05.04 Population Change: Field Excursion

We are just about close enough to land get ready! It is time to make some observations.

Let's take a closer look at the island and find out about one big bug of a problem they have!             

A Bug of a Problem!

Look what we found! Yuck! This is not a pretty bug and we have learned that it is eating a lot of the plants.

The Galapagos Conservation Trust had to come up with a way to try to get rid of this pesky insect named the cottony cushion scale.  The trust wanted to find the best way possible to rid the islands of these insects so they brought in a natural predator the lady bug!

The lady bug was introduced a few years ago and the lady bug is doing a great job.  There were three different colors of lady bugs that were introduced to the island. They were red, black, and spotted.  I wonder what the population of ladybugs is like today. Do you think they are all spotted now or maybe all black?  I wonder has the population remained the same or changed over time.

Imagine all those lady bugs!  We know that by examining the genes of individuals we can make predictions about future generations.  I wonder if we could use this idea to learn what our population of lady bugs looks like today.

How Do Populations Change?

Much of what we know about populations is due to research done in the early 20th Century. Two important scientists, Godfrey Hardy and Wilhelm Weinberg, came up with a mathematical model to show what the genetics of populations would look like under certain conditions. They recognized that if conditions remained constant populations would not change.

1. Random Mating
   Mating is rarely totally random. Most species select mates based on certain traits like size or appearance.  It is also necessary that all members in the population breed and produce the same numbers of offspring.
2. Large Population
   In small populations there may be certain alleles present by chance. They would likely be passed on and become very prominent if the population is small.  Larger populations would have a lesser chance of being affected.
3. No Movement of Individuals
   No individuals can enter or exit the population. These alleles present must remain constant with none added or lost. Remember that extinctions remove genes from a population and macroevolution creates new species therefore adding genes to a population.
4. No Mutations
   A mutation, or genetic mistake, would cause a change in the genetic makeup of an individual. This would be passed on through generations and alter the genetic makeup of the population.
5. No Natural Selection
   Natural selection tells us that individuals with traits that are favorable will be more likely to survive and have more offspring. These traits over time will become more prominent in the population.

When there is no change in a population it is said to be at equilibrium. We call this equilibrium the Hardy-Weinberg equilibrium which states that if all of the above conditions are met populations will remain stable with no change over time.

Before you move on let’s check to be sure you understand what makes populations change. When you answer the question correctly a ladybug will appear on your tree. Keep the lady bugs coming…remember we need them to keep down the populations of pesky insects on the island!

Text Version

It is time to move to the Travel Log Tab.

Honors students get your gear together for our excursion. When you are all set, move to the Honors Tab.