Insular Biotas

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Island Biogeography

  • Biodiversity set by Immigrations & Extinctions
  • Biogeographic patterns created by
      selective Immigration & Extinction
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Continental vs. Oceanic Islands

  • harmonic (balanced)
  • disharmonic

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SELECTIVE: Variable Immigration Distances & Immigration Rates


Wenner, A.M. and Johnson, D.L. 1980. Land vertebrates on the California Channel Islands: Sweepstakes or bridges? p. 497-530 In: D.M. Power (ed.) The California Islands: Proceedings of a multi-disciplinary symposium Santa Barbara Museum Nat. Hist. next

















SELECTIVE: Establishment of Immigrants

Population-Ecology Life Strategies
  • r-Selected: early-successional ecosystems, broad ecological tolerance, rapid population growth
  • K-Selected: mature ecosystems, stable population

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Selective Extinction

Reduced resources on islands
  • low energy requirements (small size [island rule])
  • more available energy (lower trophic level)
Brown, J.H. 1971. Mammals on mountaintops: Non-equilibrium insular biogeography American Naturalist 105: 467-478
Brown, J.H. 1978. The theory of insular biogeography and the distribution of boreal birds and mammals. Great Basin Nat. Memoirs 2: 209-277.
Patterson, B.D. 1984. Mammalian extinction and biogeography in the southern ROcky MOuntians. p. 247-294 in M.H. Nitecki (ed.) Extinctions Univ. Chicago.
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Selective Extinction

Extinction of Birds in the Hawaiian Islands
James, H.F. 1995. Prehistoric extinctions and ecological changes on oceanic islands. p. 87-102. in P.M. Vitousek, L.L. Loope, and H. Anderson. Islands: Biological Diversity and Ecosystem Function. Springer Verlag, NY. next
















Patterns created by Selective Immigration & Extinction

Patterns among Groups of Islands
Example: "Filter" Dispersal Route
Williamson, M. 1981. Island Populations, Oxford Univ. Press. next
















Patterns among Groups of (continental) Islands

  • immigrant pattern
  • relict pattern
  • relaxation model

Darlington, 1957. Zoogeography: The Geographical Distriburion of Animals. John Wiley & Sons, NY. next
















Single-species Distributions

  • Metapopulation analysis: area needed to escape extinction
  • Insular Distribution Function: tradeoff of immigration and extincton
    Present (rescue)
    Absent
Lomolino, M.V. 1986. Mammalian community structure on islands: Immigration, extinction and interactive effects. Biol. Journal Linnean Soc. 28: 1-21.
Lomolino, M.V. 1998. A species-based, hierarchical model of island biogeography. In E. Wiher and P.A. Keddy (eds.) The search for assembly rules in ecological communities. Cambridge Univ. Press.
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Patterns Reflecting Interspecific Interactions

  • Checkerboard Distribution: only one or the other of two competing species occur on each island.
  • Example: Bismark Archipelago flycatchers
      Pachycephala pectoralis and P. melanura dahli
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Patterns Reflecting Interspecific Interactions

Diffuse competition
Incidence Function: proportion of islands inhabited vs. number of species on island
  • Supertramps
  • Widespread Species
  • Large-island Onlies
Diamond, J.M. 1975. Assembly of species communities. p. 342-444 In. M.L. Cody and J.M. Diamond (eds.) Ecology and evaluation of Communities. Belknap Press, Cambridge. next
















Patterns Reflecting Interspecific Interactions

Existence of close-competitors on island being invaded
Moulton, M.P. and Pimm, S.L. 1986. The introduced Hawaiian avifauna: Biogeographical evidence for competition. American Naturalist 121: 669-690. next
















Patterns Reflecting Interspecific Interactions

Niche shift: atypical habitats occupied on islands where preditor absent

Lomolino, M.V. 1984. Immigrant selection, predatory exclusion and the distributions of Microtus pennsylvanicus and Blarina brevicauda on islands. American Naturalist 123: 468-483. next
















Patterns Reflecting Intrageneric Interactions

Niche shift: Anolis size differentiation when more than one species on island [finches]

Roughgarden, J. 1974.Niche width: Biogeographic patterns among Anolis lizard populations. American Naturalist 108: 429-442.
Roughgarden, J. and Fuentes, E.R. 1977. The environmental determinants of size in solitary population of West Indian Anolis lizards. Oikos 29: 44-51.
Foughgarden, J. Heckel, S. and Fuentes, E.R. 1983. Coevolutionary thoery and the biogeography and community structure of Anolis. p. 371-410 IN Huey, R.B. and Pianka, E.R. and Schoener, T.W. (eds.) Lizard Ecology: Studies of a model organism. Harvard Univ. Press.
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Patterns Reflecting Interspecific Interactions

Predator Release: species (example spiders) more aboundant where predator absent
Schoener, T.W. and Spiller, D.A. 1987. High population persistence in a system with high turnover. Nature 330: 474-477. next
















Patterns Reflecting Interspecific Interactions

  • Density Overcompensation: abundance higher on island
      release from diffuse competition?
  • Density Compensation: abundance constant despite increasing species
  • Density Stasis: abundance increases with increasing species
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EVOLUTIONARY TRENDS

Flightlessness and reduced dispersal ability
  • Birds
      absence of predators
      limited resources
  • Insects
      Expansion into vacant niches
        (Orthopteran "wettas" of New Zealand)
      Precintiveness: dispersal away from hatching area is fatal
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EVOLUTIONARY TRENDS

  • Land Snails
      Wind-dispersed - smaller is better
  • Plants
      loss of pappus, heavier, less resistant to saltwater
        Precintiveness
      Become Trees
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EVOLUTIONARY TRENDS

Body Size Change on Islands
  • Dwarfism
      reduced resource need
      better shelter in treeless islands
  • Gigantism
      traits that allowed dispersal (small size) a disadvantage
      wider range of prey
      greater energy and water reserves for famines
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The Island Rule: "big get smaller, small get bigger"
  • Optimal size 250 grams (red squirrel)
  • Predators: canids, felids - dwarfism
      reduced resources
  • Rodents - gigantism
      immigrant selection: small animals disperse more easily
      ecological release: small size not needed to avoid predators
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EVOLUTIONARY TRENDS

Size variation
  • squirrel size vs. island area

    Heaney, L.R. 1978. Island area and body size of insular mammals: Evidence from the tri-colored squirrel (Callisciurus prevosti) of Southwest Africa. Evolution 32: 29-44.
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EVOLUTIONARY TRENDS

Size variation
  • mouse size vs. isolation

    Ebenhard, T. 1988. Introduced birds and mammals and their ecological effects. Swedish Wildlife Research 13: 1-107.
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EVOLUTIONARY TRENDS

Size variation
  • lizard size vs. number of lizards per island
Soulé, M.E. 1966. Trends in insular radiation of a lizard. American Midland Nat. 100: 47-64. next
















EVOLUTIONARY TRENDS

Taxon Cycles
  • Island speciation ends in extinction
    1. Invasion of Most Islands
    2. Speciation and Range Restriction
    3. Few Relictual Populations
    4. Replaced by new Stage 1 Species
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