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Ecology Notes

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Biology 2483A
Hugh Henry

Ecology Notes Sept. 13/12 - Potential causes of salmon declines in the North Pacific ocean dam construction (interfere with salmon migrating), sediment from logging operations, water pollution, and overharvesting. But the conditions of oceans, where salmon spend most of their time as adults, have also been implicated (the problem has more to do with oceans than streams). 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. There is a lot of variability in salmon harvests from year to year, with abrupt increases and decreases in production. Mantua et al. (1997) found that periods of high salmon production in Alaska corresponded with period of low production in Oregon and Washington. They also found a correlation between salmon production shifts and sea surface temperatures. Spatial context is important not all pacific salmon were decreasing in numbers. It would switch from place to place. - 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. - Weather is the current conditions temperature, precipitation, humidity, cloud cover. Climate is the long-term description of weather, based on averages and variation measured over decades. Climatic variation includes daily and seasonal cycles (associated with changes in solar radiation as earth rotates on its axis), 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 CO2 and other gases that are emitted in the atmosphere due to human activities. These gases absorb and radiate energy back to Earths surface, creating a greenhouse effect. 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. Therefore, the physical environment must also be characterized by its variability over time, not just by average conditions, if we are to understand its ecological importance. - Earths energy balance: The sun is the ultimate source of energy that drives the global climate system. Of the incoming solar radiation, 19% is absorbed by the atmosphere, 49% is absorbed by land and water at the earths surface, and the rest is reflected back out of the atmosphere by clouds, aerosol, and earths surface. These energy gains from solar radiation must be offset by energy losses if earths temperature is to remain the same. Most of the solar radiation that is absorbed by earths surface is emitted to the atmosphere as infrared or longwave radiation (114%). The atmosphere and clouds also emit longwave radiation. Earths surface loses energy when water evaporates. The change from liquid water to water vapour absorbs energy and is a cooling process. The heat loss due to evaporation (evapotranspiration) is called latent heat flux (23%). Energy transfer from the warm air immediately above earths surface to the cooler atmosphere by convection and conduction is called sensible heat flux (7%). Earths surface releases more energy than it receives from direct solar radiation. But the atmosphere absorbs and re-radiates most of the longwave radiation emitted by the earth (95%) and the earths surface re-absorbs this. The atmosphere contains greenhouses gases that absorb and re-radiate the longwave radiation emitted by earth. These gases include water vapour (H2O), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Without greenhouse gases, earths climate would be about 33C cooler. The greenhouse effect is important to live, but increases in atmospheric concentrations of greenhouse gases due to human activities are bad and are altering earths energy balance, changing the climate system, and causing global climate change. - Latitudinal differences in solar radiation at earths surface: Near the equator, the suns rays strike earths surface perpendicularly. At the poles, the angle of the suns rays becomes steeper, so that thesame amount of energy is spread over a larger area of earths surface. Also, the amount of atmosphere the rays must pass through increases toward the poles, so more radiation is reflected and absorbed before it reaches the surface (it is absorbed back by the atmosphere). More solar energy is received per unit area in the tropics than in regions near the poles. This is why the equator is warmer than the poles. This difference in solar radiation is responsible for warm and cold fronts and storms (hurricanes). - When solar radiation heats the earths surface, the surface warms and emits infrared (longwave) radiation to the atmosphere, warming the air above the surface. The heating of earths surface varies with latitude, so this creates pockets of warm air surrounded by cooler air. Warm air is less dense than cool air (has fewer molecules per unit of volume), so it rises. This is called uplift. Atmospheric/air pressure decreases with altitude. Atmospheric pressure is the pressure exerted on a surface due to the mass of the atmosphere above it. As the warm air rises it expands (volume increases as pressure decreases) and it begins to cool (the molecules become farther apart and so dont collide as much, reducing the temperature). Cool air cannot hold as much water vapour as warm air, so the water vapour contained within it begins to condense into droplets and form clouds. The tropics receive the most solar radiation and therefore the most precipitation because they experience the greatest amount of surface heating, uplift of air, and cloud formation. The uplift of air in the tropics results in a low atmospheric pressure zone (because there is not as great a force or pressure being exerted on the earths surface, the air going up alleviates the pressure on the earth). When air masses reach the troposphere-stratosphere boundary, air flows towards the poles. This is because the stratosphere has warmer temperatures than the troposphere, and the rising warm air stops rising once it reaches the stratosphere and begins to flow toward the poles. Eventually, this poleward-moving air cools as it exchanges heat with the surrounding air. Once the air reaches a temperature similar to that of the surrounding atmosphere (a cool temperature), it descends towards ea
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