Populations

1
Populations
2
Population Density

• The number of organisms in a population per unit
  area.
• Ex. 5 snakes per square mile
• Ex Tigers low density, mosquitoes high density

3
Growth Rate

• Change in population size over time
• Positive growth rate- population is increasing
• Negative growth rate- population is decreasing
• Zero growth rate- population size is not changing

Negative
4
Exponential Growth

• Population will increase exponentially (J-curve)
• Not realistic because as population increases
  resources become limited. (ex food shortage)

5
Logistic Growth

• Starts out exponential, but levels off at a
  certain population size (S-curve)
• Carrying Capacity- the maximum population size an
  ecosystem can support, leveling off point
• Ex. goldfish in a tank

6
R vs. K

• R-selected species- reproduce fast, have many
  young, develop quickly. (rabbits)
• K-selected species- reproduce steadily, have few
  young develop slowly. (kangaroos)

7
Density Dependant Factors

• Factors that have a greater influence on
  population size as the population increases
• Generally biotic factors
• Ex. competition, predation, parasitism, crowding
  stress

8
Density Independent Factors

• Factors that have an impact on population size
  regardless of what the population size is.
• Generally abiotic factors
• Ex. weather, fires, drought, human activities

9
Succession

• Succession- changing of plant communities
• Primary succession- begins with bare rock from
  volcanic activity
• ex. Rock- moss grass- shrubs forest

10
Secondary Succession
Secondary succession- begins with soil from a
previous community ex. Fire -Soil- grass-
shrubs-forest Pioneer community- first community
(ex moss,grass) Climax community- ending
community (ex forest)