Ecological niches

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Ecological niches

• Niches fundamental and realized
• Principle of competitive exclusion
• Realized niche as competitive refuge
• Niche crossovers
• Character displacement
• Adaptive radiation

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Ecological niche concept
Habitat occupance Where are you
from? Whats your address? Ecological niche
What do you do? Do you eat meat?
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Specialized habitat occupance
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Niche breadthgeneralist vs. specialist
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Categorizing niches
Niche overlap?
Main food generalist/ source
specialist
seeds ? specialist
Junco Chickadee Douglas squirrel Deer
mouse Deer Coyote Cougar
seeds insects ? generalist
seeds ? specialist
seeds ? specialist
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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 Gauses
principle after mathematical formulation by
Gause in 1930. In consequence, the loser is
excluded, at least locally, unless
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1. There are refuges from competition the potential
   loser hangs on in marginal habitats or
2. The loser can re-immigrate from elsewhere or
3. Disturbances in the environment prevent the
   winner from gaining a complete monopoly.

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Categorizing niches dietary segregation amongst
local granivores
Species Habitat Other foods?
junco floor berries, insects (esp. ants and beetles)
chickadee canopy insects
Douglas squirrel canopy insects, mushrooms, flowers, birds eggs
deer mouse floor insect larvae (esp. moths)
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Reducing niche overlap through habitat segregation
upper canopy
lower canopy
habitat segregation
shrub floor
resource overlap?
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Fundamental vs. realized niche
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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.

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Determining niche compression
Natural experiments
compression
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Niche compression barnacles on Scotlands rocky
shores
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Connell, J. 1961. Ecology 42, 710-723
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Sedge niches Fraser delta
high tide
low tide
Scirpus Carex
Rel. growth rate
Rel. growth rate
Daily Rare
Inundation
H1 realized fundamental
H2 Scirpus occupies refuge
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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?
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Dominance hierarchy
dominant sp. subdominant sp.
in the absence of competition
with competition
refuge exclusion refuge
zone
resource gradient
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Dominance hierarchies are environmentally
contingent
dominant sp. subdominant sp. B
A C
in the absence of competition
with competition
exclusion refuges
zone
resource gradient
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Flexible dominance hierarchies
B
resource gradient
salinity
A
C
resource gradient
inundation/ waterlogging
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Niche crossovers
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Character displacement
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Redwood forest niches
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Competitive release or are niches and habitat
occupance more-or-less fixed?
NB hypothetical !
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Can niches be vacant?
absent
mainland vs. island
new invader? evolution of new species?
competitive release OR
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Does evolution fill a finite number of jobs?
(e.g. community wants burrower?)Is there a
restricted guild?
Placental mammals Australian marsupials
Burrower
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Hawaiian honeycreepersseed-eating finch evolves
into vacant niches?
insect-eater seed-eater
woodpecker nectar-feeder
http//biology.swau.edu/faculty/petr/ftphotos/hawa
ii/postcards/birds/
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Galapagos finchesopportunistic evolution
Source Lack, D. 1966. Darwins Finches.
Harper, N.Y.
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Parallel (or convergent) evolutionof animals
inhabiting African (right) and S. American (left)
tropical forest
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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)
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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
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Stickleback pairs

• A single episode of colonization of coastal lakes
  by a marine stickleback about 11 000 to 13 000
  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?

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Situations vacant?
Large generalist herbivore wanted??
Tapirus bairdii (Belize)
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Niches and diversity
6 species community
original state
10 species community
more resources
10 species community
more specialization
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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.
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The Panama Canal Experiment fishesFish
censused in 1922-2 canal completed in 1914fish
re-censused in 2002
Rio Grande 5 additions 0 extinctions
Rio Chagres 7 additions 0 extinctions
Invaders contradict thesaturation model
Smith et al. ( 2004) Proc. Roy Soc., 271,
1889-1896.
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Islandinvasions and community saturation plants
NY Times, Sept. 09, 2008
Sax D.F. and Gaines S.D. 2008. PNAS 105
11490-11497
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Island invasions and community saturation plants
New Zealand 2000 native plants 2000 naturalized
aliens 3 natives extinct
California 5000 native plants 1000 naturalized
aliens lt30 natives extinct
Brown, JH and Sax, DF 2004. Austral Ecology 29,
530-536.
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Island invasions and community saturation fish
Hawaii 5 native freshwater fish species 40
naturalized aliens no extinctions
124 watersheds in temperateNorth America Fish
diversity increased in 100 declined in 20
Brown, JH and Sax, DF 2004. Austral Ecology 29,
530-536.
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The challenge to classical niche theory
Hubbells unified neutral theory
Hubbell champions the idea that tree species in
the tropical forests of Panama, are competitively
equivalent (i.e. neutral red line).
Coexistence is not a function of niche
segregation across a spatially heterogeneous
landscape (blue line).
See Hubbell, S.P. 2001. The Unified Neutral
Theory of Biodiversity and Biogeography.
Princeton U.P. Graphic New Scientist, 9 February
2002.
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What is a community?
An ecological (or biological) community refers to
a group of interacting organisms living together
in a specific geographical area or habitat. An
equivalent (and now somewhat anachronistic) term
is biocenosis (proposed by Karl Möbius in 1877 to
describe the interacting organisms of the oyster-
and mussel-bearing tidal flats of the North Sea).
or is it a commutiny?
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Community structure

• Closed vs. open communities
• Ecotones (community boundaries)
• The continuum concept
• Biogeoclimatic zones

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Are communities closed, or open?
community named after dominant(s) e.g. Douglas
fir, hemlock- cedar.



E ecotone
fidelity?
species abundance
a continuum?
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Characteristics of open and closed communities
OPEN CLOSED Early proponent H.A. Gleason F.E.
Clements Organization Individualistic Holistic B
oundaries Diffuse Distinct Species
ranges Independent Coincident Coevolution Uncommo
n Prominent
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Testing the community concept inmontane forests
of the American West
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Plant associations

Environmental gradient
1 2 3
4
trees shrubs mosses
1 2 3 4
5
1 2 3
4
Ass 111 122 232 343 345
454
An association is a local grouping (a
sub-community)
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Local plant association mapping
UBC Research Forest, Haney (after Klinka, 1975)
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Map of plant associations in part of UBC
Research Forest, Haney, BC
100 m
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Plant associations as environmental indicators
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Biogeoclimatic zones and subzones purple
mountain hemlock green coastal western
hemlockyellow coastal Douglas-fir
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Terrestrial biomes(plants and animals)
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Bioclimates(highly schematic)