14.3 Population Density And Distribution
KEY CONCEPT
Each population has a density, a dispersion, and a
reproductive strategy.
14.3 Population Density And Distribution
Population density - number of individuals that live in a
defined area.
14.3 Population Density And Distribution
Dispersion shows how individuals in a population are
spaced.
Clumped
dispersion
Uniform
dispersion
Random
dispersion
14.3 Population Density And Distribution
• There are three types of dispersion.
1. Clumped – Individuals clustered together
• Occur when resources such as food or living space
are clumped
• Or because of social behavior
14.3 Population Density And Distribution
• There are three types of dispersion.
2. Uniform (Even) – Individuals are separated by a fairly
consistent distance
• Result from social interactions resulting in
individuals getting as far away from each other as
possible
• Ex: establishing territories
• x
14.3 Population Density And Distribution
• There are three types of dispersion.
3. Random – Individual’s location is independent of the
locations of other individuals
• Usually results from seed dispersal by the wind or
by birds
14.3 Population Density And Distribution
A survivorship curve is a diagram showing the number of
surviving members over time from a measured set of
births.
14.3 Population Density And Distribution
• Survivorship curves can be type I, II or III.
– Type I — low level of infant mortality and an older
population
– common to large mammals and humans
– Type II — survivorship rate is equal at all stages of life
– common to birds
and reptiles
– Type III — very
high birth rate,
very high infant
mortality
– common to
invertebrates
and plants
14.4
Growth
Patterns And Distribution
14.3Population
Population
Density
KEY CONCEPT
Populations grow in predictable patterns.
14.4
Growth
Patterns And Distribution
14.3Population
Population
Density
The size of a population is always changing.
• Four factors affect the size
of a population.
– Immigration
– Emigration
– Births
– Deaths
14.4
Growth
Patterns And Distribution
14.3Population
Population
Density
Population growth is based on available resources.
• Exponential growth is a rapid population increase due to an
abundance of resources.
14.4
Growth
Patterns And Distribution
14.3Population
Population
Density
• Logistic growth is due to a population facing limited
resources.
14.4
Growth
Patterns And Distribution
14.3Population
Population
Density
• Carrying capacity - maximum number of individuals in a
population that the environment can support.
• A population crash is a dramatic decline in the size of a
population over a short period of time.
14.4
Growth
Patterns And Distribution
14.3Population
Population
Density
Ecological factors limit population growth.
• A limiting factor is something that keeps the size of a
population down.
14.4
Growth
Patterns And Distribution
14.3Population
Population
Density
• Density-dependent limiting factors are affected by the
number of individuals in a given area.
– Predation
– Competition
– Resources (food)
14.4
Growth
Patterns And Distribution
14.3Population
Population
Density
• Density-independent limiting factors limit a population’s
growth regardless of the density.
– Unusual weather
– Natural disasters
– Human activities
14.5
Succession
14.3Ecological
Population
Density And Distribution
KEY CONCEPT
Ecological succession is a process of change in the
species that make up a community.
14.5
Succession
14.3Ecological
Population
Density And Distribution
Succession regenerates or creates a community after a
disturbance.
14.5
Succession
14.3Ecological
Population
Density And Distribution
• There are two types of succession.
1. primary succession — started by pioneer species
14.5
Succession
14.3Ecological
Population
Density And Distribution
• There are two types of succession.
2. secondary succession — started by remaining species