Alien Mammals in the Afrotropical Region and Their Impact on Vertebrate Biodiversity: A Review

Abstract

The introduction of alien species may pose an enormous threat to indigenous flora and fauna. Among introduced animals, probably the most destructive to the natural environment are mammals. This is true at least in regard to the Afrotropical Region (sub-Saharan Africa). This review attempts to summarize our knowledge on alien mammals in this region and their impact on indigenous vertebrate fauna. This review includes 56 mammal species, belonging to 20 families, introduced to sub-Saharan Africa over the last 2000 years. Most are representatives of the following orders: Artiodactyla, Carnivora, and Primates. Most species introduced to sub-Saharan Africa originated from the Oriental (n = 20) and Palearctic (n = 19) regions. Two species, Mus musculus and Rattus rattus, were introduced before 1400 (probably as early as 800 AD), while three others were introduced between 1401 and 1700. The first half of the 17th century saw the highest number (n = 10) of introduced species. Between 1651 and 1850, only two species were introduced; in the following 175 years (1851–2025), as many as 24 species were introduced. Ten of the introduced mammal species, namely Sus scrofa, Capra hircus, Rattus rattus, R. norvegicus, Mus musculus, Felis catus, Canis familiaris, Viverricula indica, Urva auropunctata, and Maccaca fuscicularis, have become invasive species. A total of 39 mammal species were relocated (mainly for hunting purposes) within sub-Saharan Africa. Most of them were representatives of the family Bovidae (76.9%). Relocations are not considered introductions. Based on published records of the impacts of alien mammals on the vertebrate fauna of sub-Saharan Africa, the following mechanisms may be distinguished: predation, competition, hybridization, transmission of diseases and parasites, and habitat destruction (grazing, herbivory, browsing). Most vertebrate species (79.4%) were affected through direct predation, predation and habitat destruction (7.1%), or predation and competition (1.4%). Alien mammals have caused habitat destruction for only 10 species (7.1%). Other effects (competition and genetic pollution) were marginal (3.5%). At least 144 vertebrate species, representing 52 families, have been affected by alien mammals in sub-Saharan Africa: 3 amphibians, 23 reptiles, 89 birds, and 29 mammals. As a result of mammal introductions, 65 species in sub-Saharan Africa have become globally extinct, 45 are considered threatened (listed in the RDB), and 31 other species are in decline, although not included in the RDB. Most extinct birds were affected by introduced rats, mice, feral cats, and dogs. In continental Africa, only seven vertebrate species have been negatively affected by alien mammals. All other affected vertebrates occur on islands. An especially high rate of extinction has been recorded in the Mascarene Islands. In comparison with alien birds in sub-Saharan Africa, the number of introduced mammal species is much lower, but their negative impact on vertebrate fauna is significantly greater.

1. Introduction

Sub-Saharan Africa harbors the richest and most diverse mammal fauna in the world, especially in regard to larger mammals (ungulates, carnivores, primates). For a long time, this fauna was also the best preserved. In other regions of the world, most members of the mammal megafauna were decimated and driven into extinction, but in Africa, the majority survived [1,2,3]. However, the conservation status began to change following the European penetration of the continent, started in the 15th century by Portugal and later by the Netherlands, France, Belgium, and Great Britain. For the first four centuries of European presence in sub-Saharan Africa, the environment of the African interior remained largely unchanged [4,5]. The coasts and small islands surrounding the continent, however, were affected [6]. Even earlier, beginning in the first century AD, the fauna of the largest African island, Madagascar, was negatively affected by Malayan–Polynesian (Austronesian) colonizers, who were joined in the ninth century by Bantu peoples from East Africa [7].

European contact with sub-Saharan Africa began with the Portuguese penetration of the world at the beginning of the 15th century. Most of the small oceanic islands were systematically occupied by humans and their domestic animals. These changes greatly accelerated on the coasts, islands, and in the interior towards the end of the 19th century, mainly due to French and British colonization of Africa. The 20th century saw dramatic devastation of the natural environment. Many animal species, especially larger mammals, became threatened to such an extent that a need for special protection in reserves and national parks arose. Fortunately, in many countries (e.g., South Africa Namibia, Botswana, Zimbabwe, Zambia, Tanzania, Kenya, and Uganda), extensive networks of protected areas were established, often covering more than 10% of a country’s surface area with national parks and reserves [8,9,10,11].

Humans have negatively affected nature in sub-Saharan Africa primarily through excessive hunting (mainly targeting vertebrates), habitat destruction, and pollution. However, in the last centuries, alongside habitat destruction, alien species, directly or indirectly introduced by humans, have become one of the greatest threats to fauna, not only in Africa but throughout the world [10]. This process became especially acute at the end of the 20th century and the beginning of the 21st century, with the increase in commerce and tourism. In many regions of the world, efforts have been undertaken to investigate and mitigate this negative process. In Africa, these efforts have been concentrated in South Africa and on some islands surrounding Africa, e.g., Cape Verde, São Tomé, Mauritius, Seychelles, and Marion [11].

Throughout the world, mammals are the most destructive alien animals [12]. Some species have been domesticated and brought to Africa as farm animals; others have been introduced as highly valued game animals, while still others, like rodents, have been introduced accidentally. In many regions of sub-Saharan Africa, these mammals have become destructive to local biodiversity, especially to vertebrate fauna [13,14,15]. These alien species and their impacts on local fauna have been the subject of some regional reviews, e.g., South Africa [13,14] and the western Indian Oceanic islands [15]. However, both the introduced mammal species and their impact on vertebrate fauna across the whole of sub-Saharan Africa have not been comprehensively reviewed to date. Such reviews are available for Europe [16], South America [17,18], and Australia [19]. In this review, an attempt is undertaken to present a similar review for sub-Saharan Africa. The aim is not only to facilitate intercontinental comparisons but also to encourage researchers to further investigate this urgent conservation issue, so that it can be sufficiently controlled, mitigated, and ultimately resolved. The primary purpose of this overview is to provide information on the threats posed by alien mammal species, in order to more efficiently control invasive species, mitigate their negative effects, and plan eradication efforts where necessary.

2. Material and Methods

This review includes all mammal species ever introduced to Africa and its islands over the last 2000 years (since Madagascar has been colonized by the Austronesian people). The time is especially important in the case of islands, which had not been occupied by humans in earlier times. Accounts are provided for such species that have formed self-sustaining populations, including all stages, up to full invasions.

The literature on mammalian introduction in Africa south of the Sahara was reviewed from 1950 to present. All islands around this continent were also included in this review, i.e., Cape Verde; São Tome and Principe, Bioko and Annobón of the Equatorial Guinea; Madagascar; small oceanic islands around Madagascar, i.e., Mascarenes (Mauritius, Reunion, Rodrigues and others), Seychelles, Comoros; Mafia, Zanzibar, Pemba off Tanzania; Socotra in the Gulf of Aden; and two sub-Antarctic islands, Marion and Prince Edward.

To search the relevant literature, the Google Scholar bibliographic database (scholar. google.com) was used. The following keywords were applied: introduced mammals (or alien mammals) + Africa (or particular African country or specific island). The particular mammal species (both common and scientific names) has also been used as a keyword + Africa (or the particular African country or specific island), e.g., Cervus dama + Africa, Fallow Deer + Zimbabwe, etc. To investigate the impact of an alien mammal on the vertebrate fauna, the following keywords have been applied: extinct (or threatened or endangered) + mammal (or bird or reptile, or amphibian, or fish) + Africa (or the particular African country or the particular African island). Special websites dealing with introduced mammal species were also consulted through direct searches on the internet.

Definitions related to the introduction and the invasive species follow those in [20].

• Indigenous species (native, autochthonous): a species living within its natural range.
• Alien species (introduced, non-native, non-indigenous, foreign, exotic): a species introduced by human intentionally or accidentally.
• Invasive alien species (invader): a species which has been introduced, to areas not previously occupied, established a viable breeding population, spread and become a pest affecting ecosystem, local biodiversity, economy and society (including human health).
• Non-invasive alien species: introduced species with a developed viable population of low dispersal abilities, and not adversely affecting ecosystems, economy and society in the conquered areas.
• Translocated species: accidental escapee from an enclosure; it may reproduce in the wild but has not developed a viable population.

The nomenclature and systematics of mammals follow [21], birds [22], reptiles [23], amphibians [24]. The conservation status of each species has been assessed according to the IUCN Red List of Threatened Species.

