Communities, Formations, and Biomes

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Chapter 6

• Communities, Formations, and Biomes

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Biogeographic Patterns

• The initial approaches to explaining
  biogeographic patterns, developed in the 16th and
  17th centuries, were based on the Bible.
• All the plants and animals on Earth were
  represented on Noahs Ark
• Therefore the New World should have the same
  plants and animals as the Old World
• Age of Exploration Captain Cook and Sir Joseph
  Banks 1000 new species of plants

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• So many new plants and animals discovered in the
  18th century, how could they have all fit on the
  ark?
• Buffon (1756) The Earth makes the plants the
  Earth and the plants make the animals
• Buffons Law - environmentally similar but
  isolated regions have distinct assemblages of
  plants and animals first principle of
  biogeography
• Exception cosmopolitan species

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• Buffons Law led to
• Biomes subdivisions of the biosphere based on
  similarities in vegetation structure and climate
• Community assemblage of all organisms living in
  a prescribed place or habitat
• Associations groups of plant species commonly
  found in similar habitats

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• Ecological equivalents widely separated but
  physiognomically and structurally similar species
  and vegetation formations
• Von Humbolt
• Life zones elevational and latitudinal bands of
  similar climate and vegetation

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• Superorganism community concept
• Clement
• Species in a community have coexisted for long
  periods of time and evolved together
• Each species depends on the others for survival
• Individualistic community concept
• Gleason
• Communities are areas of similar habitat where
  species coexist because they have somewhat
  comparable environmental tolerances and resource
  demands
• Species do not have to occur together
• The youthfulness of many present plant
  associations means they didnt evolve together as
  superorganisms

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Six basic vegetation structural types

• Brown and Lomolino (1998)
• Forest trees with continuous canopy
• Woodland widely spaced trees with shrubs,
  grasses, or herbs
• Shrubland continuous shrubs
• Grassland grass
• Scrubland widely spaced shrubs
• Desert sparse xerophytic plant cover and bare
  ground

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Figure 6.6
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Figure 6.1
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Tropical Rain Forest

• Found between 25N and 25S latitude
• No distinct dry season, Frost free
• Equal insolation
• Major centers of distribution South and Central
  America (50), Africa (20), and SE Asia and
  eastern Australia(30)
• Occurs in 70 countries
• Highest biodiversity 50 to 80 of species on 6
  to 7 of Earths land surface
• 300 tree species per hectare, but only 2
  individuals per species
• Structural complexity
• Seed dispersal

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Tropical Rainforest

• Epiphytes rooted in other plants not
  parasites, but do compete for light
• Lianas rooted in soil
• Stranglers born epiphytes, become lianas
  hemiepiphytes the strangler fig
• Poor soil quality rapid nutrient cycling
• Shallow, butressed root systems
• Time stability hypothesis
• Pleistocene aridity and refugial hypothesis
• Podocarpus

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Tropical Seasonal Forest

• Between Tropical Rainforest and 30 latitude
• Monsoon rainfall pattern
• Little seasonal temperature change
• Mainly deciduous canopy
• Large, fleshy canopy leaves
• Strata canopy, shrub, sapling
• High biodiversity

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Tropical Seasonal Forest
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Tropical Savanna

• Centered around 20 latitude
• Winter dry season
• More seasonal temperature variation
• Grassland with scattered trees and shrubs
• Trees have thick bark to avoid water loss
• Seasonal die off of some species
• Fewer trees because of water availability, large
  grazing animals, and lightning

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• Many bird species, large grazers, predators
• Sahel and Serengeti
• Threatened by desertification, over grazing,
  poaching, changes in fire regimes

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Desert

• Found in areas dominated by subtropical high
  pressure cells, rainshadows, and continental
  areas
• Tropical deserts receive rainfall from the
  Intertropical Convergence Zone (ITCZ)
• Cool deserts receive rainfall from winter
  midlatitude cyclones
• Biodiversity depends on rainfall
• Few trees
• Most vegetation along waterways and roadways

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Figure 6.13