Scientists say 2 out of 3 invasive animals cause harm to South African ecosystems

In a 2020 book chapter, scientists say about 30 alien animal species have been introduced into South Africa from elsewhere, and some are negatively affecting the economy and the environment. Researchers and authorities could use his information to help control the spread of these invasive birds, mammals, reptiles and frogs. 

‘Invasive species’ are organisms that are introduced into a new area that they are not native to. These non-native aliens may thrive at the expense of native species and harm the native ecosystem. Researchers who have studied invasive species in South Africa have mostly worked with plants because their impacts are easy to notice, but information on invasive animals is still lacking.

In this chapter, the authors reviewed what scientists knew at the time regarding animals that had been introduced into South Africa from other countries.

They found that 30 different species of mammals, birds, reptiles and amphibians (like frogs and toads) were introduced into South Africa over the previous 10 000 years. Interestingly, 2 out of 3 of those became invasive, or harmful, in the last 150 years. Half of the species were mammals, a third were birds, with 3 reptiles and 2 amphibians.

The authors said mammals introduced included domestic animals like pigs, cats, goats, donkeys and horses. Mammals are animals that feed their babies with milk from their mammary glands. The animals were introduced for food (pigs, goats) and transport (donkeys and horses), but were later problematic. For example, cats now feed on other animals, and donkeys mate with zebras.

Wild mammals such as roan antelope, sambar deer, himalayan tahr, European rabbits, rats (brown and Asian), and grey squirrels had been introduced as well.  The authors said some like the antelopes, were intentionally introduced, while others, like mice, were introduced accidentally through shipping. 

Rabbits were intentionally introduced for their meat, but their numbers grew such that they became difficult to control. Others, like rodents, threatened food production and transmitted diseases. In some cases, invasive animals like rats outcompeted the native animals and pushed them out of their natural environments.

The authors also said birds such as mallards, house sparrows, chaffinches, chukar partridges, pigeons, starlings and common mynas, house crows and peacocks had been deliberately introduced to South Africa. Some were brought in as pets or for sporting purposes, and some destroyed crops and poultry, spread diseases, or competed with native birds.

The authors also said reptiles such as corn snakes, tropical house geckos, the common dwarf gecko, and the flowerpot snake were introduced into South Africa by mistake as eggs or as adults, but researchers had not studied their impact yet.

Apparently, some travellers might have introduced painted reed frogs and guttural toads deliberately into South Africa through some aquatic plants.

The authors expressed their worries that there was an increasing number of animals introduced into the country as pets.

The authors, who were based in South Africa, hope this review brings together some of the information needed to better manage invasive animals in the country.

Abstract

In this chapter we review the current knowledge on terrestrial vertebrate invasions in South Africa. Thirty species of mammals, birds, reptiles and amphibians are considered to have arrived over the last 10,000 years, with two thirds having become invasive in the last 150 years. Half of the species are mammals, a third birds, with three reptiles and two amphibians. Although there are multiple pathways, there appears to be a trend from species that were deliberately introduced in the past, to accidental introductions in the last ~100 years, which are a by-product of increasing trade, both internationally and within South Africa. Few invasive terrestrial vertebrate species have had their impacts formally assessed within South Africa, but international assessments suggest that many can have Moderate or Major environmental and socio-economic impacts. Of particular concern is the growing demand for alien pets within the region, with increasing amounts of escapees being encountered in the wild. We consider the importance that the NEM:BA Alien and Invasive Species Regulations have had on the research of invasive terrestrial vertebrates in South Africa, and emphasise the importance of regulations for domestic exotics.

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