International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.3, 101-110 http://ecoevopublisher.com/index.php/ijmec 103 decline rapidly (Vaughn et al., 2022). In urban and agricultural landscapes, dominant "broadly adaptable" snake species often appear: for example, red-banded snakes are common in farmlands in Southeast Asia, and there are still a large number of colubrids and king snakes in suburban areas of North America. These species often have a broad-spectrum diet, strong reproductive capacity, and a certain ability to avoid humans, so they can survive in human environments with fragmented landscapes and mosaic habitats (Lettoof et al., 2021). In addition, some snakes with weak or non-venomous venom are more likely to be tolerated in areas with human disturbance because they are not considered a direct threat (Kontsiotis et al., 2022). On the contrary, many snakes are extremely sensitive to human activities. Habitat-specific species, such as blind snakes or rock-dwelling pit vipers that live in leaf litter at the bottom of the forest, are difficult to survive once their habitat is slightly damaged, and they usually disappear first in disturbed areas. Secondly, large and highly venomous snakes are often directly eliminated by humans. Although some snakes are not actively hunted, they have poor ability to avoid human activities, so they cannot maintain their populations under disturbances such as farmland expansion and road construction. Under human disturbance, snake communities often show a trend of homogenous species composition and reduced functional diversity, that is, a few disturbance-resistant species dominate, while sensitive species gradually disappear (Zipkin et al., 2020). 3 Mechanisms of Human Impact on Snake Diversity 3.1 Habitat loss and fragmentation Habitat loss and fragmentation are widely considered to be the primary drivers of global biodiversity decline, and snakes are no exception (Leal-Santos et al., 2020). The sharp decline in habitats has directly led to the disappearance of habitats for many snake populations. Large snakes (such as pythons and boas) are particularly sensitive to habitat loss because of their large range of movement and their greater reliance on large intact habitats. For example, the Asian reticulated python has lost its egg-laying and foraging sites due to lowland rainforest deforestation and swamp development, and its population has plummeted in some areas (Marshall et al., 2020). Habitat fragmentation isolates and divides snake populations. The dense distribution of roads, farmlands, and towns has fragmented previously connected habitat patches, and snake individuals face a high risk of death (such as road crushing) when moving between different patches, or simply cannot cross open areas. Studies have found that many snakes are reluctant to cross open farmland or urban built-up areas, but prefer to move along remaining forest belts or wetlands, which limits their range of activities to fragmented habitat patches. In addition, habitat fragmentation increases the chances of snakes coming into contact with humans. In fragmented landscapes, snakes may break into farmland and villages for food and reproduction, leading to an increase in human-snake conflicts (Kjoss and Litvaitis, 2001; Nordberg et al., 2021). 3.2 Environmental pollution Environmental pollution caused by human activities is quietly threatening the survival of snakes, including the accumulation of pollutants such as pesticides, heavy metals and industrial chemicals in the ecosystem, which has an adverse effect on individual health and population dynamics of snakes. As a predator at a high trophic level in the food web, snakes will undergo bioaccumulation by feeding on organisms, further concentrating pollutants in their prey into themselves. This makes snakes often the "terminal victims" of environmental pollution (Lettoof et al., 2020; Hoang et al., 2021). Pesticide pollution affects snake populations in many ways. Highly toxic pesticides and herbicides may directly poison snake prey (such as frogs and small mammals), causing a shortage of snake food. Chemicals such as anticoagulants and rodenticides harm snakes through the food chain. The endocrine disruption effects of pesticides may also affect the sexual differentiation and behavior of snakes. It should be noted that snakes are secretive animals, and the impact of pollution on their populations is often not easy to detect. Phenomena such as changes in body color and decreased athletic ability of snakes may be ignored, but the population may have been quietly decreasing.
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