Population Dynamics Day 4

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Population DynamicsDay 4
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Population Characteristics

• Population Density
• The number of organisms per unit area
• Dispersion
• The pattern of spacing a population within an
  area
• 3 main types of dispersion
• Clumped
• Uniform
• Random
• Resource availability determines dispersion
  patterns

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Population Limiting Factors

• 1) Density-independent factors
• Factors that limit population size, regardless of
  population density.
• usually abiotic
• include natural phenomena
• Ex. drought, flood, fire extreme temperature,
  tornadoes, etc.

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Population Limiting Factors (cont.)

• 2) Density-dependent factors
• Any environmental factor that depends on the
  density of the population
• Usually biotic
• For ex.
• Predation
• Disease
• Parasites
• Competition

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Population Limiting Factors (cont.)

• 3) Population growth rate
• How fast a population grows
• Factors that influence this are
• Natality (____ rate)
• Mortality (_____ rate)
• Emigration (the number of individuals moving
  _________ a population)
• Immigration (the number of individuals _________
  a population)

birth
death
away from
moving to
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Break here
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Understanding Exponentials

• Put your pens down for a minute think about
  this
• An employer offers you two equal jobs for one
  hour each day for fourteen days.
• The first pays 10 an hour.
• The second pays only 1 cent a hour, but the rate
  doubles each hour.
• Which job will you accept?

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Understanding Exponentials
Now, how much would your employer owe you if you
stayed at this job for another 2 weeks?
Job 2 lags for a long time before exponential
growth kicks in!
What would happen if this type of growth took
place within a population?
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Population Growth Models

• 1) Exponential growth model
• Also called geometric growth or J-shaped growth.
• First growth phase is slow and called the lag
  phase
• Second growth phase is rapid and called the
  exponential growth phase
• Bacteria can grow at this rate, so why arent we
  up to our ears in bacterial cells?

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Population Growth Models (cont.)

• Limits to exponential growth
• As population density increases, competition
  follows as nutrients and resources are used up
• The limit to population size that a particular
  environment can support is called carrying
  capacity (k)
• When youre done writing, put your pens down

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What population do you think this is?
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So, what do you think is going to happen to the
human population?

• We will probably reach our carrying capacity.
• Our growth rate will start to look like most
  organisms, which is the Logistic Growth Model

Carrying Capacity (k)
What letter does this curve kind of look like?
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Population Growth Models (cont.)

• 2) Logistical growth model
• Often called the S-shaped growth curve
• Growth slows or stops following exponential
  growth at the populations carrying capacity
• Populations stop increasing when
• Birth rate lt Death rate
• Emigration gt Immigration
• Carrying capacity can be raised or lowered. How?
• Ex. 1 Artificial fertilizers have raised
• Ex. 2 Decreased habitat can lower k

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Community Dynamics

• Day 5

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Communities

• Review
• A community is a group of interacting populations
  that occupy the same area at the same time.

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Limiting Factors of Communities

• Any abiotic or biotic factor that restricts the
  numbers, reproduction, or distribution of
  organisms.

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Range of Tolerance

• Upper and lower limit of conditions in which an
  organism can survive.
• Ex. Temperature, Salinity, pH

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Ecological Succession

• The change in an ecosystem that happens when one
  community replaces another as a result of
  changing biotic and abiotic factors

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Ecological Succession (cont.)

• 2 types
• 10 Primary Succession
• 20 Secondary Succession

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Primary Succession

• In primary succession (10), the community
  establishes in an area of exposed rock (no soil)
• It occurs very slowly at first

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Primary Succession (cont.)

• Pioneer species, or the first organisms to
  arrive, are usually lichens or mosses
• They secrete acids that can break down rock,
  creating soil.

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Primary Succession (cont.)

• Small weedy plants and other organisms become
  established.
• As they die, more soil is made

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Primary Succession (cont.)

• Animals, water and wind bring seeds that sprout
• Eventually there is enough soil for shrubs and
  trees to grow.

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Primary Succession (cont.)

• The stable, mature community that eventually
  develops from bare rock is called a climax
  community.

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Secondary (20) Succession

• Disturbances (fire, flood, windstorms) can
  disrupt a community.
• After a disturbance, new species of plants and
  animals might occupy the habitat.

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Secondary Succession (cont.)

• Pioneer species in 20 succession are usually
  plants that grow in disturbed area.
• Much fasterthan 10succession

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Succession End point?

• Cannot be predicted
• Different rates of growth human
  involvementmake it impossible toknow if a true
  climaxcommunity has beenreached.