Download Section 14.4: Population Growth Patterns

Objectives
 How are changes in population size determined by
immigration, births, emigration and deaths?
 How is population growth based on available
resources?
 Compare exponential growth and logistic population
growth.
 What are the ecological factors that limit population
growth?
Changes In Population
 The size of the population is supported by the amount
of resources
 Abundant resources = population growth
 Few resources = population decreases
 Therefore, population change as the supply of
resources changes
Four Factors
Of Population Change
 Immigration: Movement of individuals into a
population from another population
 Births: Births increase the number of individuals in a
population.
 Emigration: Movement of individuals out of a
population and into another population.
 Deaths: Size of a population decreases when
individuals die.
Population & Resources
 Population growth is a response to the environment
 Amount of growth is directly related to the amount of
resources available.
 Two type of population growth:
 Exponential Growth
 Logistic Growth
Exponential Growth
 When a population
increases in size in a
short period of time
 Occurs when resources
are abundant
 Example: Introduction
of an animal into a
previously uninhabited
area
Logistic Growth
 Period of slow and quick
growth, making an S
shaped curve
 Due to limited resources
 Abundance creates
growth, then as resources
deplete growth slows,
finally population growth
stops as the environment
cannot support the
population size.
Exponential vs. Logistic
Carrying Capacity
 Environment determines how many individuals of the
species can be supported based on natural cycles and
species diversity.
 Carrying Capacity: the maximum number of
individuals of a particular species that the environment
can normally and consistently support
 Carrying capacity can change when an environment
changes
 Population size can rise and fall depending on the
natural changes in the supply of resources
Population Crash
 Population crash is a dramatic decline in the size of a
population over a short period of time.
 Occurs when the carrying capacity for a population
suddenly drops
 Heavy snow or rain decreases expected food stores
 Not enough precipitation means not enough food for
existing population
Factors Affecting
Carrying Capacity
 There are many factors that affect the carrying capacity
of an environment
 The factor that has the greatest effect is called the
limiting factor
 Two Categories of Limiting Factors:
 Density-Dependent
 Density Independent
Density Dependent
Limiting Factors
 Limiting factors that are affected by the number of
individuals in a given area
 Include many different species interactions
 Competition
 Predation
 Parasitism & Disease
Density Dependent
Limiting Factors
 Competition
 Members of populations compete with one another for
resources
 As the population becomes denser the resources are
used up, limiting how large a population can grow
Density Dependent
Limiting Factors
 Predation:
 Population of a predator can be limited by the number
of available prey
 Prey numbers can be limited by the fact that they are
being used as food
Density Dependent
Limiting Factors
Density Dependent
Limiting Factors
 Parasitism & Disease:
 Parasites and disease spread quickly through dense
populations
 The parasite or disease can then cause the size of the
population to decrease
Density Independent
Limiting Factors
 Aspects of the environment that limit a population’s
growth regardless of the density of the population
 Unusual Weather
 Natural Disasters
 Human Activities
Density Independent
Limiting Factors
 Unusual Weather
 Changes in normal weather patterns can affect the size
of a population independent of its density
 Example:
 Change in water flow of the ocean can cause a change
in the food chain of the ocean
 This can affect small populations, but can also be felt all
the way up the food chain
Density Independent
Limiting Factors
 Natural Disasters:
 Volcanoes, tsunamis, tornados, hurricanes, and
earthquakes can all cause a population to be wiped out
no matter its density
 Example
 Earthquake in Nepal has caused large loss of life no
matter where, or how dense, the population was
Density Independent
Limiting Factors
 Human Activities: Humans drastically change any
ecosystem or habitat that they move into in a variety of
ways
 Destruction of habitat (loss of wetlands due to
developments)
 Introduction of nonnative species causes population
crashes in many parts of the world, especially where
biodiversity is part of the ecosystem’s function
 Pollution of land, water, and air can cause population
crash in populations that support other populations
Output
 Use the Frayer model to outline the concepts densitydependent limiting factors and density-independent
limiting factors.
 List and briefly describe the four factors that determine
the growth rate of a population.
 Draw and label graphs showing exponential growth
and logistic growth.