3. CHARACTERISTICS OF
POPULATIONS
Population size: number of individuals in the gene pool
Population density: number of individuals in a given area
Population distribution: pattern of distribution (uniform, random,
clumped)
Age structure: pre-reproductive, reproductive, post-reproductive
Reproductive base: those individuals in the pre-reproductive or
reproductive stage
4. POPULATION SIZES
Births and immigration increase
population size,
Deaths and emigration decrease
population size
Zero Population Growth (ZPG) =
no net increase or decrease
For a small population, as long as the
birth rate is slightly above the death
rate, a population grows
exponentially with a characteristic J-
curve
9. THE PHILIPPINE
POPULATION
Average Annual Exponential Growth Rates,
Philippines: 2000-2040
Year Growth Rate Projected Total Fertility Rates, by Five-
Year Interval, Philippines: 2000-2040
2000-2005 2.05 (Medium Assumption)
2005-2010 1.95
Year Rate
2010-2015 1.82
2000-2005 3.41
2015-2020 1.64 2005-2010 3.18
2020-2025 1.46 2010-2015 2.96
2025-2030 1.27 2015-2020 2.76
2030-2035 1.09 2020-2025 2.57
2035-2040 0.92 2025-2030 2.39
2030-2035 2.23
2035-2040 2.07
10. ISSUES RELATED TO
POPULATION GROWTH
Public health:
U n c l e a n w a t e r, a l o n g w i t h p o o r
sanitation, kills over 12 million people
each year, most in developing countries.
Air pollution kills nearly 3 million more.
Heavy metals and other contaminants
also cause widespread health problems.
Food supply:
Will there be enough food to go around?
In 64 of 105 developing countries
studied by the UN Food and Agriculture
Organization, the population has been
growing faster than food supplies.
Population pressures have degraded
some 2 billion hectares of arable land —
an area the size of Canada and the U.S.
11. ISSUES RELATED TO
POPULATION GROWTH
• Freshwater:
The supply of freshwater is finite,
but demand is soaring as
population grows and use per
capita rises. By 2025, when world
population is projected to be 8
billion, 48 countries containing 3
billion people will face shortages.
• Coastlines and oceans:
Half of all coastal ecosystems are
pressured by high population
densities and urban development. A
tide of pollution is rising in the world’s
seas. Ocean fisheries are being
overexploited, and fish catches are
down.
12. ISSUES RELATED TO
POPULATION GROWTH
• Forests:
Nearly half of the world’s original forest cover has
been lost, and each year another 16 million
hectares are cut, bulldozed, or burned. Forests
provide over US$400 billion to the world economy
annually and are vital to maintaining healthy
ecosystems. Yet, current demand for forest
products may exceed the limit of sustainable
consumption by 25%.
Th e de m a n d for forest products exceeds
sustainable consumption by 25%.
• Biodiversity:
The earth’s biological diversity is crucial to the
continued vitality of agriculture and medicine — and
perhaps even to life on earth itself. Yet human
activities are pushing many thousands of plant and
animal species into extinction. Two of every three
species is estimated to be in decline.
13. ISSUES RELATED TO
POPULATION GROWTH
• Global climate change:
The earth’s surface is warming
due to greenhouse gas emissions,
largely from burning fossil fuels. If
the global temperature rises as
projected, sea levels would rise by
several meters, causing
widespread flooding. Global
warming also could cause
droughts and disrupt agriculture.
15. WHAT CAN BE DONE
Taking action:
Many steps toward sustainability can be taken today. These include: using energy more
efficiently, managing cities better, phasing out subsidies that encourage waste, [etc.]
The world must sustain 1 billion more people every 13 years
Stabilizing population:
While population growth has slowed, the absolute number of people continues to increase
— by about 1 billion every 13 years. Slowing population growth would help improve living
standards and would buy time to protect natural resources. In the long run, to sustain
higher living standards, world population size must stabilize.
Environmentalists and economists increasingly agree that efforts to protect the
environment and to achieve better living standards can be closely linked and are mutually
reinforcing. Slowing the increase in population, especially in the face of rising per capita
demand for natural resources, can take pressure off the environment and buy time to
improve living standards on a sustainable basis
16. CARRYING CAPACITY
The resources in any given habitat can
support only a certain quantity of wildlife
As seasons change, food, water, or cover
may be in short supply.
