1. PRESENTATION
ON
Estimating Population
Density or Frequency

2. Definition of a population
Examples of a population
Growth of Populations
Growth of populations refers to
change in size of population
which can be either positive or
negative over time.

3. Population density
Is a measurement of population
per unit area or per unit
volume.
Population frequency
As the number of samples in
which the species occurs.

4. Factors in population change
• Birth rate or natality
• Death rates or mortality
• Emigration
• Immigration
• Biotic factors
• Abiotic factors

5. Exponential growth
Is where population doubles in each
generation.
Environmental resistance
Is due to population increase as
competition on resources increases.
Carrying capacity
Is where population stabilises at level
in a habitat.

6. Census is the total count of all
members of population.
Sampling techniques
• Capture, mark, release, and recapture
techniques (which are used for
mobile animals).
• Quadrat method which is used for
immobile or sessile organisms like
plants.

7.  Capture, Mark, Release, and
Recapture Techniques
Some capture techniques
• Pitfall traps
• Sticky traps
• Corrugated paper traps
• Nets
• Hand capture

8. Limitations
-May avoid capture.
-May preferably be trapped.
-Species may be harmed.
Example, if 80 deer are captured
,tagged, and released into the forest, and
later 100 deer are captured with 20 of
them are already marked. we can
determine the population size (N) using
the following equation:

9. N=(n1*n2)/n3
n1=number s captured, marked and
released.
n2=total numbers captured on the
second occasion.
n3=number of marked individuals
recaptured.
Thus, N=(80*100)/20
=400 (Lincoln Index)

10. Quadrats
are used when estimating the
population of terrestrial plants of
the field or herb layer.
Estimating Density/Percentage
Frequency/Percentage Cover
• Density is the mean number of
individuals per unit area.

11. Estimating Density/Percentage
Frequency/Percentage Cover
• Frequency
is the number of quadrats in
which a species occur as a percentage.
• Cover
is the percentage of the ground
covered by a species within the area
sampled.

12. Autecology
Autecology is the study of an
individual species (population and its
environment). The fluctuations of a
population and the effects of parasites
and predators might underpin
economic control of pests or weeds,
when contrasting biological control
measures with the use of conventional
pesticides.

13. THANK YOU