Chpater 19 - Populations In Ecosystems

Question 1

What do the terms biotic and abiotic refer to?

Answer 1

Biotic = a factor that makes up part of an organism living environment (e.g. competition and predation with other living organisms)

Abiotic = a factor that makes up part of an organism’s non living environment (temp, pH, rainfall)

Question 2

What do the terms biosphere and ecosystem refer to?

Answer 2

Biosphere = the regions of the earths surface and atmosphere that support life

Ecosystem = a dynamic system involving interactions between all the living and non-living components of a particular area

Question 3

What does the term niche mean in regards to environment and the term carrying capacity?

Answer 3

Niche = describes how an organism fits into an environment
- it refers to where an organism lives and what it does/ the role it has there.

Carrying capacity = the maximum population size of a species that an ecosystem can support

Question 4

List the abiotic factors affecting population size [4]

Answer 4

1. Temperature - each species has an optimum temp for survival
2. Light - the ultimate source of energy for ecosystem (affects rate of photosynthesis for producers)
3. pH - every species has an optimum pH which it operates most effectively as pH affects enzyme action
4. Water and humidity - water is required for life, where water is scarce, populations will consist mainly of species adapted for dry conditions. Humidity affects transpiration rates in producers

Question 5

What is the term used to describe bacterial cells multiplication?

Answer 5

Exponential

Question 6

What’s the formula for calculating number of bacterial cells if a culture of bacteria increase by a factor of 2 in each generation?

Answer 6

N = No x 2^n

No = initial number
n = number of divisions

Question 7

When is a log scale used on y axis?

Answer 7

When numbers increase rapidly and become so large

Question 8

What do the terms immigration and emigration mean?

Answer 8

Immigration - where individuals join a population from outside

Emigration - where individuals leave a population

Question 9

How is population growth calculated?

Answer 9

= (births + immigration) + (deaths + emigration)

Question 10

How is population growth rate as a % calculated?

Answer 10

Population change during period / population at start of period x 100

Question 11

What does the term competition mean and what are the 2 types?

Answer 11

Competition = when 2 or more individuals share any resource that is insufficient to satisfy all their needs fully

• intraspecific = when individuals of SAME species compete for resources. The availability of resource determines size of population
• interspecific = when individuals of DIFFERENT species compete for resources. One species will have competitive advantage over other causing it to increase in size and others diminish

Question 12

What is the link between predators and prey?

Answer 12

When predators population size increase, the preys population size decreases

HOWEVER

When the predators population size decreases, the preys population size increases

Question 13

Describe binary fission [3]

Answer 13

1. Replication of circular DNA
2. Replication of plasmids
3. Division of cytoplasm to produce daughter cells

Question 14

What are quadrats in terms of investigating populations?

Answer 14

They are square frames of a known size that are divided into smaller segments that can be used to investigate populations of non-motile species

Question 15

What are the factors to consider when using a quadrat?

Answer 15

• size of the quadrat
• number of quadrat samples to record
• positions of each quadrat within the study area

Question 16

Describe how you would use a quadrat to measure population size through random sampling [6]

Answer 16

1. Divide the area that you want to sample into a grid and use a random number generator to select coordinates in that chosen area
2. Find each coordinate and place a quadrat on the ground in that position
3. Use quadrat to measure the abundance of the organism of interest
4. Repeat using many randomly generated coordinates to obtain a large sample
5. Calculated the mean number of organisms per m²:
   = total number of organisms/ number of quadrats
6. Calculate population size:
   = mean number x total area

Question 17

What are the two ways for measuring population size of a specific organisms in an area?

Answer 17

1. Count number of a particular organism in the quadrat
2. Estimate the % of the quadrat that was covered by the organism.
   - Count number of squares that are more than half covered and divide that number by total number of squares in quadrat and x100

Question 18

What is a belt transect?

Answer 18

Transects are used to study the effect of a factor on the distribution of a species across an area, in a straight line.

Question 19

How is systematic sampling done along a belt transect?

Answer 19

1. Lie out a tape measure across the area that is being studied
2. Place a quadrat at regular intervals along the tape measure (eg. every 2 metres) and the abundance of organisms is counted at each

Question 20

What are the 3 main statistical tests?

Answer 20

• students T test
• chi-squared
• Spearman’s rank correlation coefficient

Question 21

What are the null hypothesis’ for each statistical test?

Answer 21

1. Students T test = no statistically significant differences between the means of sample x and sample y
2. Chi-squared = no statistically significant difference between the observed and expected frequencies
3. Spearman’s rank correlation coefficient = no statistically significant correlation between x and y

Question 22

How does Spearman’s rank correlation coefficient work?

Answer 22

• rank the number of (?) from highest to lowest
• if two numbers are the same, then find the difference (e.g 7 and 8 = 7.5)
• then skip the next number (8 skipped so go to 9)

Question 23

What is the rs equation for Spearman’s rank correlation coefficient?

