14.3 Population Density And Distribution
Dispersion spatial distribution of individuals within a
population
14.3 Population Density And Distribution
• Three types of dispersion.
1. Clumped
– resources or living space are clumped,
– or because of social behavior
14.3 Population Density And Distribution
• Three types of dispersion.
2. Uniform (Even)
• social interactions result in individuals getting as far away
from each other as possible
14.3 Population Density And Distribution
• Three types of dispersion.
3. Random
• Ex: seed dispersal by winds or birds
13.1
Ecologists
Study
Relationships
14.3 Population
Density
and Distribution
Understanding Populations
•Population size
# of individuals it contains
•Population density
How crowded a population is
# of individuals/unit of area or volume
14.3
Population
Density
14.4 Population
Growth
Patterns And Distribution
Measuring Populations
Population Dynamics
• change in size and composition over time
• Birth rate, death rate, life expectancy
Population Growth Rate
• Depends on birth, death, emigration (movement out of a
population), and immigration (movement into a
population)
14.3
Population
Density
14.4 Population
Growth
Patterns And Distribution
Survivorship curves
• show the number of surviving members over time from a
measured set of births.
14.3
Population
Density
14.4 Population
Growth
Patterns And Distribution
Exponential Model
Increases rapidly after only a
few generations
Assumption
– Birth rates & death rates
remain constant no matter
how large the population
becomes
Populations cannot grow
indefinitely because of
availability of resources and
accumulation of wastes
14.3
Population
Density
14.4 Population
Growth
Patterns And Distribution
Logistic Model
• Accounts for the influence of limiting factors
– Limiting factor – restrains the growth of a population
• Birth rates decline and death rates rise as population
grows
• Carrying capacity – the # of individuals the environment
can support over a long period of time
– the birth rate equals the death rate and growth stops
Assumption
• Carrying capacity is constant and does not fluctuate with
environmental changes
14.3
Population
Density
14.4 Population
Growth
Patterns And Distribution
• Logistic and exponential models are not accurate
representations of real populations
• They are tools used to study population growth and
regulation
14.3 Population Density And Distribution
14.3
Population
Density
14.4 Population
Growth
Patterns And Distribution
Population Regulation – Limiting Factors
Density-independent factor – weather, floods, and fires
• Reduce the population by the same proportion regardless
of population size
Density-dependent factor – food shortages or nesting sites
• Triggered by increasing population density
14.3
Population
Density And Distribution
14.5 Ecological
Succession
KEY CONCEPT
Ecological succession is a process of change in the
species that make up a community.
14.3
Population
Density And Distribution
14.5 Ecological
Succession
Succession
– a sequence of biotic changes
– damaged communities are regenerated
– new communities arise in previously uninhabited areas
14.3
Population
Density And Distribution
14.5 Ecological
Succession
• There are two types of succession.
– primary succession — started by pioneer species
14.3
Population
Density And Distribution
14.5 Ecological
Succession
• There are two types of succession.
2. secondary succession — started by remaining species