FWT-3205:
Population of Wildlife
What is a Population?
Population is derived from the latin word “popular”, which essentially
means people. In the biological sense, it can be considered as an
assemblage of organisms – plants or animals – which may belong to a
single species or to several closely related species occupying a
definite area.
“ all coexisting individuals of the same
species living in the same area at the
same time”
Why same species can be different ?
i. Spatial structure
ii. Genetic structure
iii. Demographic structure
Population
Wynne-Edwars (1962) referred to population as a self regulating
system. Clarke (1954) has recognized two types of population, viz.
the “monospecific populations” having individuals of the same
species, and the “mixed or poly-specific populations” having
individuals of several species.
A population has many characteristics or attributes which are
typical; these function for the entire group and do not pertain to
an individual.
Thomas Park (1939) has listed out various such characteristics,
population census, density, sex ratio, birth rate, death rate, age
distribution, growth form, population equilibrium, biotic potential,
dispersal, dispersion and population fluctuations.
Change in population is affected by changes in these parameters.
The population has the following components:
Population census, Density, Sex ratio, Age structure, Social
organization, and Natality and mortality
Population parameters and Growth
Nt= Number of Population at year t
B = The number of births
D = The number of deaths
I = The number of Immigrants
E = The number of emigrants
Then, at (t+1) period, the population would be,
Or, we can write population growth as,
Wildlife Census
Annual census or count of population of all wild animals in a nature
reserve is very essential for wildlife management. It gives an idea
as to how the wildlife responds to the habitat improvement like
water holes, meadows, food supply, etc. under the management
plan.
It also comes to know how the animal population responds to
particular managerial practices and may indicate whether it would
be beneficial to continue for them or not.
Types of Wildlife Census
A. Direct Methods (Visual counts):
1. Direct count (Total count, head count)
2. Arial count
3. Waterhole, salt lick count
4. Total capture (Trapping)
5. Drive count/Beats (Drive beat, silent beat)
Types of Wildlife Census
A. Direct Methods (Visual counts):
6. Roadside count
7. Territory mapping
8. Temporal count
9. Breeding bird census
10. Transect line/walk
B. Indirect Methods (Count of animal signs and evidences):
1. Pug mark census
2. Nest count, deer bed count, rabbit form count
3. Count of dens and burrows
4. Pellet group count
5. Kill evidence count
6. Call count
7. Counts of tracks and trails
Population Census
Statistical Method
There are various methods of population census but the
statistical methods give the population data of one unit in similar
condition which reflects the growth of the entire population.
Even though the total population may not be known but provides
the trend of population growth which serves the basic purpose of
the count. In the statistical methods “Bounded Count” is an
important one used by Choudhury (1987) in Taboda National Park
of India.
Statistical Method
This method was applied in America to count Brown Bears who wait
along a stream for the salmons arrive during the spawning season.
There was a good possibility of counting all bears in such situation.
The situation around the water holes during the summer in India is
almost similar, as all the wildlife would come to drink at the water
holes.
For this count camouflaged machans (platforms) to be constructed
at a suitable place near each water hole which do not disturb the
normal drinking of wild animals. The count would be made at the
peak time of drinking of animals which would be justified by
previous observation and final count should be made at the same
time in more successive days (3-4 days).
Population Census
Lincoln/Peterson Index (Marking and capturing) method
A known number of individuals are captured and marked and
these are released. A sample is taken from the population and the
ratio of marked and unmarked individuals is recorded. From the
formula M/N = m/n the total population can be calculated, as for
example:
M = Total no. of marked animals in the population
N = Total no. of animals in the population
m = Marked animals in the sample
n = Total no. of animals in the sample
Say 10 banded/marked animals are released in population. 50
animals are captured of which 2 are banded/marked then the
calculation: M/N = m/n
10/N = 2/50
N = 250 animals in the population
Population Census
Transect line/ Transect walk
This method is used for censusing primates. An observer usually walks
slowly along the trail scanning ahead through an arc of 1800 and stopping
every 50-100 m at a point, affording good visibility to look and listen for any
sign of primates. All groups on the transect line will be encountered.
The density of groups in an area is then calculated from the number of
groups encountered divided by the area covered by the transect, which is
the length of transect multiplied by its estimated width.
Count of animals
The most commonly used density indices are count of animals, e.g.
