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Geographic Ecology. Chapter 22. Outline. Introduction Island Area, Isolation, and Species Richness Terrestrial Aquatic Equilibrium Model of Island Biogeography Latitudinal Gradients in Species Richness Historical and Regional Influences. Introduction.

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  • Introduction
  • Island Area, Isolation, and Species Richness
    • Terrestrial
    • Aquatic
  • Equilibrium Model of Island Biogeography
  • Latitudinal Gradients in Species Richness
  • Historical and Regional Influences
  • MacArthur defined geographic ecology as the search for patterns of plant and animal life that can be put on a map.
    • Geographic ecology is the study of ecological structure and process at large geographic scales.
island area and species richness
Island Area and Species Richness
  • On islands and habitat patches on continents, species richness increases with area and decreases with isolation.
island area and species richness5
Island Area and Species Richness
  • Prestonfound fewest bird species live on smallest islands and most species on largest islands.
island area and species richness6
Island Area and Species Richness
  • Nilsson found island area was best single predictor of species richness among woody plants, carabid beetles, and land snails.
habitat patches on continents mountain islands
Habitat Patches on Continents: Mountain Islands
  • As Pleistocene ended and climate warmed, forest and alpine habitats contracted to the tops of high mountains across American Southwest.
    • Woodlands, grasslands, and desert scrub, invaded lower elevations.
    • Once continuous forest converted to series of island-like fragments associated with mountains: Montane.
lakes as islands
Lakes as Islands
  • Lakes can be considered as habitat islands.
    • Differ widely by degree of isolation.
      • Tonn and Magnuson found the number of species increases with the area of an insular environment.
      • Barbour and Brown found positive relationship between area and fish species richness.
island isolation and species richness
Island Isolation and Species Richness
  • There is often a negative relationship between the isolation of an island and the number of species it supports.
    • An island that is very isolated for one group of organisms may be completely accessible to another group.
marine islands
Marine Islands
  • MacArthur and Wilson found isolation reduces bird diversity on Pacific Islands.
marine islands11
Marine Islands
  • Williamsonsummarized data from relationship between island area and species richness in Azore Islands:
    • Birds show clear influence of isolation on diversity, pteridophytes do not.
    • Land birds fly across water barriers, and pteridophytes produce large quantities of light spores easily dispersed in the wind.
isolation and habitat islands on continents
Isolation and Habitat Islands on Continents
  • Lomolino found a strong negative relationship between isolation and the number of montane mammal species living on mountaintops across the American Southwest.
equilibrium model of island biogeography
Equilibrium Model of Island Biogeography
  • MacArthur and Wilson: Model explaining patterns of species diversity on islands as result of immigration and extinction rates.
    • Rates of immigration would be highest on new island with no organisms.
      • As species began to accumulate, rate of immigration would decline since fewer arrivals would be new species.
equilibrium model of island biogeography14
Equilibrium Model of Island Biogeography
  • They predicted the rate of extinction would rise with increasing number of species on an island for three reasons:
    • Presence of more species creates a larger pool of potential extinctions.
    • As number of species increases, population size of each must diminish.
    • As number of species increases, potential for competitive interactions between species will increase.
equilibrium model of island biogeography15
Equilibrium Model of Island Biogeography
  • Point where two lines cross predicts the number of species that will occur on an island.
  • Proposed rates of extinction on islands would be determined mainly by island size.
    • Large near islands will support highest number.
    • Small far islands will support lowest number.
    • Small near and large far will support intermediate number.
equilibrium model of island biogeography16
Equilibrium Model of Island Biogeography
  • Predictions of the equilibrium model:
    • Island diversity is the outcome of a highly dynamic balance between immigration and extinction.
    • Rates of immigration and extinction are determined mainly by the isolation and area of islands.
  • Predicts that the species composition on islands is not static – it changes over time.
    • Species Turnover
species turnover on islands
Species Turnover on Islands
  • Diamond found birds in nine California Channel Islands in a stable equilibrium as a result of immigration and extinction.
experimental island biogeography
Experimental Island Biogeography
  • Simberloff and Wilson studied insect recolonization in Florida Keys.
    • They chose 2 stands of mangroves as control islands, and 6 others as experimental islands which were defaunated.
experimental island biogeography19
Experimental Island Biogeography
  • Followed recolonization for 1 yr.
    • Species number stayed constant, but composition changed considerably.
colonization of new islands by plants
Colonization of New Islands by Plants
  • Rydin and Borgegardfound variation in species richness correlated positively with island area and accounted for 44-85% of variation in species richness among islands. Small and medium islands continued to accumulate species.
    • Large islands attained equilibrium of immigration and extinction.
