Thursday, November 27, 2008


As the semester has progressed Dr. Baines has hammered the concept of tradeoffs into our brains. So it makes sense that she asked us the following question on a previous exam: “Explain why organisms are not able to adapt to ALL environmental conditions.” Here is my response: “This is due to the concept of tradeoffs and constraints. Some characteristics may allow individual organisms to be optimally equipped to survive in their own unique environments, however if the environment changes, then that individual might be at a disadvantage (in terms of survival and reproduction) because of their characteristic(s) which was or were previously beneficial. Previously advantageous characteristics might be detrimental to an organism in an environment which has changed drastically from the one they were well adapted to.” I have found the concept can be applied to a variety of situations. Specifically, an example which represents how tradeoffs work would be the changing composition of a tree population. The environment in which these trees exist has a varying moisture gradient (moist to dry). Of the three tree types within the environment, the Douglas-fir is the dominant (or numerous) tree type under moist conditions because it is a superior competitor. The next most numerous tree types under the same conditions would be the Port-Oxford Cedar, followed by the Pacific Madrone. However, as the environment becomes increasingly dry, it is the Pacific Madrone that becomes the dominant tree type (again, the most numerous) because it is well adapted to stressful environmental conditions (when water is limiting). During very dry conditions the Port-Oxford Cedar completely drops out of the picture while the Douglas-fir is found in relatively limited numbers. Therefore no single organism is well adapted to all environmental conditions and tradeoffs exist between stress tolerance and competitive aptitude.

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