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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.
Note: all of these activities
can be done using the offspring of
Brassica rapa and Pieris rapae that result from studying their
life cycles in
the “Brassica & Butterfly System.”
You can follow
along online and Track Our Progress with “Assessing
Variation” and “Selective
Herbivory.”
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