    • Difficult to separate effects of habitat diversity from area effects.
manipulating island area
Manipulating Island Area
  • Simberloff tested effect of island area on species richness.
    • In all cases where area was reduced, species richness decreased.
      • Richness on control island increased slightly.
    • Islands with reduced area lost species with each reduction in area.
      • Showed area has positive influence on species richness.
island biogeography update
Island Biogeography Update
  • Brown and Kodric-Brown found higher immigration rates to near islands can reduce extinction rates.
  • Lomolinofound island area can have a significant effect on immigration rates.
  • Area and isolation are only two of several environmental factors affect island species richness.
latitudinal gradients in species richness
Latitudinal Gradients in Species Richness
  • Species richness generally increases from middle and high latitudes to the equator.
    • Most groups of organisms are more species-rich in the tropics.
latitudinal gradients in species richness24
Latitudinal Gradients in Species Richness
  • Brown grouped hypotheses that explain geographic gradients into six categories:
    • Time Since Perturbation
      • More species in the tropics because tropics are older and disturbed less frequently.
      • More time for speciation, and less frequent disturbance reduces extinction rate.
latitudinal gradients in species richness25
Latitudinal Gradients in Species Richness
  • Productivity
    • High productivity contributes to high species richness.
      • More energy to divide among population.
  • Environmental Heterogeneity
    • More heterogeneity, thus more potential habitat areas and niches.
latitudinal gradients in species richness26
Latitudinal Gradients in Species Richness
  • Favorableness
    • Tropics have more favorable environments.
      • No extremes to limit diversity.
  • Niche Breadth and Interspecific Interactions
    • Brown suggests biological processes must play secondary role.
      • Ultimate causes must by physical differences.
latitudinal gradients in species richness27
Latitudinal Gradients in Species Richness
  • Differences in Speciation and Extinction Rates
    • Tropical species richness is greater because the tropics have experienced higher rates of speciation and/or lower rates of extinction.
area latitudinal gradients in species richness
Area & Latitudinal Gradients in Species Richness
  • Terborgh and Rosenzweig proposed that the greater species richness of the tropics can be explained by the greater area covered by tropical regions.
area latitudinal gradients in species richness29
Area & Latitudinal Gradients in Species Richness
  • In addition, temperatures are more uniform across this tropical belt.
continental area and species richness
Continental Area and Species Richness
  • Brown analyzed the number of non-flying mammals on five major continents plus Madagascar and New Guinea.
    • Strong positive relationship between mammalian richness and the area of continents or large islands.
continental area and species richness31
Continental Area and Species Richness
  • Rosenzweig found a strong positive relationship between area and species diversity in the tropics.
historical and regional influences
Historical and Regional Influences
  • Long-term historical and regional processes can significantly influence species richness and diversity.
    • Exceptions to the common patterns.
historical and regional influences33
Historical and Regional Influences
  • Latham and Ricklefs: Reported striking contrast in diversity of temperate zone trees that cannot be explained by area effect.
historical and regional influences34
Historical and Regional Influences
  • Temperate forest biome in Europe, Eastern Asia, and Eastern North America all have roughly equitable area, but support vastly different levels of biological diversity.
    • Eastern Asia: 3x North America and 6x Europe.
historical and regional influences35
Historical and Regional Influences
  • Ralph found a negative correlation between foliage height diversity and bird species diversity.
cape floristic region of south africa
Cape Floristic Region of South Africa
  • Bond and Goldblatt attributed unusually high species richness of the Cape floristic region to several historic and geographic factors.
    • Continental drift
    • Wide variety of soil types.
    • Repeated expansion, contraction, and isolation of plant populations.
    • Refuge areas
diversity of temperate trees
Diversity of Temperate Trees
  • Latham and Ricklefs: Must examine conditions trees in these regions faced during the last glacial period.
    • Mountains in Europe form east-west oriented barriers.
    • During last ice age, temperate trees had southward retreat largely cut-off.
    • Lower species richness as consequence of higher extinction rate.
historical and regional influences38
Historical and Regional Influences
    • Appalachian Mountains in North America run north-south, thus temperate trees had an avenue of retreat as temperatures became colder.
      • Also no mountain barriers in Asia.
  • Concluded from various lines of evidence that most temperate tree taxa originated in Eastern Asia and dispersed to Europe and North America.
    • After dispersal lines were cut, speciation continued in Asia.
bird diversity in the beech forests of south america
Bird Diversity in the Beech Forests of South America
  • Shrub habitats contain more bird species than the beech forests with a greater diversity of heights.
    • Shrub habitats occupy a much larger area than beech forest.
    • Beech forests isolated from tropical forests by arid habitat.