Controlling alien species

Controlling alien species is a crucial conservation strategy aimed at managing or eradicating non-native species that pose significant threats to biodiversity and native ecosystems.

Definition and Introduction

Alien species, also known as invasive species, are plants and animals that have been accidentally or deliberately transferred from their native habitats to new environments where the abiotic conditions are suitable for them. Their introduction can occur through various human activities, such as trading animals and plants, unwittingly carrying them on ships, or even introducing them as biological control agents to manage pests.

Damage Caused by Alien Species

Once introduced, invasive species can cause substantial damage to their new environments due to several factors:

• Predation and Competition: They often act as successful predators with few natural controls, preying on native animals. They also effectively compete with native organisms for resources such as light, minerals, water, space, and breeding sites, often occupying the same niche and pushing native species to extinction. This interspecific competition can lead to the less well-adapted native species being out-competed.

• Disease Introduction: Invasive species can introduce diseases to which native species have no immunity, causing significant damage to populations. For example, the grey squirrel carries the "squirrelpox" virus that kills many red squirrels without causing symptoms in the grey squirrels.

• Habitat Degradation and Alteration: Some invasive plants grow so successfully that they cover huge areas of land or water, blocking sunlight from reaching native aquatic plants and reducing oxygen concentration in the water, which can kill fish. They can also degrade environments by outcompeting native species by reducing the space where they can grow. Certain species, like Japanese knotweed, possess vigorous root systems that can damage buildings, roads, and walls.

• Economic Impacts: The spread of invasive species can lead to significant economic costs for farmers, gardeners, and local councils due to management efforts.

Examples of Invasive Species and Their Impacts

The sources provide several examples of alien species and their detrimental effects:

• Grey Squirrel (Sciurus carolinensis): Accidentally introduced to Britain, it has outcompeted the native red squirrel and carries a squirrelpox virus that is lethal to red squirrels.

• Rabbit (Oryctolagus sp.): Deliberately introduced from Europe to Australia in 1859, it became a voracious herbivore that rapidly spread, damaging grassland and agricultural production due to a lack of natural predators. Rats introduced to the Galapagos Islands also fed on the eggs of native birds, tortoises, and reptiles, endangering these species.

• Japanese Knotweed (Fallopia japonica): Introduced to northern Europe as an ornamental plant, it forms dense thickets, overshadows native water plants, blocks waterways, and damages infrastructure with its strong root system.

• Cane Toad (Rhinella marina): Introduced to Australia in 1935 to control a sugar cane pest, it became a pest itself, breeding rapidly and spreading due to few predators and its powerful toxin.

• Red Lionfish (Pterois volitans): Likely escaped from aquaria, it has invaded Caribbean waters, eating many local species on coral reefs, lacking natural predators.

• Sea Lampreys: Artificially linked shipping canals allowed sea lampreys to enter the Great Lakes in Canada and the USA. Without natural predators, they fed on trout, causing fisheries to collapse.

• Possums: In New Zealand, introduced possums eat large quantities of leaves from native trees, reducing food for native species and tree diversity.

Conservation Strategies for Control

Controlling alien species is a vital part of conservation, and various methods are employed:

• Direct Removal and Habitat Restoration: This involves physically removing alien animal species and digging up or destroying invasive plants. Efforts to restore degraded habitats (e.g., wetlands, deforested areas) also support native species. Draining swamps and clearing vegetation can reduce breeding sites for vectors like mosquitoes.

• Biological Control: Introducing natural enemies of the alien species, such as the myxoma virus against rabbits in Australia, although this can sometimes lead to the development of resistance in the target population. Stocking water bodies with fish that feed on mosquito larvae is another biological control measure.

• Population Management:

  • Culling: Selected animals in an overpopulated species can be killed, sometimes through licensed hunting, to prevent them from exceeding the carrying capacity of their habitat and damaging other species.

  • Contraception: Methods of birth control can be used to manage populations. For example, female elephants have been given vaccines that stimulate an immune response against glycoproteins surrounding their eggs, preventing fertilization. In grey squirrels, bait with oestrogenic chemicals has been used to compromise fertility.

• Public Awareness and Policy: Education programs can raise awareness about the importance of protecting species and managing invasive ones. For instance, the Jamaican government encouraged people to develop a taste for red lionfish to increase fishing and reduce their population. Establishing protected areas like national parks and marine parks also helps safeguard native ecosystems from invasive species by limiting human interference and allowing for their removal.

• International Cooperation: Organizations like CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) play a vital role by regulating worldwide commercial trade in wild animal and plant species to ensure it does not threaten the survival of any species. For example, all sea turtles are listed in CITES Appendix I, banning their trade.

Overall, controlling alien species requires a dynamic and adaptive approach, often involving a combination of strategies to mitigate their negative impacts and protect vulnerable native species and ecosystems.