The introduction of species from one place to another has been occurring throughout the history of mankind. the magnitude and frequency of these events, however, have increased substantially as a result of activities associated to the globalization of trade, transportation and migration of persons.

Although only a small percentage of species transported from one location to another become invasive species, these may have a substantial impact and cause environmental and economical damages, to the extent that their propagation and dispersion is acknowledged as one of the worst threats to the earth’s economic and ecological welfare (GISP, 2005).

The International Union for the Conservation of Nature (IUCN) defines invasive species as those that settle in natural or semi-natural ecosystems or habitats, becoming agents of change and threatening the native biological diversity (IUCN, 2000). Also included are species that are hazardous (or potentially hazardous) to the economy, environment and human health (Emerton and Howard, 2008). An invasive species or population is capable of surviving, becoming settled and reproducing outside its original habitat, competing heavily with local species. Invasive species are characterized primarily by: rapid growth, high dispersion rate, huge reproductive capacity and wide tolerance to both environmental variations and native competing species (Emerton and Howard, 2008).

Today, there are no definite lists of invasive species; many countries and organizations are developing regional or global databases that are being continuously updated. The Invasive Species Specialist Group (ISSG) at IUCN has recorded 479 invasive species worldwide, belonging to virtually all taxonomic groups (viruses, fungi, algae, ferns, higher plants, invertebrates, fish, amphibians, reptiles, birds and mammals). Of these, 100 species have been regarded as impacting significantly both biological diversity and human activities (Lowe et al., 2004). According to Conabio, 32 of these species are established in Mexico (Figure a).

Environmental and economic costs of invasive species

All the invasive species that colonize a new habitat affect the composition of native biological communities. Invasive species may modify the ecosystem’s structure as a result of the direct exclusion of native species through competition for resources, or indirectly through the modification of the local habitat. Invasive species may also cause changes in the environmental services associated with the regulation of the hydrological cycle, flood control, water supply, waste processing, soil conservation and regeneration, crop pollination and seed dispersion.

It is estimated that invasive species are accountable for the extinction of 39% of the species that have disappeared since the year 1600, that is, a percentage above the one caused by habitat destruction over the same period of time, calculated at 36% (Hernández et al., 2002). Today, 20% of mammal species, 5% of bird species, 15% of reptiles and 3.3% of amphibians living in continental areas are threatened of extinction as a result of the invasion of alien species in local habitats. This issue is aggravated in islands, where the percentage of threatened animal species surpasses estimates for continental areas: 38% of bird species, 32% of reptiles and 30% of amphibians.

In some cases, the environmental issues and costs associated with invasive species are enormous for some countries. For instance, in New Zealand it is calculated that there are more invasive than native species: 1700 invasive versus 1400 native species (Hernández et al., 2002).

The economic aspects of biological invasions involve current and potential costs of damages caused by invasions, as well as the management responses related to the possibility of preventing the invasion, controlling its dispersion, eradicating invasions or not conducting any type of action. The total worldwide economic cost associated with invasive species has not been calculated yet. Nevertheless, only in the United States, the economic burden of actions related to control measures, losses and damages associated with invasive species was estimated at 120,000,000 millions USD per year (Pimentel et al., 2005).

Human health and exotic invasive species

Invasive species may be vectors of pathogen viruses, protozoans and bacteria causing serious diseases in both man and wildlife. In the case of human diseases, these species may transport pathogens producing malaria, dengue, schistozomiasis, trypanosomiasis, lymphatic filariasis, cholera and hemorrhagic fevers (GISP, 2005).

National and international fight against invasive species

At a national level, the National Plan for Invasive Species (Plan Nacional de Especies Invasoras in Spanish), coordinated by the National Commission for the Use and Knowledge of Biodiversity (Comisión Nacional para el Uso y Conocimiento de la Biodiversidad, Conabio in Spanish) and other government agencies dedicated to preparing, updating and setting forth strategies directly focused on addressing the fight against invasive species. As for concrete actions, there are several directives in relation to plant- and animal-health regulations aimed at preventing the entrance of pests and species with a potential quarantine interest (Conabio, 2008).

At an international level, there are several binding and non-binding instruments related to invasive species. These include the Agreement on Biological Diversity subscribed by Mexico in 1993, which states that each subscribing party shall “prevent the introduction, control or eradicate the exotic species that threaten native ecosystems, habitats or species”. The World Invasive Species Program (GISP), created in 1997, is also worth mentioning, aimed at supporting governments and other organizations in using the best available practices for controlling invasions and promoting the development of ancillary tools and strategies required to improve invasive-species management at a world level.

References:

Conabio. Sistema de información de especies invasoras en México. México. 2008. Available at: www.conabio.gob.mx/invasoras/index.php/Especies Consulted on: 21-10-2008.

Emerton, L. y G. Howard. A Toolkit for the Economic Analysis of Invasive Species. Global Invasive Species Programme. Nairobi. 2008. Available at:  www.gisp.org/publications/toolkit/index.asp Consulted on: 28-10-2008.

GISP. Sudamérica invadida. El Programa Mundial sobre Especies Invasoras. 2005. Available at: www.gisp.org/publications/invaded/gispSAmericasp.pdf Consulted on: 28-10-2008.

Hernández, G., E. Lahmann y R. Pérez-Gil. Invasores en Mesoamérica y el Caribe. Costa Rica. IUCN. 2002. Available at: www.iucn.org/resources/publications/publications_search/index.cfm Consulted on: 27-10-2008.

IUCN. IUCN Guidelines for the Prevention of Biodiversity Loss caused by Alien Invasive Species. 2000. Available at: www.issg.org/infpaper_invasive.pdf Consulted on: 28-10-2008.

Lowe S., M. Browne, S. Boudjelas, M. De Poorter. 100 de las Especies Exóticas Invasoras más dañinas del Mundo. Una selección del Global Invasive Species Database. ISSG, IUCN, CSE. 2004. Available at: www.issg.org/spanish.pdf Consulted on: 17-10-2008.

Pimentel, D., R. Zuñiga y D. Morrison. Update on the environmental and economic costs associated with alien. Invasive species in the United States. Ecological Economics 52:273-288.