Biosphere                        SECTION 5.3


                                  Environmental Science

                                          SECTION 5.4
• What makes you stressed out?
• What do you do when you’re stressed out?
• Is this a positive feedback loop or a negative
  feedback loop?
• Do your actions make the problem worse or
  do you feel better?
• In the end, though, don’t you recover?
                 • THIS IS STABILITY
 What about major disturbances?
• Can be natural disasters or caused by humans
               • Some examples…
• Either can be Catastrophic  quick & painful
      or Gradual  slow & building
               • Some examples…

• What is climate change considered?
II. A.          STABILITY
• An ecosystem deals with these disturbances
• INERTIA  a body in motion will stay in motion
• Aka: persistence  ability of a system to resist
                 being disturbed or disrupted
• Your examples…
• CONSTANCY  stay the course; ability to
           maintain a certain size population
• Your examples…
• RESILIENCE  ability to bounce back
• Your examples…
                 Free write
    • Choose a population of plant or animal
• Write how they exhibit INERTIA in the face of
  change (look at your notes: can be natural or
• Write how they exhibit CONSTANCY in the face
  of change
• Write how they exhibit RESILIENCE in the face
  of change.
           • I will call on you to share!
 II. B. There is a breaking point…
• How do we know when an ecosystem is
  REALLY in trouble?
  – Drop in PP (autotrophs leave)
  – Nutrient loss
  – Indicator species decrease
  – A lot of pests or disease organisms
  – Decrease in species diversity
                    (food webs are shrinking)
  – Contaminants are present
III. Sometimes we notice things too late…TIME DELAYS

• Just like it takes several years for lung cancer
  to develop in a smoker…
  – quitting smoking is often an ineffective negative
    feedback action
• Depletion of the ozone layer, introduction of
  toxins, industrial emissions all take time to
  show their effects

  • A proposed negative feedback action for global
  climate change is to plant more trees – why? Do you
                   think it’s too late?
                   IV. Synergy

• Occurs when the sum is greater than its parts
• Example
  – 2 people working together to move a log that
    neither could move on their own
V.          Diversity is Good!
• Biodiversity is Nature’s Insurance Policy
• Don’t put all of your eggs in one basket

• In the next picture, what happens if the
  carnivorous zooplankton is stricken with a
  deadly virus?
• What happens if dissolved oxygen decreases
  just enough to kill all benthic invertebrates?
             Putting it together…
• How diverse is diverse enough? How do things
  still go wrong? What’s the breaking point?

• RAINFOREST ecosystems:
  – (H) diversity, (H) inertia/resistance, (L) resilience

• GRASSLAND ecosystems:
  – (L) diversity, (L) inertia, (H) resilience

• Everything is unique and constantly changing
   VI. Species Equilibrium Model
• The “Island” Model: Immigration & Extinction
  determine who lives there

• Depending on size (big vs. small) and distance
  from others, the ecosystem might get a lot of
  new immigrants (can they find it?) or species
  could die (is it too small/too much
      Conservation Biologists
• How big should nature
  reserves be to provide
  adequate “islands” with
  enough resources for
• Example:
   – A Grizzly needs ~ 400 mi2
   – A pop of 90 would need 36,000
   – Yellowstone NP ~ 21, 000 mi2
Island Biogeography
           Sec 5.4

• To understand
  ecosystems fully, we need                 Ecosystems
  to understand the
  populations that make it
  up.                                       Communities

• Biotic potential versus
  environmental resistance
• Growth curves
• Density dependence and critical
  number                            Organisms
       I. A.       Population Dynamics
•   Populations differ by:
•   Size
•   Density                  •   Populations change by:
•   Dispersion (spacing)     •   Births
•   Age distribution         •   Deaths
                             •   Immigrations
                                 – Coming in
                             • Emigrations
                                 – Leaving
             Population Equilibrium
               Population change =
(births + immigration) – (deaths + emigration)

    Births                           Deaths
    I. B. What determines the existence of a
• 2 opposing forces
• BIOTIC POTENTIAL  focus is on increasing
                           the organism
  – How much of yourself can you make?
                 limiting the organism
  – How well can you survive?

