Abstract:
We investigate population dynamics models given by difference equations with stochastic parameters. In the absence of harvesting, the development of the population at time points k=1,2,… is given by the equation X(k+1)=f(X(k)), where X(k) is amount of renewable resource, f(x) is a real differentiable function. It is assumed that at times k=1,2,… a random fraction ω∈[0,1] of the population is harvested. The harvesting process stops when at the moment k the share of the collected resource becomes greater than a certain value u(k)∈[0,1), in order to save a part of the population for reproduction and to increase the size of the next harvest. In this case, the share of the extracted resource is equal to ℓ(k)=min{ω(k),u(k)},k=1,2,…. Then the model of the exploited population has the form
X(k+1)=f((1−ℓ(k))X(k)),k=1,2,…,
where X(1)=f(x(0)),x(0) is the initial population size.
For the stochastic population model, we study the problem of choosing a control ¯u=(u(1),…,u(k),…) that limits at each time moment k the share
of the extracted resource and under which the limit of the average
time profit function
H(¯ℓ,x(0))≐limn→∞1nn∑k=1X(k)ℓ(k),where¯ℓ≐(ℓ(1),…,ℓ(k),…),
exists and can be estimated from below with probability one
by as a large number as possible.
If the equation X(k+1)=f(X(k)) has a solution of the form X(k)≡x∗,
then this solution is called the equilibrium position of the equation.
For any k=1,2,…, we consider random variables A(k+1,x)=f((1−ℓ(k))A(k,x)),B(k+1,x∗)=f((1−ℓ(k))B(k,x∗)); here A(1,x)=f(x),B(1,x∗)=x∗.
It is shown that when certain conditions are met, there exists a control ¯u
under which there holds the estimate of the average time profit
1mm∑k=1M(A(k,x)ℓ(k))⩽H(¯ℓ,x(0))⩽1mm∑k=1M(B(k,x∗)ℓ(k)),
where M denotes the mathematical expectation.
In addition, the conditions for the existence of control ¯u are obtained
under which there exists, with probability one, a positive limit to the
average time profit equal to
H(¯ℓ,x(0))=limk→∞MA(k,x)ℓ(k)=limk→∞MB(k,x∗)ℓ(k).
Keywords:
stochastic model of the population subject to harvesting, average time profit, optimal exploitation.
Citation:
A. V. Chernikova, “About existence of the limit to the average time profit in stochastic models of harvesting a renewable resource”, Russian Universities Reports. Mathematics, 27:140 (2022), 386–404
\Bibitem{Che22}
\by A.~V.~Chernikova
\paper About existence of the limit to the average time profit in stochastic models of harvesting a renewable resource
\jour Russian Universities Reports. Mathematics
\yr 2022
\vol 27
\issue 140
\pages 386--404
\mathnet{http://mi.mathnet.ru/vtamu273}
\crossref{https://doi.org/10.20310/2686-9667-2022-27-140-386-404}
Linking options:
https://www.mathnet.ru/eng/vtamu273
https://www.mathnet.ru/eng/vtamu/v27/i140/p386
This publication is cited in the following 1 articles:
M. S. Voldeab, “Svoistva srednei vremennoi vygody dlya veroyatnostnykh modelei ekspluatiruemykh populyatsii”, Vestnik rossiiskikh universitetov. Matematika, 28:141 (2023), 26–38