Roles in Ecosystems

Lesson 6November 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 Trent-Severn 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