Number of migratory birds flying across the moon per hour,
Number of deer seen per hour of walk,
Number of elephants seen at a waterhole/salt lick per night, and
Number of basking crocodiles counted per km of river.
Population Census
Tracks and signs
Animals leave droppings, tracks, trails, browsed/grazed plants, burrows,
mounds, nests, and other evidences of an occupancy area. Census can be
made by counting these evidences than by counting the animals
themselves.
Sample-Area count/Quadrat count
In these case total number of animals are counted within small areas of
known size and results are then applied to the total area occupied by the
population. Result will be influenced by the location of the sample area and
the number of samples taken. The quadrat or the area which will be
selected for sample study should be more or less cover the ecological
parameters of the whole study area.
Population Census
Pellets (droppings) count
Deer are censused by pellet group count, say they drop 13 pellets
group/day.
Then calculation:
Deer/acre = 10 deer days/ 100 days = 0.1 deer
Pellet gr. / acre: 130
Deer/days/acre: 130/13 = 10
13 pellet group are counted on the 10 plots dropping rate as 13/day.
As long as numbers are low in relation to availability of food, cover and
water, the animals are free from mortality. With an abundance of space and
necessities, the birth rate can be high, the rate of increase may be
approached the biotic potential.
Population of Mammals
Tiger (Panthera tigris)
About 65 tigers were killed by men in the Sundarbans of Bangladesh
between 1959/60 to 1970/71 recorded in the Khulna Forest Division office
(Hendrichs, 1975). A number of tigers are shot in chandpai range of
Sundarbans due to maneating habits are reported to consultant during his
field trip in the Sundarbans June, 1992.
In the Sundarbans, 350 tigers were estimated including forest official
records and the density estimated 0.1 km2. Sex ratio of tiger estimated in
the Sundarbans (Khulna) as 58.5% adult males and 41.5% adult females =
1.4 on the basis of 200 tigers shot in 19 years (Hendrich 1975).
120 tigresses (adults) would reproduce 50 cubs per year and annual
productivity would be of about 4000 kg (Hendrichs 1975). The population
of tiger is increased from North to Southern part of the Sundarbans. It is
directly correlated to the population of deer.
Tiger Census Method
Population of tiger can be estimated by two methods.
Direct method: In this method, each tiger is counted by direct seeing. This
method is not applied in the Sundarbans.
Indirect method: Population of tiger is estimated on the basis of indirect
method following examination of some evidences like pugmarks, foot
prints, scats, and additional information collected by interviewing of people
available in the forests and official records of Sundarbans Forest Division,
Khulna and camera trapping.
In this method, the sanctuary was divided into a number of equal square
blocks, each of which was surveyed by boat, trawler, launch and on foot.
Tiger Conservation
As the national animal of our country, the tiger represents an ideal focal point for
our conservation efforts. To protect the tigers of the Sundarbans following
measures have been taken:
• The National Tiger Action Plan (2018-27) and the National Tiger Recovery
Program have been updated to protect Tiger and its prey.
• With the joint collaboration of Forest Department, Police, Border Guard,
Customs and Coast Guard a Wildlife Crime Control Unit (WCCU) has been
established. It is playing a vital role in the protection and conservation of
tiger and other wildlife.
• Tiger Co-ordination Committee (TCC) has been formed in national and
regional level to control wildlife poaching and illegal trafficking and
working effectively.
• To reduce the human-tiger conflict, 49 Village Tiger Response Team (VTRT)
with 332 community people and a 3-member Forest Tiger Response Team
(FTRT) has been formed and working at the Sundarbans Impact Zone (SIZ).
Tiger Conservation
• Compensation Policy for wildlife victims 2012, has been approved which is
helping to reduce the human-tiger conflict in the Sundarbans Impact Zone.
• The GoB has become the member of CITES, GTI, GTF and SAWEN for the
conservation of biodiversity of the country including the SRF.
• A Protocol and Memorandum of Understanding has been signed between
the government of India and Bangladesh on 6th September 2011 to
conserve tiger and the Sundarbans. Exchange of views, visits, and technical
co-operations are taking place between two countries.
• Bengal Tigers are symbol of healthy ecosystems of the Sundarbans. Regional
Wildlife Protection Project started Tiger counting and abundance survey
including tiger track and behavioral monitoring through “Camera Trapping”
in 2015 and second time camera trapping was accomplished in 2018.
