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Population Characteristics
•
Populations are groups of the same species in the same area
•
Characteristics of populations include density, distribution, and growth rate
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Population Dynamics
Population Characteristics
Population density
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The number of organisms per unit area is the population density.
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Population Dynamics
Population Characteristics
Spatial distribution
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Dispersion is the spacing pattern of a
population.
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Can be uniform, clumped groups, or
random
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Pattern primarily driven by resources such
as food
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Population Dynamics
Population Characteristics
Population ranges
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A species’ range is its distribution across the
environment.
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A species might not be able to expand its
population range because it cannot survive the
abiotic conditions found in the expanded region.
•
Dispersion
1. Uniform
2. Clumped
3. Random
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Population Dynamics
Visualizing Population Characteristics
Animation
FPO
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Population Dynamics
Population-Limiting Factors
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Limiting factors are biotic or abiotic forces that keep populations from
increasing indefinitely.
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Limiting factors are either density-independent or density-dependent.
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Population Dynamics
Population-Limiting Factors
Density-independent factors
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Any factor in the environment that does not depend on the number of
members in a population per unit area is a density-independent factor.
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Usually abiotic, and include:
• Weather events
• Fire
• Human alterations of the landscape
• Air, land, and water pollution
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Population Dynamics
Population-Limiting Factors
Density-dependent factors
•
Any factor in the environment that depends on the number of members in a
population per unit area is a density-dependent factor.
•
Often biotic, and include:
• Predation
• Disease
• Competition
• Parasites
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Population Dynamics
Population-Limiting Factors
Population growth rate
•
The population growth rate (PGR) explains how fast a given population
grows.
• Natality: birthrate of a population in a given year
• Emigration: number of individuals moving away from a population
• Immigration: number of individuals moving into a population
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Population Dynamics
Population-Limiting Factors
Population growth rate
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Exponential growth model:
• Occurs when growth rate is proportional to population size
• All populations grow exponentially until they encounter a limiting
factor.
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Population Dynamics
Population-Limiting Factors
Population growth rate
•
Logistic growth model:
• Occurs when a population’s growth slows or stops following
exponential growth
– number of births < number of deaths
– when emigration > immigration.
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Population Dynamics
Population-Limiting Factors
Population growth rate
•
Carrying capacity
• Carrying capacity is the maximum number of individuals in a species
that an environment can support
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Population Dynamics
Characteristics of Population Growth
Animation
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Population Dynamics
Population-Limiting Factors
Reproductive patterns
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Species vary in the number of births per reproduction cycle, age that
reproduction begins, and in the life span.
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Plants and animals are placed into groups based on their reproductive
factors.
r-strategy
k-strategy
Rate strategy
Carrying-capacity strategy
Adapted for fluctuating
environment
Adapted to stable
environment
Generally small
Generally large
Short life span
Long life span
Many offspring
Few offspring
Expend little energy to raise
young
Invest more energy into
nurturing young
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Population Dynamics
Review
Essential Questions
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•
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What are the characteristics of populations and how they are distributed?
What are the differences between density-independent and densitydependent limiting factors?
What are the similarities between the different models used to quantify the
growth of a population?
How does carrying capacity affect reproductive rates?
Vocabulary
•
•
•
population density
dispersion
density-independent
factor
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density-dependent
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factor
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population growth rate •
emigration
immigration
carrying capacity
Population Dynamics