Tutor profile: Amanda S.

Explain the importance of fire in a fire-adapted ecosystem.

Historically, fire has been suppressed, regardless of whether the cause was man or nature. It wasn't until 1988 when the catastrophic fire of Yellowstone revealed to scientists that the ecosystem was actually much healthier after the fire. Small, frequent, low intensity fires reduce fuel loads, stimulate new growth of grasses and shrubs, and recycle nutrients into the environment. In some cases, tree cones will only release their seeds when exposed to fire. If fire is suppressed, then the increased fuel load will cause natural fires to burn out of control and more intensely, which damages the ecosystem and also puts more lives in danger.

Describe the significance of a keystone species.

A keystone species maintains the checks and balances of an ecosystem. Their role is typically to regulate the next species in the trophic chain, maintaining the ecosystem in its optimal state. Without the keystone species, an ecosystem could potentially collapse. The sea otter is a prime example of a keystone species. Sea otters eat sea urchins, and if they did not, the sea urchins would increase in numbers and eat the sea kelp. Sea kelp provides food and shelter for other organisms within the environment, as well as sequester carbon dioxide from the environment.

Explain the differences between natural and artificial selection, and give one example of each.

Natural selection is the process by which traits that improve fitness are preferentially passed down to the next generation. Improving fitness means improving the number of offspring produced, so if a trait decreases fitness, there will not be offspring to pass the trait onto, and therefore the trait will disappear over time. The converse is true for traits that increase fitness, for example, as is seen in animals adapted for living on islands. They typically are smaller in size than their mainland counterparts, which is evidence that a smaller body size is more advantageous for island life, since space is a constraining factor. On the other hand, artificial selection occurs when humans manually select desirable traits, regardless of the fitness impact on plants. This is very evident in the development of modern corn. Corn originated as as small seed-producing grass, but humans started selecting plants which produced the biggest seeds. Over time, continuously only breeding plants with the largest seeds resulted in plants that produced a stable food source for humans.