3. The Introduced Species

3.1. Feral/Domestic Species

Prior to the arrival of Arabs and Europeans, sub-Saharan Africa had been inhabited by peoples already using domestic animals, such as sheep Ovis aries, goats, Capra hircus, cattle, Bos taurus and dogs Canis familiaris, that were all alien to the region. Many of these domestic animals became feral, causing serious environmental problems. The feral goats, donkeys Equus asinus, pigs and cattle caused massive impacts through a competition with native species for the food, altering the structure and the composition of plant communities by grazing and rooting e.g., [25,26]. This led to habitat loss, resulting in the local extinction of some native species, and accelerated soil erosion. Other feral species, such as dogs and cats Felis catus, caused huge impacts on the local fauna through predation, causing extinctions of numerous animals once common on islands [12,27]. In many of these islands, and in some places on the continent, the problem still continues.

3.1.1. Feral Cat Felis catus

It occurs worldwide, including many small oceanic islands. Together with the rat, it is the most invasive and destructive mammal species in the world. It often occurs in large numbers in urbanized landscapes. For example, population densities of cats in Cape Town, South Africa, have been estimated as 80–300 exx./km². In an urban conservancy in KwaZulu-Natal, South Africa, the density of cats was found to be between 23 and 40 exx./km² [27].

The feral cat can cause major impacts through predation, leading to population declines and, in some cases, to a local extirpation of native mammals, reptiles, and birds [28,29,30]. On small oceanic islands, feral cats contributed to the global extinction of some endemic species. The feral cat is also known to hybridize with the African wild cat Felis sylvestris lybica [31]. It is regarded as one of the 100 worst invasive species in the world [27].

In 1949, five cats were introduced to the sub-Antarctic Marion Island, South Africa, to help to eradicate the mouse (it had been introduced to the island earlier). However, the cat also preyed on seabirds, especially burrowing petrels (Procellariidae), decreasing their breeding success and, as a consequence, causing their population declines [32]. The cat soon became feral and began to reproduce at a fast rate. By the year 1975, its population was so high that it became very destructive to marine birds breeding on the island. It was estimated that, each year, cats were able to eliminate c. 450,000 petrels. An eradication scheme was implemented in the 1980s, and the cat was eliminated from the island by the end of that decade [32,33].

3.1.2. Feral Dog Canis familiaris

The domestication of the dog began at least 14,000 BP and, from that time, there has been an ever-increasing problem of feral dogs, which threatens biodiversity [34,35]. Domestic dogs encompass feral and free-ranging animals, as well as those owned and completely dependent on humans; all can interact with wildlife [34]. The dog population has expanded around the globe alongside the human population, and in 1993, the global population estimate was made at 500 million [35]. Free-roaming dogs, those that are not permanently restrained or under human control, may account for about 75% of the global dog population. In Africa, there are, today, about 100 million dogs [35].

Feral dogs came from domestic dogs that escaped, were abandoned or were born to feral animals. As a result, today, dogs are present in each corner of the world, in smaller or larger numbers. On most African islands, they have been present since European colonization started, e.g., in São Tomé, since the 16th century; in Madagascar, about c. 1000 years ago [36,37].

Dogs can affect other vertebrate species by spreading serious diseases and parasites. They are considered the main carriers/reservoirs of rabies. Species affected include the lion Panthera leo, side-striped jackal Canis adustus, black-backed jackal Canis mesomelas, bat-eared fox Otocyon megalotis, Ethiopian wolf Canis simensis, African wild dog Lycaon pictus, spotted hyena Crocuta crocuta, white-tailed mongoose Ichneumia albicauda and honey badger Mellivora capensis. The dog may also transmit the Canine Distemper Virus (CDV), leishmaniasis and one of the hydatid diseases caused by the transmission of Echinococcus granulosus [38]. However, 79% of dogs’ impact on biodiversity is through predation [25].

Doherty et al. [34] listed 200 vertebrate species (96 mammals, 78 avians, 22 reptiles and 3 amphibians), whose populations suffer from feral dogs, with 11 extinct, 30 critically endangered, 71 endangered and 87 vulnerable. Especially bad was the impact of feral dogs on giant lemurs in Madagascar, after their introduction to the island about 1000 years ago. They have greatly contributed to the global extinctions of most of them. Today, in sub-Saharan Africa, 10–16 vertebrate species are affected by dogs [34].

3.1.3. Feral Donkey Equus asinus

The feral donkey is present in the following countries: South Africa, Namibia, São Tome and Principe and Socotra [39]. Aerial counts conducted around Steinkopf and Leliefontein estimated that there are as many as 274 donkeys in this area [40].

In Namibia, feral donkeys have occurred since 1837, in the Orange River valley in the extreme south and in the Cuvelai Drainage System in Ovamboland in the central-north, where they were brought from 1851 [41]. In 2000, there were about 100,000 donkeys in Ovamboland, with many of them being actually feral. During prolonged droughts, they are destructive to vegetation, and through overgrazing, they may promote invasive plant species as, for example, the bitter bush Pechuel-Loeschea leubuitziae (Asteraceae) and the bush encroachment (G. Kopij, own observ.). Also, around Paulshoek in the Karoo, South Africa, residents complained that donkeys were destructive towards vegetation [42].

The greatest threat the donkey poses is hybridization with other species of the family Equidae, especially with the endangered Cape mountain zebra Equus zebra zebra producing the so-called ‘zonkey’ [43].

3.1.4. Feral Horse Equus ferus caballus

There are four known wild horse populations in South Africa, Namibia and Ethiopia. In South Africa, a population of at least 200 animals occupies an area of about 170 km² around Kaapsehoop in Mpumalanga province, with a population of more than 100 animals in the Steinkopf area of the Northern Cape province [40].

In Namibia, feral horses occur in the Gaub Plains of the Namib Desert near Aus, Karas Region, southern Namibia. Today, the area is incorporated with the Namib-Naukluft National Park. In 1964–1984, the number of animals varied between 50 and 200 (in most years, 140–160). In 1984, an aerial survey was conducted, in the course of which 168 animals were recorded. A ground survey carried out in 1988 estimated the population at 150–200 individuals. Between 1993 and 2005, the population was between 89 and 149 animals [44]. The most likely ancestors of these horses are a mix of riding horses and cavalry horses from Germans. They were released from various farms and camps in the early 20th century, most of them during World War I. Despite the fact that the horses are alien to this region, they have not been removed from the park, due to their historical attest and tourist attraction. The endangered Hartmann’s mountain zebras Equus zebra hartmannae also occur in the Namib-Naukluft Park, but their range does not overlap with that of the feral horse, and hybridization between the two species has not been recorded [45].

Feral horses from the Mount Kundudo in eastern Ethiopia may have come from the Abyssinian–Adal War (1528–1560). The population has sharply declined in recent decades, so that in 2022, only 30 individuals remained. The Ethiopian government has a plan to revitalize and protect the relict population in a national park for their historical attest and as a tourist attraction [46].

3.1.5. Wild Boar/Feral Pig Sus scrofa

The pig was introduced to sub-Saharan Africa by Neolithic farmers in about 9000 BC.

In South Africa, the wild boar Sus scrofa was introduced for biological control against the pine tree emperor larvae of the emperor pine moth Nudaurelia cytherea (Lepidoptera: Sphingidae) in pine plantations of Tulbach (1926) and Franschhoek (1941) in the Western Cape [47,48].

Feral pigs damage some critically endangered plants in the Western Cape, affecting the succession and facilitating alien plant spread [47]. They have been eradicated from some areas; e.g., a total of 1209 feral pigs have been removed from the Kasteelberg area [49]. Feral pigs are also present in Mafia and Pemba off Tanzania, with the wild boar in Gabon, Sudan, and Burkina Fasso [50].

3.1.6. Feral Goats Capra hircus

Apart from an established population on the Prince Edward Island [51], feral populations are assumed to exist throughout South Africa. Feral goat grazing has reduced the cover and density of endemic geophytes and succulent shrubs in thicket vegetation, and conservation of this endemic-rich flora is seriously threatened [52]. The feral goat is responsible for the desertification in the Sahel zone and other arid regions of Africa. It is regarded as one of the 100 worst invasive species in the world [27].

3.1.7. Other Feral Mammals

Some feral animals like the cattle Bos taurus, sheep Ovis aries and dromedary Camelus dromedarius may cause habitat degradation (

Table 1. Mammal species introduced to sub-Saharan Africa. Invasive species in bold case.

