Download Population Dynamics

Population Dynamics
Populations are
shaped by
interactions between
organisms and the
environment
3.1 Populations have many characteristics.
Populations go through three stages.
• Population dynamics - study of why
populations change and what causes them to
change.
• Populations go through stages of growth,
stability, and decline and follow two patterns
of growth: rapid growth and gradual growth.
The maximum number of individuals an area
can support is its carrying capacity.
Four characteristics define a population.
1. Population size is the number of individuals
in a population at a given time. Population
sizes vary from one habitat to another and
within single habitats.
– Examples: mosquitos, flowering plants
2. Population density is a measure of the
number of individuals in a certain space at a
particular time. Population densities may
vary over a population range.
– Low densities – few individuals in an area
• Example – wolves or herons
– High densities – many individuals in an area
• Example – bees or mice
3. Population spacing describes how individuals
in a population arrange themselves.
Three patterns of spacing include
4. Age structure divide a population into groups
based on age:
– Pre-reproductive – not yet able to
reproduce
– Reproductive – capable of reproducing
– post-reproductive – no longer reproduce
Scientists can predict population change.
• Scientists use the four factors of a population
to describe a population and predict how it
may change.
• May change in response to surroundings
3.2 Populations respond to pressures
Population growth is limited.
• Birth and immigration lead to population growth.
– Immigration – movement into a population
• Death and emigration lead to population decline
– Emigration – movement out of a population
Population change = (birth + immigration)-(death + emigration)
• Limiting factors prevent the continued growth
of a population in an ecosystem.
– May be
• Abiotic – air, light, and water
• Biotic – other living organisms
Density-Dependent Factors
Factors include:
• Competition
• Disease
• Parasitism
• Predation
Density-Independent Factors
Density-independent factors are typically changes
in weather. These factors affect low-density and
high-density populations equally.
Factors include:
• Drought
• Hurricane
• Tornados
• Fires
• Floods
Populations have distinct reproductive strategies.
• There are two main strategies but many species
may fit somewhere in between
• Opportunists have adaptations that allow them
to reproduce rapidly if their populations fall
below carrying capacity.
– Characteristics are:
• Short life span
• Large quantity of offspring
– Example: pine trees, or algae
• Competitors have adaptations that allow
them to remain at carrying capacity for
sustained periods.
– Characteristics are:
• Take care of young for longer periods
• Longer life span
• Few offspring
– Example:
wolves
elephants
3.3 Human populations have unique
responses to change
Human populations differ from populations of
other species.
• Humans are able to shape their environment
through habitat expansion and technology.
• Two key factors that have increased Earth’s
carrying capacity for humans are
– Habitat expansion
– technology
• Habitat expansion allows humans to live
comfortably in extreme environments by
controlling indoor temperatures.
• Technology has increased life expectancy
through improved sanitation and medicine.
Human populations are growing.
• Human population has increased rapidly in the
past 300 years due to
– availability of resources
– lack of predation
– survival of offspring to reproductive age.
• Population projections forecast how a
population will change based on present size
and age structure.
• Other factors, such as life expectancy, health,
and the age of individuals that are having
children also affect the growth of a
population.
Human population growth affects the
environment.
• As the human population grows, it has
contributed to the decline and extinction of
other populations through
– Introduction of new species
• upset the balance of nature in that
environment by competing with native
species for food and space.
– Pollution
• addition of harmful substances to the
environment such as chemical dumping,
pesticides, and animal wastes.
– Overfishing
• depletes fish populations and may
prevent them from reproducing to
maintain their numbers.