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Article Summaries for BIO120


Department
Biology
Course Code
BIO120H1
Professor
Paul Thompson

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1 introduction to the basic drivers of climate
Climate is the long term prevailing weather determined by temperature and precipitation
- Largest determinant of life in a region
Long term changes in climate are due to changes in intensity and distribution of solar radiation
Sunlight and Atmospheric Ciruclations
Sunlight intensity is key in climate energy from the sun is not evenly distributed throughout earth
- Higher latitudes receive less solar energy
The different orientation of the earth as it orbits the sun creates seasons
- Tropics have minor temperature changes their seasons are characterized by the presence or absence of
rain
- Both hemispheres have equal solar input during spring and fall equinox
The sun is most intense at the equator this warms up the air, making it less dense, and causes it to rise
- The warm arm rising in the tropics is wet, as it rises and cools, the water condenses and falls as rain
- Sunlight also creates winds that push the now dry tropical air away from the equator
Descends at 30 degrees north or south and absorbs moisture from the ground, creating dry areas
- At 60 degrees, the air rises again and precipitates
- Some of the cold, dry, rising air flows to the poles, absorbs moisture, and create cold polar climates
Oceanic Currents
Wind is also generated through earth’s rotation (east and westward winds)
- Warm tropical water carry heat on the east side of continents to the poles, and cold water is forced down
the west side from the poles
Brings temperate climates to areas away from tropics
- Melted ice caps flow deep underwater towards the equator
Oceanic currents depend on earth’s rotation, and temperature differences between the poles and the equation
- Current flow varies with depth
Wind and ocean currents redistribute heat
- 60% by atmospheric circulation, 40% by ocean currents
High heat capacity of water leads to the moderating effect along with heat redistribution of heat by currents,
creates mild climates
Coastal regions are wet, continental regions are dry (They lack bodies of water to recharge moisture)
- E.g. mountain ranges force air to rise, cool, and precipitate on the windward side
Consequently, the dry air descends on the leeward side and absorbs ground moisture
Creates a dry and arid rain shadow
Microclimates are the variation in physical structure of an area
- Due to different ground colour, vegetation, etc.
El Nino: usually winds blow strong from east to west, carrying with it the warm surface water. This warm water
piles around the west pacific, and the cold water rises in the east to replace it. As the winds decrease, the warm
water starts pooling around the east as well, which then decreases the winds even more (positive feedback)
- Consequences: precipitation in the eastern pacific
Flooding in north and south America, drought in Australia, Indonesia, and Africa
- Typical arid regions become wet and experience a population boom in Americas
Causes an increase in diseases and viruses
- Marine life: cold water rising brings nutrients as well, with El Nino, the nutrient supply is cut.
Phytoplankton declines and marine populations decline
2 Terrestrial Biomes
Biomes differ most in vegetation, and are defined by temperature and rainfall
Warm and wet climates cool and dry climates

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- Decrease in height, density, and species diversity of plants
Raunkiaer classified life form based on the perannating organ location on the plant
Climate regions are classified into biomes
Tropical
- centered around equator
- little seasonal variation
- high rainfall, biodiversity, and productivity
- poor, phanerotype dominated soils
- high decomposition rates due to heat and moisture (and mycorrhizae)
- contains ½ of terrestrial species on Earth
Savanna
- lower rainfall, longer dry seasons
- dominated by grasses and small trees
- transition from tropical forests to deserts
- repetitive fires releases nutrients in dead plant
- decomposition is fast dung beetles break down animal droppings
- large herbivore diversity
Deserts
- between 15 and 30 degrees latitudes
- low precipitation and productivity
- different types: hot, cold, high elevation, rainshadow deserts
- perennial shrubs dominate
- annuals survive dry periods as seeds
Grassland
- occur in the interior of continents
- temperature varies largely over seasons hot summers and cold winters
- summer-peak precipitation
- transition into deciduous on wet side, and deserts on dry side
- fire, droughts, and grazing are the selective forces on plants
- world’s largest terrestrial animals can be found
Temperate
Deciduous
- high precipitation, high litter production, high biodiversity
- cool winters, warm summers
- trees that drop their leaves
Mediterranean
- divided into 5 separate regions
- hot dry summers, cool moist winters
- productivity decreases after 10-20 years due to collection of litter and biomass
- fire recycles nutrients
- lots of therophytes (plants that survive unfavourable conditions as seeds)
Northern Coniferous
- needle leaved, drought tolerant, evergreen trees
- long cold winters, short cool summers, precipitates mostly in summer
- low biodiversity and productivity
- permafrost, trees have shallow root systems dependent on mycorrhizae
- slow decomposition
- mid-hight latitudes
Tundra
- below freezing temperatures
- marshy
- lots of mosses and lichens (60% hemicryptophytes budding near surface)
- animals have extended hibernation or migrate
3 Physiological Ecology
Temperature and water availability significantly affects physiological ecology (how organisms are physiologically
adapted to their environments)
4 Physiological Optima and Critical Limits
Distribution limits are dependent on biotic and abiotic factors
Organisms have an optimal environmental range where fitness is optimized and critical limits where they can only
survive for short periods of time
Thermal Performance Curves

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Illustrate how well an organisms perform across a range of environmental conditions (such as temperature)
Eurythermal: wide thermal range ectotherms
- Behaviourally thermoregulate move into different environment
- No TNZ, but still has an optimal temperature
- Pejus temperatures are when performance begins to decline
Stenothermal: narrow thermal range (must thermoregulate) endotherms
- Have a thermal neutral zone where metabolism is constant and minimized
- Going lower or higher than the TNZ leads to elevation of metabolic rate to maintain body temp
E.g. shivering or seating
Mechanistic Bases of Thermal Curves
Lower critical thermal limits
Organisms can survive temperatures below their freezing point by preventing the formation of intracellular ice
Ectotherms and marine invertebrates prevent intracellular ice formation by:
- Using solutes such as glycerol to lower the freezing point of the cystosolic/intracellular fluid
- Encourage extracellular fluid to freeze
- Concentrate solute in extracellular fluid creates an osmotic pressure gradient that draws water from
inside the cells
E.g. wood frog ice formation stimulates transportation of glucose from organs to extracellular
spaces draws water out
- Using antifreeze proteins to limit size of ice crystals by coating them
Endotherms (mammals) undergo hibernation periods of reduced temperature and metabolism
Marginal Stability
Enzymes function with conformational shifts and depend on weak bonds
Highly temperature sensitive
Temperature change higher rate of biological reactions and reduced stability of enzymes
Reduction in Metabolic Efficiency
Rising temperatures weak bonds break in membrane proton barriers are weakened proton gradient is less
efficient less ATP is produced
Cellular Stress Response
At high temperatures, proteins lose their structure and unfold
Triggers the heat shock response heat shock proteins refold proteins that are damaged
Membrane Integrity
High temperatures phospholipid bilayer breaks barred between cell and environment is gone
Homeoviscous adaptation reordering membrane composition in ectotherms to maintain membrane fluidity
- A type of homeophasic adaptation any mechanism to ensure shape of membrane
Upper Thermal Limit
Neuromuscular coordination is lost
Distributional Limits
In the rocky coast, different levels contain different organisms growing in horizontal bands
Upper distribution limit is set by abiotic tolerance
Lower distribution limit is set by biotic interactions (competition for space, predation)
The performance curve or each organism on different vertical zones vary
5 Homeostatic Processes for Thermoregulation
Two major types:
- Poikilothermy cold blooded ectotherms that can’t produce body heat and instead conform to the
outside environment
Can behaviourally thermoregulate by moving into different environments
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