Scientific Species Name	Common Species Name	Family	Original Range	Distribution in Africa
Tenrec edacudatus	Common Tenrec	Tenrecidae	Madagascar and Comoros	Mauritius < 1970; Reunion, before 1882; Aldabra Atoll
Suncus madagascariensis	Madagascan Pygmy Shrew	Soricidae	Madagascar	Socotra, after 1967
Suncus etruscus	Etruscan Shrew	Soricidae	Southern Palearctic	Socotra, befre 1967
Suncus murinus	Asian House Shrew	Soricidae	SE Asia	E African Coast, Madagascar, before 1960, well-est.; Comoros, Mauritius, Reunion, established?; Zanzibar, Pemba before 1950; South Africa: Dyer Island 1912; Aldabra Atoll
Eulemur mongoz	Mongoose Lemur	Lemuridae	Madagascar	Comoros, 1665; in 2000: 45 exx./km2, 2008: 10 exx./km2, 2019: 23 ind./km2 (L. J. Ormsby)
Cercopithecus aethiops	Green Monkey	Cercopithecidae	Africa	Cape Verde, 1960’s
Cercopithecus mona	Mona Monkey	Cercopithecidae	Africa	São Tome e Principe, 1700–1800
Erythrocebus patas	Patas Monkey	Cercopithecidae	Africa	South Africa: KZN; 2000–2020; crop pest
Macaca irus	Long-tailed Macaque	Cercopithecidae	SE Asia	Mauritius Is. 1602; very invasive
Macaca fascicularis	Crab-eating Macaque	Cercopithecidae	SE Asia	Mauritius 1602; South Africa: W Cape
Ovis aries musiomn	Muflon	Bovidae	Palearctic	South Africa
Ammotragus lervia	Barbary Sheep	Bovidae	N Africa	South Africa: Tsolwana Game Reserve (E Cape, early 1980’s), Northern Cape, Free State. Total popul.: c. 1000 ind. in 2015 (S.Brody)
Capra hircus	Feral Domestic Goat	Bovidae	Iran	South Africa: 1650, escape; Namibia (Damaraland, Namaland); Assumption Is., before 1897, 1895: 300–400 exx., 1916: only few, c. 1940 extinct; Prince Edward Is.; Aldabra, 1878, est., before 1968 extinct; Mauritius, 1512, 1950: c. 100, before 1982 extinct; São Tome e Principe, 16th cen.
Hemitragus jemlahicus	Himalayan Tah	Bovidae	Himalayas; S Tibet, Nepal, India	South Africa, 1930: Table Mts. (ornamental; 600 exx. 1974; 100 exx. 1981; 2000: 50–60 exx. eradicated), Cape Peninsula, Golden Gate, Free State. Vulnerable in India; but easy to keep in Zoos, reproduce efficiently
Boselaphus tragocamelus	Nilgai	Bovidae	India	South Africa: Eastern Cape, Free State
Addax nasomaculatus	Addax	Bovidae	N Africa	SA: FE, EC.
Bison bison	American Bison	Bovidae	N America	South Africa: Ratelfontein near Richmond, Karoo; 1990’s extinct
Bubalus bubalis	Asian Water Buffalo	Bovidae	SE Asia	Namibia
Bos frontalis	Gaur	Bovidae	SE Asia	South Africa
Antilope cervicapra	Indian Blackbuck	Bovidae	India	South Africa: Eastern Cape (escapee), 1985?
Rusa unicolor	Malayan Sambar	Cervidae	SE Asia	South Africa 1880 (hunting): Eastern Cape; Mauritius: 1639
Rusa timorensis	Sunda Sambar	Cervidae	Indonesia	South Africa: EC, c.1890; Reunion
Cervus dama	Fallow Deer	Cervidae	S Palearctic	South Africa 1869 (escapee): Western Cape, Eastern Cape, Free State, Gauteng, KwaZulu Natal; Madagascar, 1932, extinct before 1974; Angola; Uganda
Cervus axis	Axis Deer	Cervidae	SE Asia	South Africa: Eastern Cape, before 1985; Free Sate; crop and forest pest
Cervus nippon	Sika Deer	Cervidae	Japan, China, Taiwan	South Africa: Groot Schuur, 1897, 1937: 20 exx.; Eastern Cape, Free State, Limpopo; Madagascar, 1932, now extinct; forest pest
Cervus elaphus	Wapiti	Cervidae	N America	Fernando Poo Isl. (Gulf of Guinea), 1954, established? South Africa: near Clocolan (Free Sate), 1895, 1930’s: 50 exx., Vereeniging (Transvaal), 1975; escapee
Cervus elaphus	Red Deer	Cervidae	Eurasia	South Africa: E Cape, Free State; escapee
Cervus timorensis	Rusa	Cervidae	SE Asia: Indonesia	Comoro Is., 1970; Madagascar, 1928, 1950’s widespread, 1990’s extinct; Mauritius, 1639, 1980’s: c. 3000 exx.
Cervus unicolor	Samba	Cervidae	SE Asia	South Africa: Groot Schuur, 1897, 1930’s: c. 50 exx.; 1990’s in a few enclosers in Westren Cape
Axis porcinus	Hog Deer	Cervidae	India	South Africa, escapee
Elaphurus davidianus	Père David’s dee	Cervidae	China	South Africa: Eastern Cape
Sus scrofa	Feral Domestic Pig	Suidae	Europe	South Africa 1926: Western Cape, Zimbabwe, Tanzania Uganda, Southern Sudan, Gabon, SE Chad; São Tome e Principe, 16th cen.; Mauritius 1606, Reunion 1629, Rodrigues c. 1792
Potamochaerus porcus	Warthog	Suidae	Africa	Madagascar, before 1962; Mayotte (Comoros), before 1982
Tayassus sp.	Peccari	Tayassuidae	S America	Gabon: Wonga-Wongue Presidential Reserve (WWPR), before 1986
Camelus dromedarius	Feral Drome-dary Camel	Camelidae	Asia	Socotra
Equus asinus	Feral Donkey	Equidae	Central Asia	South Africa: 1650, escape; Namib Desert and Ovamboland; Socotra; São Tome e Principe, 16th cen.
Equus ferus caballus	Feral Horse	Equidae	Central Asia	South Africa: 1650, escape; Gabon: WWPR, before 1986; established?; São Tome e Principe, 16th cen.
Equus africanus	Feral African Wild Ass	Equidae	Africa	Socotra
Canis familiaris	Feral Dog	Canidae	Europe	Cape of Good Hope, before 1970; São Tome e Principe, 16th cen.; Madagascar, c.1000 BP
Felis catus	Feral Domestic Cat	Felidae	Europe	South Africa: 1650, escape; Marion 1949 to control rats (1977: 3409 exx.), Mauritius c.1685, Reunion c.1685, Rodrigues c.1745, Seychelles; São Tome e Principe, 16th cen.; Marion Isl. 1949 (+1991)
Civettictis civetta	African Civet	Viverridae	Africa	São Tome e Principe, 19th cen.?
Viverricula indica	Small Indian Civet	Viverridae	SE Asia	Socotra, before 1608; Zanzibar and Pemba, before 1950; Madagascar before 1950
Urva auropunctatus	Small Indian Mongoose	Herpestidae	SE Asia	Tanzania: Mafia, Zanzibar, Pemba, before1950; Mauritius before 1985 (to control rats in sugar cane plantation)
Herpestes edwardsi	Grey Mongoose	Herpestidae	SE Asia	Mauritius, 1899 to control rats
Mustela nivalis	Weasel	Mustelidae	Europe	São Tome e Principe, 19th cen.?
Oryctolagus cuniculus	European Rabbit	Leporidae	Europe	Robben Is.: 1652 (escapee of domestic ex.); many islands around South Africa and Madagagascar, 1860, now extinct; Cape Verde c.1450, abundant, 1990’s extinct; Mauritius 1810, abundant, totally eradicated in 1987; Seychelles, 1980’s but not established; Aldabra Atoll
Lepus nigricollis	Black-naped Hare	Leporidae	India, Pakistan	Mauritius, late 19th cen., 1975: 650–1500 exx., 1982: 2450–2900 exx.; Cousin Is. (Seychelles): 1920’s, 1971: 120–170 exx.; Madagascar; Reunion
Mus musculus	House Mouse	Muridae	Middle East	South Africa: c.800, stowaway; 1500s: Namibia, Zimbabwe, Kenya, DRC, Nigeria, Benin, Niger, Senegal, Mauritius, Marion, 1800s; São Tome e Principe, 16th cen.
Rattus norvegicus	Brown Rat	Muridae	Far East	South Africa, 1650, stowaway; Mauritius 1735, Reunion 1735, Rodrigues before 1874
Rattus rattus	House Rat	Muridae	SE Asia	South Africa: c. 800, stowaway; Madagascar, c.300 BC; Madagascar, Tanzania, Mozambique, Ethiopia, Benin, Niger, Mauritius before 1598, Reunion 1672, Rodrigues before 1691, Mayotte, Comoros; São Tome e Principe, 16th cen.
Rattus tanezumi	Asian House Rats	Muridae	SE Asia	Widespread in South Africa and Eswatini c. 2005
Sciurus carolinensis	Grey Squirrel	Sciuridae	USA, Canada	Cape Town area: 1890‘s, 1920’s populated whole Cape Penis; Paarl: 1945; Ceres 1957; Swellendam: 1968
Myocastor coypus	Coypu	Echymyidae	S America	Hanynki (140 km N of Nairobi), c. 1940; Lake Naivasha: 1965; Lake Ol Bolossat, 1970; Tanzania; Zambia
Hydrochoerus hydrochaeris	Capybara	Caviidae	S America	South Africa, c. 2020

Data from: [13,17,27,46,47,49,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80].

