Notes-Populations in EcosystemsBIO by pptfiles


									    Thursday Sept 12/Friday Sept 13
• Stamp and review homework
• Activity: Interactions Among Organisms
• Notes: Populations in Ecosystems
• Read pg 119-127
• Complete Population Growth Activity
• Begin Test Review. Complete #1-24
   Populations in Ecosystems
        •Growth of Populations
     •Long-Term Survival of Species
   •Impact of Environmental Change
•Populations Respond to External Factors
  A group of the same kind of
 organism that lives in the same
       place is called a ….

Three important characteristics of a population
  are its:
• Geographic distribution or range.

• Population density – the number of
  individuals per unit area.

• Growth rate
• Number of individuals __per unit area_____
• Varies depending on species and its
           US Population Density 1990
High or Low Density?
High or Low Density?
Three factors can affect population size:
• The number of ___births___
• The number of deaths.
• The number of individuals that enter or leave
  the population.

A population can grow when
its birthrate is greater than
 its __death rate_____.
           Exponential Growth
• Under ideal conditions with unlimited resources, a
population will grow exponentially_____.

• Exponential growth occurs when the individuals in a
population reproduce at a constant rate.

• The population becomes LARGER and LARGER
until it approaches an infinitely large size.
Turn to the person next to you and explain how
   the two graphs are similar OR different?

                Exponential Growth
   Do populations really grow

Can populations continue to grow
     exponentially forever?

      What do you think?
• As resources become less available, the
  growth of a population slows or __stops__.

• The result looks more like
the S-Shaped graph 
Logistic Growth
                 Carrying Capacity
• The environment can
  only HOLD or
  __CARRY__so many

• Largest number of
  individuals that a given
  environment can
  support =
__Carrying Capacity__
     What Limits Growth of a


Factor that causes population growth
             to DECREASE
            Density Dependent
             Limiting Factors
• Density-dependent factors operate only when a
  population is large and dense.
• Examples:
     • competition
     • predation
     • parasitism
     • disease
            Density Independent
              Limiting Factors
• Density-independent affect all populations in a
  given area in similar ways, regardless of the
  _____population size_________.
• Examples:
      • unusual weather like droughts
      • natural disasters like hurricanes, forest fire
      • seasonal cycles
      • certain human activities
What is Environmental Stability?

  How do ecosystems maintain
stability despite constant limiting
     What is ecosystem stability?
• The vast majority of natural ecosystems
  experience regular environmental
  change, or disturbances.
• Most ecologists describe ecosystem
  stability as the ability of an ecosystem
  to maintain its structure and function
  over long periods of time despite
  How do Ecosystems maintain
stability with all of these limiting
• The sum total of the genetically based variety of all
  the organisms in the biosphere is called biodiversity.

                             • Biodiversity______
                                is one of our greatest
                                natural resources.
                                Species of many kinds
                                have provided us with
                                many foods, industrial
                                products, and
          Environmental Adaptations
• Populations have become __adapted__ to
  live in specific conditions as a result of their
• For Example:
   – Desert cacti
   – Palm trees
   – Snow Owls
What threatens BIODIVERSITY and
Threats to Biodiversity
• __Human activities____ can cause decreases in
  the amount of biodiversity by:
   – Habitat alteration       -- Pollution
   – Improper hunting         --Introduced species
Introduced Species
• Throughout history humans have
  transported apparently harmless
  plants or animals which have
  become invasive in a
  new habitat_______
• Invasive species (also called exotic
  species or nonnative species) are
  those that rapidly increase their
  populations due to lack of natural
  predators and/or parasites
  thereby giving it an advantage
  over native species.
  How does environmental change
  affect ecosystem stability?
• Changing environmental conditions can cause
  the decline of local __biodiversity___.
• Ecosystems that are ___less stable__
 may not be able to respond to a normal
 environmental disturbance.
 How does natural environmental
change affect ecosystem stability?

• Fires, heavy storms, and natural climate
  change can cause major changes in local
  populations of plants and animals.
• A decline in natural biodiversity can make
  an ecosystem less stable.
Something to think about for the futu

• How will the Earth’s increasing average
  temperatures affect ecosystem structures
  and functions?
• Scientists are not yet sure how predicted
  changes in global climate within the next
  several decades will affect ecosystem
  stability worldwide.

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