7 Human Population and Environment part 1
7 Human Population and Environment
Introduction
Human society is governed by interaction and cooperation with other human beings.
Latest trends in technology and medical knowledge are available to control human population
growth and to improve the health. Still population continues to increase and poverty become
greater than ever before. Humans are social animals who have freedom of choice. They
largely take decision by heart rather than mind. It is evident from historical records, social
situations, ethical and religious considerations and personal desires. Today the greatest
hindrance to controlling human population is no more biological but falls into the province
of philosophers, theologians, politicians, sociologists, and others. The cause of the population
problem is to be understood if we are to deal successfully with the population problem.
Carrying Capacity
The carrying capacity of an area is the number of individuals of a species that can
survive in that area over time. In most populations, four broad categories of factors determine
the carrying capacity for a population. These factors are: (1) the availability of raw materials,
(2) the availability of energy, (3) the accumulation of waste products and their means of
disposal and (4) interactions among organisms. The total of all of these forces acting together
to limit populations size is known as environmental resistance, and certain limiting factors
have a primary role in limiting the size of a population. In some cases, these limiting factors
are easy to identify and may involve lack of food, lack of oxygen, competition with other
species, or disease.
Population Characteristics
A population can be defined as a group of individuals of the same species inhabiting
an area. Some of the characteristics or a population are nasality (birth rate), mortality
(death rate), sex ratio, age distribution, growth rates, and special distribution.
Natality refers to the number of individuals added to the population through
reproduction. In human populations, natality is usually described in terms of the birth
rate, the number of individuals born per one thousand individuals in the population per
year. It is important to recognize that the growth of a population is not determined by the
birth rate (natality) alone.
This is expressed as
B (Natality rate) = Nn/t which means = No. of new individuals added to population time.
Mortality is the number of deaths per year. In human population studies, mortality is
usually discussed in terms of the death rate, the number of individuals who die per one
thousand individuals in the population per year.
Population Density is population size in relation to some unit of space and time. It
varies with food availability and climatic conditions. It can be measured as:
D = N/a
t
where D is population density, n = number of individuals, a = area and t = time.
Population Age Distribution refers to the individuals of different age groups in a
population. The natality and mortality is also different for respective ages. Bodenhelmer
(1938) recognized three ecological ages as: (i) Pre reproductive, (ii) Reproductive and
(iii) Post reproductive Fig. 1. Duration of these ages varies in different organisms e.g.
Insects have a very long pre-reproductive period, a very short reproductive period but no
post reproductive period at all. In man all the three stages are equal in length.
Post reproductive
Reproductive
Pre reproductive
Age structure
Expanding
Population
(A)
(B) Stable (C)
Population
Dim inishing
Population
Type of Population
Figure 7.1. Age structure in different types of populations
Biotic Potential is the maximum reproductive power. The constant percent growth
rate of a population under optimum environmental conditions thus represents its biotic
potential or reproductive potential. Letter designates it g.
g
AN AT
N
=
∆ /
where, N = number, t = time, D = constant.
The sex ratio refers to the number of males relative to the
Number of females in the population.
The Human Population Issue
Current population growth has led to famine in areas where food production cannot keep
pace with population growth; political unrest areas with great disparities in availability of
resources (jobs: goods, food); environmental degradation by poor agricultural practices (erosion,
desertification); water pollution by human and industrial waste; air pollution caused by the
human need to use energy for personal use and for industrial applications; extinctions caused
by people converting natural ecosystems to managed agricultural ecosystems; and. destructive
effects of exploitation of natural resources (strip, mining, oil spills, groundwater mining). In
addition to population size, the kind of demands a population places on its resources is also
important. Highly industrialized populations require much more energy and material resources
to sustain their way of life than do the populations of the less-developed world.
A Population Growth Curve
Sex ratios and age distributions within a population directly influence the rate of
reproduction within a population. Each species has an inherent reproductive capacity, or
biotic potential, which is its ability to produce offspring. However, this high reproductive
potential results in a natural tendency for populations to increase. For example, two mice
produce four offspring, which, if they live, will also produce offspring while their parent’s
are also reproducing. Therefore, the population will tend to grow in an exponential fashion.
Population growth tends to follow a particular pattern, consisting of a lag phase, an
exponential growth phase, and a stable equilibrium phase. Fig. 15 shows a typical population
growth curve. During the first portion of curve, known as the lag phase, the population
grows very slowly because the process of reproduction and growth of offspring takes time.
