Transcript Factors Affecting Human Population Size

Populations Key Concepts
 Factors affecting population size
 Species reproductive patterns
 Species survivorship patterns
 Conservation biology and human impacts
on ecosystems
Population Dynamics and Carrying Capacity
 Population dynamics
 Biotic potential (intrinsic rate of increase [r])
 Environmental resistance
 Carrying capacity
 Exponential and Logistic Growth
 Population Density
The biotic potential rmax is the population's
capacity for growth.
The intrinsic rate of increase (r) is the rate of
population growth with unlimited resources.
No population can grow indefinitely due to limited
resources such as light, water, and nutrients and
also due to competitors and/or predators.
Reproductive Strategies
Reproductive Strategies
Population Dynamics
Populations change in size, density, dispersion and age
structure.
Population density —the number of individuals of a
population that inhabit a certain unit of land or water area.
Population dispersion —refers to how individuals of a
population are spaced within a region.
Age structure of a population is usually described as the
pre-reproductive stage, the reproductive stage and the
post-reproductive stage. A population with a large
reproductive stage is likely to increase, while a population
with a large post-reproductive stage is likely to decrease.
Population dispersion
clumping dispersion the most common dispersion pattern for populations.
In this type of dispersion, individuals "flock together.“
uniform dispersion a type of population dispersion in which the members of
the population are uniformly spaced throughout their geographic region.
random dispersion —a type of population dispersion in which the position of
each individual is not determined or influenced by the other members of the
population.
Population Dynamics
Four variables influence/govern population size:
(1) births, (2) deaths, (3) immigration, and
(4) emigration.
1)
2)
Increase in population occurs by birth and
immigration.
Decrease in population occurs by death and
emigration.
Factors Affecting Population Size
Biotic Potential
v.
Environmental
Resistance
Fig. 9-3 p. 166
Biotic Potential v. Environmental Resistance
(Logistic Population Growth)
Environmental
resistance
Population size (N)
Carrying capacity (K)
Carrying capacity (K) is
determined by biotic
potential and
environmental resistance.
This is the number of a species'
individuals that can be
sustained indefinitely in a
specific space.
Four variables influence/govern
population size: (1) births,
(2) deaths, (3) immigration,
and (4) emigration.
Biotic
potential
Exponential
growth
Increase in population occurs
by birth and immigration.
Decrease in population occurs
by death and emigration.
Figure 9-4
Page 166
Time (t)
Exponential and Logistic Growth
Density and Limiting Factors
The density of a population may or may not affect how rapidly it can
grow.
1.
Density-independent population controls affect a population's
size regardless of its density. These are abiotic factors in the
community.
2.
Density-dependent factors or population controls have a
greater affect on the population as its density increases.
Infectious disease is an example of density-dependent
population control.
Natural Population Curves
Fig. 9-7 p. 168
The Role of Predation in Controlling
Population Size
Fig. 9-8 p. 168

