An invasive species is an introduced, nonnative organism (disease, parasite, plant, or animal) that begins to spread or expand its range from the site of its original introduction and that has the potential to cause harm to the environment, the economy, or to human health.
A few well-known examples include the unintentional introduction of the West Nile virus, chestnut blight, the South American fire ant, zebra mussels, Burmese pythons, and sea lamprey. These are in addition to the intentional introductions of salt cedar (Tamarisk), kudzu vine, house sparrows, starlings, and nutria.
Harmful, non-native species can be found in all ecosystems across the United States. These species can cause costly economic and ecological damage each year including crop decimation, clogging of water facilities and waterways, wildlife and human disease transmission, threats to fisheries, increased fire vulnerability, and adverse effects for ranchers and farmers.
he Zoological Survey of India (ZSI) has for the first time compiled a list of 157 alien invasive animal species! This list excludes the invasive microbe species.
The compilation was announced on the side-lines of National Conference on Status of Invasive Alien Species in India organized by the Zoological Survey of India and Botanical Survey of India.
The most common characteristics of invasive species are rapid reproduction and growth, high dispersal ability, ability to survive on various food types and in a wide range of environmental conditions and the ability to adapt physiologically to new conditions, called phenotypic plasticity.
Highlights:
- Out of the 157 species listed by the ZSI, 58 are found on land and in freshwater habitat, while 99 are found in the marine ecosystem
- The 58 invasive species found on land and in freshwater comprise of 19 fish species, 31 species of anthropods, 3 of molluscs and birds, 1 of reptile and 2 of mammals
- Among alien invasive marine species, genus Ascidia accounts for maximum number of species (31), followed by Arthropods (26), Annelids (16), Cnidarian (11), Bryzoans (6), Molluscs (5), Ctenophora (3), and Entoprocta (1)
Some commonly found alien species:
African apple snail (Achatina fulica): The most invasive among all alien fauna in India, this mollusc was first reported in the Andaman and Nicobar Islands. It is now found across country and is threatening the habitat of several native species.
Papaya Mealy Bug (Paracoccus marginatus): Native of Mexico and Central America, it is believed to have destroyed huge crops of papaya in Assam, West Bengal and Tamil Nadu.
Cotton Mealy Bug (Phenacoccus solenopsis): Native to North America, it has severely affected cotton crops in Deccan
Amazon sailfin catfish (Pterygoplichthys pardalis): This species is responsible for destroying the fish population in the wetlands of Kolkata.
Introduced Species
Some species are brought to a new area on purpose. Often, these species are introduced as a form of pest control. Other times, introduced species are brought in as pets or decorative displays. People and businesses that import these species do not anticipate the consequences. Even scientists are not always sure how a species will adapt to a new environment.
Introduced species multiply too quickly and become invasive. For example, in 1949, five cats were brought to Marion Island, a part of South Africa in the southern Indian Ocean. The cats were introduced as pest control for mice. By 1977, about 3,400 cats were living on the island, endangering the local bird population.