Island Biogeography

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Islands

Discrete boundaries, and easy to compare & contrast
  • "Oceanic" vs. Continental & "Landbridge"
    • Oceanic Islands:
        diversity lower but area-effect stronger
        extinction higher (no rescue-effect)
        immigration lower (distance to mainland)
    • Examples:
      • Sky Islands
      • Woodlot "Islands"
      • Prairie Potholes
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Historical Background

Static Assumption: Island composition fixed Equilibrium Theory of Island Biogeography
  • Munroe, E.G. (1948) dissertation
  • R. McArthur and E. Wilson (1963, 1967)
  • Paradigm: central idea, organizing concept
    • Dynamic Equilibrium (not historic)
      • Diversity Constant
      • but with Turnover (species list)
next Munroe, E. G. 1948. "The geographical distribution of butterflies in the West Indies." Ph. D. Dissertation, Cornell University, Ithaca.






Island Patterns - Species-Area Relationship

  • Power Model S = cAz
  • Semi-logarithmic S = d + k log(A)
  • On oceanic islands diversity less but area-effect stronger (curve steeper)
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Area and Abundance

Oceanic islands are a special case of species-abundance relationship (Preston, 1962)
  • Most Species are rare and only a few species are dominant
  • Lognormal Distribution
  • Oceanic islands = smaller populations = fewer populous species
Preston 1962. The canonical distribution of commonness and rarity. Part 1 Ecology 43: 185-215. Part 2 Ecology 43: 410-432. next






Species-Isolation Relationship

Less "general" than the Species-Area relationship
What are the routes of immigration?
  • Exponential S = k1 e-k2(I)
  • Normal S = k1 e-k2(I·I)

    k1 & k2 = constants; S = Species Richness; I = isolation (km)
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Krakatau Islands (1883 eruption):

documentation of species turnover
  Rakata
Extinction		 Rakata
Immigration		 Sertung
Extinction		 Sertung
Immigration
1908-1920   2 20 0 28
1920-1933   5 4 2 7
next Is the number of species decreasing, increasing, or stable?






Equilibrium Theory of Island Biogeography

  • Immigration Rates  = Distance
  • Extincton Rates      = Area

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Equilibrium Theory of Island Biogeography

Strengths and Weaknesses
  • Slopes of Extincton and Immigration rate curves not known
  • Slopes vary from island to island
  • Islands may not be in equilibrium
  • Extincton and Immigration vary among species
    (continued)
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Equilibrium Theory of Island Biogeography

Strengths and Weaknesses
    (continued)
  • Extincton and Immigration not independent
    (high immigration rates save species from extinction)
  • Multiple mainlands = multiple immigration routes, rates
  • Assumes no speciations on island (strict sense)
  • 2° islands - area correlated with habitat diversity
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Isolation and Speciation

Low Immigration Rates Permit Speciation (vacant niches)
Speciation increases diversity
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Equilbrium Island Biogeography & Turnover

Turnover on "Landbridge" islands (California Channel Islands)
Island Area km2 Distance km Bird Spp. 1917 Bird Spp. 1968 Extinctions Human Introd. Immigrations Turnover %
Los Coronados 2.6 13 11 11 4 0 4 36
San Nicholas 57 98 11 11 6 2 4 50
San Clemente 145 79 28 24 9 1 4 25
Santa Catalina 194 32 30 34 6 1 9 24
Santa Barbara 2.6 61 10 6 7 0 3 62
San Miguel 36 42 11 15 4 0 8 46
Santa Rosa 218 44 14 25 1 1 11 32
Santa Cruz 249 31 36 37 6 1 5 17
Anacapa 2.9 21 15 14 5 0 4 31
Diamond, J.M. 1969. Avifaunal equilibria and species turnover rates on the Channel Islands of California. Proc. Natl. Acad. Sci 64: 57-63.   Jones, H.L. and Diamond, J.M. 1976. Short-time-base studies of turnover in breeding bird populations on the Channel Islands of California. Condore 73: 526-549. [+] next






