Species Diversity and Marine Diversity

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BIODIVERSITY: "all living things on Earth"
  • species, consisting of populations of organisms
  • genetic diversity within each species
  • ecosystems diversity that fosters populations
Reasons for Preserving Diversity
  • utilitarian: loss of useful species
  • ethical: other species have the "right to exist"


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    Extinctions
  • Aldo Leopold (1947) "the first requisite of intellegent tinkering is to save all the pieces."
    Background (fossil record):
      species: ~1/century
      family: ~1/million years
    Historic:
      E.O. Wilson: ~6000/year
      over 200 species/century
    • 115 bird species have gone extinct in the last 400 years
      • Great Auk (Alca impennis) [Link]
      • Dodo (Raphus Cucullatus) [Link]
      • Passenger pigeon (Ectopistes migratorius) [Link]
    • 191 mollusc species in 400 years
    • 600 plant species in 400 years
    • Freshwater Fish: 20% of all species extinct or endangered next


HOW MANY SPECIES ARE THERE?

  • Estimated 12-30 million world-wide
  • 2 million have been described
  • many are endangered
    USA next
    Plants and Animals in USA, Nature Conservancy, 1996


Estimating biodiversity - some difficulties

  • Alias species: one species given two names (inflates)
  • Linnean Shortfall: 80% not described (underestimates)
  • Centilenan Extinctions: extinction of undescribed species

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Linnean Shortfall

Taxonomic Group# Described# Estimated% Described
Vertebrates
45,000
50,000
90
Vascular plants
250,000
300,000
83
Mollusks
70,000
200,000
35
Crustaceans
40,000
150,000
27
Protozoans
40,000
200,000
20
Algae
40,000
200,000
20
Insects
950,000
8,000,000
12
Arachnids
75,000
750,000
10
Fungi
70,000
1,000,000
7
Viruses
5,000
500,000
5
Nematodes
15,000
500,000
3
Bacteria/Archea
4,000
400,000
1

Groombridge, B. 1992. Global Biodiversity: Status of the Earth's Living Resources. London, Chapman & Hall.     next



Linnean Shortfall


Global Diversity of Organisms

Global Diversity of Taxonomists
after Barroclough (1992)
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Species Richness and Evenness Indices

  • Species Richness: number of species in an area


  • Species Diversity: diversity & evenness of distributions

    • H = Shannon-Weiner Index
    • s = number of species
    • pi = proportion of individuals in area belonging to species i

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Diversity over Geographical Scales

  • Alpha: Number of species in a local community (km2)
  • Beta: Species turnover among local communities (100 km2)
  • Gamma: Diversity of a region (106 km2)

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Habitat Heterogeneity

Beta Diversity decreases poleward

North American Mammals
Brown and Lomolino 1998.

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Latitudinal Gradients

Tropical Diversity Maximum

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Tropical Diversity next

Example - Palms [Endemics]

Good, R. 1974. The geography of the flowering plants 3rd ed. Longman, White Plains, NY.




Tropical Diversity - Exceptions next

  • Aphids
  • Pinus

Stevens, G.C. and Enquist, B.J. 1998. Macroecological limits to the abundance and distribution of Pinus. p. 183-190 IN: Richardson, D.M. (ed.) Ecology and biogeography of the Genus Pinus. Cambridge Univ. Press.




Processes involved in Tropical Diversity Maximum

BIOTIC vs. ABIOTIC
Ice-Age Extinctions
Slow speciation and colonization after glaciations restore diversity
Polar Harshness
High extinction rates, slow population growth
Tropical Climatic Stability
Low extinction rates allow specialization and speciation
Tropical Productivity
Greater evenness narrower niches
Structural Heterogeneity
Finer niche subdivision, microclimate heterogeneity
Interspecific Interactions
Competition, predation, and mutualism promote specialization
Large Tropical Area
Not !       next




Dominance-Diversity Relationships

Greater evenness of distribution in the tropics

Hubbel, S.P. 1979. Tree dispersion, abundance, and diversity in a dry tropical forest. Science 203: 1299-1309.

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Causes of the Patterns - Nonequilibrium Hypotheses

  • Glaciation and Climatic Change
    • Range Changes
        Extinction before Migration
        Extinction during Migration
    • Extinction of "Tertiary Relics"
        Europe and Western North America
  • Other Perturbations

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Causes of the Patterns
- Nonequilibrium Hypotheses next

Rapid Recovery from extinctions erases their effects (pest eradication)

Insect Pests on Sugarcane: rapid adaptation

Insect Pests on Cacao: rapid adaptation
Strong, D.R., McCoy, E.D., and Rey, J.R. 1997. Time and the number of herbivore species: The pests of sugarcane. Ecology 58: 167-175.

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Equilibrium Mechanisms

Productivity

North American Vertebrates, Nonvolant
Currie, D.J. 1991. Energy and large-scale patterns of animal and plant-species richness. American Nat. 137: 27-49.

Gobi Desert Rodents
Rosensweig 1995
(scale!)

