ECOLOGY chapter 50

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ECOLOGY chapter 50

• Ecology Study of interactions between organisms
  and their environment.
• Environment includes both abiotic (non-living)
  and biotic (living) components.
• Abiotic light, water, nutrients, chemicals,
  rocks, weather, etc.

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• Biotic organisms.
• Organisms compete with, parasitize, eat or are
  eaten by and change the environment for other
  organisms.

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• Ecology explores a wide range of questions about
  what factors control the distribution, abundance
  and behavior of organisms.
• For example, Red Kangaroos occur primarily in
  the Australian interior in semiarid regions.

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• Distribution of Kangaroos suggests an abiotic
  factor (precipitation) influences it, but perhaps
  populations also influenced indirectly by biotic
  factors such as competitors, predators, food
  availability and parasites.
• Ecologists have to consider multiple factors to
  explain patterns of abundance and distribution.

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• Ecology has many subfields of study ranging from
  ecology of individual organisms to dynamics of
  landscapes
• Organismal Ecology
• Population Ecology
• Community Ecology
• Ecosystem Ecology
• Landscape Ecology
• We will explore these sequentially

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Distribution of species

• Biogeography study of the broad patterns of
  distribution of organisms across the globe.
• Patterns strongly influenced by historical
  factors such as continental drift (see chapter
  26) and barriers including mountain ranges and
  seas.

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• For example, Australia populated by marsupial
  mammals (e.g. kangaroos, wombats, koalas) because
  placental mammals did not colonize it before it
  separated from other landmasses.
• Tapirs found only in southeast Asia and South
  America. Ancestral populations separated when
  land masses diverged.

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Role of dispersal in distribution

• Ability to cross barriers affects distribution.
• Thus, species of birds often more widely
  distributed than mammals.

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• However, inability to reach an area not only
  factor that limits distribution. Ability to
  survive in new area is critical.
• To survive and thrive species must be able to
  cope with both biotic and abiotic factors.

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Biotic factors

• The presence of competitors or predators may
  limit an organisms ability to establish itself.
• For example, algae are eaten by sea urchins and
  limpets, which limits the ability of seaweeds to
  establish themselves on rocks

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Biotic factors

• Conversely, absence of predators and competitors
  has allowed many organisms introduced into new
  areas to increase so much they become pests.
• E.g. Japanese beetles (from Asia), zebra mussels
  and purple loosestrife from Europe) (Melaleuca
  (Eucalyptus trees from Australia) and many other
  invasive species have spread widely in the U.S.

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Abiotic factors

• The major factor affecting distribution of
  terrestrial organisms is climate, which
  incorporates temperature, sunlight, wind and
  precipitation.

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Abiotic factors

• Climate is determined by global factors such as
  inputs of solar energy and the movement of the
  earth through space.
• Study discussion of climate patterns pages 1088
  and 1089

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Climate

• Local factors such as the presence of mountains
  and large bodies of water also affect climate.
• Mountains force up moist air moving across them.
  As the air cools the water condenses and falls as
  rain. The result is that one side of the
  mountain range is wet and the other side is drier
  (and perhaps a desert e.g. Mojave and Gobi
  Deserts.)

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Climate

• Large bodies of water moderate climate. Land
  heats faster than water and warm air rises.
• Cooler air over water moves in and replaces the
  warm air.
• The warm air that was over land cools at high
  altitude and sinks over water.
• Results is steady flow of cool air over land.

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Terrestrial Biomes

• Biomes are major types of ecosystems that cover
  large areas of the earth and are classified by
  their dominant vegetation types.
• (an ecosystem is the community of organisms in an
  area and their physical environment)

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• Each biome also is populated by a diverse array
  of animals, fungi and microorganisms adapted to
  that environment.

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Major terrestrial biomes include

• Tropical forest
• Desert
• Temperate Grassland
• Savanna
• Temperate broadleaf forest
• Coniferous forest (Taiga)
• Tundra
• (see descriptions pages 1100-1104)

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Savannah
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Terrestrial biomes

• Terrestrial biomes often vertically stratified.
  Layers defined by different size plants
• (e.g. in forests there is an upper canopy of tall
  trees, low tree layer, shrub layer, ground layer
  of herbaceous plants, litter layer and root
  zone).

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• Stratification provides multiple different
  habitats for animals which occupy specialized
  feeding niches.

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Convergent evolution

• Actual species in a biome differ from one area to
  another but they possess similar adaptations.
• This is convergent evolution (development of same
  evolutionary solutions to ecological problems)

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Convergent evolution

• For example vegetation in all deserts worldwide
  characterized by extensive root systems,
  long-term water storage capability, thick waxy
  coverings to reduce water loss, and extremely
  small (if any) leaves

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• Biomes often maintained by disturbance.
• Wildfires are an essential factor in maintaining
  many biomes (e.g. grasslands, savannahs, some
  coniferous forests). Fire favors trees such as
  longleaf pine whose bark resists fire and
  grasses, which recover quickly after burning.

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Aquatic biomes

• Aquatic biomes less influenced by climate than
  terrestrial biomes
• Why?

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Aquatic biomes

• Water is more thermally stable.
• It takes a lot of heat to change the temperature
  of a body of water.

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Major aquatic biomes

• Lakes
• Rivers
• Estuaries
• Intertidal zone
• Marine pelagic zone
• Coral reefs
• Marine benthic zone (benthic zone is
  sea/lakefloor)
• See pages 1094-1097.

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• Aquatic biomes often stratified by light and
  temperature.
• Light intensity decreases with depth. Upper
  (photic) zone supports photosynthesis.
• In ocean photic zone narrow but contains most
  organisms.

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• Aphotic zone sparsely populated.
• Benthic zone (bottom) organisms often depend on
  rain of dead organic matter (detritus) from
  above.

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Thermal stratification of lakes

• In temperate areas lakes are thermally stratified
  in summer and winter.
• Water densest at 4ºC so water at this temperature
  sinks through colder or warmer water.
• Thus, in spring and fall all water in lake mixes
  which redistributes nutrients throughout the lake.

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