Predator-prey cycles (Boom and Bust)
 Top-down control

Bottom-up control
Reproductive Patterns and Survival

Asexual reproduction

Sexual reproduction

r-selected species

K-selected species
Fig. 9-10 p. 170
Reproductive Patterns and Survival
Reproductive patterns can be classified into two fundamental
reproductive patterns: r-selected and K-selected species.
r-Selected species are opportunists and reproduce when conditions are
favorable or when disturbance opens a niche for invasion. Most
species of this type go through irregular and unstable boom-andbust cycles in population size.
K-selected species generally follow a logistic growth curve. Many of the
larger species with long generation times and a low reproductive
rate are prone to extinction.
Availability of a suitable habitat for individuals of a population ultimately
determines the population size.
Populations of different species vary in how long individual members
typically live.
A survivorship curve is one
way to represent age
structure of a
population.
Three generalized types of
survivorship curves
are: (1) late loss, (2)
early loss, and (3)
constant loss.
A life table shows the
numbers of individuals
at each age on a
survivorship curve.
Insurance companies
use life tables to
determine the cost of
insurance policies.
Effects of Genetic Variations on Population Size
Variations in genetic diversity can affect the survival of small, isolated
populations.
Several factors can play a role in loss of genetic diversity and survival of a small
population.
Founder effect is when a few individuals move to a new location that is
isolated from the original population. There is limited genetic diversity in
such a population.
Demographic bottleneck occurs when only a few individuals survive a
catastrophe.
Genetic drift is a third factor and involves random changes in gene
frequencies in a population. This may help or hurt the survival of the
population.
Inbreeding occurs when members of a small population mate one
another; this may increase the numbers of defective genes in a
population.
Human Impacts on Ecosystems
 Habitat degradation and fragmentation
 Ecosystem simplification
 Genetic resistance
 Predator elimination
 Introduction of non-native species
 Overharvesting renewable resources
 Interference with ecological systems
Human Populations Key Concepts
 Factors affecting human population size
 Human population problems
 Managing population growth
Factors Affecting Human Population Size
Demography is the study of the size, composition, and
distribution of human populations and the causes and
consequences of changes in these characteristics.
Population change equation
Population
Change
=
(Births + Immigration) – (Deaths + Emigration)
 Crude birth rate (BR) The crude birth rate is the
number of live births per 1,000 people in a population
in a specific year.|
 Crude death rate (DR) The crude death rate is the
number of deaths per 1,000 people in a population in a
specific year
Describing Population Changes
 Doubling Times “Rule of 70”: Doubling time is one measure of
population growth.
 Fertility-is the number of births that occur to an individual
woman in a population.
 Replacement-level Fertility —the number of children a couple
must have in order to replace themselves in a population.
 Total Fertility Rate (TFR) —the number of children a woman will
bear during her lifetime; this information is based on an analysis
of data from preceding years in the population in question.
Factors Affecting Human Population Size
There are currently more births than deaths throughout the
world.
1. The annual rate of natural population change (%)
equals birth rate minus death rate divided by
1,000 persons multiplied by 100.
2.
The rate of the world's population growth has
decreased.
3.
The annual population growth dropped by almost half
between 1963 and 2004, from 2.2% to
1.2%. But during this same period, the population
base doubled from 3.2 to 6.4 billion.
Factors Affecting Human Population Size
There is a big difference in the exponential population growth
rates of developed and developing countries, with
developed countries growing at 0.25% and developing
countries growing at 1.46%— almost six times faster.
The six fastest growing countries in terms of population are:
India, China, Pakistan, Nigeria,
Bangladesh, and Indonesia.
The populations of China and India comprise 38%
of the world's population. The next most
populated country is the United Stated with
4.6% of the world's population.
Factors Affecting Birth Rates and Total Fertility
Rates
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Children in Labor Force
Cost of raising and educating children
Availability of pension systems
Urbanization
Education and employment for women
Infant mortality rate
Average marrying age
Abortion
Availability of birth control
Factors Affecting Birth Rates and Total Fertility Rates
Many factors influence birth and fertility rates.
1.
More children work in developing countries; they are important to the
labor force.
2.
The economic cost of raising and educating children determines their
numbers. the more children cost, the less children people tend to have.
3.
If there are available private/public pension systems, adults have fewer
children because they don't need children to take care of them in old
age.
4.
People in urban areas usually have better access to family planning, so
they have fewer children.
5.
If women have educational and economic choices, they tend to have
fewer children.
6.
When the infant mortality rate is low, people have fewer children
because children are not being lost to death.
7.
The older the age at which women marry, the fewer children they bear.
8.
If abortions are available and legal, women have fewer children.
9.
The availability of reliable birth control allows women to space children
and determine the number of children they bear.
Who is Over Populated?
CNN-The People Bomb
Population Age Structure
Male
Female
Rapid Growth
Guatemala
Nigeria
Saudi Arabia
Ages 0-14
Slow Growth
United States
Australia
Canada
Ages 15-44
Zero Growth
Spain
Austria
Greece
Negative Growth
Germany
Bulgaria
Sweden
Ages 45-85+
Fig. 10-14 p. 184
The Demographic Transition
Fig. 10-20 p. 189
Stage 2
Transindustrial
Stage 3
Industrial
Stage 4
Postindustrial
High
80
70
Relative population size
Birth rate and death rate
(number per 1,000 per year)
Stage 1
Preindustrial
60
50
Birth rate
40
30
Death rate
20
10
0
Total population
Low
Increasing Growth Very high Decreasing
Low
Zero
growth rate
growth rate
growth rate growth rate growth rate growth rate
Time
Low
Negative
growth rate
Solutions: Influencing
Population Size
 Migration
 Environmental refugees
 Reducing births
 Family planning
 Empowerment of women
 Economic rewards and penalties