• Populations strive to find a balance
• Different strategies are used to survive
• R = biotic (reproductive) potential
• The maximum rate at which a pop could grow
  if it had unlimited resources

  – Early reproductive age
  – Short generation times
  – Reproduce many times
  – Produce many offspring during each event
• No matter what your capabilities, the
  environment must support your needs

• K = carrying capacity

   – The number of individuals that can be sustained
     indefinitely in an area
  Label if each is an example of BIOTIC POTENTIAL or

• Adverse weather           •   BIOTIC POTENTIAL
  conditions                •   Ability to cope…
• Predators                 •   Defense mechanisms
• Defense mechanisms        •   Reproductive rate
• Competitors               •   ENV’RNMTL RESISTNC
• Ability to cope with      •   Adverse weather
  weather conditions        •   Predators
• Reproductive rate         •   Competitors
• J- shaped growth  young populations will
  grow exponentially at first. Times are good!

• Eventually, environment resists
  – (too crowded, not enough resources)

• TWO CHOICES: stabilize or crash (dieback)
• S- shaped curve = stabilizes at carrying capacity
  – May not be smooth (time-lag)
  I. C.   Carrying Capacity can Vary
• Fluctuates depending upon:
  – Competition among and between species
  – Immigration & emigration
  – Natural & human-caused catastrophes
  – Food, water, hiding, nesting places

• Just as there is a max (K), there is also a
  minimum  the critical number = the lowest
  population level for survival and recovery
  Who wins? Get out of my way!
• How a population responds to environmental
  resistance can depend on how crowded it is.
 • Compete for resources, subject to predation,
               parasitism & disease
    • Everyone has an equal chance of dying,
           regardless of population size:
               – ex: natural disasters
   Who wins? Multiply or Survive
• There are advantages & disadvantages to each
  strategy but populations tend to be:
• r-Strategists  focused on reproduction
• K-Strategists  focused on surviving at K
         r- Strategist                      K- Strategist
•   Many, small offspring         •   Few, large offspring
•   little/no parental care       •   High parental protection
•   Early reproductive age
                                  •   Late reproductive age
•   Most offspring die before     •   Most offspring reproduce
                                  •   Large adults
•   Small adults
                                  •   Adapted to stable enviro
•   Adapted to unstable enviro
                                  •   Low pop growth rate
•   High population growth rate
                                  •   Stable, S-graph around K
•   Erratic graph/not at K
                                  •   Specialist
•   Generalist
                                  •   Good competitor
•   Not a good competitor
                                  •   Late successionist
•   Early successionist
   Which strategy is most successful?
• In the “next life” you can be any other organism
   aside from human. What strategy would you
   choose to be? An r-strategist or a K-strategist?
1. Write three benefits supporting your choice.
  Don’t just re-write characteristics – why are they good!?

2. Explain two drawbacks of the other strategy in
   this situation – write specific examples of why it
   would be a disadvantage
3. Write two drawbacks that you will face with your
   chosen strategy in this disaster
Extra slides
Define: homeostasis.
Define: dynamic
 Are these opposite terms or can they both exist
  at once?

Are disturbances bad or good? For whom?
   What are the two fundamental kinds of population growth
   curves? What are the causes and consequences of each?

• The two types of population growth curves are the J-curve and the S-
  curve. “The J-curve demonstrates population growth under optimal
  conditions, with no restraints. The S-curve shows a population at
  equilibrium.” The J-curve is caused by exponential growth of a population
  and the absence of mechanisms to cause the population to level off; the
  consequence of this type of growth is a population crash and a reduction
  in the carrying capacity. The S-curve is caused by exponential growth of a
  population until natural mechanisms cause the population to level off and
  continue in a dynamic equilibrium. The causes of this type of growth are
  the various biotic and abiotic factors that limit a population’s increase
  (environmental resistance).”
• No one anticipated the following results from the
  reintroduction of wolves to Yellowstone. Changes
  included increased riparian habitat plant diversity
  (elk, to protect themselves from wolves, spend less
  time along rivers and more time in the trees),
  increased song bird numbers and type (elk no longer
  trample riparian plants and bird habitats have
  returned), and increased raptor numbers (wolves
  have decreased coyote population resulting in the
  rodents increasing, providing raptors with more

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