BIOTIC PATTERNS - BIOTIC EXCHANGE next
























Single-Species Patterns

  • Bergman's Rule (1847): Among closely related mammals and birds, the largest forms are at higher latitudes.
    • Thermoregulation:
        easier small animals to stay cool (Hadley, 1997)
        easier for large animals to keep from freezing
    • Climate Change: packrats got smaller at the end of the Pleistocene

    Neotoma cinerea
    next
(Smith et al., 1995)








Single-Species Patterns

Ecogeographic Rules
  • Allen's Rule: Animals in hot climates have longer appendages
      thermoregulation?
      better hearing?
  • Golger's Rule: Animals in wet climates are darker colored
      predator avoidance: wetter climates have darker soils, more shade
      predators select light-colored prey, trait is heritable
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Geographical Variation in Life History

  • Clutch size: number of eggs per nest increases with latitude
      climate
      resources
      r-selection vs. K-selection
Strigidae (owls) Otus (screech owls) next








Multispecies Patterns

Sizes of Ranges
  • Rapoport's Size Rule: Size of range increases with latitude
  • Areography:
    • Most Species' ranges are small
    • Declines exponentially

    North American Land Mammals
(Brown, 1995) next








Multispecies Patterns

Shapes of Ranges
  • Rapoport's Shape Rule: Perimeter / Area = 10
    • Ecological Rule
    • Artifact of map-making
  • Brown's Rule:
    • Large ranges elongated east-west
    • Small ones elongated north-south

    North American Terrestrial Mammals
    next

    North American Birds
(Brown & Maurer, 1989)








Multispecies Patterns

Overlap of Ranges
  • Ranges of closely-related marine algae overlap more frequently than do distantly related algae (Pielou, 1978)
  • Ranges of closely-related desert rodents overlap less frequently than do distantly related desert rodents (Kelt & Brown)
  • Why
    • competition more intense among desert rodents
    • competition and relatedness more closely correlated in desert rodents
    • desert rodents allopatrically speciate
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Macroecology: assembly of continental biotas

Distribution of Range Size:
  • Large animals have large ranges
    • population density varies inversely with body size
    • to maintain minimum pop'ns, lg. animals have lg. ranges
  • Species with small ranges do not have high population densities
    North American Mammals
    next

    North American Birds



    North American Mammals
next (Brown, 1995)








Macroecology: assembly of continental biotas

Body Size and Species Diversity
  • N. American Mammals: most are small (96 gm. class)
    • Smaller geographical units (Biome, community) have "flatter" distributions
    • Because large species' ranges span the smaller units

    North America 492 spp.
    next

    N.Am. Deciduous Forest 75 spp.


    Rio Grande, NM, Bosque 27 spp.
(Brown and Nicoletto, 1991) next








Macroecology: assembly of continental biotas

Body Size and Species Diversity Processes
  • Lumpy-gappy distributions (Holling 1992)
    • Lumps: Aggregates of animals with similar sizes (but different niches)
    • Local environments select certain size classes (lumps)
    • Competition eliminates all but a few animals in each size class, or causes size divergence (gaps)
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Macroecology: assembly of continental biotas

  • Local vs. Regional Diversity
  • Local communities assembled from regional biota by small-scale ecological interactions
  • Composition of regional biota effected by historical and large-scale events
  • Local species richness increases at a lower rate than regional species richness

         California Gall Wasps


         Caribbean Birds
    (Ricklefs, 1987)
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Biotic Interchange

The Great American Interchange
  • Mammals evolve 220 Ma, before breakup of Pangea
  • K/T extinction 65 Ma, precedes Mammalian Diversification
  • Diverse S. American Fauna evolve
  • (140, 10) 3.5 Ma faunas invade S. America and diversify








Biotic Interchange

  • Results of Faunal Exchange
      Generic-level diversity of N. America remained unchanged
    • Generic-level diversity of S. America increased
    • Many S. American animals went extinct
        marsupial carnivores, eutherian herbivores
    • Current biota: 50% of S.American from North, 10% of N. American from South
      North American Mammalian Biota
      1. Better Migrations
      2. Better Speciators
      3. Better Competitors

