Ecology Lecture No. 2: The Physical Environment
Thursday September 13 , 2012
- Certain Earth regions have organisms that have adapted for survival for millions of years. The physical
environment ultimately determines where organisms can live, and the resources that are available.
Thus, understanding the physical environment is the key to understanding all ecological phenomena.
The Salmon Decline:
- The life of a salmon is quite an adventure from the moment they are born in small streams they
journey to the ocean, only to return to their freshwater birthplace. They are a very economically
important species in our society. The potential causes of salmon declines in the North Pacific Ocean
include: dam construction, sediment from logging operations, water pollution, and overharvesting.
- But the conditions of oceans, where salmon spend most time as adults, have also been implicated.
Hare and Francis (1994) studied fish harvest records and showed alternating periods of high and low
production associated with climatic variation in the North Pacific. The trends in salmon populations are
intimately connected to climate changes.
-Mantua et al. (1997): Periods of high salmon production in Alaska corresponded with periods of low
production in Oregon and Washington. They also found a correlation between salmon production shifts
and sea surface temperatures. This reveals to us the importance of spatial context in the sense that all
Pacific salmon populations were not affected.
Weather & Climate:
-Weather - Current conditions; temperature, precipitation, humidity, cloud cover, etc.
-Climate – Long-term description of weather, based on averages and variations measured over decades.
- Climatic variation includes daily and seasonal cycles, as well as yearly and decadal cycles. Long-term
climate change results from changes in the intensity and distribution of solar radiation. Current climate
change is due to increased CO a2d other gases in the atmosphere due to human activities. Climate
determines the geographic distribution of organisms. Climate is characterized by average conditions; but
extreme conditions are also important to organisms because they can contribute to mortality.
Solar Radiation & Earth’s Energy Balance:
- The sun is the ultimate source of energy that drives the global climate system. Energy gains from solar
radiation must be offset by energy losses if Earth’s temperature is to remain the same. Earth’s energy
balance is initiated with incoming energy from the sun, reflected by the Earth’s surface (only about half
of the sun’s radiation is actually absorbed by Earth). Much long-wave radiation is emitted from the
Earth’s surface. Greenhouse Gases:
-Greenhouse gases determine the extent to which long-wave radiation from Earth leaves the
atmosphere. Greenhouse gases in the atmosphere include: CO , metha2e, nitric acid, and water vapor.
The atmosphere contains greenhouse gases that absorb and reradiate the infrared radiation emitted by
Earth. Without greenhouse gases, Earth’s climate would be about 33°C cooler.
Latitudinal Differences In Solar Radiation At Earth’s Surface:
- The Earth’s equator is warmer because the sun`s amount of energy is more concentrated at that
location than at the poles. On top of that, the Earth’s atmosphere actually absorbs some of the sun’s
energy. Solar radiation heats Earth’s surface, which emits infrared radiation to the atmosphere, warming
the air above it. Warm air is less dense than cool air, and it rises—this is called uplift. Air pressure
decreases with altitude, so the rising air expands and cools. This process controls rainfall and wind
Differential Solar Heating Of Earth's Surface:
- Tropical regions receive the most solar radiation and the most precipitation. Uplift of air in the tropics
results in a low atmospheric pressure zone. When air masses reach the troposphere–stratosphere
boundary, air flows towards the poles.
Tropical Heating and Atmospheric Circulation Cells:
-Within tropical regions, weather cells known as Hadley cells, circulate through the atmosphere
depending upon the pressure and temperature of the air present. Warm air alleviates pressure in the
atmosphere and elevates the Hadley cells to the sky. Cold air causes subsidence and intensifies the
pressure in the atmosphere, causing the Hadley cells to fall to Earth.
Global Atmospheric Circulation Cells & Climatic Zones:
-Globally, three types of weather cells circulate the atmosphere, each rotating in the opposite direction
to the one proximal: Hadley cells (in the tropics), Ferrell cells (in temperate regions) and polar cells (at
the poles). Working like gears, these three cells result in the three major climatic zones in each
hemisphere— tropical, temperate, and polar zones.
The Coriolis Effect:
- Areas of high and low pressure created by the circulation cells result in air movements called prevailing
winds. The winds appear to be deflected due to the rotation of the Earth—the Coriolis Effect. This is
generally what is observed in nature, but it is different on land than it is over oceans.
Prevailing Wind Patterns:
- Water has a higher heat capacity than land—it can absorb and store more energy without changing
temperature. During the summer, the air over ocean