Most organisms do not reproduce instantaneously but must first mature into adults. Mating
and the development of the young ones into independent organisms follow this period. By
the time the first batch of young has reached sexual maturity, the parents may be in the
process of producing a second set of offspring. Since more total organisms now are reproducing,
the population begins to increase at an exponential rate. This stage in the population growth
curve is known as the exponential growth phase. This growth will continue for as long as
the, birth rate exceeds the death rate. Eventually, however, the death rate and the birth
rate will come to equal one another, and the population will stop growing and reach a
relatively stable population. size and is said to be the stable equilibrium phase. Hence,
populations cannot grow continuously because of the concept of carrying capacity.
(a) S-Shaped growth curve
When a species is introduced into a new habitat, the population grows exponentially until
the individuals become numerous. The further increase in their number is checked by the
environmental resistance factors that the population growth declines until zero population
growth is reached. (i.e. constant) and it becomes stable (K). Such curves are called sigmoid
curves.
The study of growth curves in S-shaped growth pattern is a self-limiting one where the
rate of growth is more and more as density increases. If the limitation is linearly proportional
to density we get a symmetrical S-curve so as to approach upper level or limit-K, the
carrying capacity. This pattern enhances stability as population regulates itself. Actually
the density often overshoots or is more than K and because of time lags in feedback control
resulting in oscillations as shown in graphs.
K (Carrying Capacity)
Steady State
Exponential Growth
(Log Phase) M ax. G rowth
Log Phase
Slow Growth
Figure 7.2. S-shaped growth curve.
(b) J-Shaped growth curve
The population increases whenever there is an increase in birth rate over death rate.
The factors of environmental resistance do not check population growth or stabilize the
growth (zero growth not established) then a J-shaped curve is obtained Fig. 3. It is hard to
speculate in the future of human population growth curve whether it will be S-shaped or
J-shaped. Growth curve are thus the graphical representation of a population in given time
period. It may be of S-shaped or J-shaped as mentioned.
Time
Populatio n Growth
Lim it
Figure 7.3. J-shaped growth curve.
When population increase in exponential (E) or geometric fashion (e.g. 2, 4, 8, 16, 32
.........) until the population runs out of some resources or encounters, some other limitation
(N). Growth then comes to a more or less abrupt halt in such cases and density usually
declines rapidly until conditions for another rapid growth is restored. Population with this
kind of growth form instability unless regulated by factors outside the population.
(i) Growth rate decreases as density increases. (Self-limiting or inverse density dependent type.)
(ii) Growth rate is high until density become high and factors from outside of the
population become limiting. (Density independent type.)
(iii) Growth rate is highest at intermediate density.
Causes of Population Growth
There is an ultimate carrying capacity for the human population and limiting factors
will come into play to cause populations to stabilize. However, unlike populations of other
kinds of organisms, human populations are also influenced by a variety of social, political,
economic, and ethical factors. Humans have accumulated knowledge that allows for predictions
about the future and can make conscious decisions based on the likely course of events and
adjust their lives accordingly. Part of that knowledge is the certainty that as populations
continue to increase, death rates and birth rates will become equal. This can be accomplished
by allowing the death rate to rise or by choosing to limit the birth rate. It would seem that
controlling human population should be a simple process. Once everyone understands that
lowering the birth rate is more human than allowing the death rate to rise, most people
should make the “correct” decision; however, it is not quite that simple.
Biological Reasons for Population Growth
The study of human populations, their characteristics, and what happens to them is
known as demography. Demographers can predict the future growth of a population by
looking at several different biological indicators. When we look at birth rates and death
rates in various countries of the world, in almost all cases the birth rate exceeds the death
rate. Therefore, the size of the population must increase. Some countries that have high
birth rates and high death rates, with birth rates greatly exceeding the death rates, will
grow rapidly (Afghanistan and Ethiopia). Such countries Usually have an extremely high
mortality rate among children because of disease and malnutrition. Some countries have
high birth rates and low death rates and will grow extremely rapidly ~Guatemala and
Syria). Infant mortality rates are moderately high in these countries. Other countries have
low birth rates and death rates that closely match the birth rates and will grow slowly
(Sweden and the United Kingdom). These and other more, developed countries typically
have very low infant mortality rates.
Obviously, the most important determinant of the rate at which human populations
grow is related to the number of women in the population who are having children and the
number each will have. The total fertility rate of a population is the number of children
born per woman per lifetime. A total fertility rate of 2.1 is known as replacement fertility,
since in the long run, if the total fertility rate is 2.1, population growth will stabilize. When
population is not growing and the number of births equals the number of deaths, it is said
to exhibit zero population growth. The age structure of a population also has a great deal
to do with the rate of population growth. If a population has a large number of young people
who are in the process of raising families or who will be raising families in the near future,
the population will continue to increase even if the families limit themselves to two children.
Factors Controlling Population Growth
Man is the only one who has regulated his population by developing new astonishing
technologies for better and secured future on one hand. And on other hand, created a
problem of population explosion. Some factors are:
(i) Famines in a country or state lead to destruction.
