Invasive Species Drive Biodiversity Loss

by S. Pagad and M. Browne

In 2005, the Millennium Ecosystem Assessment (MA) determined that “across the range of biodiversity measures, current rates of loss exceed those of the historical past by several orders of magnitude and show no indication of slowing.” 1 Current trends in biodiversity loss show no indication of a slowdown. The MA lists invasive species as one of five direct drivers behind biodiversity loss (the others are land use change, climate change, overexploitation, and pollution).2

Only a small proportion of invasive alien species—living organisms that are moved around the world through human activity and global trade—actually cause harm. But this subset of introduced non-native species, whether brought in intentionally or unintentionally, has major ecological and socioeconomic impacts. And they are found in all major taxonomic groups.3 (See Table 1.)

Invasive species cause a reduction in native biodiversity through predation, parasitism, hybridization, or competition with native species for habitats and resources.4 They alter ecosystem functioning by causing changes in the nutrient and hydrological regime.5 Socioeconomic damages can include loss of livelihoods and the expenditure of vast amounts of resources on control and mitigation of the risks caused by invasives.6

Nearly 30 percent of globally threatened birds are under threat from invasive aliens.7 The problem is more severe on islands: 67 percent of this group of birds on islands are threatened by non-native species.8 The extinction of at least 65 species of birds has been tied to predation by introduced rats, cats, pigs, dogs, and mongooses; to habitat destruction by sheep, goats, and rabbits; and to diseases caused by introduced pathogens.9 For example, predation by rats has caused the near extinction of the Campbell Island teal in New Zealand, while avian malaria has caused the near extinction of birds in Hawaii.10

Candleberry myrtle or firebush, an invader of wet and mesic forests in Hawaii, forms dense, monotypic stands and has a negative effect on the recruitment and persistence of native plant species.11 Firebush, a nitrogen- fixer, has altered primary successional ecosystems in the Hawai’i Volcanoes National Park by quadrupling inputs of nitrogen and is now reported to be spreading through drier submontane forests.12

Five major aquatic weeds that have spread over large areas of the natural and seminatural freshwater ecosystems of South Africa cause water availability and use problems.13 They have reduced the quality of drinking water, increased the incidence of waterborne, waterbased, and water-related diseases, and caused a decline in aquatic biodiversity.14

The global footprint of invasive alien species on biological diversity is yet to be quantified; a measure of the footprint will provide a better understanding of the need and priorities for effective conservation responses.

In 1993, the Office of Technology Assessment of the U.S. Congress documented economic damages of up to $97 billion between 1906 and 1991 due to 79 non-native invasive species.15 More recently, David Pimentel and his colleagues at Cornell University estimated economic damages for the United States, the United Kingdom, Australia, India, South Africa, and Brazil to be in excess of $336 billion per year.16

Practical responses to biological invasions include preventing the intentional and unintentional introduction of invasive aliens, management and control of the ones already present and established, and mitigation of the risks and impacts they cause. The collection and exchange of authoritative data and information is a key component of these responses, and the wide dissemination of summary information helps raise public awareness. Examples of global, regional, national, and thematic information systems include the Global Invasive Species Database (GISD), the North European and Baltic Network on Invasive Alien Species, Pacific Island Ecosystems at Risk, and Non-indigenous Aquatic Species.17 A network that will link all these information systems together, the Global Invasive Species Information Network, is also being developed.18

The most detailed and accurate data on invasive alien species at the global scale is available in the Global Invasive Species Database.19 The GISD is a free searchable source of authoritative information about species that have a negative impact on biodiversity. It aims to facilitate effective prevention and management activities by disseminating specialist knowledge and experience to a broad global audience. Development of the GISD began in 1998 as part of the global initiative on invasive species led by the Global Invasive Species Programme.20

GISD profiles include information on the ecology, impacts, distribution, and range expansion of invasive alien species, along with images and descriptions, information about effective prevention and management options, and contact details for experts on each species. Users include natural resource managers, extension agents, environment and biodiversity specialists, quarantine and border control personnel, educators and students, and other individuals and organizations concerned with the environment.

The GISD has recently launched two new initiatives: the Global Register of Invasive Species (GRIS) and the Global Management Project Register (GMPR).21 The GRIS will identify species with a history of being invasive by integrating invasive alien species checklist data generated by collection and observation databanks around the world. The GMPR will have case studies about prevention, eradication, control, and containment and mitigation activities.

Fortunately, those working on invasive species exhibit a willingness to share information and knowledge because they understand its importance for improving biodiversity outcomes. The GISD is just one of many responses to the need to collect and disseminate accurate, up-to-date, relevant information about invasive species. As awareness grows, people and communities are able to make informed choices that will have lasting effects on their descendants.

Includes the following charts and graphs
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Notes
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