California Channel Islands


Porcasi, P., Porcasi, J.F., O'Neill C. Early Holocene coastlines of the California Bight: The Channel Islands first visited by humans. Pacific Coast Archaeological Society Quarterly 35 (2&3): 1-24. http://www.pcas.org/Vol35N23/3523Porcasi.pdf next






Effect of Island Size on Turnover rates

Turnover rates lower in larger islands:

    Wright, S.J. 1980. Density compensation in island avifaunas. Oecologia 45: 385-389.     Wright, S. J. 1985. How isolation affects rates of turnover of species on islands. Oikos 44:331-340.
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Experimental Biogeography

Defaunation of Florida Mangrove Islands
rapid increase, overshooting, stabilization
"E1" is small isolated island

    Simberlof & Wilson 1970. Experimental zoogeography of islands: a two-year record of colonization. Ecology 51: 934-937.
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Continental Islands

Rescue Effect: reduced turnover due to replacement


    Wright, S.J. 1980. Density compensation in island avifaunas. Oecologia 45: 385-389.     Wright, S. J. 1985. How isolation affects rates of turnover of species on islands. Oikos 44:331-340.
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Target Area Effect:

greater immigration rate on larger islands


Buckley, R.C. and S.B. Knedlhans (1986). Beachcomber biogeography: interception of dispersing propagules by islands. Journal of Biogeography, 13: 69-70. next






Small Island Effect:

no area-diversity effect on small islands too few habitats

    Niering, W.A. 1963. Terrestrial ecology of Kapingamarangi Atoll, Caroline Islands. Ecological Monographs 33:131-160.
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Sky Islands

Nonequilibrium: no isolation effect, slow extinction, no dispersal
    S = cAz

    next Smammal = 1.188 A0.326     Sbird = 2.526 A0.165
    Brown, 1978. The theory of insular biogeography and the distribution of boreal birds and mammals. Great Basin Nat. Mem. 2: 209-277.






Great Basin Sky Islands - RELAXATION

Pleistocene Species Supersaturation
next Brown, 1978. The theory of insular biogeography and the distribution of boreal birds and mammals. Great Basin Nat. Mem. 2: 209-277.






Sky Island Biogeography

Southwestern Sky Islands In Equilibrium: frequent dispersal

    next Lomolino, Brown, Davis, 1989. Island biogeography of montane forest mammals in the American Southwest. Ecology 70: 18-194.






Sky Island Biogeography

Southwestern Sky Islands In Equilibrium

    next Lomolino, Brown, Davis, 1989. Island biogeography of montane forest mammals in the American Southwest. Ecology 70: 18-194.






Sky Island Biogeography

Andean Birds: Holocene colonization

    (Nores, 1995)
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Freshwater Lakes Biogeography

Speciation vs. Immigration
Effect of Antiquity ( !) and Speciation on Diversity

    Barbour & Brown, 1974. Fish diversity in lakes American Nat. 108: 473-489
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Krakatau Islands Biogeography

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Krakatau Islands Biogeography

Speciation vs. Immigration
Volcanic vs. Mature Islands


Thornton 1996. Krakatau: The destruction and reassembly of an island ecosystem. MA, Harvard. next






Krakatau Islands Biogeography

Differential Immigration Rates for Plants
Bush Whittaker 1991. Krakatau: Colonization patterns and hierarchies. Journal Biogeography 18: 341-356. next






Extinction on Sky Islands

Small generalist herbivores have lower extinction rates.
  • low energy requirements (smaller size, larger popn.)
  • more available energy (lower trophic level)
Brown, J.H. 1971. Mammals on mountaintops: Non-equilibrium insular biogeography American Naturalist 105: 467-478.   next 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.






