Study on the Variability of the Sex Ratio of Sea Lamprey Based on the Improved Predator Model

The change in sex ratio in response to food availability is a unique ecological trait that distinguishes lampreys from many other aquatic species. This trait not only affects the reproductive dynamics of the lamprey population but also has cascading effects on the broader ecosystem. This paper proposes a functional model that quantitatively describes the relationship between environmental resource abundance and the sex ratio (female-to-male) in sea lampreys. The sex ratio function, characterized by a quadratic growth trend, is integrated into an improved predator–prey model to account for the lamprey’s dynamic interactions with food resources, host species, and natural predators such as birds and fish.Subsequently, a system of coupled differential equations is established to simulate the population dynamics of lampreys and other key species within the food web. The model considers parasitic behavior, predator types (human and non-human), and the impact of adaptive sex ratios on ecosystem stability. Numerical simulations compare scenarios with fixed versus resource-driven sex ratios.Results demonstrate that allowing the sex ratio to adapt leads to greater stability in lamprey population size, more regular predator-prey oscillations, and reduced short-term fluctuations in food resources. Although the influence on host populations remains minimal, the overall system exhibits improved resilience and ecological balance.This study provides novel insights into the ecological role of sex ratio plasticity and offers a modeling framework for evaluating species adaptability under varying environmental conditions, contributing to future ecosystem management and conservation planning.