answer 16

1) Organisms of the same species competed for the same resources.
2) This causes a cyclical change in population size around the ecosystem’s carrying capacity.
3) When resources are plentiful, population size increases.
4) However, because there are more organisms within the population, resources become limited and the population size falls.
5) Then, there is less competition, so population size increases once again.

Question 17

How do biotic factors affect population size: Predation

Answer 17

1) One organism (predator) eats another (prey).
2) As the prey population decreases, there isn’t enough food to support the predator population, so the predator population size falls.
3) Therefore, the prey population increases, which means there is more food availability for the predators.
4) This allows the predator population to increase once again, meaning more prey are being fed on, and the prey population falls.

Question 18

How do you investigate population growth in bacteria?

Answer 18

1) Produce a broth culture containing bacteria
2) Pass light through the broth culture.
3) Use a spectrophotometer to measure the absorbable value.
4) Repeat at regular time intervals.

The more bacteria present in the culture, the less light will pass through and be detected by the spectrophotometer, producing a higher absorbance value.

Question 19

Definition: Abundance

Answer 19

The number of individuals of one species in a particular area.

Question 20

How is abundance measured?

Answer 20

• Counting the number of individuals in a sample.
• Finding the frequency by calculating the percentage of samples in which the species was present.
• Finding the percentage cover of the sample.

Question 21

Definition: Distribution

Answer 21

Where a particular species is within an area which you are investigating.

Question 22

How do you carry out random sampling?

Answer 22

1) Choose an area to sample using a random number generator to avoid bias.
2) Take a sample of the population using a technique such as a quadrat.
3) Repeat the process to increase reliability.
4) Calculate an estimate for the distribution of the whole area.

Question 23

Methods for investigating population: Quadrats

Answer 23

1) Randomly place on ground at different places to avoid bias.
2) Record the species frequency in each location.

Question 24

Methods for investigating population: Transects

Answer 24

1) Place quadrats side by side or at regular intervals along a line.
2) Measure how species frequency changes from one quadrat to the next.

Question 25

Methods for investigating population: Capturing motile organisms

Answer 25

1) Use a net or pitfall trap to capture organisms.

2) Investigate any organisms you have captured.

Question 26

Why is the mark-release-recapture method used?

Answer 26

To measure the abundance of more mobile species.

Question 27

How do you carry out the mark-release-recapture method?

Answer 27

1) Capture a sample of a species and count them.
2) Mark then in a harmless way before releasing them back into their habitat
3) After a period of time, take a second sample from the same population.
4) Count how many of the second sample are marked and use the equation to estimate the total population size.

Question 28

Mark-release-recapture: Equation

Answer 28

Total population size = (no. caught in first sample x no. caught in second sample) / no. marked in second sample

Question 29

What does the accuracy of the mark-release-recapture method depend on?

Answer 29

• Marked sample must have enough time to mix back in with original population.
• Marking mustn’t affect chances of survival.
• There mustn’t be any changes in population size during study.

Question 30

Definition: Succession

Answer 30

A process by which an ecosystem changes over time, as one community of organisms is replaced by another.

Question 31

What is the process of primary succession?

Answer 31

1) A pioneer species colonise the area.
2) Pioneer species die and are decomposed by microorganisms, which produces soil.
3) This makes conditions more favourable for a new species, which move in and out compete the old species.
4) This increases diversity as the conditions become less hostile.

Question 32

What limits the size of a climax community?

Answer 32

• Availability of sunlight/nutrients for LDR’s of photosynthesis, which provide energy for consumers.
• Disease.
• Predation.
• Competition for food/space.

Question 33

What is secondary succession?

Answer 33

The same as primary succession but there is already a layer of soil present (e.g. after deforestation) meaning the pioneer species is often larger.

Question 34

What are the human impacts on succession?

Answer 34

• Human activities can prevent succession, meaning a climax community will not be produced.
• Instead, a plagioclimax is produced.

Question 35

Definition: Conservation

Answer 35

The protection and management of species and habitats in a sustainable way.

Question 36

Definition: Sustainable

Answer 36

Enough resources are used to meet the needs of people today, without reducing the ability of people in the future to meet their own needs.

Question 37

Conservation methods: Management of succession

Answer 37

Succession is prevented in order to preserve an ecosystem in its current stage of succession.

Question 38

Conservation methods: Seed banks

Answer 38

• A seed bank is a store of seeds from lots of different plant species, which act as a back up for the conservation of plant species in the wild.
• Large amounts can be conserved in a small area, and can be stored anywhere in the world for long periods of time.

Question 39

Conservation methods: Captive breeding

Answer 39

• Captive breeding programmes involve breeding animals in a controlled environment, so that endangered species can be bred in captivity to help increase their numbers.
• These animals can then be reintroduced to the wild, increasing the natural population.

Question 40

Conservation methods: Fishing quotas

Answer 40

• Fishing quotas are limits to the amount of certain fish species that fisherman are allowed to catch, reducing the number of fish being captured and killed.
• Fisherman are unhappy with quotas as it limits their possible income and dead fish are often discarded.

Question 41

Conservation methods: Protected areas

Answer 41

• Protected areas protect habitats and the species in them by restricting industrial developments and farming.