13.1 Investigating populations

Question 1

Species

Answer 1

1. Group of similar organisms / organisms with similar features / / organisms with same genes / chromosomes;
2. Reproduce to produce fertile offspring;

Question 2

Population

Answer 2

All the individuals of a given species living together in the same area at the same time

Question 3

Carrying capacity

Answer 3

Maximum equilibrium number of organisms of a particular species that can be supported in each stable environment.
Birth rates and death rates are in equilibrium

Question 4

Community

Answer 4

All the individuals of all the species living together in the same area at the same time.

Question 5

Habitat

Answer 5

Place where an organism lives in an ecosystem

Question 6

Niche

Answer 6

Describes where an organism lives, what it does, what it feeds on and how it interacts with other organisms and the environment

Question 7

Biotic factors

Answer 7

Living factors which affects the distribution of an organism
E.G.,
Prey
Food availability
Disease

Question 8

Abiotic factors

Answer 8

Non-living factors which affect the distribution of an organism
E.G.,
Temperature
Light intensity
Wind speed

Question 9

Interspecific competition

Answer 9

Between different species

Question 10

Intraspecific competition

Answer 10

Between same species// Within a species

Question 11

Conditions for estimating abundance

Answer 11

ENSURE:
Data is not biased
Data selected at random
Large samples must be taken
Method for collection is appropriate to the species

Question 12

Quadrats

Answer 12

Frame of known area which is placed on the ground and an estimate of the population sizes within them are made

Question 13

How is the abundance of a species within a quadrat measured

Answer 13

Actual count of all individuals
Percentage cover
Frequency

Question 14

Describe random sampling/using quadrats

Answer 14

• Use a grid / split area into squares/sections;
• Method of obtaining random coordinates / numbers, e.g. 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 15

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

Answer 15

• 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 16

Transect

Answer 16

Recording what species are touching the line at each sampling point

Question 17

Belt transect

Answer 17

Placing two parallel lines across, a metre apart and recording what species are found between the two lines

Question 18

Interrupted belt transects

Answer 18

Using one line and placing a quadrant down at equally spaced sampling points and recording abundance of species within the quadrant

Question 19

Describe systematic sampling

Answer 19

• 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 20

Describe the mark, release, recapture technique

Answer 20

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

Question 21

Considerations for mark, capture, release

Answer 21

• Should be very few/no increase in birth/death/emigration/immigration rates
• Marking should not make the animals more susceptible to predators or harm AS the formula is based on the ratio of marked to unmarked indiv. remaining the same
• The marking should not rub off or be lost
• sufficient time should be left after release to be fully dispersed BUT not too long that death may occur

Question 22

Abiotic factor- Temperature

Answer 22

Temp too cold:
Enzymes have too low kinetic energy to catalyse reactions.
Overall activity will drop and may not be sufficient for survival
Temp too high:
Enzymes denature
Overall activity will drop and may not be sufficient for survival
Temp can be measured using a thermometer

Question 23

Abiotic factor- Light intensity

Answer 23

Light needed for photosynthesis therefore the higher the intensity the more the growth via photosynthesis
The more photosynthesis the more energy for spore production so increase in population
The more the plants grow the more respiratory substrates is available for animal populations
Light intensity also effects leafing and flowering in plants along with reproductive cycles in animals
Water rapidly absorbs light

Question 24

Abiotic factor- Water availability and humidity

Answer 24

Water= a solvent in cells
Organisms tend to lose water via evaporation but for thermoregulation eg. sweating or mass transport
The lower the humidity the more water loss will occur
Humidity is measured using a whirling hygrometer

Question 25

Abiotic factor- pH

Answer 25

the more extreme the pH the more the organism is affected and the lower the population size and range is
pH can also affect the availability of mineral salts in the soil and therefore can affect growth in plants

Question 26

Biotic factor- competition

Answer 26

The more individuals present the greater the competition for the resources
Competition increases when resources are limited
If two species initially occupy the same niche, one species tends to out-compete the other so the niche will be occupied by only one species.= COMPETITIVE NICHE EXCLUSION PRINCIPLE
INTRASPECIFC= between same species
INTERSPECIFIC= between different species

Question 27

Biotic factor- predators

Answer 27

=One animal species feeding on another
Predators have evolved mechanisms to improve capturing such as high speed, venomous secretions
Prey have also evolved defence mechanisms eg. camouflage and protective spines

Question 28

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

Answer 28

• 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;