Interdependence of Life:

1
Interdependence of Life Introductions to
Populations
By Deanne Erdmann, MS Evan Siemann, Ph.D.
2
Populations

• Definition Groups of organisms of the same
  species that live within a given area
• Key characteristics
• Growth rate
• Population density
• Dispersion patterns

Ostriches are nomadic, wandering in small groups.
Aspen trees are quick to pioneer areas that have
been disturbed by fire.
3
Population Growth

• Types of Growth
• Exponential vs. Logistical Growth
• Factors Affecting Growth
• Birth rate
• Death rate
• Immigration
• Emigration

4
Limits on Population Growth

• Density Dependent Limiting Factors
• Food
• Water
• Shelter
• Disease
• Density Independent Limiting Factors
• Weather
• Climate
• Human Disturbances

Water and shelter are critical limiting factors
in the desert.
Fire is an example of a Density independent
Limiting factor.
5
Reproductive Strategies

• r- Selected (maximum growth rate, below carrying
  capacity)
• Early reproduction
• Short life span
• High mortality rate
• Little or no parental care
• Large investment in producing large numbers of
  offspring
• Tend to occur in unpredictable environments
• Examples
• Bony fish
• Grasshoppers

• K-Selected (maximizes population size near
  carrying capacity)
• Late reproduction
• Long life span
• Low mortality rate
• Extensive parental care
• Greater investment in maintenance and survival of
  adults
• At or near carrying capacity
• Experience effects of population density
• Examples
• Sharks
• Elephants

6
Survivorship in Populations

• Survivorship curves graphically represent the age
  structure of a given population. We use them to
  predict future population growth.

7
Human Population Growth

• Human population growth does not currently show
  density effects that typically characterize
  natural populations.
• Human population growth rate has been growing
  more than exponentially.
• Limited resources eventually will cause human
  population growth to slow, but global human
  carrying capacity is not known.

8
Population Age Structure

• Differences in environmental conditions and past
  history may cause populations to differ in their
  age distributions.
• The future growth of a population depends on its
  current age distribution.

9
Population Density

• Population density is total population size per
  unit of area.
• Population densities depend on
• Interactions within the environment
• Quality of habitat
• Density-dependent factors
• Density-independent factors
• Carrying capacity is the maximum number of
  organisms that can be supported in a given
  habitat.

10
Dispersion Patterns Within Populations

• Three common patterns of population distribution
  are