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BIO120H1 Lecture Notes - Convergence Zone, Atmospheric Circulation

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Ingrid L.Stefanovic

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Lecture 1 & 2 22:17
Organic life is distributed patchily, due to:
Abiotic factors
Physiological ecology (auto ecology)
Biotic factors
Population ecology
Community ecology
Abiotic (physical/chemical) factors: resources and conditions
Resources are exhaustible: nutrients, space, etc
Conditions are not exhaustible: temperature, pH, salinity, etc
Conditions vary across space and time; we envision gradients of conditions
Organisms perform best at certain levels, i.e., at certain portions of a gradient.
Species have ranges of tolerance along environmental gradients (e.g., optimal
conditions for the survival of a species) For a growth range, conditions must be
better than for the survival range; for reproductive ranges, conditions must be more
optimal than both.
Most important factors
For terrestrial plants:
Soil moisture
Nutrients (Nitrogen most important, then Phosphorous, then Potassium)
Herbivory, disease, pollinators, seed dispersers, mycorrhizal fungi
For aquatic plants:
Phosphorous is more important
For terrestrial animals:
Food and water
Habitat quality (cover, nesting sites)
Predation, disease
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For aquatic mammals:
Osmotic pressure
Atmospheric Circulation: Hadley cells make equatorial regions rainy
Low pressure areas = rainy weather i.e., in the tropics
Hadley cells: the idea that air circulates between cooling down as it rises and
heating up as it falls.
Inter-tropical Convergence zone: high rising air with precipitation following.
Variability between temperatures are more drastic in the northern hemisphere
because of greater land mass and less moisture.
Inter-tropical convergence zone shifts seasonally, producing rainy and dry seasons
in some parts of the tropics.
Monsoon: rainy season
Coupled cells + Coriolis effect = prevailing wind patterns
Ferrel Cell: some of the hot air from the Hadley cell travels into the Ferrel cell. The
Ferrel cell and the Hadley cell are coupled. They have air circulation in the opposite
Polar Cell: Coupled to the Ferrel cell in the same way that the Ferrel cell is coupled
to the Hadley cell.
Sailors tended to get stuck in the middle of the ocean on the inter-tropical
convergence zone (equator) where there wasnt much wind. Also called the
equatorial doldrums.
Coriolis effect: The wind that comes from the Hadley cells wants to travel due south,
but since the earth spins they ultimately end up travelling eastward (coming from
the west called westerlies; coming from the east called easterlies, travelling
Wandering Albatross: bird with the worlds largest wingspan only found in the
southern hemisphere because of the roaring 40s which were strong winds.
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