). However, their negative effect on vertebrate species has not been evidenced so far [53].

3.2. Ungulates Introduced for Ranching and Hunting

3.2.1. Fallow Deer Cervus dama

It was introduced to South Africa to Cape Town in the 19th century, and it slowly expanded around the city. By 1970, it occurred all over the Western and Northern Cape [49]. At the beginning of the 21st century, it occurred in all provinces of South Africa, except the Limpopo province [48]. Although the fallow deer is the most widely sold alien ungulate species in South Africa, only 11 game farms in this country are permitted to stock them [50]. A stable population is also present on the Robben Island, South Africa.

3.2.2. Red Deer Cervus elaphus elaphus/Wapiti C. e. canadensis

Recently, this species was introduced to South Africa; earlier, this occurred in Australia, New Zealand, Argentina and Chile. It is regarded as one of the 100 worst invasive species in the world [27], but in sub-Saharan Africa, it is not an invasive species

3.2.3. Sambar Deer Rusa unicolor

In the 1880s, it was introduced to the C. Rhode’s Groote Schur estate in Cape Town, and from there, it spread to Table Mountain in the Cape Peninsula [47]. Today, it occurs in the woodlands of the Orange Kloof and the Twelve Apostles.

3.2.4. Himalayan Tahr Hemitragus jemlahicus

The Himalayan tahr in the Cape Peninsula, South Africa, originated from a small number of animals that escaped from the Cape Town Zoo in the 1930s [47], and it invaded the Table Mountain section of the Table Mountain National Park [33]. The following numbers of the Himalayan thar were recorded in the Table Mts.: 1974: 600 animals; 1981: 100; 2000: c.40–50 [81].

3.2.5. Other Species

The muflon Ovis aries musiomn, Barbary sheep Ammotragus lervia, nilgai Boselaphus tragocamelus, American bison Bison bison, Asian water buffalo Bubalus bubalis, gaur Bos frontalis, Indian blackbuck Antilope cervicapra, addax Addax nasomaculatus, Sunda sambar Rusa timorensis, axis deer Cervus axis, and sika deer Cervus nippon were introduced for hunting purposes and kept in enclosures, mostly in South Africa. Some of them may escape from enclosers and disperse in natural habitats, but such incidental ‘introductions’ are unsuccessful in most cases.

3.3. Leporids

3.3.1. European Rabbit Oryctolagus cuniculus

In 1658, it was successfully introduced to Robben Island. In 2009, the population on Robben Island was estimated to exceed 24,000 individuals [55]. In the 17th century, rabbits were also introduced to all other islands off the South African coast, and they still occur on Jutten, Dassen, Vondeling, Schaapen, Bird and Seal Islands, and to Possession near Lüderitz in Namibia [82,83]. The rabbit was also introduced to several other small islands near the Soth African coast, but they are now extinct there [83]. Rabbits on Schaapen Island are currently all albino [82]. Brooke et al. [42] suggested that rabbits remained unsuccessful on the African mainland as there are too many natural predators.

The rabbit is regarded as one of the 100 worst invasive species in the world [27]. In 1996, it was successfully removed from the Birds Island, Seychelles, and, in 1998, from the Gunners Qouins Island. By the year 2019, about 13,000 rabbits were eliminated from Robben Island [33].

3.3.2. Black-Footed Hare Lepus nigricollis

It is native to the Indian subcontinent. It was introduced to Madagascar, Seychelles, Comoros, Mauritius, Reunion and Mayotte. Since its introduction to Mauritius, it has become an agricultural pest [84]. On the Cousin Island, its browsing prevents the regeneration of Casuarina equisetifolia, which provides staple food for some endemic terrestrial birds [85].

3.4. Rodents

European ships brought early invaders, such as rats and mice, although there is evidence that rats and mice were present long before this contact began. The increasing commerce of alien pets in South Africa (mainly rodents) causes increasing amounts of escapee in the wild [14].

It should be emphasized that the introduction of mice and rats was followed in many instances by the introduction of the cat to control them, and their impacts may become exacerbated/reinforced.

Three alien murid rodent species, viz. the black rat Rattus rattus, brown rat R. norvegicus and house mice Mus musculus, have caused local extinctions of native species of invertebrates, birds, bats and rodents on several islands through predation, competition for food, and disease transmission (e.g., [85]).

The black rat, brown rat (or Norway rat), Pacific rat R. exulans and house mouse are implicated in at least 11 extinctions. Today, over 80% of the world’s major island groups host at least one of the rat trio (R. rattus, R. norvegicus, R. exulans) reviewed here [75,86]. They pose a major threat to the native biota throughout the world (reviewed in [85,86,87,88]). It is interesting that the black rat is implicated in the majority of impacts. This may be explained by its extensive distribution and ecological plasticity.

3.4.1. House Mouse Mus musculus

On the mainland, its impact appears to be mostly socio-economic (moderate) [89], including spoiling stored foods. The house mouse was also introduced to many islands. Among others, it was introduced accidentally to Marion Island (before 1818), as a stowaway on ships [90]. On this island, it preys on invertebrates [91,92], changing their population densities, reproduction strategies and growth rates [93]. Similarly, declines in albatross populations, and other colonially breeding marine birds, have been attributed to the predation of eggs and chicks by the house mouse [92].

3.4.2. Black Rat (House Rat) Rattus rattus

The black rat, also called the house rat, could have been introduced to South Africa in pre-historical times (700–800 AD; [94]). The house rat was reported to be abundant on Robben Island from 1614 [95]. It has invaded considerably into the African interior [96]. It was introduced via Arab and European ships and then dispersed by rivers, railways and roads. It was recorded in Mombasa and Dar es Saalam in 1895; Tabora: 1895; Kisumu: 1901; Kampala: 1911; Serengeti: 1976; eastern DRC: 1950s. It is very common in optimal habitats, but it is characterized by a big seasonal and yearly variation in numbers. In Lagos, Nigeria, the proportion of R. norvegicus to R. rattus was 5:95 in 1931–1934 [97]. Recently, the black rat was recorded in south-western Niger [98]. The black rat, in fact, colonized most of the world following ship-mediated trade. It is regarded as one of the 100 worst invasive species in the world [27].

3.4.3. Brown Rat Rattus norvegicus

It was introduced to South Africa via ship traffic between Asia and Europe in the 16th century [48]. It is a strongly commensal species occurring mostly on the coastal ports and in urban areas. It was introduced mainly in the 19th and 20th centuries [99]. It was recorded in Bamako on the Niger River in 2000. In sub-Saharan Africa, the brown rat is limited to coastal areas, while the black rat is more widely distributed but restricted by drier areas [100]. The two rat species are widely regarded as pests. In South Africa, specifically, they damage infrastructure, contaminate foodstuffs, and act as reservoirs of zoonotic diseases e.g., [67,101,102], such as the plague (caused by the bacillus Yersinia pestis transmitted from rats via fleas to humans), leptospirosis, and toxoplasmosis [103]. They also carry several co-invasive parasites [101]. Bartonella and Helicobacter were recorded in all three rat species in South Africa [104].

3.4.4. Asian House Rat Rattus tanezumi

In recent decades, the Asian house rat was introduced to South Africa. Today, it appears to be widespread throughout both South Africa and Swaziland [105].

3.4.5. Grey Squirrel Sciurus carolinensis

It was introduced from North America via the U.K. in c. 1890 to Cape Town [106]. Today, it is confined to an area of c. 7000 km² around Cape Town, Stellenbosch, Paarl, Eldin, Swellendam and Ceres. It inhabits urban, agricultural and afforested environments. It is fairly common, but no estimation of its population is available [106,107]. The grey squirrel is indigenous to the USA and Canada. It is regarded as one of the 100 worst invasive species in the world [27], but no damage is recorded in South Africa.

3.4.6. Coypu Myocaster coypus

The Coypu originates from South America. It was introduced to Nanyuki, central Kenya in 1947 and released/escaped and spread in the Central Highlands, east of the Rift Valley c. 1950. In the 1960s, the coypu invaded Lake Naivasha in the Rift Valley. It was released in the 1960s in Zambia, NE Tanzania, Botswana, Zimbabwe, and South Africa. However, the introductions failed everywhere [108].

3.5. Carnivores

Three Oriental small carnivores, the small Indian civet Viverricula indica, small Indian mongoose Urva auropunctatus and grey mongoose Herpestes edwardsi, were introduced to the Tanzanian islands: Mafia, Zanzibar and Pemba. They may pose a serious threat to the local herpetofauna, although there is no evidence of their negative role.

The small Indian mongoose has decimated partridges, quails and black-naped hares (an introduced species) and has contributed to the extirpation of the Timor deer that was introduced to Mauritius and Reunion island in 1639 from Batavia [65,70]. It is regarded as one of the 100 worst invasive species in the world [27].

