Ecosystems and Changes: Investigation 4

Environmental Changes

In the previous Investigation, students were introduced to the concept that certain structures and behaviors reflect adaptations of an organism to live in its environment. They also learned that when the environment changes, not all organisms have adaptations that permit them to survive as well as others. As we continue our study of ecosystems and adaptations, students will now perform experiments that demonstrate the ultimate consequence of a species not possessing appropriate numbers of individuals with adequate adaptations to permit survival in a changing environment – extinction.

There are a number of ways in which a species can become extinct. One way is the occurrence of a major, often violent change in the environment, such as widespread volcanic eruptions or an asteroid impact on the surface of the Earth. Such “catastrophes” have occurred numerous times during geological history, many with corresponding evidence in the fossil record of the extinction of numerous species. Such catastrophic events result in extremely rapid changes in the environment and rapid extinctions. Even if certain species are not immediately killed off by the violence of the catastrophe, the environmental changes that accompany the change are so rapid, that populations simply don’t have time (generations) to adapt. This is the prevailing idea of how the dinosaurs became extinct 65 million years ago.

Another way a species may become extinct is by slow environmental changes that, over very long periods of time, perhaps millions of years, favor one species, with its particular environmental adaptations, over others that it may compete with for food, shelter, or other resources. Therefore, several important factors are in play in this type of extinction.

The first is change. Something in the environment must change – such as rainfall, temperature, amount of predators, amount or type of food, availability of shelter, etc. Second, the change must be of a sort that has an effect on the ability of the species to survive and reproduce. For example, if a species is capable of surviving in a wide range of temperatures, slow changes in environmental temperature would be unlikely to cause its extinction. If, however, the environmental temperature change also causes the species’ essential food source to disappear, the species itself may face extinction if it is unable to survive by changing to another food source.

Natural Selection: Survival of the Fittest

This brings us to another important factor in the process of extinction, competition. Competition occurs when two or more species require the same environmental resource (such as food type, for example). The concept of competition suggests that when species compete, the one best adapted for the competition will “out-compete” the other species. Thus, the result of the competition is that one species tends to benefit at the expense of another. If driven far enough, extinction of the least “fit” species may occur.

This idea of the “survival of the fittest” was introduced by the English biologist, Charles Darwin, in the second half of the nineteenth century. Darwin referred to this process as natural selection, to distinguish it from the artificial selection man performs when breeding new forms of agricultural crops and animals. The idea of competition and natural selection in the process of extinction is crucial. Without competition, a species or population may have enough time to adapt to a changing environment. On the other hand, if a competing species is already better adapted to the new environment, the other species may simply not be given enough time to adapt (or evolve).

Extinction

An important point to consider about extinction – one that students may have difficulty with – is that once a species becomes extinct, it is permanently gone from the face of the Earth forever. It does not exist in some low numbers, hidden away awaiting environmental conditions to change again to something more favorable. It is not dormant, sleeping, latent, or inactive. It no longer exists alive on the face of the Earth. Even if environmental conditions were to change to suit its particular physical and behavioral adaptations perfectly, it would be irrelevant – once extinct, it is no longer has anything to do with the process of life whatsoever. Below are just a few of the animals that are facing extinction today. Unfortunately, there are many more. These were chosen since they may be familiar to students.

Students will become familiar with this aspect of extinction in the experiments they will perform in this Investigation. They will simulate beak types of birds and see how the different beak structures are able to compete for food as the type of food changes through four moments in time, millions of years apart. The “loser” at each stage drops out – it no longer takes part in the rest of the experiment.