3.7.4 Populations in ecosystems

Question 1

Why is sampling used on populations?

Answer 1

investigates the abundance and distribution of species and populations

Question 2

What are the benefits of random sampling?

Answer 2

-no bias

Question 3

What are the negatives of systematic sampling?

Answer 3

-potential bias towards certain areas
-unrepresentative data of whole area

Question 4

What are the 3 main sampling methods used when estimating size of population?

Answer 4

-quadrats (non-motile/ slow-moving)
-transects (non-motile/ slow-moving)
-mark-release-recapture (motile)

Question 5

Method of measuring population size using quadrats

Answer 5

1. Lay 2 tape measures at right angles to create a gridded area
2. Use a random number generator to generate 2 random coordinates
3. Place quadrat in location and collect data (% cover/ no. organisms/ frequency)
4. Repeat at least 30 times
5. Calculate mean/ multiply up for area size

Question 6

What is species frequency?

Answer 6

probability that the species will be found within any quadrat in the sample area

Question 7

What are the benefits of calculating % cover using a quadrat?

Answer 7

-fast
-no problem of identifying where organism starts/ finishes or if there is any overlapping of organisms

Question 8

What are the benefits of calculating density (number of individuals of a particular species) using a quadrat?

Answer 8

-estimates species richness
-accurately represents population size
-able to identify individual species

Question 9

When is systematic sampling more appropriate?

Answer 9

where abiotic factors change throughout an area (uneven distribution)

Question 10

What is a belt transect?

Answer 10

placing quadrat at every position along tape measure

Question 11

What is an interrupted belt transect?

Answer 11

place quadrat at uniform intervals along tape measure (e.g. every 5 metres)

Question 12

How do you sample motile organisms?

Answer 12

mark-release-recapture

Question 13

What is the method of mark-release-recapture?

Answer 13

1. Capture first sample + mark
2. Release + leave (for 24 hours) to allow distribution within habitat
3. Reset traps and capture second sample
4. Count number marked vs total number captured
5. Use calculation to estimate size of population
6. Multiple repeats (to increase accuracy and reliability)

Question 14

Equation for estimated population size using mark-release-recapture

Answer 14

no. organisms initially caught * no. organisms in second sample / no. organisms marked that were recaptured

Question 15

What are the 2 main assumptions made when calculating population size using mark-release-recapture?

Answer 15

1. Population size is constant (no new births/ deaths/ migration - in reality this will not happen)
2. Evenly distribute when released (reality they will distribute to one location - rich in food, shelter, water, lack of predators)

Question 16

What is succession?

Answer 16

sequential changes within an ecosystem over time

Question 17

What is each stage of succession called?

Answer 17

seral

Question 18

Seral 1: What species colonise the bare habitat?

Answer 18

pioneer species

Question 19

What are key features of pioneer species?

Answer 19

-tolerant to extreme conditions
-grow quickly
-are not able to compete for resources
-are not influences by or dependent on animal species

Question 20

Example of species colonising bare rock

Answer 20

Lichen
-algae (photosynthesis - glucose)
-fungi (release extracellular enzymes and break down rock to access minerals)

Question 21

Seral 2: What forms as pioneer species die and decay?

Answer 21

thin layer of hummus - retains water and some minerals (allows growth of small and simple plants)

Question 22

Seral 3: What species grow and why?

Answer 22

larger species - soil depth has increased, so more nutrients and water are retained in soil so larger species can dig in roots and survive

Question 23

Seral 4: Why are pioneer species and smaller species not present?

Answer 23

taller/ larger species create shading (outcompeted for resources/ sunlight)

Question 24

Seral 5: What are the species called that are found here?

Answer 24

climax species (trees e.g. oak)

Question 25

Seral 5: What is the biodiversity like?

Answer 25

Increased - increased range of species (more stable environment as abiotic conditions are more favourable)

Question 26

What are some key features of the climax species?

Answer 26

-larger -able to compete for resources -can be 1 dominant species -not tolerant to harsh conditions -has a specialised niche -have large energy stores -strongly influenced by other organisms -found in end point of a community

Question 27

When does secondary succession occur?

Answer 27

-seral is abruptly removed -succession will happen more rapidly

Question 28

What are features of deflected succession?

Answer 28

climax community is not reached (due to human activity - e.g. agriculture)

Question 29

Why would you want to prevent progression of succession?

Answer 29

hold a distinct diversity of plant species and conserve a greater range of habitats

Question 30

Methods to prevent succession through conservation

Answer 30

-coppicing -agriculture -ploughing/ cutting grass regularly -burning

Question 31

What is a population?

Answer 31

a group of individuals of the same species that occupy a habitat at the same time

Question 32

Population curves show the change of population over time in...

Answer 32

ideal conditions (not realistic as there would be limiting factors)

Question 33

What is carrying capacity?

Answer 33

maximum number of individuals an environment can support in the long-term

Question 34

If a population is near its carrying capacity...

Answer 34

resources are limited

Question 35

Why are there natural fluctuations in carrying capacity?

Answer 35

predator vs prey relationship

Question 36

What abiotic factors affect where an organism lives?

Answer 36

-temperature -light intensity -humidity -pH -salinity -oxygen conc. -gradient -topography -periods of desiccation

Question 37

What is intraspecific competition?

Answer 37

competition between same species for resources

Question 38

What is interspecific competition?

Answer 38

competition between different species for resources

Question 39

What is the competitive exclusion principle?

Answer 39

only one species can occupy a niche at a time -if 2 species coexist, the resource will be partitioned (each species uses a different part of resource)

Question 40

What are the main problems with looking at predation in a lab?

Answer 40

-range of habitat is limited due to confined lab -area over which population can travel is less in the lab -environment is less diverse

Question 41

What is a niche?

Answer 41

the role of an organism (what it does, where it lives)