# Persistence in Stochastic Lotka--Volterra food chains with intraspecific competition

## TL;DR

This paper analyzes the persistence and extinction of species in a stochastic Lotka-Volterra food chain with intraspecific competition, providing criteria based on invasion rates and extending previous work to include predator intraspecific competition.

## Contribution

It introduces a comprehensive analysis of stochastic food chains with intraspecific competition, classifying species persistence using invasion rates and extending results to degenerate noise cases.

## Key findings

- Classified species extinction and persistence based on invasion rates.
- Provided criteria for food chains of length up to 3.
- Extended analysis to both non-degenerate and degenerate noise.

## Abstract

This paper is devoted to the analysis of a simple Lotka-Volterra food chain evolving in a stochastic environment. It can be seen as the companion paper of Hening and Nguyen (J. of Math. Biol. `18) where we have characterized the persistence and extinction of such a food chain under the assumption that there is no intraspecific competition among predators. In the current paper we focus on the case when all the species experience intracompetition. The food chain we analyze consists of one prey and $n-1$ predators. The $j$th predator eats the $j-1$st species and is eaten by the $j+1$st predator; this way each species only interacts with at most two other species - the ones that are immediately above or below it in the trophic chain. We show that one can classify, based on the invasion rates of the predators (which we can determine from the interaction coefficients of the system via an algorithm), which species go extinct and which converge to their unique invariant probability measure. We obtain stronger results than in the case with no intraspecific competition because in this setting we can make use of the general results of Hening and Nguyen (Ann. of Appl. Probab.). Unlike most of the results available in the literature, we provide an in depth analysis for both non-degenerate and degenerate noise. We exhibit our general results by analysing trophic cascades in a plant--herbivore--predator system and providing persistence/extinction criteria for food chains of length $n\leq 3$.