POPULATION ECOLOGY
Chapter 19
ECOLOGY
Study of interactions of organisms with each other and
the physical environment
 Can be divided into increasingly comprehensive levels:

Organismal ecology
 Population ecology
 Community ecology
 Ecosystem ecology

ORGANISMAL ECOLOGY
Concerned with
evolutionary
adaptations
 Enable individual
organisms to meet the
challenges posed by
their abiotic
environments

POPULATION ECOLOGY

Concentrates mainly
on factors that affect
population density
and growth
COMMUNITY ECOLOGY

Focuses on how
interactions between
species affect
community structure
and organization
ECOSYSTEM ECOLOGY
All abiotic factors in
addition to the
community of species in a
certain area
 Focuses on energy flow
and the cycling of
chemicals


among the various abiotic
and biotic factors
WHAT IS POPULATION ECOLOGY?
Study of how members of a population interact with
their environment
 Focuses on factors that influence a population’s:

Size
 Growth rate
 Density
 Structure

POPULATIONS

Distribution
Pattern of dispersal of individuals across an area
 Affected by availability of resources



Limiting factors


nonliving (abiotic) and living (biotic) components of an
environment that support living organisms
Environmental aspects that particularly determine where
an organism lives
Range

Portion of the globe where the species can be found
POPULATIONS

Density


Number of individuals per unit
area
How do we measure population
density?
impossible to count all individuals in
a population
 estimated by indirect indicators
 number of bird nests

INFLUENCES ON POPULATION

Carrying capacity

Number of individuals of a
species that a particular
environment can support
PATTERNS OF DISPERSION….
way individuals are spaced within the
population’s geographic range
 Three main models of dispersion:

Clumped
 Uniform
 Random

PATTERNS OF DISPERSION

Clumped pattern of
dispersion

Individuals aggregate in
patches
PATTERNS OF DISPERSION

Uniform pattern of
dispersion

Results from
interactions among
the individuals of a
population
PATTERNS OF DISPERSION

Random pattern of
dispersion

Individuals are spaced
in a patternless,
unpredictable way
COMPARISON OF SPECIES
Survivorship
 Life history traits

1.
SURVIVORSHIP
Chance an individual in a population survives to
various ages
 Represented graphically in a survivorship
curve

Plot of individuals surviving at each age in maximum
life span
 Uses a percentage scale
 Can compare species with various life spans on same
graph

SURVIVORSHIP

Type I survivorship
curve


Type II survivorship
curve


Most individuals survive
until old age
Decreases consistently
over time
Type III survivorship
curve

Most individuals die early
2.

LIFE HISTORY
Set of traits that affect the organisms:
Reproduction
 Survival

Key feature of a populations pattern of survivorship
 Key life history traits are:

Age at first reproduction
 Frequency of reproduction
 Number of offspring
 Amount of parental care provided

TYPES OF LIFE HISTORIES

Organisms with an
opportunistic life history:
Take immediate advantage of
favorable conditions
 Typically exhibit a Type III
survivorship curve


Organisms with an equilibrial
life history:





Reach sexual maturity slowly
Produce few, well cared for
offspring
typically large-bodied and longer
lived
Typically exhibit a Type I
survivorship curve
occur in environments where
population size is at or near
carrying capacity
POPULATION GROWTH MODELS
Populations fluctuate
 Mathematical models to
illustrate changes:



Exponential population
growth
Logistic population growth
POPULATION GROWTH MODELS

1. J-shaped Curve –
Exponential Growth
 Lag phase: Growth is small
because the population is small

Exponential growth phase:
Growth is accelerating, and the
population is exhibiting its biotic
potential
POPULATION GROWTH MODELS

2. S-shaped Curve – Logistic
Growth
 Lag phase: Growth is small because
the population is small

Exponential growth phase:
Growth is accelerating, and the
population is exhibiting its biotic
potential

Deceleration phase:

Stable equilibrium phase:
The rate of
population growth slows down
Little
if any growth takes place because births
and deaths are about equal.
REGULATION OF POPULATION GROWTH

1. density-dependent
factor



Intraspecific competotion
population-limiting factor
effects intensify as the
population increases in
density


Percentage of population
affected does increase as
density of population
increases
Includes:
Accumulation of toxic
wastes
 Limited food supply
 Limited territory


Competition and
predation
100
Survivors (%)
80
60
40
20
0
20
40
60
80
100
Density (beetles/0.5 g flour)
(b) Decreasing survival rates with increasing density in a
population of flour beetles
120
REGULATION OF POPULATION GROWTH

2. Density-independent
factors
population-limiting factors
 intensity is unrelated to
population density



Population of individuals killed
remains same regardless of
population size
Includes abiotic factors such as:
Fires
 Floods
 Storms

Sudden
decline
Number of aphids
Exponential
growth
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
EFFECTS ON POPULATIONS INVASIVE SPECIES




Non-native species that has
spread far beyond the original
point of introduction
Causes environmental or
economic damage by colonizing
and dominating suitable
habitats
In United States, invasive
species cost about $137 billion
a year
Invasive species typically
exhibit an opportunistic life
history pattern
INVASIVE SPECIES

Kudzu





1876
invasive Asian vine
Covers about 12,000
square miles of the
southeastern United
States
Has a range limited by
cold winters
Grows 60 feet per
season!
INVASIVE SPECIES

Biological control
intentional release of a
natural enemy to
attack a pest
population
 used to manage an
invasive species
 Does NOT always
work!!!

HUMAN POPULATION GROWTH
Growing almost
exponentially for
centuries
 Based on the same
parameters that affect
other populations

Birth rates
 Death rates

HUMAN POPULATION GROWTH
 Approximately
225,000 people are added to
the world’s population every day
 Approximately 82 million people are added to
the world’s population every year
 Current doubling time is 56 years

(length of time it takes for population size to
double)
 More
Developed Countries (MDC’s)
versus Less Developed Countries (LDC’s)
ESTIMATES OF POPULATION

Age structure of a
population
Proportion of
individuals in different
age groups
 Can help predict the
future growth of
populations in different
countries
