7.4 Populations in ecosystems

Question 1

Define ecosystem:

Answer 1

A community and all the non living factors of it’s environment

Question 2

Define Population:

Answer 2

A group of organisms, of the same species, that occupy the same habitat at the same time and which potentially can interbreed.

Question 3

Define Community:

Answer 3

All the populations of different species living and interacting in a particular place at the same time.

Question 4

Define Habitat:

Answer 4

The place where an organisms usually lives

Question 5

Define biotic factor:

Answer 5

A living factor in an ecosystem.

Question 6

Define abiotic factor:

Answer 6

A non living factor in an ecosystem

Question 7

Define abiotic factor:

Answer 7

A non living factor in an ecosystem

Question 8

What is an ecological niche:

Answer 8

How an organism fits into an ecosystem. It includes where the organism lives and what it does there. It also includes the biotic and abiotic conditions to which it is adapted. In an ecosystem no two organisms can occupy exactly the same niche.

Question 9

What is carrying capacity?

Answer 9

The largest population a particular environment can sustain

Question 10

What is carrying capacity?

Answer 10

The largest population a particular environment can sustain

Question 11

What is meant by limiting factor:

Answer 11

Any factor that stops the population increasing in size. Can be abiotic/biotic

Question 11

How does population size vary as a result of interactions between organisms?

Answer 11

Interspecific competition = competition between species
- Reduces resources available to both -> limits both populations
If one species is better adapted, it will out-compete the others

Intraspecific competition = competition within species
- Smaller population = less competition -> better for growth and reproduction -> larger population = more competition -> less growth and reproduction -> smaller population.

Predation
- Population sizes of predators and prey are interlinked
Increased predator population size -> more prey eaten -> prey population falls -> less food for predators -> predator population size falls -> prey population rises -> predator population rises again

Question 12

What are specialists?

Answer 12

• Narrow niche
• Less adaptable because of specialised needs
• More likely to become extinct
• Use of specific set of resources
• Easily affected by changing conditions
• Have an advantage when conditions are more constant

Question 13

What are generalists?

Answer 13

• Broad niche
• Adaptable to many environments
• Less likely to become extinct
• Use a variety of resources
• High range of tolerance
• Have an advantage when conditions change

Question 14

When does competition occur?

Answer 14

Happens when resources are not present in adequate amounts ot satisfy all the individuals that depend upon them

Question 15

Describe how you would use frame quadrats to compare the number of daisies in two different fields?

Answer 15

Use a grid / split area into squares
Obtain random coordinates using a random number generator / calculator – place quadrats here
Deciding the number of quadrats to use to collect representative data:
- Calculate running mean
- When enough quadrats, this shows little change
- Count frequency of species in quadrat
Calculate mean per quadrat
Calculate population size by multiplying the mean by the number of quadrats that would cover the habitat

Question 16

Describe how you would use frame quadrates to investigate how the percentage cover serrated wrack (a seaweed) changes with distance from the shore-line?

Answer 16

• Used to look at changes in distribution
• Lay tape measure from one place to another
• Place quadrats at regular intervals along the line
• Count frequency / percentage cover in quadrats

Question 17

How would you go about estimating the size of a population of motile (moving) organisms?

Answer 17

Mark-release recapture:

• Capture sample (harmlessly)
• Count and mark the sample
• Release sample back into the environment - and allow time for organisms to re-integrate
• Capture a second sample
• Count marked individuals in the second sample

Question 18

What is the formula for mark-release-recapture?

Answer 18

Estimated population size = no. of individuals in first sample x no. of individuals in second sample / number of marked individuals recaptured

Question 19

Assumptions made when using the mark-release-recapture method:

Answer 19

1. Sufficient time for marked individuals to mix within the population
2. Marking not removed and doesn’t affect chances of survival e.g. more visible to predators
3. No immigration/emigration
4. No births/deaths/breeding

Question 20

What is succession?

Answer 20

The changes that happen over time in the species that occupy a particular area. In an uncolonised piece of land the first organisms to grow would be the pioneer species. Succession will then take place, and the ecosystem will change, until the climax community is reached.

Question 20

Define pioneer species:

Answer 20

First species to colonise a previously un-colonised habitat.

Question 21

Define climax community:

Answer 21

Final, stable community – Usually mixed woodland in the UK.

Question 22

Describe the process of succession:

Answer 22

1. Colonisation by pioneer species
2. Pioneer species (or generally just certain species at each stage in succession) change the abiotic conditions and make the environment less hostile e.g. die and decompose, forming soil which retains water
3. Environment becomes more suitable for other species with different adaptations, and may be less suitable for the previous species – better adapted species outcompetes previous species
4. As succession goes on, biodiversity increases
5. Climax community: final, complex, stable community

Question 23

Explain the characteristics of a pioneer species?

Answer 23

• Survive in tough/harsh conditions
• Photosynthetic
• Asexual production
• Nitrogen fixation
• Rapid germination

Question 24

What is the difference between primary and secondary succession? Give an example of each.

Answer 24

Primary succession: development of community on an area previously never colonised eg/ volcanic islands, sand dunes

Secondary succession: takes place on previously colonised habitats that have been disrupted eg/ after a forest fire

Question 25

Define conservation:

Answer 25

The management of habitats and ecosystems in a way that ensures they can continued to be used in the future

Question 26

What are the reasons for conservation?

Answer 26

1. Conservation sometimes involves preventing succession in order to preserve an ecosystem in its current stage of succession
2. Food eg/ hunting and fishing
3. Resources - eg/ medicinal plants
4. Aesthetics (tourism, ethics)

Question 27

What are the reasons for conservation?

Answer 27

1. Conservation sometimes involves preventing succession in order to preserve an ecosystem in its current stage of succession
2. Food eg/ hunting and fishing
3. Resources - eg/ medicinal plants
4. Aesthetics (tourism, ethics)