3.7.4 Populations in ecosystems

Question 1

Define populations

Answer 1

group of organisms of the same species living in the same area at the same time that can interbreed to make fertile offspring

Question 2

Define habitat

Answer 2

Part of ecosystem where an organism lives

Question 3

Define community

Answer 3

All populations of different species living in the same area at the same time

Question 4

Define ecosystem

Answer 4

A community and the biotic and abiotic factors

Question 5

Define niche

Answer 5

Organisms role in an ecosystem, e.g. position in the food web, habitat. Each species occupies its own niche governed by adaptations to biotic and abiotic factors

Question 6

Define carrying capacity

Answer 6

Maximum population size an ecosystem can hold

Question 7

Define abiotic factors

Answer 7

non - living conditions

Question 8

Define biotic factors

Answer 8

living conditions

Question 9

Name 5 abiotic factors

Answer 9

1) oxygen and carbon dioxide concentration
2) temperature
3) light intensity
4) pH
5) soil conditions

Question 10

How do abiotic factors affect population size?

Answer 10

The less harsh the abiotic factors the larger the range of species and the larger the population size

Question 11

How does temperature affect population?

Answer 11

• Extreme temperatures affect enzymes. Too cold - enzyme does not have enough kinetic energy to catalyse reaction. Too hot - enzyme will denature. Reducing overall metabolic
  activity. Reduces survival
• Too hot causes excess water loss and dehydration
• The more extreme the temperature, fewer species survive. Those who do survive have a smaller population size

Question 12

How does light intensity affect population?

Answer 12

• Light is needed for photosynthesis. Higher light intensity, greater rate of photosynthesis so more energy for seed/spore production and the population will increase faster
• More plants grow the more respiratory substrates available for animal populations (glucose and amino acids)

Question 13

How does water availability affect population?

Answer 13

Water needed as solvent and in metabolic reactions. Lower the humidity means more water loss. Different species water toleration varies.

Question 14

How does pH affect population?

Answer 14

pH affects enzymes and proteins. More extreme pH, more organism is affected, lower population size and range of species present.

Question 15

What is interspecific competition?

Answer 15

Members of different species compete for the same limited resource. Individual better adapted to environment is more likely to succeed.

Question 16

What is intraspecific competition?

Answer 16

Members of the same species are competition for resources. Tends to be fiercer as same species have the same requirements.

Question 17

What three patterns do predator and prey patterns always follow

Answer 17

1) Size of predator and prey population both fluctuate
2) Prey population will peak at a higher point
3) Size of population will change in prey and then predators (lag time)

Question 18

How does predator and pray relationships affect population?

Answer 18

• as prey population increases, more food for predators, inftaspecific competition reduces. Population of predator increases
• as more prey is consumed, prey population falls. Intra-specific competition increases and there’s less food. Predator population decreases

Question 19

When would you use mark-release-recapture?

Answer 19

Mobile/moving organisms

Question 20

Describe mark-release-recapture method

Answer 20

1) Initial species ethically captures
2) Individuals marked
3) Individual released and left for a period of time to randomly redistribute through habitat
4) Catch a second sample. Record total of sample and number who were recaptured (had marking)
5) Estimate population size

Question 21

How to estimate population size mark-release-recapture?

Answer 21

N1 x N2 / Nm

N1 - sample one
N2 - sample two
Nm - Number of second sample which were marked

Question 22

How to get more accurate results in mark - release - recapture?

Answer 22

Repeat and calculate mean to make it more reliable

Question 23

Ethics to consider in mark - release - recapture

Answer 23

• How species are captures and marked must cause no permanent harm
• Mark not toxic
• Mark mustn’t increase predation
• Marks must not reduces chances of reproduction

Question 24

Why might mark - release - recapture may not be accurate (2)

Answer 24

• we assume population is constant (no births/death/migration)
• we assume animals redistribute evenly

Question 25

What is succession?

Answer 25

Change in ecological community over time

Question 26

What is the pioneer species?

Answer 26

Organisms that first colonise an area

Question 27

What is a climax community?

Answer 27

Is stable and changes very little. Last stage in succession

Question 28

Describe and explain how succession occurs?

Answer 28

1) Colonisation by names pioneer species
2) Changes in environment caused y organisms
3) Enables other named species to colonise and survive
4) Changes in biodiversity
5) Stability increases and makes a less hostile environment
6) Climax community represented by named species

Question 29

When do you use percentage cover when investigating populations? (4)

Answer 29

• Too many individuals to count
• Organism is too small
• Hard to identify
• Overlap with other species

Question 30

When would you use quadrats?

Answer 30

Non-mobile or slow moving organisms with uniform distribution

Question 31

When would you use transects?

Answer 31

Slow moving/ non-mobile organisms with uneven distribution

Question 32

Random sampling method

Answer 32

1) Lie two tap measures at a right angle to create a gridded area
2) Use a random number generator to generate coordinates
3) Place the quadratic and collect the data
4) Repeat at least 30 times to collect a mean

Question 33

What is a belt transect

Answer 33

Place quadratic at every position along tape measure

Question 34

What is an interrupted belt measure?

Answer 34

Quadra placed at uniform intervals along the tape

Question 35

Describe line transect method

Answer 35

1) Place the tape measure at a right angle to shore line
2) Place the quadrat every 4 meters
3) Collect the data
4) Repeat by placing another 30 transects along the beach at right angle to the shore lone

Question 36

What is and how to measure frequency?

Answer 36

• The proportion of quadrats that contain a particular species

Question 37

What is and how to measure density?

Answer 37

• The number of one species in a given area
• density = (area of whole area/area of quadrat) X number of species in quadrat

Question 38

What is and how to measure percentage cover?

Answer 38

• proportion of ground occupied by species
• (total area covered by species/ total area of all quadrants) x 100

Question 39

Advantages of frequency (2)

Answer 39

• quick to sample large area
• useful if its difficult to identify or too many to count

Question 40

Disadvantages of frequency (1)

Answer 40

Poor accuracy as it doesn’t consider overlapping or size of plant

Question 41

Advantages of density (2)

Answer 41

• More accurate if organism is easy to distinguish
• Used to estimate species richness (count the number of different species present)

Question 42

Disadvantages of density (1)

Answer 42

Time consuming

Question 43

Advantages of percentage cover (2)

Answer 43

-Quicker
- Useful for organisms that are hard to identify or too many to count