A sequences that arises in ecology as a model for population growth is defined b

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ID: 2836544 • Letter: A

Question

A sequences that arises in ecology as a model for population growth is defined by the logistic

equation

where Pn measures the size of the population of the n-th generation of a single species. To

keep the numbers manageable, Pn is a fraction of the maximal size of the population, so

0 ? ?? ? 1. Notice that the form of this equation is similar to the logistic differential

equation. The discrete -model with sequences instead of continuous functions- is preferable

for modeling insect populations, where mating and death occur in a periodic fashion.

An ecologist is interested in predicting the size of the population as time goes on, and ask the

question: Will it stabilize at a limiting value? Will it change in a cyclical fashion? Or will it

exhibit random behaviour?

Write a program to compute the first n terms of this sequence starting with an initial

population P0, where 0 < ?? < 1. Use this program to do the following

1. Calculate 20 or 30 terms of the sequence for ? po=1/2

and for two values of k such that

1 < ? < 3. Graph the sequences. Do they appear to converge? Repeat for a different

value of P0 between 0 and 1. Does the limit depend on the choice of P0? Does it

depend on the choice of k?

2. Calculate terms of the sequence for a value of k between 3 and 3,4 and plot them.

What do you notice about the behaviour of the terms?

3. Experiment with values of k between 3,4 and 3,5. What happens to the terms?

4. For values of k between 3,6 and 4, compute and plot at least 100 terms and comment

on the behaviour of the sequence. What happens if you change P0 by 0,001? This type

of behaviour is called chaotic and is exhibited by insect populations under certain

conditions.

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