There are also two carnivores in São Tomé, the African civet Civettictis civetta and the least weasel Mustela nivalis from Europe [62,109,110]. They are suspected to cause a decline in some endangered endemic species.

3.6. Primates

Five African primate species, the mona monkey Cercopithecus mona, mongoose lemur Eulemur mongoz, green monkey Cercopithecus aethiops, brown lemur Eulemur fulvus and Patas Monkey Erythrocebus patas, and two primate species from the Oriental Region, the long-tailed macaque Macaca irus and crab-eating macaque Macaca fascicularis, were introduced mainly to small oceanic islands and to southern and eastern Africa [60,62,78,79,109,110,111,112].

The impact of the crab-eating macaque Macaca fascicularis is not well documented in South Africa. As a generalist feeder, it is a highly adaptable species. It is suspected to negatively affect threatened birds by destroying their nests with eggs or chicks. It may also compete for fruits with some frugivorous bird species [78,79]. It is listed among the 100 worst invasive species of the world [27].

3.7. Insectivores

Two Suncus shrews, namely the Etruscan shrew Suncus etruscus from the southern Palearctic Region and the Madagascan pygmy shrew Suncus madagascariensis from Madagascar, were introduced to Socotra Island. Another species of this genus, the Asian House Shrew Suncus murinus from the Oriental Region, was introduced to East Africa, Madagascar and the surrounding islands. The common tenrec Tenrecus ecaudatus was introduced to the Mascarenes. With the help of the introduced frog Rana mascariensis, tenrecs are reported to cause the extinction of three endemic frogs, viz. Sooglossus thomasetti, Sooglossus sechellensis and Sechellophryne gardinieri, in the Seychelles [70].

3.8. General Characteristics of the Mammal Introductions in Sub-Saharan Africa

A total of 56 mammal species belonging to 20 families have been hitherto introduced to sub-Saharan Africa. Most were representatives of the following orders: Artiodactyla (n = 26, including Cervidae—12 species and Bovidae—9 species), Carnivora (n = 7) and Primates (n = 6).

Most species introduced to sub-Saharan Africa originated from the Oriental (n = 20) and the Palearctic Region (n = 19). Only a few species were introduced from other regions, i.e., Africa (n = 9), Nearctic (n = 3) and Neotropics (n = 3).

Only two species, the house mouse and black rat, were introduced before 1400 (probably as early as 800 AD); five others were introduced between 1401 and 1700. The first half of the 17th century saw the highest number (n = 11) of introduced species, while, during the years 1651 and 1850, only two species were introduced. In the following 175 years (1851–2025), as many as 24 species were introduced to sub-Saharan Africa, and the trend is increasing (Figure 1).

Ten of the introduced mammal species, namely Sus scrofa, Capra hircus, Rattus rattus, R. norvegicus, Mus musculus, Felis catus, Canis familiaris, Viverricula indica, Urva auropunctata and Maccaca fuscicularis, became invasive species in sub-Saharan Africa (Table 1).

4. Relocated Mammal Species in Sub-Saharan Africa

Some mammal species, especially representatives of game animals, were relocated within or close to their original range, usually within the same or similar vegetation type (e.g., within savanna). They are kept in enclosures and their numbers are strictly controlled by humans. However, these animals were actually not introduced but relocated. Most of these relocations took place in South Africa and Namibia. A number of mammal species was also relocated from the Tanzanian interior to a small island, Rubondo (240 km²), on Lake Victoria. Most animals relocated there were representatives of the family Bovidae (Artiodactyla), with some species from the orders Perissodactyla and Primates and single species from other orders.

A total of 39 mammal species were relocated within sub-Saharan Africa (Table 2). Most of them were representatives of the family Bovidae (76.9%) and only 7.7% each from the orders Perissodactyla and Primates. The numbers may be even higher than listed in Table 2, as many relocations could have passed unrecorded. It should be mentioned that some of the relocated mammals may escape from enclosure or be purposefully released and develop viable populations. In this way, they may become introduced or even invasive species.

There is a striking disproportion in the composition of relocated versus introduced mammal species. While 46% of introduced species belong to Artiodactyla, as many as 79% of relocated species belong to this order. No Rodentia and Eulypotyphla species were relocated, while they comprise 13% and 9%, respectively, of all introduced mammal species (Figure 2).

The main problem of relocated species is linked to gene pollution. Relocation may lead to hybridizations between two subspecies, which are often released to the same area, e.g., Hippotragus equinus, Kobus ellipsyprimnus, Aepyceros melampus, Equus zebra, Equus burchelli, Ceratotherium simum.

One of the most interesting mammal species relocated is the roan antelope Hippotragus equinus. It has been estimated that in South Africa, only 300 roan antelopes are living in the wild, while the remainder (c. 3500) are stocked on ranches [113]. Most of the ranched roan antelopes are now extralimital to the natural distribution of Hippotragus equinus equinus, in the northern part of the Limpopo province, South Africa [114]. The popularity of this species in the game industry has given rise to concerns for its genetic purity, as imported Hippotragus equinus koba from West Africa hybridizes with the native Hippotragus equinus equinus [115,116,117,118].

Table 2. Introduced/translocated/escaped from captivity, did not establish viable population, or established it but now are as regarded extinct.

Species Scientific Name	Species Common Name	Family	Original Range	Translocated to
Kobus ellipsiprymnus ellipsiprymnus	Waterbuck	Bovidae	South Africa	Namibia, Senegal
Kobus vardonii	Puku	Bovidae	South Africa	South Africa
Kobus leche	Lechwe	Bovidae	South Africa	South Africa
Syncerus caffer	African Savanna Buffalo	Bovidae	Africa	South Africa, Namibia
Aepyceros melampus petersi	Black-faced Impala	Bovidae	Namibia, Angola	Angola, Namibia
Antidorcas marsupialis	Springbok	Bovidae	South Africa	South Africa, Namibia
Redunca arundineum	Common Reedbuck	Bovidae	South Africa	Namibia
Redunca fulvorufula	Mountain Reedbuck	Bovidae	South Africa	Namibia
Pelea capreolus	Grey rhebok	Bovidae	South Africa	South Africa
Oryx dammah	Scimitar-horned Oryx	Bovidae	N Africa	South Africa
Oryx gazella gazella	Southern Oryx	Bovidae	South Africa	Senegal
Tragelaphus derbianus	Derby’s Eland	Bovidae	C and W Africa	South Africa
Tragelaphus euryceros	Bongo	Bovidae	Central Africa	South Africa
Tragelaphus imberbis	Lesser Kudu	Bovidae	NE Africa	South Africa
Tragelaphus scriptus	Greater Kudu	Bovidae	South Africa	South Africa; Tanzania: Rubondo (240 km2), Lake Victoria island
Tragelaphus angasi	Nyala	Bovidae	South Africa	Botswana, Namibia, Angola
Tragelaphus spekii	Sitatunga	Bovidae	Southern Africa	South Africa; Tanzania: Rubondo (240 km2), Lake Victoria island
Taurotragus oryx oryx	Common Eland	Bovidae	Southern Africa	Senegal
Cephalophus natalensis	Natal Duiker	Bovidae	South Africa	South Africa
Neotragus moschatus	Suni	Bovidae	South Africa	South Africa, Tanzania: Rubondo (240 km2), Lake Victoria island
Madoqua kirkii	Kirk’s Dik-dik	Bovidae	E Africa	South Africa
Capra ibex	Nubian Ibex	Bovidae	NE Africa	Namibia
Hippotragus niger	Sable Antelope	Bovidae	Botswana, Namibia, Angola	South Africa
Hippotragus equinus koba	Roan Antelope	Bovidae	West Africa	South Africa; Tanzania: Rubondo (240 km2), Lake Victoria island
Damaliscus pygargus dorcas	Bontebok	Bovidae	South Africa	South Africa
Damaliscus pygargus phillipsi	Blesbok	Bovidae	NE South Africa	SW South Africa, Botswana, Mozam-bique, Namibia, Zimbabwe, Angola
Beatragus hunteri	Hirola	Bovidae	SE Kenya	W Kenya (Tsavo)
Oreotragus oreotragus	Klipspringer	Bovidae	South Africa	South Africa
Connochaetes gnou	Black Wildebeest	Bovidae	Africa	Namibia
Connochaetes taurinus	Blue Wildebeest	Bovidae	Africa	Gabon: W.WP.R., <1986, now?
Giraffa camelopardalis	Giraffa	Giraffidae	South Africa	South Africa; Tanzania: Rubondo (240 km2), Lake Victoria island
Equus zebra hartmannae	Hartmann’s Mountain Zebra	Equidae	Namibia	South Africa: Western cape, Eastern Cape
Diceros bicornis michaeli	Black Rhinoceros	Rhinocerotidae	Kenya	South Africa; Tanzania: Rubondo (240 km2), Lake Victoria island
Ceratotherium simum simum	White Rhinoceros	Rhinocerotidae	South Africa, Kenya	Uganda, Kenya, Zambia
Loxodonta africana	African Elephant	Loxodontidae	Africa	Tanzania: Rubondo (240 km2), Lake Victoria island
Panthera leo melanochaita	African Lion	Felidae	South Africa	Rwanda
Colobus abyssinicus	Angola Pied Colobus	Cercopithecidae	Central Africa	Tanzania: Rubondo (240 km2), Lake Victoria island
Cercopithecus aethiops	Vervet Monkey	Cercopithecidae	Africa	Tanzania: Rubondo (240 km2), Lake Victoria island
Pan troglodytes	Chimpanzee	Hominidae	Cental Africa	Tanzania: Rubondo (240 km2), Lake Victoria island

Data from: [113,118,119,120,121,122,123,124]. Invasives South Africa. https://invasives.org.za/national-list-of-invasive-mammal-species/ accessed on 19 February 2025.

