# Fish population- project help!

• Jun 5th 2010, 11:32 AM
bridget24
Fish population- project help!
Any help on this would be appreciated!! Even if its just one of the parts of the question or any help at all! (ps. please give as much explanation as possible!)

If P(t) denotes a fish population at time t, then the model to be considered ishttp://s3.amazonaws.com/answer-board...1550009322.gif
where r, K, A, P are positive constants. This model is more realistic in two aspects: it has a fixed point at P=0 for all values of the parameters, and the rate at which fish are caight decreases with P. This is plausible- when fewer fish are available, it is harder to find them so the daily catch drops.

(A)
Compare (by plotting) the harvesting rate in this model with the constant harvesting rate H and linear rate HP(t). Give a biological interpretation of the parameter A; what could it measure?(B) In order to analyze this differential equation, first we reduce the number of parameters, by using the following dimensionless variables:http://s3.amazonaws.com/answer-board...3112503098.gif

By applying the chain rule http://s3.amazonaws.com/answer-board...9362504887.gif, show that the system can be rewritten in dimensionless form ashttp://s3.amazonaws.com/answer-board...2175009866.gif. In this way, the new equivalent system has only two parameters. From now on, we are going to work with the dimensionless system.

(C)
Assume h = 0.2 . Analyze the number of fixed points and their stability properties as parameter a varies. Explain the long term behavior of the population in each case. Plot in the ax plane the fixed points vs. a (bifurcation diagram). Can you pinpoint some values of a where important changes in the behavior of the system happen? Such values of a are called bifurcation points. What type of bifurcations do you notice (pitchfork, saddle-node, or transcritical)? Give an interpretation of this situation.

(D) Assume now that a = 0.2 . Analyze the number of fixed points and their stability properties as parameter h is varied. Explain the long term behavior of the population in each case. Plot in the hx plane the fixed points vs. h (bifurcation diagram). Can you pinpoint some values of h where important changes in the behavior of the system happen? What type of bifurcations do you notice? Give an interpretation of the situation.
• Jun 5th 2010, 02:20 PM
mr fantastic
Quote:

Originally Posted by bridget24
Any help on this would be appreciated!! Even if its just one of the parts of the question or any help at all! (ps. please give as much explanation as possible!)

If P(t) denotes a fish population at time t, then the model to be considered ishttp://s3.amazonaws.com/answer-board...1550009322.gif
where r, K, A, P are positive constants. This model is more realistic in two aspects: it has a fixed point at P=0 for all values of the parameters, and the rate at which fish are caight decreases with P. This is plausible- when fewer fish are available, it is harder to find them so the daily catch drops.

(A) Compare (by plotting) the harvesting rate in this model with the constant harvesting rate H and linear rate HP(t). Give a biological interpretation of the parameter A; what could it measure?(B) In order to analyze this differential equation, first we reduce the number of parameters, by using the following dimensionless variables:http://s3.amazonaws.com/answer-board...3112503098.gif

By applying the chain rule http://s3.amazonaws.com/answer-board...9362504887.gif, show that the system can be rewritten in dimensionless form ashttp://s3.amazonaws.com/answer-board...2175009866.gif. In this way, the new equivalent system has only two parameters. From now on, we are going to work with the dimensionless system.

(C) Assume h = 0.2 . Analyze the number of fixed points and their stability properties as parameter a varies. Explain the long term behavior of the population in each case. Plot in the ax plane the fixed points vs. a (bifurcation diagram). Can you pinpoint some values of a where important changes in the behavior of the system happen? Such values of a are called bifurcation points. What type of bifurcations do you notice (pitchfork, saddle-node, or transcritical)? Give an interpretation of this situation.

(D) Assume now that a = 0.2 . Analyze the number of fixed points and their stability properties as parameter h is varied. Explain the long term behavior of the population in each case. Plot in the hx plane the fixed points vs. h (bifurcation diagram). Can you pinpoint some values of h where important changes in the behavior of the system happen? What type of bifurcations do you notice? Give an interpretation of the situation.

This looks like something that counts towards your final grade. MHF policy is to not knowingly help with such work. It's meant to be the student's own work, not the work of other people.