# The Impact of Significant Geographical Barriers on the Invasion Risk of Non-Native Aquatic Animals: A Case Study of the Qinling Mountains, China

## TL;DR

The Qinling Mountains act as a natural barrier affecting where non-native aquatic animals invade, but human activities like water projects are weakening this barrier.

## Contribution

This study identifies how geographical and climatic barriers influence invasion patterns of non-native aquatic species and how human activities undermine these barriers.

## Key findings

- The Qinling Mountains serve as a physical and climatic barrier limiting cross-basin dispersal of non-native aquatic species.
- Human activities such as water-transfer projects and damming reduce the barrier effect, increasing invasion risks.
- Mean annual temperature is the primary factor influencing species distribution across the Qinling Mountains.

## Abstract

Biological invasions are an important cause of biodiversity loss. The Qinling Mountains form a key natural barrier in central China: they separate the warmer south from the colder north, and they also lie between the Yangtze and Yellow River basins. Using field surveys and existing distribution records, we examined whether this barrier affects the invasion risk of non-native aquatic animals and whether their distributions differ on the two sides of the mountains. Our results show that temperature is the strongest factor shaping invasion risk. Species that tolerate colder conditions are more common north of the Qinling Mountains, while species that prefer warmer conditions are more common to the south. However, human activities—such as water-transfer projects, dam building, and aquaculture—can reduce the barrier effect by creating new pathways for movement between river basins. We therefore suggest giving priority to monitoring areas where water systems are connected by engineering projects and strengthening early detection and rapid action to reduce potential ecological harm.

Biological invasion is a major driver of biodiversity loss and ecosystem disruption, with non-native aquatic species threatening ecological integrity and economic stability. The Qinling Mountains, located in central China, serve as a crucial barrier between temperate and subtropical climate zones, and separate the Yellow and Yangtze River basins. This study investigates the role of these geographical barriers in regulating the distribution and invasion risk of non-native aquatic species. We identified 27 non-native species in Shaanxi Province based on occurrence records compiled from field survey conducted between 2012 and 2024 (and from 2019 to 2024 in the Yellow River mainstream of the Shanxi–Shaanxi Gorge), including 13 high-risk species, such as Trachemys scripta elegans, Procambarus clarkii, Sander lucioperca, and Hypomesus olidus. Using the Aquatic Species Invasiveness Screening Kit and species distribution models, we identified the Hanjiang River in the Yangtze basin and Weihe River estuary in the Yellow River basin as high-risk areas for these species. Mean annual temperature was the primary environmental factor influencing species distribution, with species adapted to cooler conditions predominantly found north of the Qinling Mountains, while those preferring warmer climates are more common in the south. Our findings highlight the Qinling Mountains as both a physical and climatic barrier, limiting cross-basin dispersal and creating distinct invasion patterns. However, human activities such as inter-basin water-transfer projects, damming, and aquaculture practices have gradually weakened the barrier’s effectiveness, facilitating the spread of invasive species. We recommend prioritizing monitoring efforts in cross-basin water-transfer regions, focusing on high-risk species adapted to both cooler and warmer climates, and incorporating environmental DNA (eDNA)-based monitoring in recipient areas of inter-basin water-transfer projects for early detection and control to minimize ecosystem damage.