Carrying capacity is the number of
animals the habitat can support all
year long
The carrying capacity of a certain tract of
land can vary from year to year. It can be
changed by nature or humans
The number of animals the habitat can
support throughout the year without
damage to the animals or to the habitat.
17. CARRYING CAPACITY
Factors that limit the potential If the conditions are balanced, game
production of wildlife include: animals will produce a surplus, which
can be harvested on an annual,
Disease/parasites sustainable basis.
Starvation
Predators
Pollution
Accidents
Old age
Hunting
19. ANALYSIS OF AGE
STRUCTURE PYRAMIDS
Age structure diagrams show how a population
is distributed
It divides the population into pre-reproductive,
reproductive and post-reproductive phases
The shape of the diagram can show you if a
country is growing rapidly, slowly, or negatively
It can also show is there is zero growth
The wider the base of the diagram the more
individuals below the age of fifteen
The more individuals under fifteen the more
individuals poised to reproduce increases
The left hand side is always the males.
20. AGE STRUCTURES
RELATIVE PROPORTION OF INDIVIDUALS BELONGING TO DIFFERENT AGE
CLASSES IN A POPULATION
CATEGORIES: PRE-REPRODUCTIVE; REPRODUCTIVE; POST-REPRODUCTIVE
DEPENDING ON ITS AGE STRUCTURE:
PYRAMID
LESS INDUSTRIALIZED
HIGH PRE-REPRODUCTIVE
MAY CONTINUE TO GROW : 2 CHILDREN
HIGH WOMEN ENTERING REPRODUCTIVE THAN LEAVING
BULLET
STABLE
SAME NUMBER PER GROUP
21. COMMUNITY AND
SUCCESSION
EARLY SUCCESSION SPECIES
HIGH GROWTH RATE, WIDE DISPERSAL,
SMALL, FAST POPULATION GROWTH
LATE SUCCESSION SPECIES
LOWER RATES OF DISPERSAL, SLOWER
GROWTH RATE, LONGER LIVES, LARGER
PRIMARY SUCCESSSION vs SECONDAY
SUCCESSION
DISTURBANCE: SMALL SCALE or LARGE SCALE
22. IMPORTANT TERMS IN
SUCCESSION
Succession is a directional non-seasonal cumulative
change in the types of plant species that occupy a given
area through time.
It i nvolves t he p ro c e s s e s o f c o l o n iz a tio n ,
establishment, and extinction which act on the
participating plant species.
Succession begin when an area is made partially or
completely devoid of vegetation because of a
disturbance.
Some common mechanisms of disturbance are fires,
wind storms, volcanic eruptions, logging, climate
change, severe flooding, disease, and pest infestation
Succession stops when species composition changes no
longer occur with time, and this community is said to be a
climax community.
23. TYPES OF SUCCESSION
Primary succession - is the
establishment of plants on land
that has not been previously
vegetated - Mount Saint Helens.
Begins with colonization and
establishment of pioneer species
Secondary succession - is the
invasion of a habitat by plants on
land that was previously
vegetated. Removal of past
vegetation may be caused by
natural or human disturbances
such as fire, logging, cultivation, or
hurricanes.
24. TYPES OF
SUCCESSION
Allogenic succession - a succession
where the stimulus for change is an
external one.
An allogenic succession can be
brought about in a number of ways
which can include: Volcanic
eruptions; Grazing animals; Human
i n t e r f e re n c e ; F l o o d i n g ; N o n -
anthropogenic climate change
Autogenic succession - a succession
where the stimulus for change is an
internal one.
For example gradual soil
improvement could allow a new
species to develop
25. TYPES OF
SUCCESSION
Progressive succession - is a
succession where the community
becomes complex and contains
more species and biomass over
time
Retrogressive succession - is a
succession where the community
becomes simplistic and contains
fewer species and less biomass over
time. Some retrogressive
successions are allogenic in nature.
For example, the introduction of
g r a z i n g a n i m a l s re s u l t i n
degenerated rangeland.