Relaxation and Nested Island Biotas

  • immigrant pattern: dominated by "best migrators"
  • relict pattern: random extinctions of original biota
  • relaxation model: patterned extinction of original biota
Darlington, 1957. Zoogeography: The Geographical Distriburion of Animals. John Wiley & Sons, NY.
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Nested Island Distributions

Malaysian Archipelago ants
Wilson, E.O. 1959. Adaptiave shift and dispersal in a tropical ant fauna. Evolution 13: 122-144. next






Single-species Distributions

  • Metapopulation analysis: minimum area needed to escape
        extinction
  • Insular Distribution Function: tradeoff of immigration & extincton
        small islands OK if they're close to the mainland

    next 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.
















    • Variable Immigration Abilities

    Channel Island Distances (& 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 Immigration & Extinction

    Biased insular community composition
    • harmonic (balanced)
    • disharmonic (proportions different from mainland)

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    Establishment of Immigrants

    Population-Ecology Life Strategies
    • r-Selected: disturbed ecosystems, broad ecological tolerance, rapid population growth
    • K-Selected: mature ecosystems, stable population
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    Extinction of Birds in the Hawaiian Islands

    Selective extinction of ground-dwelling and carnivorous birds
    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





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    Nested Island Distributions

    Aleutian Island Archipelago
    Land plant dispersal - "Filter" Dispersal Route
    Williamson, M. 1981. Island Populations, Oxford 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

    Incidence Function: proportion of islands inhabited vs. number of species per island (diffuse competition)
    next 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.






    Patterns Reflecting Interspecific Interactions

    Effect of close-competitors on an island being invaded
    success correlated with difference from resident species
    next Moulton, M.P. and Pimm, S.L. 1986. The introduced Hawaiian avifauna: Biogeographical evidence for competition. American Naturalist 121: 669-690.






    Patterns Reflecting Interspecific Interactions

    Niche shift: atypical habitats occupied on islands where preditor absent (shrews are predators on voles)

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






    Patterns Reflecting Interspecific Interactions

    Niche shift: Anolis size differentiation when more than species on island

    next 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.






    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: combined populations on several small islands greater than on a single large island of equal area.
    • Density Compensation: abundance constant despite increasing species (fewer per species)
    • Density Stasis: abundance increases with increasing species biomass

      Wright, S.J. 1980. Density compensation on small islands. Oecologia 45: 385-389.
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    Applications of Island Biogeographic Theory to Nature Preserves

    SLOSS Single Large or Several Small next






    Applications of Island Biogeographic Theory to Nature Preserves


    Single Large vs.
    Several Small

    Circular vs.
    "Peninsular"

    Clumped vs.
    Spread out

    Connected vs.
    Unconnected
    Wilson, E.O. & E.O. Willis 1975. Applied biogeography. pp. 522-534 in M.L. COdy & M.M. Diamond (eds.) Ecology and Evolution of Communities. Cambridge, Belknap Press.
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    Applications of Island Biogeographic Theory to Nature Preserves

    • Reserves should be as large as possible
        Area - Diversity
    • Unique habitats (biotas) should have multiple preserves (nearby)
        Redundancy
        Isolation
    • Preserves should be round and continuous
        Peninsula effect
        Isolation
    • Priority given to highest endemicity and vulnerability
    • Corridores between preserves should be maintained

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    Evolutionary Trends on Islands

    Flightlessness and reduced dispersal ability
    • Birds
        absence of predators (no need to fly)
        limited resources (expensive to fly)
    • Insects
        Expansion into vacant niches
          (Orthopteran "wettas" of New Zealand)
        Precintiveness: dispersal away from hatching area is fatal
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    Evolutionary Trends on Islands

    • Land Snails (smaller)
      • Wind-dispersed - smaller is better
    • Plants (bigger, simpler)
      • loss of pappus, heavier, less resistant to saltwater
          (precintiveness)
      • Become Trees
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    Evolutionary Trends on Islands

    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: "the big get smaller & the 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
    Wilson, E.O. 1959. Adaptive shift and dispersal in a tropical island fauna. Evolution 13: 122-144. next