CS 170: Computing for the Sciences and MathematicsAdministriviaConstrained GrowthUnconstrained GrowthRate of change of populationRate of change of populationDeathBehaviorSlide 9Death, part 2Behavior, part 2If population is greater than M…Continuous logistic equationsDiscrete logistic equationsIf initial population < M, S-shaped graphIf initial population > MEquilibriumStabilitySlide 19HOMEWORK!Constrained GrowthCS 170:Computing for the Sciences and MathematicsAdministriviaLast timeUnconstrained GrowthTodayUnconstrained GrowthHW3 assignedThursday’s class will be in P115Constrained GrowthPopulation growth usually has constraintsLimits include:Food availableShelter/”Room”DiseaseThese all can be encapsulated in the concept of “Carrying Capacity” (M)The population an environment is capable of supportingUnconstrained GrowthRate of change of population is directly proportional to number of individuals in the population (P)where r is the growth rate.rPdtdPRate of change of population D = number of deathsB = number of birthsrate of change of P = (rate of change of B) – (rate of change of D)dPdtdBdtdDdtRate of change of populationRate of change of B proportional to PdBdt rPdPdt rP dDdtDeathIf population is much less than carrying capacity, what should the behavior look like?No limiting pressure!BehaviorIf population is much less than carrying capacity, almost unconstrained modelRate of change of D (dD/dt)0dDdt 0dPdtdBdtDeathIf population is nearing the carrying capacity, what should the behavior look like?Death, part 2If population is less than but close to carrying capacity, growth is dampened, almost 0Rate of change of D larger, almost rate of change BdDdtdBdt rPBehavior, part 2For dD/dt = f(rP), multiply rP by something so thatdD/dt 0 for P much less than MIn this situation, f 0dD/dt dB/dt = rP for P less than but close to MIn this situation, f 1What is a possible factor f?One possibility is P/MdPdt rP dDdtIf population is greater than M…What is the sign of growth?NegativeHow does the rate of change of D compare to the rate of change of B?GreaterDoes this situation fit the model?Continuous logistic equationsdDdt(rP)PMdPdt(rP) (rP)PM r 1PMPDiscrete logistic equationsD D t D(t t) rP t t P t t MtP births deathsP rP t t t rP t t P t t MtP k(1P t t M)P t t , where k rtIf initial population < M, S-shaped graphIf initial population > MEquilibriumEquilibrium solution to differential equationSolution where derivative is always 0 M is an equilibrium point for this modelPopulation remains steady at that valueDerivative = 0Population size tends to M, regardless of non-zero value of populationFor small displacement from M, P MStabilitySolution q is stable if there is interval (a, b) containing q, such that if initial population P(0) is in that interval thenP(t) is finite for all t > 0P qP = M is stable equilibriumThere is an unstable equilibrium point as well…P = 0 is unstable equilibriumViolates P qHOMEWORK!READ Module 3.3 in the textbookHomework 3Vensim Tutorial #2Due NEXT MondayThursday class in P115 (Lab)Chance to work on HW #3 and ask
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