Alien species in Namibia

Alien species are species that are not indigenous to Namibia, i.e., they did not naturally occur here, and only came to be found here because they were introduced through human intervention. This could have been intentional or accidental. Different categories of non-indigenous species may be distinguished.

Invasive alien species are aggressive competitors that tend to spread rapidly, while transforming habitats and/or replacing indigenous species. They are a cause of grave concern, and one would generally prefer to eradicate or at least contain them.

Naturalised alien species have a less severe impact on the environment. They do not spread rapidly, may be localised in distribution, and generally do not transform habitats or replace indigenous species. They are a cause of lesser concern, and while new introductions should be discouraged, existing populations are usually tolerated.

Anthropophilic species are those that are associated with humans - our livestock, crops and pets. We are so used to them that we tend to forget that they are also alien species. When they escape from captivity and survive as feral (wild) populations, different species may have effects that resemble either invasive or naturalised aliens.

Biocontrol agents are a special class of beneficial aliens. These are alien species that were intentionally introduced for the biological control of other aliens. Well-researched and well-behaved biocontrol agents do a good job of controlling their hosts, and have little or no negative effect on the environment.

Genetic contamination takes place when individuals from non-Namibian populations are introduced to Namibia and allowed to interbreed with indigenous Namibian populations. This subspecific hybridisation compromises the genetic integrity of indigenous Namibian populations. Most of the known cases are associated with the game industry.

Undesirable species are invasive aliens that have not yet been recorded from Namibia, but are already present elsewhere in the region, and could potentially spread here, too. They are listed to highlight the dangers they pose.

Source: mostly based on Namibia's National Review of Invasive Alien Species.
Document details: Bethune, Griffin & Joubert (2004).
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