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Roles in Ecosystems
Lesson 6
November 23, 2010
• Each organism has their own ecological niche in an
ecosystem
•
Ecological niche- the organism’s place in the food web, its habitat, breeding area and the time of
day it is most active
• So its niche includes everything it does to survive and
reproduce
• Each species of an ecosystem tends to have a different
niche helping reduce competition between species for
the same territory and resources.
Example
• Owl and hawk feed on similar organisms, but they occupy
different niches.
• The owl has short broad wings to help it hunt within forests
• The hawk has long wings good for soaring above grasslands
and open fields
• Owls are active at dusk and night
• Hawks hunt by day
• Although they do prey on the same species, different
animals are active during night and day
• To support their roles owls and hawks have different
adaptations
• Besides their wings they have different senses.
• Hawk eyes are excellent at detecting changes in colour
patterns, helping them see rodents
• Owl eyes are poor with colour, but excellent at
detecting motion
• Owls also have excellent hearing allowing them to
detect the tiniest rustling noises of rodents
• Owls and hawks also nest in different areas
• Owls seek the deep cover of trees
• Hawks nest near the tops of trees giving a
better view of grassland
Competition for Niches
• The introduction of a species to an ecosystem
causes a disturbance because it will come into
competition for a niche with one or more of
the species already in the ecosystem
• New species are called exotic species
• How does a new species come into an
ecosystem?
• Animals are mobile and can move from one
ecosystem to another
• Plant seeds can be carried by wind or animals
• A new route to an area may open up and
allow organisms that were separated from
each other to mix
• Sometimes results are dramatic
• i.e. when North and South America came together
about 5 mya animals could move freely from one to
another
• Result was devastating to South America as many of its
native species came into competition with invaders
from the North and lost
• Only a few animals from south crossed over to north
and survived
Humans and Exotic Species
• Humans constantly bring ecosystems in contact with each other
because they tend to take organisms with them when they travel
• Example from Brazil in 1957- honey producers introduced wild
African bees to increase honey production
• The African does produce more honey but it displaced many native
species ad led to an overall decline in honey production
• African bees aka killer bees because they swarm and attack
animals they see as a threat
• Cattle, dogs and humans have all been killed by the bees
• In Brazil their population grew and began to spread
• By 1986 the bees had spread as far as Mexico claiming the
lives of more than 150 people
• By 1994 killer bee colonies could be found in Arizona, Texas
and New Mexico
• The bees continue moving North but Canada is considered
safe as they don’t do well in cold climates
The Zebra Mussel: An Exotic Species
• The zebra mussel was found in Lake Erie in the early 1990s and set
off a media frenzy
• Is a native of Western Asia
• Believed to have entered the Great Lakes through water discharged
from ships
• This species found a lot of food in the great Lakes and spread
quickly
• In 1991- zebra mussels were in Lake Ontario
and Lake Huron
• By 1994- common in Rideau canal and TrentSevern Waterway
• By 1995- Ohio River and could be found all the
way to the Gulf of Mexico
• Attaches to hard objects in water
• Blocked water intake pipes from Great Lakes, choking
hydroelectric plants and freshwater supply for a
number of industries
• Ontario Hydro, municipalities, and the Ontario Ministry
of the Environment undertook massive campaigns to
prevent the mussels from moving up intake pipes
• These efforts took funds away from pollution efforts in
the Great Lakes
Ecology and the Zebra Mussel
• Wherever zebra mussels moved in, there was a decline
in the pearly mussel
• They occupied different niches as the pearly mussel
burrowed into mud
• The shells of pearly mussels are hard and layers of
zebra mussels formed on top of pearly mussels
• Mussels feed by putting out small threads
covered with a sticky mucous and comb the
water to remove small organisms
• With zebra mussels attached to pearly mussels
little food was filtering down to the zebra mussels
• Pearly mussels were unable to relocate because
the zebra mussels attached to them
• Zebra mussels have not been detrimental to
other species
• Ducks and other birds feed on the mussel
• Discarded shells provide shelter for snails,
aquatic insects, crustaceans, and water mites
• They have caused problems, just not
devastating problems to the Great Lakes
ecosystem
• They do not cover the shore line and did not
eliminate competing species
• Some studies credit the mussel with long term
benefits
• Algae has increased due to pollution and mussels eat the
algae
• The algae was blocking sunlight from reaching aquatic
plants
• They also removed pollutants from the water as each
mussel takes in 1.5L of water daily, retaining the pollutants
and expelling the water
• So much water is filtered that Lake Erie is now 60% clearer
than it was before the zebra mussels were introduced
• However, these pollutants are passed onto predators and
can be toxic
• But could these benefits have a negative
possibility?
• Some ecologists are studying the reduction in
algae, because algae are important in the food
web
• Clearer water may cause warmer water which
would hurt fish species that need higher levels
of oxygen
Economics and the Zebra Mussel
• Clogged pipes resulted in multi-million dollar clean up bills was an
exaggeration
• Chlorine has prevented the mussel from choking off water intake
systems
• Ontario Hydro’s control efforts initial cost was $20 million with a
annual cost of $1 million for maintenance
• Commercial fishing went from generating $600 million to $200
million since the zebra mussel was introduced
Review
• Name 4 reasons frogs are disappearing.
• Why should we care that frogs are disappearing?
• What are the classifications of Endangered
Species?
• Name 2 species that are considered at risk in
Canada
• Name 3 causes of mass extinctions in the past
• What is the major cause of extinction in
modern times?
• Why do we need mosquitoes?
• What is an artificial ecosystem?
• What is the source for all energy on Earth?
• What is the albedo effect?
• What does a high Earth albedo cause?
• Draw a trophic level, identifying each level
• In the food chain, spruce tree--- deer --- wolf
what would happen if all the spruce trees in
that ecosystem were removed?
• What ecosystems are the most stable?
• Explain the transfer of energy from the tree to
the wolf. How is it used ?
• What are the 2 Laws of Thermodynamics