Introduction

The Bengal region has experienced significant environmental changes due to extensive agricultural activities, deforestation, and habitat destruction. These changes have profound impacts on local wildlife, particularly on the predator populations of Russell's vipers (Daboia russelii), a highly venomous snake with well-developed dentition and venom apparatus capable of inflicting deadly bites (De Silva, 1980). Adult specimens yield varying amounts of venom, typically ranging from 130 mg to 268 mg (Mallow et al., 2003). A lethal dose for most humans falls within this range, making it a significant threat to human life.

In the 1920s, the Russell's viper was one of the main causes of death from snakebites. Since then, no cases of bites from this snake were reported for many years, leading to its declaration as extinct in Bangladesh in 2002 (Ethirajan, 2024). However, in 2013, the first incident of death from a Russell's viper bite was reported again. Consequently, the population of Russell's vipers has increased in recent years and is spreading from the Barind region to other districts, traveling through rivers and floods. By 2018, the species had spread to a total of 17 districts along the lands adjacent to the Padma River and its branches, as well as other connected rivers (Ahsan & Saeed, 2018). According to the latest report in June 2024, this snake has spread to 28 districts across Bangladesh (Somoy News, 2024). Hospitals in rural Bangladesh have reported an increase in people being bitten by snakes, especially by the Russell’s viper, which is found in South Asia. These incidents have become a focal point on Bangladeshi social media platforms (Ethirajan, 2024).

As Russell's viper primarily feeds on rodents, this snake is often found in highly urbanized areas, near human settlements, and in farmlands, particularly during the crop harvesting season (Daniel, 2002). As a result, farmers who work outside in these areas are at great risk of being bitten. However, early medical treatment and prompt access to antivenom play a crucial role in preventing and significantly reducing the risk of severe or potentially lethal complications associated with snakebites.

Rural paddy farmers are common victims of this snake's bite, and it has become a major concern for human safety and daily activities, posing a significant threat to human health (Animal Encyclopedia, 2023). Envenomation symptoms include pain at the bite site, bleeding from the gums and urine, necrosis, vomiting, facial swelling (Mallow et al., 2003), kidney failure, disseminated intravascular coagulation, and damage to the pituitary glands, leading to hypopituitarism (Tun-Pe et al., 1987; Antonypillai et al., 2010).

This literature review examines the effects of deforestation, habitat destruction, monoculture cropping, and pesticide use on predator populations of Russell's viper using the Lotka-Volterra model to understand predator-prey dynamics and the resulting ecological imbalances.

Russell's Vipers and Their Predators

Russell's vipers (Daboia russelii) play a critical role in controlling rodent populations in South Asia, contributing significantly to the maintenance of ecological balance. These vipers, however, face predation from several species, including foxes, wild boars, monitor lizards, mongooses, other snake species like king cobras, and various birds of prey such as eagles, hawks, and owls (Animal Matchup, 2024; Answers.com, 2024; Martin, 2022). Specific studies have noted the predation of Russell's vipers by large birds like the crested serpent eagle (Spilornis cheela) and the short-toed snake eagle (Circaetus gallicus), both of which are known for their snake-hunting prowess (Chou et al., 2004). The presence of these predators is essential for regulating viper populations, preventing their overabundance, and thereby sustaining ecological equilibrium. A thorough understanding of the interactions between Russell's vipers and their natural predators is crucial for ecological studies and effective wildlife management strategies.

Source: Wikipedia

Impact of Deforestation and Habitat Destruction

Deforestation and habitat destruction are major environmental concerns that lead to biodiversity loss and habitat fragmentation. In the Bengal region, extensive agricultural activities have resulted in rapid deforestation, significantly impacting predator populations of Russell's vipers. The reduction in predator numbers due to habitat loss disrupts the ecological balance, as fewer predators are available to control viper populations. Agricultural expansion and urban development exacerbate these effects, leading to a decline in habitat quality and availability.

Monoculture Practices in the Bengal Region

Monoculture cropping, the practice of cultivating a single crop species over a large area, is prevalent in the Bengal region due to its economic benefits and efficiency. However, this practice leads to habitat simplification and a reduction in biodiversity. The lack of diverse habitats adversely affects predator species that rely on a variety of environments for survival. Monoculture fields provide limited resources and shelter for these predators, resulting in decreased predator populations and disrupted predator-prey dynamics (Ijaz et al., 2019; Nath & O'Reilly, 2016).