(
Introduction
Human society is governed by interaction and cooperation with other human beings.
Latest trends in technology and medical knowledge are available to control human population
growth and to improve the health. Still population continues to increase and poverty become
greater than ever before. Humans are social animals who have freedom of choice. They
largely take decision by heart rather than mind. It is evident from historical records, social
situations, ethical and religious considerations and personal desires. Today the greatest
hindrance to controlling human population is no more biological but falls into the province
of philosophers, theologians, politicians, sociologists, and others. The cause of the population
problem is to be understood if we are to deal successfully with the population problem.
Carrying Capacity
The carrying capacity of an area is the number of individuals of a species that can
survive in that area over time. In most populations, four broad categories of factors determine
the carrying capacity for a population. These factors are: (1) the availability of raw materials,
(2) the availability of energy, (3) the accumulation of waste products and their means of
disposal and (4) interactions among organisms. The total of all of these forces acting together
to limit populations size is known as environmental resistance, and certain limiting factors
have a primary role in limiting the size of a population. In some cases, these limiting factors
are easy to identify and may involve lack of food, lack of oxygen, competition with other
species, or disease.
Population Characteristics
A population can be defined as a group of individuals of the same species inhabiting
an area. Some of the characteristics or a population are nasality (birth rate), mortality
(death rate), sex ratio, age distribution, growth rates, and special distribution.
Natality refers to the number of individuals added to the population through
reproduction. In human populations, natality is usually described in terms of the birth
rate, the number of individuals born per one thousand individuals in the population per
year. It is important to recognize that the growth of a population is not determined by the
birth rate (natality) alone.
This is expressed as
B (Natality rate) = Nn/t which means = No. of new individuals added to population time.
Mortality is the number of deaths per year. In human population studies, mortality is
usually discussed in terms of the death rate, the number of individuals who die per one
thousand individuals in the population per year.
Population Density is population size in relation to some unit of space and time. It
varies with food availability and climatic conditions. It can be measured as:
D = N/a
t
where D is population density, n = number of individuals, a = area and t = time.
Population Age Distribution refers to the individuals of different age groups in a
population. The natality and mortality is also different for respective ages. Bodenhelmer
(1938) recognized three ecological ages as: (i) Pre reproductive, (ii) Reproductive and
(iii) Post reproductive Fig. 1. Duration of these ages varies in different organisms e.g.
Insects have a very long pre-reproductive period, a very short reproductive period but no
post reproductive period at all. In man all the three stages are equal in length.
Post reproductive
Reproductive
Pre reproductive
Age structure
Expanding
Population
(A)
(B) Stable (C)
Population
Dim inishing
Population
Type of Population
Figure 7.1. Age structure in different types of populations
Biotic Potential is the maximum reproductive power. The constant percent growth
rate of a population under optimum environmental conditions thus represents its biotic
potential or reproductive potential. Letter designates it g.
g
AN AT
N
=
∆ /
where, N = number, t = time, D = constant.
The sex ratio refers to the number of males relative to the
Number of females in the population.
The Human Population Issue
Current population growth has led to famine in areas where food production cannot keep
pace with population growth; political unrest areas with great disparities in availability of
resources (jobs: goods, food); environmental degradation by poor agricultural practices (erosion,
desertification); water pollution by human and industrial waste; air pollution caused by the
human need to use energy for personal use and for industrial applications; extinctions caused
by people converting natural ecosystems to managed agricultural ecosystems; and. destructive
effects of exploitation of natural resources (strip, mining, oil spills, groundwater mining). In
addition to population size, the kind of demands a population places on its resources is also
important. Highly industrialized populations require much more energy and material resources
to sustain their way of life than do the populations of the less-developed world.
A Population Growth Curve
Sex ratios and age distributions within a population directly influence the rate of
reproduction within a population. Each species has an inherent reproductive capacity, or
biotic potential, which is its ability to produce offspring. However, this high reproductive
potential results in a natural tendency for populations to increase. For example, two mice
produce four offspring, which, if they live, will also produce offspring while their parent’s
are also reproducing. Therefore, the population will tend to grow in an exponential fashion.
Population growth tends to follow a particular pattern, consisting of a lag phase, an
exponential growth phase, and a stable equilibrium phase. Fig. 15 shows a typical population
growth curve. During the first portion of curve, known as the lag phase, the population
grows very slowly because the process of reproduction and growth of offspring takes time.
Most organisms do not reproduce instantaneously but must first mature into adults. Mating
and the development of the young ones into independent organisms follow this period. By
the time the first batch of young has reached sexual maturity, the parents may be in the
process of producing a second set of offspring. Since more total organisms now are reproducing,
the population begins to increase at an exponential rate. This stage in the population growth
curve is known as the exponential growth phase. This growth will continue for as long as
the, birth rate exceeds the death rate. Eventually, however, the death rate and the birth
rate will come to equal one another, and the population will stop growing and reach a
relatively stable population. size and is said to be the stable equilibrium phase. Hence,
populations cannot grow continuously because of the concept of carrying capacity.
