The Physical Environment

Introduction

The physical environment can have a profound influence on ecology at a variety of levels. For example, the physical environment can act as a strong selective presssure to produce adaptations or can influence the rates of nutrient cycling through an ecosystem. For our simple purposes here, the two most important components of the physical environment are temperature and precipitation. I suggest that we can predict a lot about what is going on ecologically in an environment if we know something about temperature and precipitation patterns.

From watching the nightly news we all know how difficult it is for the local weatherperson to accurately predict what the weather is going to be like tomorrow. Fortunately, it is much easier to understand broad patterns of variation in temperature and precipitation.

Temperature



The dominant global temperature pattern is that it tends to get cooler as you move away from the poles. The cause of this is relatively simple. Because the earth is so far from the sun, the light rays hitting the earth are basically paralell to each other. Because of the curvature of the earth, sunlight hitting the earth near the equator falls over a smaller area than sunlight hitting near the poles. Because the same amount of light energy is hitting a smaller area near the equator, the concentration of energy/area is greater near the equator than the pole thus resulting in higher temperatures.

Elevation is another factor that influences global temperatures. Because there is less insulating atmosphere above areas of high elevation temperatures tend to decrease as you go up in elevation.

Large bodies of water can mediate temperature variations. For example, seasonal and daily variation in temperatures are much lower in areas near the ocean (maritime climates) than they are in areas far from the ocean (continental climates).

Global temperature patterns can also be affected by patterns of ocean circulation. For example, the west coast of continents are often cooled by cool water flowing from the poles to the tropics while the east coasts of continents can be warmed by warmer water from the tropics to the poles (e.g., the Gulf Stream). If you have ever been to the beach in southern California you surely noticed how cold the water was; east coast beaches at similar latitudes have much warmer water.

Precipitation

In order to understand global precipitation patterns you need to understand global patterns of atmospheric circulation. Hopefully, after studying the article on atmospheric circulation you will be able to explain-

1. why there tends to be high precipitation in tropical regions and

2. why precipitation tends to be low at 30 degrees North and South of the equator.

Patterns of precipitation can also be influenced by the presence of mountains. As air masses containing moisture hit a mountain they are forced upward. Because rising air cools and cool air







holds less moisture, precipitation occurs on the windward side of mountains. Once the air mass has passed over the mountain in falls to lower elevations and gets warmer. Because most of the moisture has been lost as precipitation on the windward side of the mountain and the warmer air holds more moisture there is very little precipitation on the leward side of the mountain resulting in a "rainshadow desert".

Let's think about Lubbock!

Let's see if we can use our newfound understanding of some of the factors influencing temperature and precipitation to make predictions about what the climate should be like in Lubbock. What information do we need about the geographic location of Lubbock to help us understand the climate? First, we need to know the latitude; Lubbock is located approximately 33 degrees north. Second we need to know something about the proximity to the ocean. As an old beach boy, I can guarantee you that we are a long, long way from the ocean in Lubbock. Third, where is Lubbock in relation to mountains? Lubbock is located to the east of the southern extension of the Rockies.

Why is all of this important?

1. What can we learn from the latitude of 33 degrees North? This latitude is still close enough to the equator to be warm so we expect relatively high temperatures. Because Lubbock lies near the 30 degree zone of low precipitation we would predict relatively low precipitation. At 30 degrees North we would predict that Lubbock would receive predominately winds from the west.

2. From the continental location of Lubbock we would predict fairly extreme daily and seasonal fluctuations of temperatures.

3. Because Lubbock lies in the Westerlies most of the precipitation that is arriving in Lubbock comes from the Pacific Ocean. Because these winds have passed over the Rockies we would predict that Lubbock would lie in a rainshadow, again causing low precipitation.

How did we do. If anyone has ever been in Lubbock (especially in the spring time) you would know that the wind almost always blows in from the west. Temperatures are relatively warm but there is fairly large seasonal and daily variations in temperature. Lubbock has a semi-arid climate and receives on average about 18 inches of precipitation per year. Thus, with just a little bit of knowlege about the factors that influence global patterns of temperature and precipitation we were able to fairly accurately the climate in Lubbock. Thus, I would expect that organisms native to Lubbock should be well adapted to the low precipitation, continental climate of the region (the short grass prairie was the dominant vegetation type presettlement).

See use these patterns to understand climate in your town (note climate patterns in Texas are complicated in central and eastern Texas becasue of the influence of air masses coming up from the Gulf). Compare the temperature and precipitation of your town with that if very divergent locations around the globe.


Further Reading

If you would like some more detailed information about factors affecting climate and the atmosphere you can check out the Atmosphere Chapter in Michael Pidwirny's online Physical Geography textbook http://www.physicalgeography.net/fundamentals/contents.html.

Powerpoint Presentation

Click here to see the powerpoint presentation "Factors Influencing the Physical Environment".
http://www.slideshare.net/secret/EaVq4nm5KuSsBI

Expected Learning Outcomes

At the end of this course a fully engaged student should be able to

- describe global patterns of variation in temperature and precipitation and be able to explain the causes of these patterns

- describe the physical environment of the Rio Grande drainage and explain the causes of these conditions