Flashcards in F215:03:05 Studying ecosystems Deck (29):
Why do ecologists usually study ecosystems?
to find out whether the abundance or distribution of a species is related to that of another species, or to environmental factors such as light intensity or soil pH
What is a quadrat?
a square frame that defines the sample area
often 1m square
can have strings across every 10cm, creating 100 smaller squares
What are the two types of data that can be taken from a quadrat?
distribution or abundance of a species
What is distribution?
the presence or absence of each species
What is abundance?
An estimate or count of the number of individuals
When are percentage covers used?
When it is too difficult to count individuals (e.g. plants)
What is the problem with percentage covers and what can be done to improve this?
they are not very accurate
using a point frame
What is a point frame?
Stand the point quadrat firmly on the ground
Lower each needle downwards
Record the species that the tip touches on the way
The number of needles that touch each species is proportional to the percentage cover of that species
What are the 3 things that must be decided before you can begin taking a sample of an ecosystem?
- where to place the quadrat
- how many samples to take
- how big a quadrat should be
What problems may occur if a sample is taken from a corner of a field?
the soil in the corner may be particularly rich in nitrates and the species growing there may be different to the crops growing in the rest of the field
How is bias sampling avoided?
1, randomly position the quadrats in the habitat, using random number generators to plot co-ordinates for each one
2. Take samples at regular distances across the habitat
How does taking samples at regular distances across the habitat avoid bias sampling?
As every part of the habitat has been sampled to the same extent
Why is it beneficial to Take samples at regular distances across the habitat or randomly position the quadrats in the habitat, using random number generators to plot co-ordinates for each one when sampling a habitat
As it helps to avoid bias sampling and and provides a sample that is representative of the entire habitat
How do ecologists determine how many samples they are going to take of an ecosystem?
use a pilot study
What is a pilot study?
take random samples across a habitat and make a cumulative frequency table (see page 201) until the total number of different species begins to level off
Then often double that number
How do ecologists determine how big a quadrat should be when they are sampling a field?
Count the number of species found in a bigger and bigger quadrat
Plot the area of the quadrat on the x-axis and the number of new species on the y-axis
Read the optimal quadrat size at the point where the curve starts to level off
What is the equation that estimates the size of each population in the whole habitat?
mean number of individuals of the species in each quadrat /
fraction of total habitat area covered by quadrat
Give an example of when transects may be used
If you were wanting to look at changes in abundance and distribution of species as you walk up the beach and through the sand dunes, measuring the environmental conditions at the same time
What is a transect?
a line taken across a habitat
What is the easiest way to use a transect?
Have a tape measure as the transect and then take regular samples along the tape
What affects the frequency of the intervals along a transect?
the length of the line you want to look at
the density of the plants in the habitat
What are the two different approaches to using a transect?
Using a line transect or a belt
What is a line transect?
at regular intervals along a line, make note of which species are touching the line
What is a belt transect?
at regular intervals place a quadrat next to the line (interrupted)
or move it all the way along the line (continuous)
Explain why you have to take samples from a habitat
Because it is often impossible to count or measure all the individuals in a population
Suggest the advantages of taking samples at random
No bias influences the individuals chosen and hence we avoid skewing the eventual results
Explain how you would estimate the abundance and distribution of species between a school playing field and a meadow
Use a quadrat to take a sample from each area
Suggest the advantages and disadvantages of using a continuous belt transect compared to a line transect
Adv: Cont. gives a more detailed info as line transect only tells you a presence/absence of a species
Dis: Belt transect takes a lot more work