Table 2. Introduced/translocated/escaped from captivity, did not establish viable population, or established it but now are as regarded extinct.

Species Scientific Name	Species Common Name	Family	Original Range	Translocated to
Kobus ellipsiprymnus ellipsiprymnus	Waterbuck	Bovidae	South Africa	Namibia, Senegal
Kobus vardonii	Puku	Bovidae	South Africa	South Africa
Kobus leche	Lechwe	Bovidae	South Africa	South Africa
Syncerus caffer	African Savanna Buffalo	Bovidae	Africa	South Africa, Namibia
Aepyceros melampus petersi	Black-faced Impala	Bovidae	Namibia, Angola	Angola, Namibia
Antidorcas marsupialis	Springbok	Bovidae	South Africa	South Africa, Namibia
Redunca arundineum	Common Reedbuck	Bovidae	South Africa	Namibia
Redunca fulvorufula	Mountain Reedbuck	Bovidae	South Africa	Namibia
Pelea capreolus	Grey rhebok	Bovidae	South Africa	South Africa
Oryx dammah	Scimitar-horned Oryx	Bovidae	N Africa	South Africa
Oryx gazella gazella	Southern Oryx	Bovidae	South Africa	Senegal
Tragelaphus derbianus	Derby’s Eland	Bovidae	C and W Africa	South Africa
Tragelaphus euryceros	Bongo	Bovidae	Central Africa	South Africa
Tragelaphus imberbis	Lesser Kudu	Bovidae	NE Africa	South Africa
Tragelaphus scriptus	Greater Kudu	Bovidae	South Africa	South Africa; Tanzania: Rubondo (240 km2), Lake Victoria island
Tragelaphus angasi	Nyala	Bovidae	South Africa	Botswana, Namibia, Angola
Tragelaphus spekii	Sitatunga	Bovidae	Southern Africa	South Africa; Tanzania: Rubondo (240 km2), Lake Victoria island
Taurotragus oryx oryx	Common Eland	Bovidae	Southern Africa	Senegal
Cephalophus natalensis	Natal Duiker	Bovidae	South Africa	South Africa
Neotragus moschatus	Suni	Bovidae	South Africa	South Africa, Tanzania: Rubondo (240 km2), Lake Victoria island
Madoqua kirkii	Kirk’s Dik-dik	Bovidae	E Africa	South Africa
Capra ibex	Nubian Ibex	Bovidae	NE Africa	Namibia
Hippotragus niger	Sable Antelope	Bovidae	Botswana, Namibia, Angola	South Africa
Hippotragus equinus koba	Roan Antelope	Bovidae	West Africa	South Africa; Tanzania: Rubondo (240 km2), Lake Victoria island
Damaliscus pygargus dorcas	Bontebok	Bovidae	South Africa	South Africa
Damaliscus pygargus phillipsi	Blesbok	Bovidae	NE South Africa	SW South Africa, Botswana, Mozam-bique, Namibia, Zimbabwe, Angola
Beatragus hunteri	Hirola	Bovidae	SE Kenya	W Kenya (Tsavo)
Oreotragus oreotragus	Klipspringer	Bovidae	South Africa	South Africa
Connochaetes gnou	Black Wildebeest	Bovidae	Africa	Namibia
Connochaetes taurinus	Blue Wildebeest	Bovidae	Africa	Gabon: W.WP.R., <1986, now?
Giraffa camelopardalis	Giraffa	Giraffidae	South Africa	South Africa; Tanzania: Rubondo (240 km2), Lake Victoria island
Equus zebra hartmannae	Hartmann’s Mountain Zebra	Equidae	Namibia	South Africa: Western cape, Eastern Cape
Diceros bicornis michaeli	Black Rhinoceros	Rhinocerotidae	Kenya	South Africa; Tanzania: Rubondo (240 km2), Lake Victoria island
Ceratotherium simum simum	White Rhinoceros	Rhinocerotidae	South Africa, Kenya	Uganda, Kenya, Zambia
Loxodonta africana	African Elephant	Loxodontidae	Africa	Tanzania: Rubondo (240 km2), Lake Victoria island
Panthera leo melanochaita	African Lion	Felidae	South Africa	Rwanda
Colobus abyssinicus	Angola Pied Colobus	Cercopithecidae	Central Africa	Tanzania: Rubondo (240 km2), Lake Victoria island
Cercopithecus aethiops	Vervet Monkey	Cercopithecidae	Africa	Tanzania: Rubondo (240 km2), Lake Victoria island
Pan troglodytes	Chimpanzee	Hominidae	Cental Africa	Tanzania: Rubondo (240 km2), Lake Victoria island

Data from: [113,118,119,120,121,122,123,124]. Invasives South Africa. https://invasives.org.za/national-list-of-invasive-mammal-species/ accessed on 19 February 2025.

5. Impacts of Introduced Mammals on Vertebrate Biodiversity

In sub-Saharan Africa, at least 144 vertebrate species represented by 52 families were affected by alien mammals, i.e., 3 amphibians, 23 reptiles, 89 birds and 29 mammals. No fish are recorded as negatively affected by alien mammals so far. Among affected reptiles, the most specious were Scincidae (n = 11) and Testudinidae (n = 6); among birds, Procellariidae (n = 9), Columbidae (n = 9) and Rallidae (n = 9); among mammals, three lemur families, Palaeopropithecidae, Megalodapidae and Archeolemuridae (n = 11).

Based on published records of impacts exerted by alien mammals on the vertebrate fauna of sub-Saharan Africa, the following mechanisms may be distinguished: predation, competition, hybridization, transmission of diseases and parasites and habitat destruction (grazing/herbivory/browsing).

Most vertebrate species (79.4%) were affected by alien mammals through direct predation. Alien mammals caused habitat destruction for only 10 (7.1%) vertebrate species. Other effects (competition and genetic pollution) were marginal (3.5%). Predation by alien mammals has affected 13 (72.2%) reptile species, 82 (92.1%) bird species, and 17 (54.8%) mammal species. Most affected species (83.0%) were endemic to small oceanic islands, 19 (13.5%) were marine bird species from eight families (e.g., Procellariidae, Sulidae and Laridae), and only 5 affected mammal species (3.5%; including three species from the genus Equus) were not endemic.

As a result of mammal introduction, 65 species in sub-Saharan Africa became globally extinct, 45 are threatened (included in Red Data Books) and 31 other species are in decline, although not included in Red Data Books/Lists. Among extinct species, 10 are reptiles, 37 birds and 18 mammals. Threatened species include 9 reptiles, 31 birds and 5 mammals. Most declining species are birds (n = 21), with few mammals (n = 6), reptiles (n = 4) and amphibians (n = 3). No fish species were found to be negatively affected by alien mammals. It should, however, be emphasized that many of these species were negatively affected not only by alien mammal species but often directly by humans through excessive hunting and habitat destruction.

Most extinct birds were affected by introduced rats, mice and feral cats (Figure 3). They affected other vertebrate species through predation, often acting together, as a kind of deadly trio. At least 25 bird species were affected in this way, with an additional 23 bird species affected by both cats and rats but without mice. These three invasive species are especially destructive to the endemic vertebrate fauna on small oceanic islands. Among carnivores, feral dogs are also very destructive. They have affected at least 34 vertebrate species. Unlike rodents, feral dogs mainly affect mammals (n = 20 species). They were the ultimate cause of the global extinction of at least 14 giant lemurs in Madagascar. In some regions of Africa, the feral dog may transmit rabies to other carnivore species, especially the endangered Ethiopian wolf Canis simensis, and other members of the family Canidae [34,38]. Only two wild carnivores have been introduced to sub-Saharan Africa: the small Indian mongoose and small Indian civet. The former species negatively affects at least six bird species, while the latter proved to be destructive to only one species, the vulnerable Socotra bunting Emberiza socotrana.

