Ecology Studying Populations

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EcologyStudying Populations
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Levels of Organization
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Levels of Organization

• Species- A group of organisms that can mate with
  each other and produce fertile offspring
• Population-a group of the same kind of species
  living in an area
• Community- all the different populations that
  live together in an area
• Ecosystem- a community plus abiotic factors

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Studying Populations

• What is an estimate? It is an approximation of
  number, based on reasonable assumptions
• Direct Observation
• Counting each member of a population
• Example counting all the crabs in a tide pool.
• Indirect Observation
• Counting evidence or traces of a population
• Example Look at the mud nests built by cliff
  swallows, by counting the entrance holes, you can
  determine the number of swallows per nest in this
  area.

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• In many cases, it is not possible to count signs
  of every member of a population. The population
  may be to large or spread over a wide area. In
  this case scientists make an estimate.
• Sampling
• Counting the number of a population in a small
  area to estimate the number in the whole habitat
• Mark-and-Recapture
• Catching some, tagging/marking them and
  releasing, recapture and count how many
  tagged/marked

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Studying Populations

• What method am I using if
• I dig up and count each worm in the football
  field?
• I count how many worms are in 1 square yard and
  use that information to estimate the total number
  of worms in the entire football field?
• I look for birds nests?
• Capture birds, put a tag on them, and then come
  back later to catch them again and see how many
  are tagged?

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Changes in Population Size

• What is the main way new organisms join a
  population?
• What is the main way they leave?
• Moving In Moving Out/Exit
• Immigration Emigration

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• Birth rate is the number of births in a
  population in a certain amount of time.
• Example a population of 100 rabbits produces 600
  young a year. The birth rate in this population
  would be 600 young per year.
• Death rate is the number of deaths in a
  population in a certain amount of time.
• -Example If 400 rabbits die in a year
• the death rate would be 400 rabbits
• per year.

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Population Statement

• If birth rate gt death rate, population size
  increases.
• If death rategt birth rate, population size
  decrease.

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Population Density

• How many members of a population are in an area
  at one time.

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• of individuals
• Population density -----------------------
• 
  unit area
• For example You count 20 butterflies in a garden
  measuring 10 square meters. The population
  density would be 20 butterflies per 10 square
  meters, or 2 monarchs per square meter.

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Limiting Factors

• Carrying Capacity
• The largest population an area can support
• Causes a population to stop growing or get
  smaller
• What are some limiting factors?
• Food, water, space, and weather conditions

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Limiting Factors

• Living space is another limiting factor.
• Example Sunflowers growing in a field.
• The field has reached its carrying capacity for
  sunflowers when no more can grow in the field.
• Weather conditions such as temperature and the
  amount of rainfall can also limit population
  growth.