Answer 23

Rs = 1- 6∑D² / n(n² - 1)

Rs = spearman’s rank correlation coefficient
D = difference between rankings for two variables being investigated
n = number of pairs of observations

Question 24

After calculating Spearman’s rank correlation coefficient, what is done next?

Answer 24

Use table to find critical value:
- Df = number of pairs - 2
- then look along the p value of 0.05

Question 25

What does it mean in the following scenarios?

• if p value is less than 0.05
• if p value is greater than 0.05

Answer 25

1. P value less than 0.05 = probability the correlation is due to chance is less than 5% so there is a significant correlation
   = reject null hypothesis
2. P value greater than 0.05 = probability the correlation is due to chance is more than 5% so there is no significant correlation
   = accept null hypothesis

Question 26

Explain the mark-release-recapture technique [3]

Answer 26

1. Capture 1st sample of organism - mark them (ensuring the marking doesn’t affect survival of organism
2. Allow time for individuals to randomly distribute again before collecting second sample
3. Calculate population size

Question 27

What assumptions/ precautions need to be made when using the mark-release-recapture method?

Answer 27

• The proportion of marked to unmarked individuals in the second sample is the same as the proportion of marked to unmarked individuals in the whole population
• The marked individuals released from the first sample distribute themselves evenly amongst the remainder of the population and have time to do so
• The population has a boundary so that there is no movement of individuals into or out of the population (no immigration or emigration)
• There are few, if any, deaths or births within the population during the time of the investigation
• The method of marking is not toxic to the individual or make them more visible to predators (doesn’t affect the survival of the individual)
• The mark is not rubbed off or lost during the investigation

Question 28

What is ecological succession?

Answer 28

• the observed changes, over time, in the species that occupy a particular area in an ecosystem

Question 29

What are the two types of succession?

Answer 29

1. Primary succession = occurs when bare rock or barren land is present and then first colonised with a species of organism (volcano, glacier)
2. Secondary succession = when land that has previously sustained life is suddenly altered/ destroyed (forest fire, flood)

Question 30

What are the components of the soil?

Answer 30

Inorganic matter of soil - composed of rock which is slowly broken down into smaller particles that vary in size

Organic matter of soil - composed of microorganisms (dead and alive) and macroorganisms (dead animals and plants in varying stages of decay)

Question 31

What are the stages of primary succession?

Answer 31

• starts with bare rock/ barren land (hostile/ inhospitable environment)
• colonisation by initial species called a pioneer species

Question 32

What is a key example of a pioneer species?

Answer 32

Lichens
- they can survive considerable drying out
- over time they slowly eat away (chemical breakdown) at rock which produces sand/soil
- when lichens die, they decompose releasing nutrients into soil

Question 33

What are the key features of lichens that suit them as a pioneer species for colonisation?

Answer 33

• Asexual reproduction (a single organism can rapidly reproduce to form a population)
• Production of large quantities of wind-dispersed seeds or spores, so they can spread and easily reach isolated areas
• Ability to photosynthesise as light is usually available but food is not
• Ability to fix nitrogen from the atmosphere (because no soil containing nutrients or bacteria to do this)
• Tolerance to extreme conditions (eg. limited water)

Question 34

What can then form after lichens breakdown the rock?

Answer 34

Mosses
- rock continues to be eroded
- an amount of organic matter and nutrients becomes available from death of these plants
- causes ethical layer of soil to be built up
- can hold water making it easier for other large plants to grow

Question 35

What is a climax community?

Answer 35

A stable community which has:
- the same species and many present over a long period of time
- stable population numbers over long periods of time (around max carrying capacity)

Question 36

What is the mark scheme for a question on succession? [6]

Answer 36

1. Begins with colonisation by a pioneer species
2. Changes the abiotic environment.
3. This change causes it to become more suitable for the next species to survive and less suitable for the current species
4. Leads to an increase in biodiversity/ species richness
5. Causing it to become less hostile
6. This results in a climax community which is stable

Question 37

Explain secondary succession in more detail

Answer 37

• the process by which land that has previously sustained life + was suddenly altered returns back to climax community
• occurs more rapidly than primary succession as soil already exists so pedogenesis doesn’t need to take place
• sometimes spores and seeds may remain alive in soil which may be dispersed + animals may migrate in

Question 38

What is conservation?

Answer 38

The method for maintaining ecosystems and the living organisms that occupy them (biodiversity) by human intervention

• preserving the natural landscape + wildlife as well as reclamation (returning to former state) of those already damaged by human activity

Question 39

What are the 4 key reasons for conservation?

Answer 39

1. Personal - to maintain our planet
2. Ethical - other species have occupied the Earth far longer than us and should be allowed to coexist with us
3. Economic - living organisms have a huge pool of genes with the capability to make millions of substances which may be valuable to us in the future.
4. Cultural and aesthetic - habitats and organisms enrich our lives by adding interest to everyday life and inspires writers, poets, artists, composers and others who entertain and fulfill us

Question 40

What is a key way of conserving habitats?

Answer 40

By managing succession

-preventing it from changing to the next stage