    Immigration of mammals


    Diversification of mammals
(Webb and Marshall, 1982) next








Biotic Interchange

Other Inter-American Exchange of Vertebrates
Other than Mammals
  • Bird and Reptile migrations: 3.5 Ma gradual rather than sudden
      more birds move north than south
  • Ambhibians and Fish: Northward migration much greater than southward
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Lessepsian Exchange: The Suez Canal

  • Suez Canal, completed 1869
  • South to North: 50 fish, 20 crustaceans, 40 mollusks
  • North to South: 0
  • Hypotheses
    • Red Sea opening is saline so that biota can pass through salt lakes along canal
    • Red Sea fauna inhabits shallow sandy-muddy habitats, also like the canal "preadapted"
    • Red Sea fauna has better competitors (from the diverse Indian Sea fauna)
        "The bigger fauna wins"
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Maintenance of Distinct Biotas

  • Barriers between Regions
    • Ecological barriers to dispersal (filters, sweepstakes routes)
    • Most ranges on mainlands do not extend to dispersal route entrance (landbridge)
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Maintenance of Distinct Biotas

  • Resistance to Invasion
    • Successful alien invaders a fraction of total introductions
    • Most successful aliens depend on human-made habitats (weeds, crop pests)
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Maintenance of Distinct Biotas

  • Avian Migration and Provincialism
    • Paradox: birds have great dispersal power, but show distinct provincialism (Schlater, 1858)
    • Actually the provincialism results mostly from specialized & flightless birds
    • Also many migrants are restricted to one biogeographic region or one hemisphere
    • Long-distant migrators can't establish new seasonal migration routes after dispersing to a new region
    • Most long-distant migrators are tropical, visiting the boreal region to rear young during summer

    (McClure, 1974; Baker, 1973)

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Divergence and Convergence of Isolated Biotas

  • Divergence
    • Panamanian Isthmus divided Atlantic and Pacific biotas
    • Pacific biota is generally more diverse than Caribbean
    • Separated species generally have not diverged greatly
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Divergence and Convergence of Isolated Biotas

Convergence
  • Species (many examples)
      Cacti in N. Amer., Euphorbiaceae in Africa
      Agaves in N. Amer., Bromeliads in S.Amer.
      Long-tailed jumping rodents on all continents
  • Entire assemblages
      Mediterranean-Climate regions: sclerophyll leaves and growth forms
      Australian - North American mammals
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Baker, R.R. 1978. The evolutionalr Ecology of Animal Migration. Hodder & Stoughton, London.

Brown, J.H. 1995. Macroecology. Univ. Chicago Press.

Brown, J.H. and Maurer, B.A. 1989. Macroecoogy: the division of food and space among species on continents. Science 243: 1145-1150.

Brown, J.H. and Nicoletto, P.F. 1991. Spatial scaling of species assemblages: Body masses of North American land mammals. American Naturalist 138: 1478-112.

Hadley, E.A. 1997. Evolutionary and ecological response of pocket gopher (Thomomys talpoides) to late-Holocene climatic change. Biological Journal of the Linnean Society 60: 277-296.

McClure, H.E. 1974. Migration and Survival of the BIrds of Asia. Applied Sci. Res. COrp. Thailand., Bangkok.

Ricklefs, R.E. 1987. Community diversity: Relative roles of local and regional processes. Science 235: 167-171.

Smith, F.A., J.L. Betancourt and J.H. Brown. 1995. Evolution of body size in the woodrat over the past 25,000 years of climate change. Science 270: 2012-2014.

Webb, S.D. and Marshall, L.G. 1982. Historical biogeography of recent South American land mammals. p. 39-52 IN: M.A. Mares and H.H. Geonowas (eds.) Mammalian Biology in SOuth America. Univ. Pittsburgh Pymatuning Lab. Special Publ. Ser. 6.