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Lecture 2

Lecture 2 - The Physical Environment

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Biology 2483A
Hugh Henry

LECTURE 2: THE PHYSICAL ENVIRONMENT Case Study: Salmon Decline  Potential causes of salmon declines in the North Pacific Ocean: o Dam construction o Sediment from logging operations o Water pollution o 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.  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.  The physical environment ultimately determines where organisms can live, and the resources that are available  Thus, understanding the physical environment is key to understanding all ecological phenomena Climate  Weather: Current conditions—temperature, precipitation, humidity, cloud cover  Climate: Long-term description of weather, based on averages and variation 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 2nd 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  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  The atmosphere contains greenhouse gases that absorb and reradiate the infrared radiation emitted by Earth.  These gases include: o Water vapor (H O)2 o Carbon dioxide (CO )2 o Methane (CH ) 4 o Nitrous oxide (N O2  Without greenhouse gases, Earth’s climate would be about 33°C cooler. Latitudinal Differences in Solar Radiation at Earth’s Surface  Amount of energy per square meter coming in at the equator is much higher than that of the amount of energy coming in at the poles  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 Differential Solar Heating of Earth’s Surface  Pockets of warm air rises up, causing it to expand and cool  Moisture can no longer be retained, thus producing rain  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 Global Atmospheric Circulation Cells and Climatic Zones  Polar cells, Ferrell cells, and Hadley cells result in the three major climatic zones in each hemisphere – tropical, temperate, and polar zones  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 rotations of the Earth – the Coriolis effect  Water has a higher heat capacity than land – it can absorb and store more energy without changing temperature  Summer: air over oceans is cooler and denser, so air subsides and high pressures develop over the oceans  Winter: air over continents is cooler and denser; high pressure develops over continents  These are known as semi-permanent high and low pressure cells  Prevailing wind patterns in July: o Over land – low pressure systems o Over water – high pressure systems  Prevailing wind patterns in January: o Over water – low pressure systems o Over land – high pressure systems  Major ocean surface currents are driven by surface winds, so patterns are similar  Speed of ocean currents is about 2 – 3% of the wind speed  Ocean currents affect climate, the warm Gulf Stream warms the climate of Great Britain and Scandinavia  At the same latitud
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