Populations have many Characteristics

1
Populations have many Characteristics

• Populations go through 3 Stages
• Scientists study how populations or organisms
  change as they interact with each other the
  environment
• POPULATION DYNAMICS study of why populations
  change what causes them to change.
• 4 Characteristics define a Population
• Population size population density population
  spacing age structure
• Scientists can predict a Population Change

2
Growth, Stability Decline

• All populations go through growth, stability
  decline.
• CARRYING CAPACITY maximum number of individuals
  an ecosystem can support(with its available
  resources) if a habitat has enough resources,
  the population grows fast, then it stabilizes and
  population stays about the same for a while. This
  stability stage is usually the longest time
  period. Often, it is followed by a sharp
  decrease in population size.
• During growth phase it can occur very quickly (as
  in bacteria reproducing, or gradually as in a
  population of seals).

3
Darwins Observations of Population Growth

• Charles Darwin was a naturalist scientist who
  wrote On the Origin of Species based on his
  observations in the Galapagos Islands. He noted
  the following about population growth
• All populations are able to grow rapidly
• Populations tend to remain constant in size
• There are limits to natural resources
• Within a given population there is genetic
  variation
• He knew that if there were no limitations to
  growth, populations would grow rapidly. But also
  realized, there are natural limits to growth in
  the real world. If birth rate doesnt match the
  death rate, a population can decline until it
  becomes extinct.

4
Population Size

• Population size number of individuals in a
  population at a given time. (varies from habitat
  to habitat, even within a habitat). In our
  area, mosquito population size changes during
  different times of the year.
• Many deserts experience blooming growing during
  our spring, but by summer (with less water
  higher temperatures) there is a rapid decline in
  plant population size.

5
Population Density

• Population density measure of the number of
  individuals in a certain space at a particular
  time. Related to population size if size
  increases and they all stay in same area, density
  increases too. Some species live in high density
  (bees) while others live in low density
  populations (blue herons).
• RANGE the distribution of a population across a
  large geographic area. The population density
  within that range may vary (more grasshoppers in
  middle of prairie than its edge). Habitats
  located in the middle of a population range
  usually have a greater density than its edges
  (more resources)

6
Population Spacing

• Population spacing the pattern in which the
  individuals of a population are found. 3 main
  types clumped, uniform and random.
• Clumped spacing individuals form small groups
  within a habitat (elephants do this due to social
  nature, salamanders due to habitat-moist rotten
  logs found in 1 area)
• Uniformly spaced individuals living at an equal
  distance from each other plants often due this
  due to competing resources (if too close, some
  die out)
• Random spacing dandelions/weeds grow where ever.

7
Age Structure

• Scientists divide a population into 3 groups
  based on age
• Postreproductive organisms can no longer
  reproduce
• Reproductive organisms capable of reproduction
• Prereproductive organisms not yet able to
  reproduce
• The age structure of a population affects how
  much it can grow. On graph below,
  postreproductive age range is over 45, while
  prereproductive range is 0-14

8
Predicting Population Change

• Scientists use size, density, spacing age
  structure to describe a population predict how
  it may change over time.
• A population may change due to its
  surroundings(frogs living in pond that gets
  saltier will probably experience a population
  decrease).
• Scientists can also predict change by looking at
  the distribution of a population. (New York City
  released a population of 60 starlings in 1890
  they now number over 200 million spread across
  the U.S., Canada Mexico. The population rose as
  they moved into new habitats with available
  resources.