Q.Elaborate how invasion by an alien species reduces the species diversity of an area.

When alien species are introduced into a new geographical area, either intentionally or unintentionally, they can become invasive and significantly reduce the species diversity of that area. These introduced species often lack natural predators or competitors in their new environment, allowing their populations to proliferate rapidly.

They impact native species primarily through:

• Competition: Alien species can outcompete native species for vital resources such as food, space, and light, leading to a decline in native populations.
• Predation: Some alien species act as predators on native species, which may not have evolved defenses against them.
• Disease Transmission: They can introduce new pathogens or diseases to which native species have no immunity. …

Species diversity refers to the variety of different types of life forms found in a particular area, encompassing genetic diversity, species diversity, and ecosystem diversity. Maintaining this diversity is crucial for the health and stability of ecosystems. However, various factors threaten this delicate balance, and among the most significant is the invasion by alien species. These are species introduced, either intentionally or unintentionally, from one geographical area to another where they are not naturally found. While many introduced species do not establish themselves, some become invasive, causing profound ecological damage.

The primary ways in which an invasion by an alien species reduces the species diversity of an area are through:

• Competition with Native Species: Alien species, when introduced into a new environment, often find themselves free from the natural predators, parasites, and diseases that kept their populations in check in their native habitats. This lack of natural control allows them to multiply rapidly and exploit resources aggressively. They often outcompete native species for essential resources such as food, water, light, and space. For instance, invasive weeds like Parthenium (carrot grass), Lantana, and the notorious water hyacinth (Eichhornia crassipes) have spread rapidly in India. Water hyacinth, often called the "Terror of Bengal," grows profusely in standing water bodies, depleting oxygen and outcompeting native aquatic plants, leading to the death of fish and other aquatic organisms.

• Predation on Native Species: Some alien species are predators that, upon introduction, find a new prey base in the native species of the invaded area. The native prey species, having evolved without the presence of this new predator, often lack effective defensive mechanisms against it. This makes them highly vulnerable, leading to a drastic decline in their populations and even extinction. A classic example cited in the NCERT textbook is the introduction of the Nile Perch into Lake Victoria in East Africa. This predatory fish led to the extinction of more than 200 species of cichlid fish in the lake, which were unique to that ecosystem.

• Introduction of Diseases or Parasites: Alien species can sometimes carry novel pathogens or parasites to which native species have no immunity. When these diseases spread to the native populations, they can cause widespread mortality, further reducing species diversity. While not always the primary mechanism, it can exacerbate the impact of other factors. …

Trace the mechanism chain: an alien species arrives without natural checks, so it can outcompete/prey on/spread disease to native species. Anchor …