Download Ecological Sampling

Ecological Sampling
Measuring biotic components of a
system
Ecological Sampling

What is a sample?
 “A portion, piece, or segment that is representative
of a whole”

Why do we sample?

it is usually impossible to measure the whole
One big assumption…



That the sample is representative of the
whole
It is necessary to take enough samples so
that an accurate representation is obtained
It is important to avoid bias when sampling
Sampling Methods

Transects and Quadrants


Plants and Non-motile animals
Lincoln Index

Capture –Mark- Recapture


Small animals
Aerial observations

Large trees and animals
Sampling along Transects


Samples taken at fixed intervals
Set up along an environmental gradient (e.g.
high to low on a mountain)
Line transect method



A measured line laid across the area in the
direction of the environmental gradient
All species touching the line are be recorded
along the whole length of the line or at
specific points along the line
Measures presence or absence of species
Belt transect method


Transect line is laid out and a quadrant is
placed at each survey interval
Samples are identified and abundance is
estimated



Animals are collected
For plants an percent coverage is estimated
Data collection should be completed by an
individual as estimates can vary person to
person
Quadrats


Used to measure coverage and abundance of
plants or animals
A grid of known size is laid out and all the
organisms within each square are counted.
Lincoln Index

Capture-Mark-Recapture




Animals are captured,counted, tagged and
released.
After a period of time another capture occurs.
Previously tagged animals are counted and
unmarked organisms are marked.
Abundance is calculated using the following
formula: n1 x n2
n =total marked after catch 1
n3
1
n2=total marked after catch 2
n3=total caught in catch 2 but
marked in catch 1
Measurements

Sampling methods measure





Density
Coverage
Frequency
Biomass
Diversity
Density (D)

The number of individuals per unit area



n =number of individuals for
i
D=ni/A
species i
Eg. 10 dandelions/m2 A=the area sampled (could
Relative density i (Rdi)be the volume V)



The Density of species i, Di, Divided by the sum of
all the densities of the other species sampled
Rdi=Di/S D
Eg. 10/5+8+16
Coverage (C)

The proportion of ground that is occupied or
area covered by the plant/species


Ci=ai/A
Relative coverage

ai=the area covered by
species i
A=the total area
The Coverage of species 1, Ci, divided by the sum
total of the coverage of the other species sampled
Frequency (f)

The number of times a given event occurs



Eg. the number of quadrants that contain maple
trees as a ration of all the quadrants
ji=number of quadrants with
fi=ji/k
Relative frequency

species i
k=total number of quadrants
The frequency of species i relative to the sum total
of the frequencies of the other species found
Biomass (B)

Can be calculated by measuring the mass of
the individuals per unit area


B= S W/A
More appropriate measure than density or
frequency when


Number of individuals in hard to determine
Photosynthesis and carbon fixation, energy and nutrient
transfer are more dependent upon biomass than the total
number of individuals
Biomass Measurement
methods

Fresh or wet weight


Dry weight



Used when organisms are alive
Used when the water content varies greatly
Oven dry at 105oC to remove water
Ash-Free Weight


Used when inorganic content varies greatly
Oxidize at 500oC until only inorganic ash remains
Diversity


The measure of variety of an ecosystem
Consists of 2 components


The number of different species or the richness of
species in a specific area
The relative abundance of the individuals of each
species in a specific area
Simpson's Diversity (D)

Measures species richness
D=N(N-1)
S n(n-1)
D=Diversity
N=total number of organisms of all
species found
n=number of individuals of a
particular species


If D is high the area may be a stable ancient
site.
Low D may suggest pollution, recent
colonization, or agricultural management