Ecosystems and Changes: Investigation 5

Interactions in Nature

Previous Investigations developed the concept of interactions between organisms in an ecosystem and between organisms and the physical properties of their environment. In Investigation Three, students were introduced to the important concepts of adaptation and natural selection by performing experiments to see how “beak” structure in model birds affected their survival under changing environmental conditions. Importantly, it was emphasized that natural selection takes place in nature over vast periods of time.

In the bird feeding simulation in Investigation Three, for example, students were told that a period of one million years passed before the food source (split peas and oat cereal) changed. The concept of the passage of vast quantities of time is extremely important in explaining how natural selection actually works. This is because adaptation is an extremely slow process, as the modification of the prevalence of adaptive structures in the population of a species takes place over hundreds and thousands of generations. To get a sense of the extreme periods of time that have passed in the Earth’s 4.5 billion year history, examine the time chart below. Look at how recent humans have appeared. On a geological time-scale, it was only yesterday! You can click on this image to open a large copy of it in a new window to examine it more closely.

In this Investigation, students will study the impact of rapid environmental changes caused by pollution. Recall that a pollutant was defined as any harmful material released into the environment. Students were also introduced to the notion that pollutants may actually be compounds that are naturally found in the environment (e.g. carbon dioxide gas), but which are released in excess amounts.

How is the process of natural selection impacted by pollution? Pollution causes detrimental environmental changes to occur so quickly that populations of organisms simply don’t have time to adapt to them (because many generations are required in order to shift the genetic prevalence of adaptive traits). Therefore, pollutants can have an immediate effect on organisms in an ecosystem.

Pollution can cause death or reductions in numbers of organisms in a species, or in some cases, cause the extinction of a species in a relatively short period of time. In this Investigation, students will first see how animals must compete with one another for resources in the ecosystem, and then conduct experiments that model the impact of pollution on a rabbit population. Finally, students will work with a model that examines the impact on the polluted rabbit population on one of their predators, the bobcat – further demonstrating the concept of interdependence in an ecosystem.