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ECOLOGY
ECOLOGY
• Ecology – The study of the distribution and abundance of
life, and the interactions between organisms and their
environment.
• Population ecology – the
study of changes in the size
and composition of
populations and factors that
cause those changes.
Isle Royale
• NW Lake Superior
• ~50 miles long and ~8miles wide
• Home to a population of wolves and moose (moose
90% of the wolves diet).
• Longest study of any predator-prey system
• Designated an International Biosphere Reserve
• 99% is legally designated wilderness
Isle Royale History
•1900 – Moose swim 15 miles from Canada and arrive
on Isle Royale.
•In absence of wolves the moose were happy (see
picture below).
•.1929 & 1930 – Adolph Murie makes the 1st scientific
observations of the Isle Royale moose, and climate.
•1931 – Isle Royale became a national park as a
“prime example of North Woods Wilderness.”
•Early 1930s – Moose food supply dwindles as well as
moose population shortly there-after.
•1936 – A fire burned more than a quarter of the island
•1937 – Moose population crashed
•1940's – Fire stimulates growth of new browse and
brood.
•1948-1949 – Ice bridge forms between Canada
and the island.
•Late 1940s & Early 1950s – Wolves were
extirpated from nearly all 48 states and migrate to
Canada
•Mid 1950s – A pack of Eastern timber wolves
crossed over to Isle Royale.
•The lives of the Isle Royale moose were never the
same……
Ecology research
• 1958 – Durward Allen
began studying the wolves
and moose of Isle Royale
• 2008 – Wolves, moose, and
researchers have been
watching each other for 50
years.
• The world's longest running
wildlife research project!
Isolation fosters conditions favorable for studying nature!
1. Relatively few species have colonized Isle Royale.
2. Essentially they represent a single-prey-single-predator
system.
• Wolves are the only predators of moose.
• Moose are nearly the only prey (~10% beaver/hare)
3. Small number of species = simpler ecosystem.
Wolf food webs
Isle Royale
Yellowstone
Simplified wolf food chain
Isle Royale is not too small, not too large, not too far, and
not too close!
If Isle Royale were...
• Smaller
 too small to support a wolf population.
• Larger
 too large to effectively study the moose population.
• Further from the mainland
 wolves and moose may never have made it to
island.
• Closer to the mainland
 mainland animals would have migrated over.
Studying species interactions becomes increasingly
difficult with increasing species diversity.
The EcoBeaker Version of Isle Royale
• Model (5 species)
• 3 plants
• Moose
• Wolves
• Environment
characteristics
• Temperature
• Seasonal changes
• Plant growth
Exponential Growth Model:
Growth rate (r) increases with
increases in population size...
Assumes population increase
at maximum per capita rate of
growth (rmax).
Instantaneous change (dN/dt)
represents changes in
population size with respect to
time.
Limitation: Applicable only to a very small population.
Population size levels off at carrying capacity!
Logistic Growth Model:
Carrying capacity (K) - the
maximum number of
individuals of that species that
the local environment can
support at a time.
Growth rate (r) decreases as
the population density
increases.
When N = K, the population will no longer grow!
Key Stone Predator
Ecological Community – is a group of species that live together and
interact with each other.
Community Structure – the composition and relative abundance of the
different types of organisms present.
Keystone Predator – a predator that has
an exceptionally great impact on the
other species in its ecosystem relative to
its abundance
Intertidal Community – comprised of
organisms living in the area covered by
water at high tide and exposed to the air
at low tide.
Experiment
• Simulated experiment based on 1960’s experiments
conducted along the rocky shore of Washington.
• You will observe which intertidal species is dominant over
one another to construct a food web diagram.
• Then you will remove a species
and see how it influences the
community.
Food Chains, Food Webs and Trophic Levels
Lowest Tropic Level –
Producers - (algae and
green plants) use energy
from the sun to produce
their own food
Herbivores - consume
producers.
Higher Tropic Level –
Predators eat herbivores
Omnivores - take up
multiple levels!
Next week……
Good luck on the final!
THEN…