1. Ecological niches Niches: fundamental and realized
Principle of competitive exclusion
Realized niche as competitive refuge
Niche crossovers
Character displacement
Adaptive radiation

2. Ecological niche concept
Habitat occupance = “Where are you from?”
“What’s your address?”
Ecological niche = “What do you do?”
“Do you eat meat?”

3. Specialized habitat occupance

4. Niche breadth: generalist vs. specialist

5. Categorizing niches Niche overlap? Main food generalist/
source specialist
Junco
Chickadee
Douglas squirrel
Deer mouse
Deer
Coyote
Cougar
seeds ? specialist
seeds & insects ? generalist
seeds ? specialist
seeds ? specialist

6. The principle of competitive exclusion
“Two species requiring approximately the same resources are not likely to remain long evenly balanced in numbers in the same habitat.”
J. Grinnell (1915)
Also known as “Gause’s principle” after mathematical formulation by Gause in 1930.
In consequence, the loser is excluded, at least locally, unless…

7. There are refuges from competition; the potential loser hangs on in marginal habitats; or
The loser can re-immigrate from elsewhere; or
Disturbances in the environment prevent the winner from gaining a complete monopoly.

8. Categorizing niches: dietary segregation amongst local granivores
Species
Habitat
Other foods?
junco
floor
berries, insects (esp. ants and beetles)
chickadee
canopy
insects
Douglas squirrel
insects, mushrooms, flowers, birds’ eggs
deer mouse
insect larvae (esp. moths)

9. Reducing niche overlap through habitat segregation
upper canopy
habitat segregation
lower canopy
shrub
floor
resource overlap?

10. Fundamental vs. realized niche

11. Niche compression
Realized niches are narrower than fundamental niches, therefore the species occupies a narrower range of habitats than it would in the absence of competition.
The realized niche can be regarded as a ‘competitive refuge’.

12. Determining niche compression
Natural experiments
compression

13. Niche compression: barnacles on Scotland’s rocky shores

14. Sedge niches: Fraser delta
high tide
low
tide
Scirpus Carex
Inundation
Daily Rare
Rel. growth rate
Rel. growth rate
Daily Rare
Inundation
H1: realized = fundamental
H2: Scirpus occupies refuge

15. Determining niche compression
A. Field experiments: reciprocal transplants
high
tide
Scirpus Carex
low
tide
Two-year transplant experiment was inconclusive. Both species grew well in other species zone.
(Mike Pidwirny)
competitive refuge?

16. Dominance hierarchy dominant sp. subdominant sp. A B C
in the absence of competition with competition
refuge exclusion refuge
zone
resource gradient
resource gradient

17. Dominance hierarchies are environmentally contingent
dominant sp subdominant sp.
B A C
in the absence of competition with competition
exclusion refuges
zone
resource gradient
resource gradient

18. Flexible dominance hierarchies
resource gradient
salinity A C
resource gradient
inundation/
waterlogging

19. Niche crossovers

20. Character displacement

21. Redwood forest niches

22. Competitive ‘release’ or are niches and habitat occupance more-or-less fixed?
NB: hypothetical !

23. new invader? evolution of new species?
Can niches be vacant?
absent
mainland vs island
competitive release OR
new invader? evolution of new species?

24. Placental mammals Australian marsupials
Does evolution fill a finite number of jobs? (e.g. community wants burrower?) Is there a restricted “guild”?
Burrower

25. Hawaiian honeycreepers: seed-eating finch evolves into vacant niches?
“woodpecker” “nectar-feeder”
“insect-eater” “seed-eater”

26. Galapagos finches: opportunistic evolution
Source: Lack, D Darwin’s Finches. Harper, N.Y.

27. Parallel (or convergent) evolution of animals inhabiting African (right) and S. American (left) tropical forest

28. Stickleback niches in coastal lakes of SW British Columbia
Pairs of stickleback species occur in these lakes
Texada Is. (4 lakes) Van. Is. (1 lake) Lasqueti Is. (extinct, 1996)

29. Stickleback pairs in coastal lakes of SW British Columbia
benthics feed on lake bed, limnetics in water column
Source: BC Min. Environment Land and Parks, 1999.
“Wildlife in BC: At Risk” brochure

30. Stickleback pairs
A single episode of colonization of coastal lakes by a marine stickleback about to years ago (when sea level was higher than at present.
Lakes colonized independently
Divergence into benthic and limnetic niches in each lake
Indicates “vacant niches” in each lake?

31. Niches and diversity 6 species ‘community’ 10 species ‘community’
original
state
10 species
‘community’
more
resources
10 species
‘community’
more
specialization

32. So, are communities ‘designed’ by natural selection for maximum efficiency and orderly function?* Does this only happen in stable ‘saturated’ communities? And how do we determine that a community is ‘saturated’?
*Source: Eric Pianka.

33. Community structure
Closed vs. open communities
Ecotones (community boundaries)
The continuum concept
Biogeoclimatic zones

34. Terrestrial biomes (plants and animals)