Population of Birds
Vulture of Sundarbans
The population status of whitebacked vultures in the Sundarbans is not
uniform in all ranges. They are common in Burigoalini, fairly common in
Nalian, few in Chandpai and rare in Sarankhola range. A study reported that
a total of 530 whitebacked vultures were observed in Burigoalini range, 165
in Nalian and 12 in Chandpai range. Population density of whitebacked
vulture was calculated one individual per 0.16 km in the study area of
forests along 1290 km on the bank of rivers.
Population density
The density of a population is the number of animals in a particular area.
Say 100 animals in 100 km2, the density will be 1/km2.
Density estimation may of two types:
Absolute density: If it is possible to count all animals in the area, it is
proper to estimate of the result as absolute density
Relative density: The collection of samples that represent a constant but
unknown proportion of the total population.
A density is expressed as “individuals per unit area”. Density may twice or
numerous in early summer as in late spring and in winter it may be of little
density. It is related to the quantity and quality of food, cover, water and
essentials of life.
Sex ratio
A sex ratio of 50:50 at birth appears to be a general rule for many species of
vertebrates. If this ratio is not maintained in a population due to variation
in mortality amongst species, then the population dynamics gets affected in
varying degrees.
For a proper management of a wildlife area, one must know the sex ratio of
various wildlife population. It indicates the procreation (reproduction)
potential. It has an effect on the main population body weight and
consequently the requirements of animals. If the food supply in a habitat is
fixed, then it will support more young females than adult males.
As per convention, sex ratio usually expressed as males per 100 females.
Sex ratio calculation:
Male: 100 Females
From field data, 1647 males and 3921 females
1647/3921 = x/100
X = 42
Therefore, 42: 100 is the conventional sex ratio
Natality or birth rate
The actual rate of birth is usually known as “fecundity”, and is measured as
the number of live births per female over a given period of time, usually
one year (Shaw 1985).
It can also be defined as the average number of new individuals produced
by a given population in a unit time. The maximum birth rate or potential
natality is the maximum number of new individuals which can be produced
per unit of time under a given set of ideal ecological conditions. The actual
or ecological birth rate or realized natality is the actual number of new
individuals which are added to a population in a given time.
Species differ widely in their fecundity; some animals may reproduce in
large numbers, whereas others may restrict their offsprings to a few only.
Natality or birth rate
Natality is the most important characteristics of population like potential yield
of population and is influenced by the following characteristics of species of
population.
✓Size of clutch or litter
✓Number of clutch or litter/year
✓Maximum and minimum breeding age of the individuals
✓Sex ratio and mating habit and population density
Mortality or death rate
Mortality rate of a population means the number of individuals which die per
unit of time; it may be expressed as potential mortality or realized mortality.
Potential mortality or the minimum mortality is understood as the number of
deaths which would occur under ideal conditions due to various physiological
changes pertaining to old age.
For a given population this value is constant. On the other hand, realized
mortality means the actual death rate, which depends upon certain physical
factors and also on the composition, density and size of the population.
Age composition
The number of animals or the percentage of individuals in a population in
different age groups is known as the age distribution of a population.
Populations vary widely in the relative numbers of young and old and thus
they show different natality and mortality. Usually three age groups are
recognized in a population, viz. pre-reproductive, reproductive and post-
reproductive.
The distribution of age in a population is usually represented in the form of
age pyramid (Fig). In an expanding population, growing at a very rapid rate,
the birth rate is very high and the population growth may appear
exponential, as in the lower organisms like bacteria, yeast (Fig A).
In a stable population, the post-reproductive and reproductive age groups
appear more or less equal in size and pre-reproductive stage becomes the
smallest making the pyramid appear in the shape of a bell (Fig B).
Age composition
If the birth rate is reduced drastically, the reproductive and post-
reproductive groups increase in proportion to the pre-reproductive age
group, and the shape of the pyramid is like an urn (jug), this is the age
pyramid of diminishing population (Fig. C).
If a population has a high percentage of young ones, then it is expanding; a
low percentage of young individuals indicates a decline in population; on
the other hand, a stable population shows a constant proportion of
individuals in all the three age groups.
Age determination in wild animals can be done by using certain criteria
such as size of the body, weight, hair, feather color and texture (in case of
birds), developmental status of the genitals tooth wear and eruption,
annular rings in teeth, weight of the eye lens, bone cartilage development
and others.