(a) S-Shaped growth curve
When a species is introduced into a new habitat, the population grows exponentially until
the individuals become numerous. The further increase in their number is checked by the
environmental resistance factors that the population growth declines until zero population
growth is reached. (i.e. constant) and it becomes stable (K). Such curves are called sigmoid
curves.
The study of growth curves in S-shaped growth pattern is a self-limiting one where the
rate of growth is more and more as density increases. If the limitation is linearly proportional
to density we get a symmetrical S-curve so as to approach upper level or limit-K, the
carrying capacity. This pattern enhances stability as population regulates itself. Actually
the density often overshoots or is more than K and because of time lags in feedback control
resulting in oscillations as shown in graphs.
K (Carrying Capacity)
Steady State
Exponential Growth
(Log Phase) M ax. G rowth
Log Phase
Slow Growth
Figure 7.2. S-shaped growth curve.
(b) J-Shaped growth curve
The population increases whenever there is an increase in birth rate over death rate.
The factors of environmental resistance do not check population growth or stabilize the
growth (zero growth not established) then a J-shaped curve is obtained Fig. 3. It is hard to
speculate in the future of human population growth curve whether it will be S-shaped or
J-shaped. Growth curve are thus the graphical representation of a population in given time
period. It may be of S-shaped or J-shaped as mentioned.
Time
Populatio n Growth
Lim it
Figure 7.3. J-shaped growth curve.
When population increase in exponential (E) or geometric fashion (e.g. 2, 4, 8, 16, 32
.........) until the population runs out of some resources or encounters, some other limitation
(N). Growth then comes to a more or less abrupt halt in such cases and density usually
declines rapidly until conditions for another rapid growth is restored. Population with this
kind of growth form instability unless regulated by factors outside the population.
(i) Growth rate decreases as density increases. (Self-limiting or inverse density dependent type.)
(ii) Growth rate is high until density become high and factors from outside of the
population become limiting. (Density independent type.)
(iii) Growth rate is highest at intermediate density.
Causes of Population Growth
There is an ultimate carrying capacity for the human population and limiting factors
will come into play to cause populations to stabilize. However, unlike populations of other
kinds of organisms, human populations are also influenced by a variety of social, political,
economic, and ethical factors. Humans have accumulated knowledge that allows for predictions
about the future and can make conscious decisions based on the likely course of events and
adjust their lives accordingly. Part of that knowledge is the certainty that as populations
continue to increase, death rates and birth rates will become equal. This can be accomplished
by allowing the death rate to rise or by choosing to limit the birth rate. It would seem that
controlling human population should be a simple process. Once everyone understands that
lowering the birth rate is more human than allowing the death rate to rise, most people
should make the “correct” decision; however, it is not quite that simple.
Biological Reasons for Population Growth
The study of human populations, their characteristics, and what happens to them is
known as demography. Demographers can predict the future growth of a population by
looking at several different biological indicators. When we look at birth rates and death
rates in various countries of the world, in almost all cases the birth rate exceeds the death
rate. Therefore, the size of the population must increase. Some countries that have high
birth rates and high death rates, with birth rates greatly exceeding the death rates, will
grow rapidly (Afghanistan and Ethiopia). Such countries Usually have an extremely high
mortality rate among children because of disease and malnutrition. Some countries have
high birth rates and low death rates and will grow extremely rapidly ~Guatemala and
Syria). Infant mortality rates are moderately high in these countries. Other countries have
low birth rates and death rates that closely match the birth rates and will grow slowly
(Sweden and the United Kingdom). These and other more, developed countries typically
have very low infant mortality rates.
Obviously, the most important determinant of the rate at which human populations
grow is related to the number of women in the population who are having children and the
number each will have. The total fertility rate of a population is the number of children
born per woman per lifetime. A total fertility rate of 2.1 is known as replacement fertility,
since in the long run, if the total fertility rate is 2.1, population growth will stabilize. When
population is not growing and the number of births equals the number of deaths, it is said
to exhibit zero population growth. The age structure of a population also has a great deal
to do with the rate of population growth. If a population has a large number of young people
who are in the process of raising families or who will be raising families in the near future,
the population will continue to increase even if the families limit themselves to two children.
Factors Controlling Population Growth
Man is the only one who has regulated his population by developing new astonishing
technologies for better and secured future on one hand. And on other hand, created a
problem of population explosion. Some factors are:
(i) Famines in a country or state lead to destruction.
(