Impact of Irrigation Advancements on Agricultural Practices and Viper Populations

Until 1990, farmers in the Bengal region typically grew crops once or twice a year, leaving the land fallow for the rest of the year due to low water availability. With advancements in irrigation systems using groundwater, farmers began growing two to three crops per year, leaving little land fallow. This increase in agricultural intensity led to a significant rise in the prey population, particularly rodents, which are the primary prey of Russell's vipers. Consequently, the population of Russell's vipers also increased, leading to more frequent encounters between humans and these snakes (Ahsan & Saeed, 2018).

Ecological Consequences of Chemical Use in Agriculture

The use of pesticides and insecticides has become widespread in modern agriculture to control pests and increase crop yields. However, these chemicals can have detrimental effects on non-target species, including predators of Russell's vipers. Pesticides can increase predator mortality by directly poisoning them or indirectly reducing their prey availability through contamination of the habitat and food chain. The widespread use of these chemicals disrupts the natural balance of the ecosystem, leading to declines in predator populations and subsequent increases in viper populations (Alengebawy et al., 2021; Castro et al., 2021; Zhang et al., 2011).

Habitat simplification, often a result of monoculture cropping and the extensive use of chemicals, further exacerbates these ecologicalimpacts. Studies have shown that these practices lead to declines in predator populations, disrupting predator-prey dynamics and causing ecological imbalances. The loss of predators results in uncontrolled growth of prey populations, which can have cascading effects on the ecosystem. For instance, increased viper populations can lead to higher risks of human-snake encounters, posing significant threats to human safety and livelihoods (Pathak et al., 2019; Serrão et al., 2022).

Source: hindustantimes.com

Combined Predator-Prey Dynamics Model Using Lotka-Volterra Equations

Let:

• R be the population of rodents (prey).
• V be the population of Russell's vipers (intermediate predator).
• P be the aggregated population of all predators (e.g., birds of prey, mongooses, foxes).

Rodent Population Dynamics

$dR/dt=aR-bRV$

Russell's Viper Population Dynamics

$dV/dt=-cV+dRV-eVP$

Aggregated Predator Population Dynamics

$dP/dt=-fP+gVP$

Explanation of Terms

• aR: Natural growth rate of the rodent population.
• bRV: Rate at which rodents are consumed by Russell's vipers.
• −cV: Natural mortality rate of Russell's vipers.
• dRV: Growth rate of Russell's vipers based on rodent consumption.
• eVP: Rate at which Russell's vipers are consumed by aggregated predators.
• −fP: Natural mortality rate of aggregated predators.
• gVP: Growth rate of aggregated predators based on viper consumption.

Conclusion

The Bengal region's significant environmental changes due to extensive agricultural activities, deforestation, and habitat destruction have had profound impacts on local wildlife, particularly on the predator populations of Russell's vipers (Daboia russelii). These highly venomous snakes, which were once considered extinct in Bangladesh, have made a resurgence in recent years, spreading across multiple districts and posing a renewed threat to human life. This resurgence is closely tied to changes in land use, such as increased irrigation, monoculture cropping, and pesticide use, which have altered the ecological balance and predator-prey dynamics in the region.

Russell's vipers play a crucial role in controlling rodent populations, contributing to the maintenance of ecological balance. However, the vipers themselves are subject to predation by a variety of species, including birds of prey, mongooses, and other terrestrial predators. The reduction in these predator populations due to habitat loss and chemical use in agriculture has disrupted these dynamics, leading to an increase in viper populations.

The Lotka-Volterra model provides a framework for understanding these predator-prey dynamics and the resulting ecological imbalances. By examining the interactions between rodents, Russell's vipers, and their predators, this model helps elucidate the complex effects of environmental changes on wildlife populations. Effective wildlife management strategies and conservation efforts are essential to mitigate these impacts and restore ecological balance in the Bengal region. Addressing the root causes of habitat destruction and promoting sustainable agricultural practices will be key to protecting both human health and biodiversity.

References