The document discusses food webs and their complexity. It notes that food chains oversimplify predator-prey relationships, as most organisms have multiple prey and predator species. A food web shows the multiple interconnected food chains within an ecological community. Some food webs, called grazing webs, begin with plants, while others called detrital webs begin with dead organic matter. There is often overlap between grazing and detrital webs. The stability of food webs depends on the number of species and links between them - webs with more complexity are less vulnerable to collapse from the removal of one species. Keystone species that greatly impact community structure if removed.

1. Food Webs
Mapping out predator-prey relationships

2. Food chains represent flow of energy in a community
but over-simplify the predator-prey relationships.
Most organisms have multiple prey species and
multiple predators (they eat many different things
and get eaten by many different things).

3. A food web shows multiple food chains within a
community.
cc licensed flickr photo by cicadas: http://flickr.com/photos/cicada/2569385115/

4. Some (parts of) food webs consist of food chains that
begin with plants. These are called grazing webs
cc licensed flickr photo by cicadas: http://flickr.com/photos/cicada/2569385115/

5. Some (parts of) food webs consist of food chains that
begin with plants. These are called grazing webs
cc licensed flickr photo by cicadas: http://flickr.com/photos/cicada/2569385115/

6. Some (parts of) food webs consist of food chains that
begin with dead organic matter. These are called detrital
webs
cc licensed flickr photo by cicadas: http://flickr.com/photos/cicada/2569385115/

7. Some (parts of) food webs consist of food chains that
begin with dead organic matter. These are called detrital
webs
cc licensed flickr photo by cicadas: http://flickr.com/photos/cicada/2569385115/

8. There is often overlap between the grazing and detrital food webs.
Which populations here are part of both webs? Which are only in the
grazing web? Which are only in the detrital web?
cc licensed flickr photo by cicadas: http://flickr.com/photos/cicada/2569385115/

9. Food Web stability
In some food webs, the populations in the
web can survive if one species is removed.
Other populations can fill in as prey or
predator species. A food web with more
populations in it and/or more links
between populations is less likely to
collapse due to the removal of one species.
(A community collapses when all/most of
the populations in the community suffer
sudden, dramatic population decrease.)
In some communities, there are species
that, if removed, can lead to collapse of
the entire community. These are called
cc licensed flickr photo by Martin LaBar (going on hiatus):
keystone species. http://flickr.com/photos/martinlabar/3376987854/

10. Species at Risk in Canada
(handout - write answers in your notes)
How many species in Canada are currently classified as at
risk
Since the first European settlers arrived in North America:
how many Canadian species are to known to have
become extinct?
how many species are no longer found in Canada?
What are three reasons why many species in Canada are
currently at risk?
What is COSEWIC? What are they responsible for?

11. Species at Risk in Canada
(handout)
What do each of the following classifications for species at
risk mean
Extinct
Extirpated
Endangered
Threatened
Special Concern
What has been done to help the recovery of the Peregrine
Falcon anatum subspecies?

12. Species at Risk in Canada
(handout)
What has caused the North Atlantic Right Whale to be
classified as at risk?
What was the size of the entire population in 2004?
What is being done to protect the Right Whale?
What are two things that can be done to help species at
risk?
Why should we be concerned about species at risk?