Life Science: Field Population System
The Field Population System
The Essential Science for Teachers Field Population System is designed to demonstrate concepts that are fundamental to understanding biological evolution. It is a companion to the videos for Sessions 5 (Variation, Adaptation, and Natural Selection) and 6 (Evolution and the Tree of Life).
The name is derived from the system that it is meant to simulate: a field in which one or more plant populations grow. In this type of natural setting, the individuals within such populations would be expected to vary in numerous ways. In the face of myriad factors that affect survival, some variants would be expected to survive better than others do. Through natural selection, these variants would be likely to leave proportionately more offspring. If this continued over many generations, the population would “evolve” — that is, the successful variants would become more common.
Essential Science for Teachers has suggested two activities to illustrate how these concepts are connected. The first, “Assessing Variation,” sets the stage for the second, “Selective Herbivory.” In the first activity, Fast Plants and turnips — both members of the same Brassica rapa species — are observed for variation as they grow. In “Selective Herbivory,” a population of both of these varieties of Brassica rapa is introduced to a voracious herbivore: the larvae of the cabbage white butterfly Pieris rapae. This activity involves observing feeding behavior of the larvae and hypothesizing about how variation in the plant population might cause certain variants to be selected over others.
“Salt Of The Earth” models what happens to a population when its physical environment changes. In this case, plants are subjected to salt in their water. The impact of this treatment on survival and reproduction is assessed and followed by selective breeding (i.e., artificial selection) of those variants that survive better than the others. While this activity is specific for salt as a variable, it can be modified to test the impact of any number of environmental changes. And, while becoming familiar with selective breeding principles, you can continue to understand how evolution through natural selection works.