7.4 - Populations In Ecosystems

Question 1

Define ‘community’.

Answer 1

All the different species that live in one are & 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 very from very small to very large.

Question 3

Describe ‘ biotic’ factors.

Answer 3

Living features of an ecosystem e.g. predators, disease.

Question 4

Describe ‘abiotic’ factors.

Answer 4

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 interaction (e.g time of day it’s active).

Question 7

What is meant by ‘carrying capacity’?

Answer 7

The maximum size of population an ecosystem can support.

Question 8

Name 4 abiotic factors that affect population growth.

Answer 8

1) Temperature
2) Light
3) pH
4) Water/humidity

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 (intraspecific 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 population 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 a 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

For motile organisms
1) capture sample of species
2) mark them in a harmless way
3) release them back into their habitat
4) wait an appropriate amount of time for sample to re-disperse into habitat
5) take a second sample from same population
6) count how many of the second sample are marked

Question 15

What is the mark-release-recapture equation?

Answer 15

Estimated population size = (total number of individuals in the 1st sample x number caught in 2nd sample) / number marked in 2nd sample

Question 16

What assumptions does the mark-release-recapture method make?

Answer 16

• marked individuals distribute evenly
• no migration in/out of populations
• no net changes in population due to births and deaths
• method of marking doesn’t effect survival
• mark doesn’t 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 & 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 & colonise newly formed land
• they change abiotic factors of their environment (as they decompose adding nutrients to soil) making environment less hostile, allowing more complex organisms to survive

Question 20

What is the climax community and how is it reached?

Answer 20

The final stage of succession, where the ecosystem is balanced & stable. It is reached when the soil is rich enough to support large trees or shrubs, and the environment is no longer changing.

Question 21

Give examples of why an environment may be described as ‘hostile’.

Answer 21

There is a limited water supply, as there’s no water to retain soil.
There are few minerals or nutrients because there’s no soil.
There may be high light intensity, exposure to wind and rain, and fluctuating temperature, because the area is directly exposed to the Sun and the elements.

Question 22

Define ‘conservation’.

Answer 22

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

Question 23

How might succession be managed in order to aid conservation?

Answer 23

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 plagioclimax.

Question 24

What is secondary succession?

Answer 24

Similar process to primary succession, but occurs on land that’s been cleared of life, but soil still remains. Can occur during any stage after pioneer stage. The established community of species is disturbed without too much soil disturbance.
Pioneer species are larger plants.

Question 25

List 5 conservation methods.

Answer 25

1) management of succession
2) seed banks
3) captive breeding
4) fishing quotas
5) protected areas

Question 26

Describe the ‘seed bank’ method of conservation.

Answer 26

A seed bank is a store of seeds from lots of different plant species. They act as a backup - if a species becomes extinct, stored seeds can be used to reintroduce it.
Seed banks are good as they don’t take up a lot of space, & can be stored anywhere thats cool and dry.
However, seeds have to be regularly tested to see if they’re still viable (expensive & time consuming)

Question 27

Describe the ‘captive breeding’ method of conservation.

Answer 27

Breeding endangered animals in controlled environments, with the aim of reintroducing them to the wild.
Cons: reintroduced animals can bring new diseases to habitats.

Question 28

Describe the ‘fishing quotas’ method of conservation.

Answer 28

Limits to the amount of certain fish species that fisherman are allowed to catch.
Cons: limits fishers potential income, ‘discards’ = when fishermen throw fish back into the ocean, which are already dead, international cooperation needed in oceans.

Question 29

Describe the ‘protected areas’ method of conservation.

Answer 29

E.g. national parks & nature reserves
Restrict urban development
Cons: used as tourist destinations which could equally harm animals

Question 30

How does evolution occur?

Answer 30

By genetic drift or by natural selection

Question 31

What causes natural selection?

Answer 31

Organisms face selectional pressures.
Due to variation of different alleles, some organisms are more adapted to certain selectional pressure than others.
Individuals with a phenotype that increases their chance of survival are more likely to survive & reproduce, passing on their genes.
So, greater proportion of next generation inherit beneficial alleles.

Question 32

What are ‘selection pressures’?

Answer 32

Pressures that affect an organisms chance of surviving, such as predation, disease and competition.

Question 33

Name the 3 types of natural selection.

Answer 33

Stabilising selection
Directional selection
Disruptive selection

Question 34

What is ‘stabilising selection’?

Answer 34

Type of natural selection.
Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.
This occurs when environment isn’t changing
Reduces range of possible phenotypes.

Question 35

What is ‘directional selection’?

Answer 35

Type of natural selection.
Where individuals with alleles for a single extreme phenotype are more likely to survive & reproduce.
Caused by an environmental change.

Question 36

What is ‘disruptive selection’?

Answer 36

Type of natural selection.
Where individuals with alleles for extreme phenotypes are more likely to survive & reproduce.
Opposite of stabilising selection, as characteristics towards the middle of the range are lost.
Occurs when the environment favours more than one phenotype.

Question 37

What is ‘speciation’?

Answer 37

Development of new species from an existing species.
Occurs when populations of the same species become reproductively isolated.
Changes in allele frequency causes changes in phenotype, which means they can no longer interbreed to produce fertile offspring.

Question 38

Name the 2 types of speciation.

Answer 38

Allopatric speciation
Sympatric speciation

Question 39

What is ‘allopatric’ speciation?

Answer 39

Occurs in populations that are geographically separated
So animals experience slightly different conditions, e.g. different climate
Populations experience different selectional pressures, so different changes in allele frequencies could occur, due to them being more advantageous, mutations & genetic drift.
Overtime, this may lead to speciation.

Question 40

What is ‘sympatric’ speciation?

Answer 40

Occurs when random mutations within a population prevent mutated individuals from breeding with other members of the population that don’t carry the mutation.
It doesn’t involve geographical isolation.
This is very rare.

Question 41

What is ‘genetic drift’?

Answer 41

Sometimes referred to as ‘random drift’
When chance dictates which alleles are passed on, rather than environmental factors.
Individuals within a population show variation.
By chance, allele for 1 genotype is passed on to more offspring than others, so number of individuals with this allele increases.
If, by chance, same allele is passed on more often again, can eventually lead to evolution.