Other groups of introduced mammals have negatively affected sub-Saharan African vertebrate fauna, mainly through habitat destruction. Three of them became especially destructive: the feral goat, feral pig, and European rabbit. The feral pig may also affect some ground-dwelling species through direct predation. It was found especially destructive to land tortoises in the Seychelles, causing global extinction of several species (

Table 3. Vertebrate species threatened by alien mammal species in sub-Saharan Africa.

Species Scientific Name	Common Scientific Name	Family	RDB Status	Eff-Ects	Place	Alien Mammals	Source
AMPHIBIA
Sooglossus thomasetti	Thomasset’s Seychelles Frog	Sooglossidae	E, CR	P **	Seychelles	Tenrecus ecaudatus	[70]
Sooglossus sechellensis	Seychelles Frog	Sooglossidae	E, EN	P **	Seychelles	Tenrecus ecaudatus	[70]
Sechellophryne gardinieri	Gardiner’s Seychelles Frog	Sooglossidae	E. EX	P **	Seychelles	Tenrecus ecaudatus	[70]
REPTILIA
Casarea dussumieri	Round Island keel-scaled Boa	Bolyeriidae	E, EX 1975	H ***	Mauritius: Round Island	Goat, rabbit, hare	[125]
Madatyphlops cariei	Hoffstetter’s Worm snake	Typhlopidae	E, EX c.1800	P ***	Mauritius	Cat, dog, other in-troduced carnivores	[126]
Chioninia coctei	Cape Verde Giant Skink	Scincidae	E, EX:1996	P **	Cape Verde	(Dog, cat)	[127]
Gongylomorphus bojeri	Bojer’s Skink	Scincidae	E, CR	H **	Mauritius: Round Island	Suncus murinus (goat, rabbit)	[126]
Gongylomorphus fontenayi	Orange-tailed Skink	Scincidae	E, EN	P, H **	Mauritius: Gunner’s Quoin	Rat, hare, rabbit	[126]
Leiolopisma ceciliae	Reunion Giant Skink	Scincidae	E, EX c.1700	P **	Reunion	Rats (introduced in 1670)	[128]
Leiolopisma mauritiana	Mauritian Giant Skink	Scincidae	E, EX?	P **	Mauritius	Rats?	[129]
Leiolopisma telfairii	Telfair’s Skink	Scincidae	E, VU	H *	Mauritius: Round Is., G. Quoin	Goat and rabbit	[126]
Phelsuma gigas	Rodrigues Giant Day Gecko	Scincidae	E, EX 1842	P ***	Rodrigues, Frigate Is.	Brown Rat	[129]
Trachylepis comorensis	Comorian Skink	Scincidae	E, LC	P ***	Comoros, Mozambique, Madagascar	Rats	a
Trachylepis socotrana	Socotra Skink	Scincidae	E, LC	P *	Socotra	Cat, Rat, Mouse	b
Nactus durrelli	Durrell’s Night gecko	Gekkonidae	E, VU	H **	Mauritius: Round Island	Goat, rabbit	[125]
Nactus coindemirensis	Lesser Night Gecko	Gekkonidae	E, VU	P, H **	Mauritius: Gunner’s quoin	Rat, hare, rabbit	[125]
Phelsuma guentheri	Günther’s Gecko	Gekkonidae	E, EN	H **	Mauritius: Round Is., Il. Aigrettes	Goat, rabbit	[125]
Tarentola gigas	Cape Verde Giant Gecko	Phyllodactylidae	E, EN	P ***	Cape Verde	Cats, rat, mouse	[130]
Psammobates geometricus	Geometric Tortoise	Testudinidae	E, CR	P *	South Africa (SA): W Cape	Feral pig, cat	[14]
Aldabrachelys abrupta	Abrupt Giant Tortoise	Testudinidae	E, EX 1230–1315	P *	Madagascar	Feral pig, cat	[131]
Aldabrachelys gigantea daudinii	Daudin’s Giant Tortoise	Testudinidae	E, EX c.1850	P *	Seychelles: Mahe	Feral pig, cat	[132]
Cylindraspis indica	Réunion Giant Tortoise	Testudinidae	E, EX c.1840	P *	Reunion	Feral pig, cat	[132]
Cylindraspis inept	Mauritius Giant Tortoise	Testudinidae	E, EX 1844	P *	Mauritius	Feral pig, cat	[132]
AVES
Hirundo atrocaerulea	Blue Swallow	Hirundinidae	E, EN	H *	SA: Mpumalanga	Feral Horse	[14]
Terpsiphone corvina	Seychelles Black Parad. Flycatcher	Monarchidae	E, VU	P *	Seychelles: La Digue	Cat, rat	[74]
Copsychus sechellarum	Seychelles Magpie Robin	Muscicapidae	E, EN	P *	Seychelles: Aride Denis, Frégate,	Cat, rat	[74]
Humboldia flavirostris	Humbolt’s Flycatcher	Muscicapidae	E, VU	P, C *	Comoros	Black Rat, Com. Myna?	a
Coracina newtoni	Réunion Cuckooshrike	Campephagidae	E, CR	P, H *	Reunion	Rat, cat, (deer)	[133]
Zosterops modestus	Seychelles White-eye	Zosteropidae	E, VU	P *	Seychelles	Cat, rat	[74]
Zosterops chloronothos	Mauritius Olive White-eye	Zosteropidae	E, CR	P *	Mauritius: Ile aux Aigrettes	Rat, cat, mongoose	[125]
Zosterops semiflavus	Marianne White-eye	Zosteropidae	E, EX 1892	P **	Seychelles: Marianne Isl.	Blak rat	[134]
Acrocephalus seychellensis	Seychelles Warbler	Acrocephalidae	E, NT	P *	Seychelles	Cat, rat	[74]
Nesillas aldabrana	Aldabra Brush Warbler	Acrocepha-lidae	E, EX 1994	P, H **	Seychelles: Aldabra	Rat, cat, goat	[135]
Foudia sechellarum	Seychelles Fody	Ploceidae	E, NT	P *	Seychelles: Denis	Cat, rat	[74]
Foudia rubra	Mauritius Fody	Ploceidae	E, EN	P **	Mauritius: Ile aux Aigrettes	Rat, cat, mongoose	[125]
Foudia delloni	Reunion Fody	Ploceidae	E, EX 1675–1680	P *	Reunion	Rats	[136]
Onychognathus frater	Socotra Starling	Sturnidae	E, LC	P *	Socotra	Cat	b
Necropsar rodericanus	Rodrigues Starling	Sturnidae	E, EX 1726	P *	Rodrigues	Rat	[136]
Fregilupus varius	Hoopoe Starling	Sturnidae	E, EX 1837	P, H *	Reunion	Rat, cat, goat?	[135]
Chalcomitra balfouri	Socotra Sunbird	Nectariniidae	E, LC	P *	Socotra	Cat	b
Hypsipetes cowlesi	Rodrigues Bulbul	Pycnonotidae	E, EX+?	P *	Rodrigues	Rat?	[136]
Cisticola haesitatus	Socotra Cisticola	Cisticolidae	E, LC	P *	Socotra	Cat	b
Incana incana	Socotra Warbler	Cisticolidae	E, LC	P *	Socotra	Cat	b
Passer insularis	Socotra Sparrow	Passeridae	E, LC	P *	Socotra	Cat	b
Rhynchostruthus socotranus	Socotra Golden-winged Grosbeak	Fringillidae	E, LC	P *	Socotra	Cat	b
Emberiza socotrana	Socotra Bunting	Emberizidae	E, VU	P **	Socotra	Cat, Rat, Indian Small Civet	b
Phaethon aethereus	Red-billed Tropicbird	Phaethonti-dae	LC	P **	Cape Verde	Cat, dog, rat, mouse	[137]
Phaethon lepturus	White-tailed Tropicbird	Phaethonti-dae	LC	P *	Seychelles: Ile du Nord	Rat	[74]
Sula dactylatra	Masked Booby	Sulidae	LC	P *	Seychelles: Grande Ile	Rat	[74]
Sula leucogaster	Brown Booby	Sulidae	LC	P **	Tromelin Island	Cat, dog, rat, mouse	[137]
Papasula abbottii	Abbott’s Booby	Sulidae	EN	P **	Mascarenes, extinct c.1670	(Monkey)	[136]
Hydrobates jabejabe	Cape Verde Storm-petrel	Hydrobatidae	E, NT	P **	Cape Verde	Cat, dog, rat, mouse	[137]
Pelagodroma marina	White-faced Storm-petrel	Procellariidae	LC	P **	Cape Verde	Cat, dog, rat, mouse	[137]
