1. Niche The niche of a species consists of:
Its role in the ecosystem (herbivore, carnivore, producer etc)
Its tolerance limits (e.g. soil pH, humidity)
Its requirements for shelter, nesting sites etc etc, all varying through time
© 2008 Paul Billiet ODWS

2. Competition
In all environments, organisms with similar needs may compete with each other for resources, including food, space, water, air, and shelter. 

3. Feeding relationships
Predators & prey
Herbivory
Parasite & host
Mutualism
Competition
Large blue butterfly
(Maculinea arion)
Mutualism   --   both species benefit
Commensalism   --   one species benefits, the other is unaffected
Parasitism   --   one species benefits, the other is harmed
Competition   --   neither species benefits
Neutralism   --   both species are unaffected
© 2008 Paul Billiet ODWS

4. Symbiotic Relationships
symbiosis: living together with another organism in close benefits at the expense of the host
     
[Symbiotic Relationships]symbiosis: living together with another organism in close association
Types of (symbiosis): mutualism, commensalism, parasitism commensalism: one organism is benefited and the other is unharmed (+,0)
                        ex. barnacles on whales, orchids on tropical treesmutualism: both organisms benefit from the association
                ex. nitrogen-fixing bacteria on legume nodules,
                        certain protozoa within termites (also ruminants)parasitism: the parasite benefits at the expense of the host
                ex. athlete's foot fungus on humans, tapeworm and heartworm in dogs

5. Types of (symbiosis):
commensalism: : one organism is benefited and the other is unharmed (+,0) ex. barnacles on whales, orchids on tropical trees
mutualism: both organisms benefit from the association. ex. nitrogen-fixing bacteria on legume nodules
parasitism: the parasite benefits at the expense of the host. ex. athlete's foot fungus on humans, tapeworm and heartworm in dogs

6. THE COMPETITIVE EXCLUSION PRINCIPLE
G.F. Gause (1934) If two species, with the same niche, coexist in the same ecosystem, then one will be excluded from the community due to intense competition
© 2008 Paul Billiet ODWS

7. The niche as a two-dimensional shape
Species A
Niche represented by a 2-dimensional area
© 2008 Paul Billiet ODWS

8. Separate niches Species B Species A No overlap of niches.
So coexistence is possible
© 2008 Paul Billiet ODWS

9. Overlapping niches Species B Species C
Interspecific competition occurs where the niches overlap
© 2008 Paul Billiet ODWS

10. Specialisation avoids competition
Species B
Species C
Evolution by natural selection towards separate niches
Species B’
Species C’
Specialisation into two separate niches
© 2008 Paul Billiet ODWS

11. This niche is not big enough for the both of us!
Species A Species D
Very heavy competition leads to competitive exclusion
One species must go
© 2008 Paul Billiet ODWS

12. Total exclusion Species A has a bigger niche it is more generalist
Species E has a smaller niche it is more specialist
Specialists, however, do tend to avoid competition
Here it is total swamped by Species A
© 2008 Paul Billiet ODWS

13. Example: Squirrels in Britain
The Red Squirrel (Sciurus vulgaris) is native to Britain
Its population has declined due to:
Competitive exclusion
Disease
Disappearance of hazel coppices and mature conifer forests in lowland Britain
Isle of Wight Tourist Guide
© 2008 Paul Billiet ODWS

14. The Alien
The Grey Squirrel (Sciurus carolinensis) is an alien species Introduced to Britain in about 30 sites between 1876 and 1929 It has easily adapted to parks and gardens replacing the red squirrel
Bananas in the Falklands
© 2008 Paul Billiet ODWS

15. Today’s distribution Red squirrel Grey squirrel
© 2008 Paul Billiet ODWS