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More about op+miza+on
UBC Math 102
Course Calendar: Quiz today
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You are here
Announcements
• How to study for my midterms? – Try out prac+ce problems and more problems.. Some in course notes, some on webwork
– Try out “test type problems” posted at the end of each of my lecture slides
– Go over concepts you had trouble with – Prac+ce your basic skills: algebra, rules of differen+a+on, graphing
– Go over HW problems/quiz problems you had trouble with UBC Math 102
Mathletes:
• You goSa get into the water to learn to “swim”
• Math is not a spectator sport
UBC Math 102
More op+miza+on
The growth rate (births per unit +me) and the mortality rate (deaths per unit +me) depend on popula+on size x. Net growth rate = growth rate -‐ mortality rate
From last +me: Type I, II, III predator responses
• C. S. “Buzz” Holling hSps://en.wikipedia.org/wiki/C._S._Holling
hSps://en.wikipedia.org/wiki/Func+onal_response
Which of these statements are true? Type I, II, III predator responses
(A) Type I: give me more! I’m always hungry! (B) Type III predators will con+nue to eat prey at a
rate propor+onal to the prey density (C) Type II Predators have trouble finding their prey
at low densi+es. (D) Type I: I can’t eat any more! (I’m too full). (E) Type II: I get hungry around Midnight.
Ladybugs ea+ng aphids M. P. Hassell, J. H. Lawton and J. R. Beddington (1977) Sigmoid Func+onal Responses by Invertebrate Predators and Parasitoids J Animal Ecology, 46, (1977), 249-‐26
hSps://www.youtube.com/watch?v=oTnTWre488s
UBC Math 102
Last week: Find the prey density such that P(x)=G(x)
growth rate mortality rate Find the popula+on size x such that F(x) is as small as possible. (Note: F(x) can be nega+ve.)
Now: minimize Net Growth Rate F(x)= G(x)-‐P(x)
Detailed set-‐up X= aphid popula+on P(x) = preda+on mortality = (number of aphids eaten per hour) G(x) = reproduc+on rate (number of aphids born per hour)
Sketch the func+on F(x)= G(x) – P(x).
Sketch the func+on F(x)=G(x)-‐P(x)
• My sketch looks like: (A) (B) (C) (D)
My sketch looks like:
• Both func+ons:
• Subtrac+ng:
UBC Math 102
Minimiza+on
We found out (in class) that this calculus problem leads to a 4th order equa+on in x, so we abandoned this problem to make +me for the quiz. However, we can easily do a closely related problem with “Type II” predator, that is for preda+on mortality given by
UBC Math 102
Revised problem: Find the popula+on x for which Net Growth Rate F(x)=G(x)-‐P(x) is as small as possible where Based on sketch, expect a local min for F(x).
Deriva+ve and cri+cal points
UBC Math 102
Cri+cal pts, con+nued
UBC Math 102 Based on sketch, this is a local min. It turns out (see graph) that F is nega+ve, so that the aphids are dying at a faster rate than being born at this popula+on density
Sketch the graph of the following func+on using calculus
(We did not have +me to do this in class in detail. Try it for yourself, then see the solu+on on following slides.)
UBC Math 102
Overall sketch
UBC Math 102
Cri+cal points
•
UBC Math 102
Type of cri+cal points:
UBC Math 102
Actual graph:
•
UBC Math 102
Related problem
Related test problems (2014 MT2)
A farmer is building a rectangular enclosure for a pemng zoo. She wants the enclosure to have an area of 100 m2 and as large a perimeter as possible. For the comfort of the animals, both the width and the length of the enclosure should be no less then to 2 m. What is the maximum possible perimeter?
UBC Math 102
Solu+on
Solu+on