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Equilibrium Mechanisms

Productivity: increased productivity allows high populations at decreased niche breadth

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Equilibrium Mechanisms - Diversity


Blondell, J. 1979. Biogeographie et Ecologie. Paris, Mason.
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"The Paradox of the Plankton": diversity in a homgeneious habitat
    vs.
  • Effect of Diversity on Allopatric speciation
    • freshwater: more barriers, higher diversity
    • marine: fewer barriers, lower diversity




Equilibrium Mechanisms

  • Harshness and abiotic stress
    • Absolute Harshness
        freezing (< 0 oC)
        high temperature (> 37 oC)
        high salinity (desiccation)
    • Relative Harshness: extinction rates higher and colonization rates lower
  • Climate Stability (less change in tropics?)
    • Seasonal Extremes
    • Decadal - Century timescale variability

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Equilibrium Mechanisms

  • Area: tropics more extensive than temperate or polar?
  • Biotic interactions: Greater diversity produces more niches
  • Speciation and extinction rates: relative rates of extinction are lower, and speciation are higher in the tropics
    • Constant environment promotes lower extinction rates
    • Reduced seasonality promotes lesser ecologic amplitude, greater isolation
    • Decreased niche breadth promotes speciation
MacArthur, R.H. and MacArthur, J.W. 1961. On bird species diversity. Ecology. 42: 594-598.

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Rapoport's Rule

Taxa have larger ranges in polar regions

North American Birds
Brown, J.H. 1995. Macroecology. Univ. Chicago Press.

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Rapoport's Rule - larger ranges in polar regionsnext

North American Trees

Pacific Coast Mollusks
Brown, J.H. 1995. Macroecology. Univ. Chicago Press.

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Rapoport's Rule - Elevational effect next


Costa Rican Trees

Venezuela Birds
Stevens, G.C. 1992. The elevational gradient in altitudinal range: An extension of Rapoport's latitudinal rule to altitude. American Naturalist 140: 893-911.

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Other Diversity Patterns next

Peninsulas: typically diversity decreases toward end of peninsula

Taylor, R.H. and Regal, P.J. 1978. The peninsular effect on species diversity and the biogeography of Baja California. American Naturalist 112: 583-593.
Due, A.D. and Polis, G.A. 1986. Trends in scorpion diversity oalong the Baja California Peninsula. American Naturalist 128: 460-468.
Brown, J.H. 1987.

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Other Diversity Patterns

Elevation: typically diversity decreases toward high elevation

Kikkawa, J. and Williams, E.E. 1971. Altitudinal distribution of land birds in New Guinea. Search 2: 64-69.
Terborgh, J. 1977. Bird species diversity on an Andean elevational gradient. Ecology 58: 1007-1019.

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Other Diversity Patterns - Elevation & Aridity


Whittaker, R.H. and Niering, W.A. 1965. Vegetation of the Santa Catalina Mountains, Arizona: A gradient analysis of the south slope. Ecology 46: 429-452.
Whittaker, R.H. 1960. Vegetation of the Siskiyou Mountains, Oregon and California. Ecological Monogr. 30: 279-338.

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Biodiversity Hot Spots: regions of high endemicity and high diversty
  • Tropical Rain Forests
    • 7% of Earth's surface
    • 50% of Earth's species

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Biodiversity Hot Spots
Terrestrial Hot Spots [link]
  • Endemic Bird Areas (EBA): two or more endemic birds
    • Tropical maximum of EBA's
    • 1/2 of all endemic birds on islands (1/10 of land surface)
    • Larger islands have more EBA's

Endemic Bird Areas

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Biodiversity Hot Spots
Terrestrial Hot Spots
  • Hotspots are concentrated
      Bird hotspots just 5% of Earth's surface
  • Do Hotspots Overlap for birds, other animals, plants?
    • Diversity Centers Do not necessarily match [pic]
      • Central America: birds and reptiles similar,
        butterflies different
      • Africa: amphibians and mammals similar,
        birds and plants different

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Aquatic Hot Spots

Aquatic Environments: typically diversity greatest in tropics
Marine Intertidal: diversity decreases toward the high-tide line

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Marine Hot Spots

  • Diversity maximum 2000 - 3000 m (slope)
  • Endemicity maximum 6000 m (hadal zone)
    • Hydrothermal Vent Communities
      One new phylum, 14 new families, 50 new genera

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Aquatic Diversity Patterns next

Pelagic Organisms: typically diversity decreases with depth
Benthic Organisms (stability of continental slopes)

Day, D.S. and Pearcy, W.G. 1968. Species associations of benthic fishes on the continental shelf and slope off Oregon. Journal Fisheries Res. Board Canada 25: 2665-2675.
Rex, M.A. 1981. Community structure in the deep-sea benthos. Annual Rev. Ecology Systematics 12: 331-354.

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Aquatic Diversity Patterns

Aquatic Environments: typically diversity increases with productivity
polluted freswater habitats are exceptions

Sanders, H.L. 1968. Marine benthic diversity: A comparative study. American Naturalist 102: 243-282.

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