Alien animals in South Africa – composition, introduction history, origins and distribution patterns

Abstract

Background: There is no comprehensive inventory and analysis of the composition, distribution, origin and rate of introduction of the alien fauna of South Africa.
Objectives: To provide such an analysis to facilitate effective ecological management, and compile a comprehensive inventory of introduced animal species across major habitats.
Methods: All available databases and references were used to compile the inventory, forming the basis of subsequent analyses. A graduated map was produced to identify concentrations of alien species.
Results: Of the 571 alien animal species analysed, insects comprised the largest component (53%, 300 species), followed by molluscs (9%, 51 species), annelids (8%, 48 species), arachnids (7%, 41 species), vertebrates (7%, 41 species) and crustaceans (6%, 36 species). Vertebrate introductions (88%) were largely intentional, whereas 84% of invertebrate introductions were unintentional.
Conclusions: Almost all marine and most terrestrial alien species were accidentally introduced, whereas freshwater introductions were almost entirely intentional. Some 13% had not spread significantly, 16% had spread significantly and 71% had become fully invasive. Vertebrate introductions virtually ceased after the 1950s, but rate of introduction of invertebrates remained linear. The overall rate of species accumulation was fairly low until 1880, but accelerated sharply thereafter. Most terrestrial alien species originated from Europe (28.6%) and Asia (25.0%) and the lowest proportion (6.1%) from Africa. Freshwater introductions largely originated from the Americas, with few from Africa. The most invaded areas were around Cape Town, (up to 162 introduced species/half-degree grid cell), followed by Gauteng and Durban