### Step 1: Expert Predictions

What will the zebra mussel population look like in 5 years?

Click on an expert to see his or her answer to this question. Read each expert’s prediction, then **click “Next”**.

#### Prof. Barrios

#### Prof. Nielsen

#### Prof. Cho

“Hello! I’m glad to meet the person who’s carrying out this important study! Here’s my model for zebra mussel population growth at Round Lake. As you can see from the graph, my model shows that the rate at which the population size (N) increases is proportional to the number of individual present, so the fastest growth will occur when the population size is largest.

An assumption of this model is that growth is not limited by external factors but only by the reproductive capacity of zebra mussels. I think this assumption is reasonable given conditions at Round Lake. In fact, I predict that the population will still be increasing by year 5 in your study.”

Predicted change in the population size (N) of zebra mussels in Round Lake over time (t) for the first five years.

“Hey there! I agree with professor Barrios, but to a point. My model also predicts that increase in population size (N) is proportional to the number of individuals currently in the population. But my model shows that external factors will slow down the growth rate as the population gets bigger.

I don’t think Barrios’ assumption of unlimited resources at Round Lake is valid. I think you’ll see the population level off during the 5 years of your study.”

Predicted change in the population size (N) of zebra mussels in Round Lake over time (t) for the first five years.

“Hi! Barrios’ and Nielsen’s models are good for describing how populations grow, however, I don’t think you’ll be able to tell which of their models fits your population. Right now, the number of zebra mussels in Round Lake is so low that the population will still be in a lag phase of growth during the five years of your study. It will look as if a small, constant number of new individuals will be added to the population every year.

The reason I predict this slow rate of growth is that zebra mussels reproduce by releasing gametes into the water. At low population densities, gametes won’t find each other.”

Predicted change in the population size (N) of zebra mussels in Round Lake over time (t) for the first five years.

Who do you think is right? **Click “Next” to investigate.**