19.5 Investigating populations Flashcards
What is abundance
How do we measure it
The number of individuals of a species in a given space
This is abundance
It would be very time consuming to count every organism, and may cause damage to the habitat being studied.
. So we use small samples of the habitat, and as long as they are representative of the habitat as a whole, the conclusion drawn from it will be reliable
What are the two types of sampling
. Random sampling using frame quadrats or point quadrats
. Systematic sampling along a belt transect
What is a point quadrat
. It consists of a horizontal bar supported by two legs
. At set intervals along the horizontal bar, there are ten holes, through each of which a long pin may be dropped
. Each species that the pin touches is recorded
What is a frame quadrat
. It is a square frame divided by a string or wire into equally sized subdivisions
. It can be folded so it is more compact for transport
. The quadrat is placed in different locations within the area being studied
The abundance of each species within the quadrat is then recorded
How do we decide what size quadrat to use
. It depends on the size of plants or animals being studied , and how they are distributed in the area
. Larger species need larger quadrats
. Where a population of species is not evenly distributed in an area, lots of small quadrats will be used to give more representative results than a small number of large ones
How do you know how many Quadrats to use
. The larger the number of sample quadrats, the more reliable the results will be
. As it is very time consuming to count all the species in a quadrat, a balance needs to be reached where the results are reliable, and it isn’t too time consuming.
Because there would be no point in using quadrats if it took the same amount of time as it would to count up all the species in the whole area
. The greater the number of different species in the area being studied, the greater the number of quadrats required to produce reliable results for a valid conclusion
Why do we do random sampling
. To avoid any bias in collecting data, so the results are reliable
Describe how to random sample using a transect
. Get two transects and place them at right angles at the sides of the area to make a grid of the field
. Obtain a series of coordinates using random number generator on calculator or online
. Place quadrats in these coordinates and record the species within it plots
What is systematic sampling
. You use it when you want to measure the distribution of plants or animals when there is a gradual change in habitat
. Eg along a line of succession so the distribution of organisms through sand dunes by the edge of the sea and inland up into woodland
Or as distance from a pond increases, how the number of a species of plants or animals change
How do you make a transect
. A belt transect can be made by using a string or tape measure across the ground in a straight line
. A frame quadrat is laid down alongside the line and the species in it is recorded
Then keep moving it by its own length down the transect
So a continuous belt has the record of species
How can abundance be measured for species that don’t move around
By frequency:
Disadvantage of this
. Frequency:
The likelihood of a particular species appearing in a quadrat
So eg if a species occurs in 15 out of 30 quadrats, the frequency of occurrence is 50%
So this method is useful for grass etc which is hard to count
It gives a quick idea of the species present and their general distribution within an area
A disadvantage of this method is it doesn’t provide information on the density and detailed distribution of a species
How is percentage cover used to find the abundance of a species
. Estimate of the area within a quadrat that a particular plant species covers.
It is useful where a species is particularly abundant or is difficult to count
The data can be collected rapidly, and individual plants don’t need to be counted
How do you get a representative number of a species from quadrats
. Ensure that the sample size is large
. So use many quadrats and find the mean of all the samples
. The more samples, the more representative of the community as a whole will be the results
How do you measure abundance when the species move around, so may run away when approached or hide so are difficult to identify
You call these animals MOTILE
What is the equation
. A known number of animals are caught and labelled eg with a stamp
. Then release them back into the community
. Then a given number of individuals is collected randomly and the number of marked individuals is recorded
Estimated population size =
Total number of individuals in first sample X total number in second sample
Divided by
number of marked individuals recaptured
What assumptions does the capture recapture technique rely on
. There are few deaths and births in this time within the population
. The population has a definite boundary so there is no immigration or emigration
. The mark or label is not rubbed off during the investigation
. Method of marking isn’t toxic so won’t harm the animal, or stop them camoflaging so they are more visable to predators so will be killed
. The proportion of marked to unmarked individuals in the second sample is the same as the proportion of marked to unmarked in the whole population
. The marked individuals from the first sample evenly distribute themselves in the population
