KEY CONCEPT Each population has a density, a dispersion, and a reproductive strategy.

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KEY CONCEPT Each population has a density, a
dispersion, and a reproductive strategy.
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• Population density is a measurement of the number
  of individuals living in a defined space.

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• When scientists notice changes in population
  densities over time, they work to determine
  whether the changes are the result of
  environmental factors or are simply due to normal
  variation

Global Warming caused by humans???
Death due to drought?
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How do scientists keep track of population
density?

• Scientists can calculate population density by
  using this formula

If there are 200 deer in a field that is 10 sq
km 200/10sq km 20 deer per square kilometers
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Geographic dispersion of a population shows how
individuals in a population are spaced.

• Population dispersion refers to how a population
  is spread in an area.

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• There are three types of dispersion.

1) Clumped- the most common
EX a school of fish, animals that graze
together, or live in packs
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2)Uniform-evenly spread out
EX Certain birds (gannet) or plants (creosote
bushes)
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• random

EX The three-toed sloth is a solitary animal (it
likes to be by itself) or dandelions that seeds
random plant themselves
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• The California red-legged frog lays 2000 to
  5000 eggs in late winter or early spring.
• If they lay so many eggs, why are they a
  threatened
• species?

Answer Many creatures feed on the eggs of the
red-legged frog. So only a very small number will
survive into adulthood. Having a lot of offspring
allow them to survive as a species.
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Survivorship curves help to describe the
reproductive strategy of a species.

• A survivorship curve is a diagram showing the
  number of surviving members over time from a
  measured set of births.

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Why use a survivorship curve?????

• By measuring the number of offspring born in
  a year and following those offspring until they
  die, survivorship curves give information about
  the life history of a species.

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• Survivorship curves can be type I, II or III.

• Type I low level of infant death and an older
  population
• common to large mammals and humans
• Type II survivorship rate is equal at all stages
  of life
• common to birds and reptiles

• Type III very high birth rate, very high infant
  mortality
• common to invertebrates and plants