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Ecological niches  Niches: fundamental and realized  Principle of competitive exclusion  Realized niche as competitive refuge  Niche crossovers 

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Presentation on theme: "Ecological niches  Niches: fundamental and realized  Principle of competitive exclusion  Realized niche as competitive refuge  Niche crossovers "— Presentation transcript:


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

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

4 Specialized habitat occupance

5 Niche breadth: generalist vs. specialist

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

7 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…

8 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.

9 Categorizing niches: dietary segregation amongst local granivores SpeciesHabitatOther foods? juncofloor berries, insects (esp. ants and beetles) chickadeecanopyinsects Douglas squirrelcanopy insects, mushrooms, flowers, birds’ eggs deer mousefloorinsect larvae (esp. moths)

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

11 Fundamental vs. realized niche

12 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’.

13 Determining niche compression Natural experiments compression

14 Niche compression: barnacles on Scotland’s rocky shores

15 Connell, J. 1961. Ecology 42, 710-723

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

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

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

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

20 Flexible dominance hierarchies resource gradient inundation/ waterlogging salinity B A C

21 Niche crossovers

22 Character displacement

23 Redwood forest niches

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

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

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

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

28 Galapagos finches: opportunistic evolution Source: Lack, D. 1966. Darwin’s Finches. Harper, N.Y.

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

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

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

32 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?

33 Tapirus bairdii (Belize) Situations vacant? Large generalist herbivore wanted??

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

35 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.

36 “The Panama Canal Experiment: fishes” Fish censused in 1922-2; canal completed in 1914; fish re-censused in 2002 Rio Chagres 7 additions 0 extinctions Rio Grande 5 additions 0 extinctions Invaders contradict the “saturation” model Smith et al. ( 2004) Proc. Roy Soc., 271, 1889-1896.

37 Island invasions and community saturation: plants Sax D.F. and Gaines S.D. 2008. PNAS 105 :11490-11497 NY Times, Sept. 09, 2008

38 Island invasions and community saturation: plants New Zealand ~2000 native plants ~2000 naturalized aliens 3 natives extinct California ~5000 native plants ~1000 naturalized aliens <30 natives extinct Brown, JH and Sax, DF 2004. Austral Ecology 29, 530-536.

39 Island invasions and community saturation: fish Hawaii 5 native freshwater fish species 40 naturalized aliens no extinctions 124 watersheds in temperate North America Fish diversity increased in 100; declined in 20 Brown, JH and Sax, DF 2004. Austral Ecology 29, 530-536.

40 The challenge to classical niche theory: Hubbell’s 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.

41 What is a “community”?* *or is it a “commutiny”? 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).

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

43 Are communities closed, or open? E = ecotone = a continuum? ** * *community named after dominant(s): e.g. Douglas fir, hemlock- cedar. fidelity? species abundance

44 Characteristics of open and closed communities OPENCLOSED Early proponentH.A. GleasonF.E. Clements OrganizationIndividualisticHolistic BoundariesDiffuseDistinct Species rangesIndependentCoincident CoevolutionUncommonProminent

45 Testing the community concept in montane forests of the American West

46 Plant associations Environmental gradient 1 2 3 4 1 2 3 4 5 1 2 3 4 trees shrubs mosses * Ass: 111 122 232 343 345 454 *An association is a local grouping (a sub-community)

47 Local plant association mapping UBC Research Forest, Haney (after Klinka, 1975)

48 Map of plant associations in part of UBC Research Forest, Haney, BC 100 m

49 Plant associations as environmental indicators

50 Biogeoclimatic zones and subzones purple = mountain hemlock; green = coastal western hemlock; yellow = coastal Douglas- fir

51 Terrestrial biomes (plants and animals)

52 Bioclimates (highly schematic)

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