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. next
















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. next
















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. next
















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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