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Starling
Shakespeare’s Henry the Fourth
1890 ~ 120 ind.
1990 ~ 100 million ind.
Chapter 4, 5, 7
Human population?
Natural Selection Conditions
Natural Selection
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Natural Selection - Process that determines
which individuals within a species will
reproduce and pass their genes to the next
generation.
Conditions:
– Individuals within a species show
genetically determined variation.
– Organisms within a species typically
produce huge numbers of offspring, most
of which die.
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Excess number of individuals results in a
shortage of specific resources.
Due to individual variation, some individuals
have a greater chance of obtaining needed
resources and thus have a greater
likelihood of survival and reproduction.
As time passes, percentage of individuals
showing favorable variations will increase
while percentage showing unfavorable
variations will decrease.
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Evolutionary Patterns
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Evolution - A change in the kinds of
organisms that exist and in their
characteristics.
Speciation - Production of new species from
previously existing species.
– Thought to occur as a result of a species
dividing into two reproductively isolated
subpopulations.
Population Density
Evolutionary Patterns
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Extinction - Loss of entire species.
– Of estimated 500 million species believed
to have ever existed on earth, 98-99%
have gone extinct.
Co-Evolution - Two or more species can
reciprocally influence the evolutionary
direction of the other.
– Grazing animals and grass species.
Dispersion pattern
• Clumped
• Uniform
• Random
• Actually count
• Sampling
• Mark-recapture method
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Population Growth
Carrying capacity
Carrying capacity
Density-dependent Factor
Density-independent Factor
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Life History
Opportunistic life history
Equilibrial life history
Human Population
Human Population
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Population Principles
Chapter 7
Age-structure Diagram
Outline
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Population Characteristics
Age Structure Diagrams
Exponential Growth
Carrying Capacity
– Environmental Resistance
Reproductive Strategies
– (r and K)
Human Population Growth
– Doubling Time
Population Characteristics
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Population - Group of individuals of the
same species inhabiting the same area
simultaneously.
– Natality and Mortality
™ Natality - Number of individuals added
through reproduction.
¾ Birth Rate (Humans Born / 1,000)
– Mortality - Number of individuals removed
via death.
™ Death Rate (Humans Died / 1,000)
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Population Characteristics
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Sex Ratio and Age Distribution
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Population Growth Rate - Birthrate minus the
death rate. Often expressed as a
percentage of the total population.
Survivorship Curve - Shows proportion of
individuals likely to survive to each age.
– High mortality in young.
– Mortality equitable among age classes.
– Mortality high only in old age.
Age Distribution in Human Populations
Sex Ratio - Age Distribution
– Sex Ratio - Relative number of males and
females in a population.
™ Females determine the number of
offspring produced in sexually
reproducing populations.
– Age Distribution - Number of individuals of
each age in the population.
™ Greatly influences population growth
rate.
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Population Density and Spatial Distribution
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Population Density - Number of individuals
per unit area.
– High population may lead to increased
competition for resources.
™ Dispersal - Movement of individuals
from densely populated locations to new
areas.
¾ Emigration - Movement from an area.
¾ Immigration - Movement into an area.
Exponential Growth Curve
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Population Growth Curve
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Biotic Potential - Inherent reproductive
capacity. (Biological ability to produce
offspring)
– Generally, biotic potential is much above
replacement level.
™ Natural tendency for increase.
¾ All living populations follow an
exponential growth curve.
Typical Population Growth Curve
Lag Phase - First portion of the curve; slow
population growth.
Exponential Growth Phase (Log Phase)More organisms reproducing causing
accelerated growth; continues as long as
birth rate exceeds death rate.
Stable Equilibrium Phase - Death rate and
birth rate equilibrate; population stops
growing.
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Carrying Capacity
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Carrying Capacity - Number of individuals of
a species that can be indefinitely sustained
in a given area without harming the habitat.
Environmental Resistance
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Reproductive Strategies
and Population Fluctuations
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Not all species reach a stable carrying
capacity.
– Species can be broadly lumped into two
categories:
™ K-strategists
™ r-strategists
Environmental Resistance - Any factor
(limiting factor) in the environment limiting
carrying capacity.
– Four main factors:
™ Raw Material Availability
™ Energy Availability
™ Waste Accumulation and Disposal
™ Organism Interactions
K - Strategists
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Large organisms
Long-lived
Produce few offspring
Provide substantial parental care
Populations typically stabilize at a carrying
capacity.
Usually occupy relatively stable
environments.
Reproductive strategy is to invest in a few,
quality offspring.
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K - Strategists
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Controlled by density-dependent limiting
factors.
– Factors that become more severe as the
size of the population increases.
™ Diseases
Deer - Lions - Swans
r - Strategists
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r - Strategists
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Controlled by density-independent limiting
factors.
– Population size is irrelevant to the limiting
factor.
™ Weather Conditions
Grasshoppers - Gypsy Moths - Mice
Small organisms
Short-lived
Produce many offspring
Little if any parental care
Usually do not reach carrying capacity
(boom-bust cycles).
Exploit unstable environments.
Reproductive strategy is to produce large
numbers of offspring to overcome high
mortality.
Human Population Growth
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Major reason for increasing human
population growth rate is an increase in
medical care, and a consequential decrease
in death rates.
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Historical Human Population Growth
Doubling Time
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Doubling Time of a Population (years) :
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70 / Population Growth Rate (%)
( 70 / 2.0% = 35 years )
Doubling Time for the Human Population
Human Population Growth
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Interactions Affecting Carrying Capacity
– Available Raw Materials
– Available Energy
– Waste Disposal
– Interaction With Other Organisms
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Social Factors Influence Human Population
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Humans are social animals who have
freedom of choice.
– People make decisions based on history,
social situations, ethical and religious
beliefs, and personal desires.
™ Biggest obstacles to controlling human
population are not biological, but are the
province of philosophers, theologians,
politicians, and sociologists.
Ultimate Size Limitation
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If the world continues to grow at current rate,
population will surpass 12 billion by 2060.
Human population subject to same biological
constraints as other species.
– Human population will ultimately reach a
carrying capacity and stabilize.
™ Disagreement about exact size and
primary limiting factors.
Review
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Population Characteristics
Age Structure Diagrams
Exponential Growth
Carrying Capacity
– Environmental Resistance
Reproductive Strategies
– (r and K)
Human Population Growth
– Doubling Time
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