Transcript 2. Ecological Techniques

© SSER Ltd.
Ecological Techniques
A variety of universal practical approaches
exist for investigating the biotic and abiotic
components of ecosystems
Field ecologists investigate communities by using
random sampling techniques that aim to:
• eliminate bias
• reduce the effects of chance
• minimise errors in obtaining
measurements/samples
Quadrat and transect sampling are commonly used
methods for investigating distribution within plant
communities and the more sedentary populations of
animals such as those found inhabiting seashores
Quadrats
Frame quadrats are wooden or metal
frames of known area (e.g. 0.25 m2, 0.5 m2,
1.0 m2) and are generally square-shaped
Various approaches are used to determine the
representation of species within an area:
• Species population density (number of individuals per
square metre) is determined by counting all individuals
within a series of randomly placed quadrat frames and
calculating the mean
• Percentage cover is determined subjectively by assessing
the extent to which different species occupy subdivided
quadrat frames or by the use of point quadrat frames
• Frequency of occurrence of a species is determined using
subdivided quadrats and point quadrat frames
Quadrats
Quadrat frames, constructed from wood or metal,
are used to investigate the distribution of species
Square quadrat frame
for determining
population densities
Subdivided quadrat frame
for determining % cover
of species
Point Quadrat Metal pins are dropped through each hole in
turn and ‘hits’ are recorded
Frame
No. of hits
% Cover = ------------------- x 100
Total no. of pins
Random Sampling
The validity of results obtained from the
various sampling methods is dependent upon
the adoption of random sampling techniques
Strategies for avoiding bias through random sampling
utilise a number of approaches – these include random
sampling using a grid
A grid is created by laying out tapes at right angles to one
another to form the axes of the gridded area
Pairs of random numbers are used to provide the
coordinates for locating quadrats
Tapes are laid out at right angles
to one another and form the axes
for locating quadrats
(the size of the grid depends upon
the area being investigated)
Pairs of random numbers are
generated on a calculator or
computer and used as coordinates
for the location of quadrats
This quadrat has
coordinates X09, Y06
Transects
A transect is a line, created with string or
a tape, along which systematic sampling
is performed
Transects are particularly useful for sampling areas
where there is a transition of species from one habitat
to another as environmental conditions change
Transect studies are used to investigate gradients such
as zonation on rocky shores and changes in the species
diversity across sand dunes
A line transect is one in which all individual organisms
touching the tape/string are recorded
The most commonly used belt transect involves laying
a tape through the area of study and sampling the
population with quadrats positioned at regular
intervals alongside the tape
Belt transect Survey
of a Dune System
A belt transect was used to investigate the distribution of
three species of grass commonly found on sand dunes
The transect line stretched from the high water mark to
the inland area and 1m x 1m quadrats were used to
determine the number of individual plants of each grass
species along the profile
Distance inland
from High
Water Mark (m)
Number of plants/m
Sand couch
grass
0-5
3
5-10
8
10-15
27
15-20
6
Marram grass
2
Sand Fescue
3
20-25
6
25-30
38
30-35
29
35-40
15
40-45
8
17
45-50
48
50-55
88
55-60
97
Present the results as a bar chart
100
90
Number of plants per m
2
80
Sand couch grass
Marram grass
Sand fescue
70
60
50
40
30
20
10
0
0-5
5-10
10-15
15-20
20-25
25-30
30-35
35-40
Distance from high water mark (m)
40-45
45-50
50-55
55-60