BIOINVASION: Threat to ecology and economy
Surrayya Khatoon and Qadeer M. Ali
Department of Botany, Marine Reference Collection and
Resource Center, University of Karachi

Introduction

The spread of the species of plants, animals and micro-organisms from one part of the world to other through intentional or unintentional human effort is now recognised as one of the most serious threats to Earth's Biodiversity and ecosystems. It is variously termed as "Bioinvasion" or "Biopollution". Some scientists consider it as more disastrous than the chemical pollution, because organisms can evolve and proliferate while chemicals cannot.

Bioinvasion is not a new phenomenon. The species keep on moving and colonising new areas wherever they can find conducive environment. The animals are motile therefore can travel more in short time. Plants do not have limbs or feet but they do travel. This is through the dispersal of their seed, a capacity that determines their natural geographic range. Moving through natural means the species spread gradually and have to face all natural enemies and competitors which maintain the ecological balance. On their own generally they cannot cross natural geographic barriers like oceans, mountains and large deserts. However, the human-assisted travel of the biota has crossed all the barriers. And this is what biopollution is about. The human-assisted arrival of exotic species is now about a million times greater than the natural rate in some instances, especially for the islands. The species so arrived in a region are termed as aliens or exotics, which now number several thousands world over. In some cases they almost equal or even out-number the native species; such as New Zealand has 1570 alien Vs 1790 native, Hawaii has 861 alien Vs 956 native, and Tristan da Cunha has 97 alien Vs 70 native plant species. The alien species are now present in almost every part of the world and belong to all taxonomic groups like plants, animals, algae, fungi, micro-organisms and viruses.

The deliberate introductions include the crop plants, farm animals, fish and shrimp for aquaculture, decorative plants, pets, biological control organisms, etc., while accidental introductions may be as contamination with various trade commodities or passengers' luggage, and most importantly through ship ballast which daily transfer millions of aquatic organisms throughout the world. In 1991 the outbreak of cholera in America, which killed about 10000 people, is believed to be due to the ballast water dumped into a Peruvian harbour. Historically, the human pathogens rapidly evolved and spread after the change in human lifestyle form nomadic to permanent settlement in the wake of agriculture about 12000 years back. And now it is globalisation, which is turning the world into a global village where the human pathogens and crop pests are exploring new dimensions of evolutions and spread.

Complete Document.