Transcript POPULATION PRINCIPLES

Population Principles
Chapter 7
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Population Characteristics
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Population - Group of individuals of the
same species inhabiting the same area
simultaneously. (6.4 Billion – 2004)
– Natality and Mortality
 Natality - Number of individuals added
through reproduction.
 Birth Rate (Humans Born / 1,000)
– Mortality - Number of individuals removed
via death.
 Death Rate (Humans Died / 1,000)
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Figure 7.1
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Population Characteristics
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Population Growth Rate - Birthrate minus the
death rate. Often expressed as a
percentage of the total population.
(Geometrically – Population)(Arithmetically – Food Supply)
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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.
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Survivorship Curve
(Fig.7.2)
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Sex Ratio and Age Distribution
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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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Age Distribution in Human Populations
(Fig.7.3)
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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.
 Emigration - Movement from an area.
 Immigration - Movement into an area.
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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.
 All living populations follow an
exponential growth curve.
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Exponential Growth Curve
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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. *Currently*
Stable Equilibrium Phase - Death rate and
birth rate equilibrate; population stops
growing.
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Biotic Potential (Fig.7.4)
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Typical Population Growth Curve (Fig.7.5)
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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.
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Environmental Resistance
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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
 Disease, Predation, and Space
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Carrying Capacity (Fig.7.6)
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Bacterial Growth Curve (Fig.7.7)
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Fig. p.138
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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
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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
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r - Strategists
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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.
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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
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Population Cycles (Fig.7.8)
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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
(Fig.7.9)
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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 )
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Doubling Time for the Human Population
(Fig.7.10)
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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.
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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.
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Elephant Trade
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Snow Goose
(Pg.145)
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