1.2 Investigating populations Flashcards
Define abundance
Number of individuals of a species in a given space.
Why is it impossible to count every organism in a habitat? (2)
Instead…
- Time-consuming
- Damaging
-small samples are used to represent whole habitat
Why should you use a large number of quadrats? (2)
Why should you use random sampling? (3)
more reliable results, effect of anomalous results reduced
avoids bias, data representative of whole population, allows use of statistical tests.
Random sampling using quadrats
Method (3)
- Lay out 2 long tape measures at right angles, along 2 sides of the study area
- Obtain a series of coordinates using numbers taken from a table/generated by a computer.
- Place a quadrat at the intersection of each pair of coordinates, record the species within it.
Systematic sampling along transects:
When is this beneficial? e.g.?
Line transect method (2)
Belt transect method (2)
Where some form of transition in communities takes place.
- String or tape stretched across the ground in a straight line.
- Any organism over which the line passes is recorded.
- A metre-wide strip is marked by putting a second line parallel to the first.
- Any organism occurring within the belt between the lines is recorded.
Measuring abundance:
Sampling used to? Frequency: - define - useful where species? (1) - gives info on? (2) - does not give info on? (2) Percentage cover: -define -useful where species? (2) -because? (2) -less useful where species? (1)
-measure abundance of plants
F:
- likelihood of a particular plant species occurring in a quadrat.
- difficult to count
- species present, general distribution
- density, detailed distribution
PC:
- estimate of the area within a quadrat that a particular plant species covers.
- difficult to count, particularly abundant
- individual plants do not need to be counted, rapid
- occur in overlapping layers
Mark-release-recapture:
Used to?
Other methods do not work because animals? (4)
- measure abundance of animals
- motile - move away when approached, hidden - difficult to find and identify
Analysis of data:
Present in table/graph? Statistical analysis? (2) Mean? Standard deviation? Correlative factors? Positive correlation? Negative correlation?
- allows easy comparison
- allows more precise comparison, checks if results are due to chance
- does not show the spread of data about the mean
- shows the spread of data about the mean
- vary in relation to each other
- increase in value of one variable causes increase in value of other variable
- increase in value of one variable causes decrease in value of other variable
EXAM QUESTION
Explain why the scientist sampled the nests at random. (2)
- Avoids bias
- Data representative of whole population
- Allows use of statistical tests
EXAM QUESTION
The scientist used percentage cover rather than frequency to record the abundance of algae present. Suggest why. (1)
Too difficult to count/too many to count
EXAM QUESTION
Explain the importance of collecting lizards from a large number of sites. (1)
Reliable (results)
EXAM QUESTION
Describe one method the scientists could have used to ensure that the sites were chosen without bias (2)
1. Find coordinates (on a grid) / split area into squares / number the sites; 2. Method of generating/finding random numbers eg calculator/computer/random number generator/random numbers table;
Mark-release-recapture:
Relies on what 6 assumptions? (6)
- Marked individuals released from 1st sample distribute themselves evenly amongst remainder of population - have sufficient time to do so.
- Marking method non-harmful/non-toxic/inconspicuous - predation chances maintained
- Mark is not lost/rubbed off during investigation
- No immigration into/emigration out of population.
- Few if any deaths/births within population
- Proportion of marked to unmarked individuals in 2nd sample same as proportion of marked to unmarked individuals in the population as a whole.
EXAM QUESTION
The ecologists could have used the mark-release-recapture method to estimate the number of one species of fish in the lake. Describe how. (3)
1. Capture sample, mark and release; 2. Appropriate method of marking suggested / method of marking does not harm fish; 3. Take second sample and count marked organisms; 4. No in No in Population = sample1 × sample2 Number marked in sample2;
EXAM QUESTION
This species of fish breeds at a certain time of the year. During this fish-breeding season, the mark-release-recapture technique might not give a reliable estimate. Suggest one reason why. (1)
One suitable reason; E.g. population increases/changes (between first and second sample) 1 Accept other valid answers, which must, however, relate to breeding/only works if population constant.
