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Lecture 2: "The Physical Environment"

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Biology 2483A
Hugh Henry

Ecology Lecture No. 2: The Physical Environment th Thursday September 13 , 2012 Introduction: - 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 circulation. 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
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