Estimation of total income with discounting for probabilistic models of population dynamics

A. A. Bazulkina

Vestnik rossijskih universitetov. Matematika, Tome 28 (2023) no. 143, pp. 217-226

Résumé

Models of homogeneous and structured populations given by differential equations depending on random parameters are considered. A population is called homogeneous if it consists of only one animal or plant species, and structured if it contains $n\geqslant 2$ different species or age classes. We assume that in the absence of exploitation, the dynamics of the population is given by the system of differential equations \begin{equation*} \dot{x}=g(x), \quad x\in\mathbb R^{n}_{+}\doteq\left\{x\in \mathbb R^{n}: x^1\geqslant 0 ,\ldots,x^n\geqslant 0\right\}. \end{equation*} At times $\tau_{k}=kd,$ where $d>0,$ $k=1,2,\ldots,$ random shares of the resource $\omega_{k}=(\omega_{k }^1,\ldots,\omega_{k}^n)\!\in\Omega\subseteq [0,1]^n$ are extracted from this population. If $\omega_{k}^i$ is greater than some value $u_{k}^i\in[0,1),$ then the collection of the resource of the $i$-th type stops at the moment $\tau_{k}$ and the share of the extracted resource turns out to be equal to $\ell_{k}^i\doteq\min(\omega_{k}^i,u_{k}^i).$ Let $C^{i}\geqslant 0$ be the cost of the resource of the $i$-th type, $i=1,\ldots,n,$ $X_k^{i}=x^{i}(kd-0)$ the quantity of the $i$-th type of resource at the time $\tau_k$ before collection; then the amount of income at the moment equals $Z_k\doteq\displaystyle\sum_{i=1}^n{C^{i}X_k^{i}\ell_{k}^i}.$ The properties of the characteristic of the total income, which is defined as the sum of the series of income values at the time $\tau_k,$ taking into account the discounting factor $\alpha>0$ are investigated: \begin{equation*} H_{\alpha}\bigl(\overline{\ell},x_{0}\bigr)=\sum_{k=1}^\infty{Z_k e^{-\alpha{k}}}=\sum_{k=1}^{\infty}e^{-\alpha{k}} \sum_{i=1}^{n}C^{i}X_k^{i}\ell_{k}^i, \end{equation*} where $\overline{\ell}\doteq(\ell_{1},\ldots,\ell_{k},\ldots),$ $x_0$ is the initial population size. The value of $\alpha$ indicates that the value of the income received later decreases. Estimates of the total income, taking into account discounting, made with probability one are obtained.

Détail

Keywords: structured population, total income estimate.