This lecture discusses sampling methods used to estimate population abundance

1. BIOL205
Ecology Lab 5
Estimating Population Abundance
Dr. Erik D. Davenport

2. Ecological measurements
 A number of basic measurements are used
in describing populations and communities.
– Density
– Abundance
– Biomass

3. density
 Density: in the ecological population studies, density
(D) is the number of individuals expressed per unit
area or per unit of volume.
 Abundance (N) is the number of individuals in a
given area.
 For example, a species may have an abundance of
100 individuals in a particular area. If the total area is
2.5 hectares, then the density of this species would
be 40 per hectare (40/ha).

4. Biomass
 Biomass (B) is the weight of the individuals of
a population or group of populations and
often is expressed per unit area or volume.
 For example, the grams of chlorophyll per
liter in a lake.
 However, what is the difference between
density and biomass???

5. Capture-recapture sampling
 Useful to estimate the population size of a
single species of highly mobile animal.
 It is called capture-recapture, or mark-
recapture.
 It is also referred as Lincoln-Peterson
method.

6. Capture-recapture sampling
 First sample: A number of individuals from a population of
interest are captured, marked by some identifiable means, and
then released within a short period of time.
 At a later date ( perhaps after a week or two), a second sample
of individuals is taken from the population.
 Some of the individuals in the second sample might be also
captured and then released in the first sample.
 Like the first sample was diluted within the populations.

7. Removal Sampling
 Removal methods of population estimation involve
successive trapping of members of the population.
 Assumption: the number of caught and removed
from the population at a given time of trapping will be
greater than the number of caught at a later trapping
using the same sampling effort.
 That is, as one reduce the population size, the size
of the catch will decrease.

8. Transect sampling
 There are several transect sampling techniques,
however, here we are going to cover the Line
transect sampling
 Line transect sampling involves a walking a line
established through an area and recording the
distance of individuals observed from that line.
 This method can be quantified to yield density
estimates useful in studies where the animals are
highly mobile, yet often difficult to see until flashed.

9.  Assumptions to use the capture-recapture
procedure:
– All individuals in the population have an equal
and independent chance of being captured.
– There is no change in the ratio of marked to
unmarked animals.
– Marked animals distribute themselves
homogenously.
Capture-recapture sampling

10. Capture-recapture sampling
 Assume the total population size in certain area
contains N individuals, and from this population, take
a sample of M individuals. Then mark and release
these M individuals.
 In the second sample, if you catch n individuals,
which contains m marked individuals from first
sample
 Then M/N = m/n
 Then you can estimate the population size
N = (M*n)/m

17. Regression method
 Involves taking a series of samples (at least 3
samples) from a population.
 Each sample involves the same amount of effort.
 Number of individuals from each collection is plotted
against the cumulative OR previous number
captured.
 Population estimation then extrapolated.
 It is also called regression method:
Y = aX + b and then N=-b/a