Investigating Populations

Question 1

Describe the process of succession

Answer 1

• Colonisation by pioneer species;
• Pioneers cause change in environmental abiotic / biotic factors(give an example);
• Pioneers make the environment less hostile for new species;
• New species change/make conditions less suitable for previous species;
• Change/increase in diversity/biodiversity;
• Stability increases [population/richness/abiotic factors];
• Climax community;

Question 2

Explain how succession results in a wide variety of fish living on coral reefs.

Answer 2

• Increase in variety/diversity of species/plants/animals; OR Increase in number of species/populations; OR Increase in species richness / biodiversity
• Provides more/different habitats/niches OR Provides greater variety/types of food OR becomes less hostile;

Question 3

Describe random sampling
[estimation of population density]

Answer 3

• Use a grid / split area into squares/sections;
• Method of obtaining random coordinates / numbers, e.g. calculator/computer/random numbers table/random number generator;
• Count number/frequency of plants in a quadrat;
• Large sample (20+ quadrats) AND Calculate mean/average number (per quadrat/section);
• Valid method of calculating total number of ……… e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in wood;

Question 4

Describe systematic sampling

Answer 4

• Transect/lay line/tape measure (from one side of the dune to the other);
• Place quadrats at regular intervals along the line;
• Count plants/percentage cover/abundance scale (in quadrats) OR Count plants and record where they touch line/transect;

Question 5

Describe how you would determine the mean percentage cover for beach grass on a sand dune.

Answer 5

• Method of randomly determining position (of quadrats) e.g. random numbers table/generator;
• Large number/sample of quadrats; (min 20)
• Divide total percentage by number of quadrats/samples/readings;

Question 6

Describe a method that could be used to determine the mean percentage cover of algae on a coral reef.

Answer 6

• Method of randomly determining position (of quadrats) e.g. random numbers table/generator;
• Large number/sample of quadrats; (>20)
• Divide total percentage by number of quadrats/samples/readings;

Question 7

Describe the mark, release, recapture technique

Answer 7

• Capture sample, mark and release;
• Appropriate method of marking suggested / method of marking does not harm fish;
• Take second sample and count marked organisms;
• No in No in Population = [No in sample1 × No in sample2] / Number marked in sample2;

Question 8

The mark-release-recapture method can be used to estimate the size of a fish population.

Explain how.

Answer 8

• Capture/collect sample, mark and release;
• Ensure marking is not harmful (to fish) OR Ensure marking does not affect survival (of fish);
• Allow (time for) fish to (randomly) distribute before collecting a second sample;
• (Population =) number in first sample × number in second sample divided by number of marked fish in second sample/number recaptured;

Question 9

Suggest why the mark-release-recapture method can produce unreliable results in very large lakes

Answer 9

• Less chance of recapturing fish OR Unlikely fish distribute randomly/evenly;
• Fish may remain in one area OR fish may congregate

Question 10

Describe how you would determine how many quadrats to use when investigating a habitat.

Answer 10

• Calculate running mean/description of running mean;
• When enough quadrats, this shows little change/levels out (if plotted as a graph);
• Enough to carry out a statistical test;
• A large number to make sure results are reliable;
• Need to make sure work can be carried out in the time available;

Question 11

Definition of species

Answer 11

group of closely related individuals that can interbreed to produce fertile offspring

Question 12

Definition of ecology

Answer 12

study of organisms and the environment they live in and how they interrelate

Question 13

Definition of population

Answer 13

all the individuals of a given species that live together in the same area at the same time

Question 14

Definition of carrying capacity

Answer 14

maximum, equilibrium number of individuals of a particular species that can be supported indefinitely in each stable environment.
birth rates and death rates are in equilibrium

Question 15

2 Species do not occupy the same niche as:

Answer 15

• different niches reduces competition between 2 species
• ensured both species survive
• called competitive exclusion principle

Question 16

Interspecific Competition

Answer 16

competition for resources between organisms of different species e.g variety of food sources, geographical territory for shelter, breeding sites

Question 17

Intraspecific Competition

Answer 17

competition for resources between individuals of the same species e.g. food sources, mates, territory, breeding sites

Question 18

Definition of ecosystem

Answer 18

a community of living organisms and their interaction with abiotic factors e.g air, water, mineral soil

Question 19

Biotic factors that effect survival

Answer 19

• competition between organisms, predation, disease
• invasive species
• human impact

Question 20

Abiotic factors that effect survival

Answer 20

• Climatic factors (temp, light, windspeed)
• physical factors (soil, water pH, slope of land)
• aspect (n, e, s, w)

Question 21

Definition of Abundance of a species

Answer 21

estimate of population size of each species

Question 22

Why is random quadrating done

Answer 22

• find out what species are present and relative abundance of species present
• compare species abundance at 2 different areas
• compare species abundance in the same area at different times (years/ season)

Question 23

Random quadrating method

Answer 23

• map the area
• use random number generator to generate coordinates
• use large sample
• count number of plants in quadrat
• calculate mean

Question 24

Measuring population density

Answer 24

count total number of individuals in quadrat area for all samples and calculate density

Question 25

Measuring frequency

Answer 25

count number of hits in quadrat area and calculate average frequency per m2

Question 26

Transect

Answer 26

recording what species touching line at each sampling point

Question 27

Belt transect

Answer 27

placing 2 parallel lines across, metre apart, and record what species found between 2 lines

Question 28

Interrupted belt transect

Answer 28

using 1 line and and placing quadrats at equally spaced intervals and recording abundance of species within the quadrat

Question 29

Mark release recapture problems

Answer 29

a) The population size does not change between the two capture times. There should be very few or no increase in birth or death rate, migration. (N2↑= overestimate)

b) The marking should not make the marked animals more susceptible to predators or harm the animals.

c) The marking should not rub off or be lost. (Nm↓= overestimate)

d) Sufficient time should be left for the released, marked individuals to fully disperse equally through the rest of the population (however, it should not be that long that births or deaths occur). ( Nm↑ = underestimate)

Question 30

Why might all species not be equally catchable?

Answer 30

may change behaviour, learn not to get caught, avoid area