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Populations

Populations. Population = a group of the same species in a particular area. Factors that impact a population:. Geographic distribution/range = the size of the area inhabited by a population Population Density = the # on individuals per unit area (ex: 1458 rabbits per square km)

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Populations

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  1. Populations • Population= a group of the same species in a particular area

  2. Factors that impact a population: • Geographic distribution/range= the size of the area inhabited by a population • Population Density= the # on individuals per unit area (ex: 1458 rabbits per square km) • Growth rate= change in growth over time • Age structure= how many individuals of different age groups are in a particular population (Is the population mostly young or mostly old?)

  3. 3 Factors Affect Population Size: 1. # births 2. # deaths 3. # of individuals that enter or leave the area Immigration= movement of individuals into an area. Emmigration= movement of individuals out of an area. A population will grow if its birthrate is greater than its death rate.

  4. Exponential Growth • Occurs when individuals reproduce at a constant rate. # of individuals increases slowly at first, then becomes very large • Graph is “J” shaped

  5. When will exponential growth occur? • Occurs in populations with ideal conditions and unlimited resources • Example: bacteria that double in number every 20 minutes

  6. Logistic growth • Occurs when the rate of population growth slows down or stops after a period of exponential growth • Graph looks like an “S” shape

  7. Carrying Capacity • Point on logistic graph where growth rate (the change in growth) = 0 This is the largest # of individuals the environment can really support. Graph “flattens out”.

  8. Limiting Factors • Anything that causes population growth to decrease--may or may not be affected by population density. • 2 Types: • Density Dependent • Density Independent

  9. 1. Density-Dependent= depends on population size, has stronger impact on very densepopulations .Examples: • Competition- compete for food, space, sun, H2O… • Predation- more predators result in more prey being eaten, but population numbers cycle • Parasites & disease

  10. 2. Density-Independent= Affects all populations equally • Weather, natural disasters, seasons, human habitat destruction

  11. Logistic or Exponential?

  12. Logistic or Exponential?

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