SECTION 5.3
Biosphere
Biosphere
Ecosystems
Communities
POPULATION
DYNAMICS
Environmental Science
302
Populations
Organisms
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
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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
human-caused).
• 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
competition?)
Conservation Biologists
• How big should nature
reserves be to provide
adequate “islands” with
enough resources for
species?
• Example:
– A Grizzly needs ~ 400 mi2
– A pop of 90 would need 36,000
mi2
– Yellowstone NP ~ 21, 000 mi2
Island Biogeography
Sec 5.4
POPULATION DYNAMICS
• To understand
ecosystems fully, we need
to understand the
populations that make it
up.
• Biotic potential versus
environmental resistance
• Growth curves
• Density dependence and critical
number
Biosphere
Biosphere
Ecosystems
Communities
Populations
Organisms
I. A.
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Population Dynamics
Populations differ by:
Size
Density
Dispersion (spacing)
Age distribution
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Populations change by:
Births
Deaths
Immigrations
– Coming in
• Emigrations
– Leaving
Population Equilibrium
Population change =
(births + immigration) – (deaths + emigration)
Births
Deaths
I. B. What determines the existence of a
population?
• 2 opposing forces
• BIOTIC POTENTIAL  focus is on increasing
the organism
– How much of yourself can you make?
• ENVIRONMENTAL RESISTANCE  focus is on
limiting the organism
– How well can you survive?
• Populations strive to find a balance
• Different strategies are used to survive
I. B. 2
BIOTIC POTENTIAL
• R = biotic (reproductive) potential
• The maximum rate at which a pop could grow
if it had unlimited resources
• CHARACTERIZED BY:
– Early reproductive age
– Short generation times
– Reproduce many times
– Produce many offspring during each event
I. B. 3
ENVIRONMENTAL RESISTANCE
• 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
ENVIRONMENTAL RESISTANCE
• Adverse weather
conditions
• Predators
• Defense mechanisms
• Competitors
• Ability to cope with
weather conditions
• Reproductive rate
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BIOTIC POTENTIAL
Ability to cope…
Defense mechanisms
Reproductive rate
ENV’RNMTL RESISTNC
Adverse weather
Predators
Competitors
GRAPHING POPULATION GROWTH
• 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.
• DENSITY DEPENDENCE
• Compete for resources, subject to predation,
parasitism & disease
• DENSITY INDEPENDENCE
• 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
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Many, small offspring
little/no parental care
Early reproductive age
Most offspring die before
reproducing
Small adults
Adapted to unstable enviro
High population growth rate
Erratic graph/not at K
Generalist
Not a good competitor
Early successionist
K- Strategist
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Few, large offspring
High parental protection
Late reproductive age
Most offspring reproduce
Large adults
Adapted to stable enviro
Low pop growth rate
Stable, S-graph around K
Specialist
Good competitor
Late 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!?
IMAGINE A DISTURBANCE
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 Scurve. “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
food).