Calonectris edwardsii	Cape Verde Shearwater	Procellariidae	E, NT	P **	Cape Verde	Cat, dog, rat, mouse	[137]
Bulweria bulwerii	Bulwer’s Petrel	Procellariidae	LC	P **	Cape Verde	Cat, dog, rat, mouse	[137]
Pterodroma feae	Cape Verde Petrel	Procellariidae	E, NT	P **	Cape Verde	Cat, dog, rat, mouse	[137]
Puffinus lherminieri boydi	Boyd’s Shearwater	Procellariidae	E, LC	P **	Cape Verde	Cat, dog, rat, mouse	[137]
Fregata magnificens	Magnificent Frigatebird	Procellariidae	LC	P **	Cape Verde	Cat, dog, rat, mouse	[137]
Ardenna pacifica	Wedged-tailed Shearwater	Procellariidae	LC	P *	Seychelles	Rat	[74]
Ardenna pacifica	Wedged-tailed Shearwater	Procellariidae	LC	H *	Mauritius: Round Island	Goat, rabbit	[125]
Pseudobulwaria aterrima	Mascarene Black Petrel	Procellariidae	E, CR	P *	Rodrigues	Cat?	[136]
Leucocarbo melanogenis	Crozet Shag	Phalacrocoracidae	NE, CR	P **	Marion Island	Mouse, cat	[32,92]
Phalacrocorax africanus	African Reed Cormorant	Phalacrocoracidae	LC	P *	Mascarenes, +1710	Rat, feral cat, pigs	[136]
Phalacrocorax nigrogularis	Socotra Cormorant	Phalacrocoracidae	E, VU	P *	Socotra	Cat	[138]
Diomedea exulans	Wandering Albatross	Diomedeidae	VU	P **	Marion Island	Mouse, cat	[32,92]
Thalassarche chrysostoma	Grey-headed Albatross	Diomedeidae	NE	P **	Marion Island	Mouse, cat	[32,92]
Thalassarche carteri	Indian Yellow-nosed Albatross	Diomedeidae	EN	P **	Marion Island	Mouse, cat	[32,92]
Phoebetria fusca	Sooty Albatross	Diomedeidae	NE, EN	P **	Marion Island	Mouse, cat	[32,92]
Phoebetria palpebrata	Light-mantled Albatross	Diomedeidae	NT	P **	Marion Island	Mouse, cat	[76,92]
Gygis alba	White Tern	Laridae	LC	P **	Tromelin Is.	Rat	[139]
Larus dominicanus	Kelp Gull	Laridae	LC	P *	Marion Island	Mouse, cat	[32,92]
Stercorarius antarcticus	Brown Skua	Laridae	LC	P *	Marion Island	Mouse, cat	[32,92]
Aptenodytes patagonicus	King Penguin	Spheniscidae	LC	P *	Marion Island	Mouse, cat	[32,92]
Eudyptes chrysolophus	Macaroni Penguin	Spheniscidae	LC	P *	Marion Island	Mouse, cat	[32,92]
Alopochen mauritiana	Mauritius Sheldgoose	Anatidae	E, EX c.1695	P *	Mauritius	Rat, feral cat, pig	[136]
Alopochen kervazori	Reunion Sheldgoose	Anatidae	E, EX c.1700	P **	Reunion	Rat, feral cat, pig	[136]
Anas theodori	Mascarene Teal	Anatidae	E, EX c.1700	P **	Mauritius	Rat, feral cat, pig	[136]
Threskiornis solitarius	Reunion Ibis	Threskiorni-thidae	E, EX 1761	P **	Reunion	Rat, feral cat, pig	[136]
Bostrychia bocagei	São Tomé Ibis	Threskiorni-thidae	E, CR	P *	São Tomé Is.	Cat, Least Weasel, rat	[140]
Nycticorax mauritianus	Mauritius Night Heron	Ardeidae	E, EX 1693	P **	Reunion	Rat, feral cat, pig	[136]
Nicticorax megacephalus	Rodrigues Night Heron	Ardeidae	E, EX 1726	P **	Rodrigues	Rat, feral cat	[136]
Pelecanus rufescens	Pink-backed Pelican	Pelecanidae	LC	P *	Madagascar, extinct 1960’s	Ras, cat?	[141]
Aphanopteryx bonasia	Mauritius Reed Rail	Rallidae	E, EX c.1695	P *	Mauritius	Monkey, pig, rat	[136]
Dryolimnas augusi	Reunion Rail	Rallidae	E, EX 1675–1705	P *	Reunion	Rat, feral cat, pig	[136]
Dryolimnas cuveri abboti	Assumption White-thr. Rail	Rallidae	E, EX 1908	P **	Seychelles: Assumption Is.	Rats	[134]
Erythromachus leguati	Rodrigues Rail	Rallidae	E, EX c.1726	P *	Rodrigues	Rat, feral cat, pig	[136]
Porphyrio caerulescens	Reunion Blue Gallinule	Rallidae	E, EX c.1720	P *	Reunion	Cat, rat	[136]
Porphyrio sp.	Seychelles Swamphen	Rallidae	E, EX c.1730	P *	Reunion	Cat	[134]
Fulica newtoni	Mascarene Coot	Rallidae	E, EX 1693	P *	Mauritius, Reunion	Rat, pig, cat	[136]
Raphus cucullatus	Dodo	Columbidae	E, EX 1640’s	P, H *	Mauritius	Black Rat, pig, goat	[136]
Peziphaps solitarius	Rodrigue’s Solitaire	Columbidae	E, EX c.1770	P *	Mascarenes	Cats	[136]
Columba thiriouxi	Mauritius Wood Pigeon	Columbidae	E, EX	P *	Mauritius	Black Rat	[136]
Nesoenas duboisi	Reunion Pink Pigeon	Columbidae	E, EX c.1700	P **	Rodrigues	Cat	[136]
Nesoenas rodericana	Rodrigues Turtle Dove	Columbidae	E, EX 1726–1761	P **	Rodrigues	Rat, cat	[136]
Nesoenas cicur	Mauritius Turtle Dove	Columbidae	E, EX c.1730	P **	Mauritius	Rat, cat	[136]
Nesoenas mayeri	Pink Pigeon	Columbidae	E, VU	P **	Mauritius: Ile aux Aigrettes	Rat, cat, mongoose	[125]
Alectroenas nitidissima	Mauritius Blue Pigeon	Columbidae	E, EX 1826	P *	Mauritius	Cats?	[136]
Alectroenas payandeei	Rodrigues Blue Pigeon	Columbidae	E, EX < 1691	P *	Rodrigues	Rats?	[136]
Mascarinus mascarinus	Mascarene Parrot	Psittaculidae	E, EX 1784	P **	Reunion	Rats, cat	[136]
Necropsittacus rodericanus	Rodrigues Parrot	Psittaculidae	E, EX c.1770	P **	Rodrigues	Rat, cat	[136]
Lophopsittacus mauritianus	Broad-billed Parrot	Psittaculidae	E, EX 1670’s?	P *	Mauritius	Monkey, rat	[136]
Psittacula echo	Echo Parakeet	Psittaculidae	E, VU	P **	Mauritius: Mauritius	Rat, cat, mongoose	[125]
Psittacula exsul	Newton’s Parakeet	Psittaculidae	E, EX 1875	P **	Rodrigues	Rat, cat, mongoose?	[134]
Otus suazieri	Mauritius Scops Owl	Strigidae	E, EX 1837	P *	Mauritius	Rat	[136]
Otus grucheti	Reunion Scops Owl	Strigidae	E, EX 1700s	P *	Reunion	Cat and rat	[136]
Otus murivorus	Rodrigues Scops Owl	Strigidae	E, EX 1726–1761	P *	Rodrigues	Rat	[136]
Otus pauliani	Grande Comore Scops Owl	Strigidae	E, EN	P **	Comoros	Cat and rats?	138; c
Otus moheliensis	Moheli Scops Owl	Strigidae	E, EN	P *	Comoros	Black Rat?	138; a
Falco punctatus	Mauritius Kestrel	Falconidae	E, EN	P **	Mauritius: Mauritius	Rat, cat, mongoose	[125]
Circus maillardi	Reunion Harrier	Accipitridae	E, EN	P *	Reunion, Mauritus, extinct 1606	Rat, cat, mongoose?	[64]
Aepyornis maximus	Elephant Bird	Aepyornithidae	E, EX 1100–700 BP	P *	Madagascar	Dog	[141]
Aepyornis hildebrandti	Hildebrand’s Elephant Bird	Aepyornithidae	E, EX 1040–1380 AD	P *	Madagascar	Dog	[141]
Mullerornis modestus	Elephant Bird	Aepyornithidae	E, EX 680–880 AD	P *	Madagascar	Dog	[141]
MAMMALIA
Gymnuromys robertsi	Voalavoanala	Nesomyidae	E, LC	C *	Madagascar	Black Rat?	[64,142]
Nesomys audeberti	White-bellied Nesomys	Nesomyidae	E, LC	C *	Madagascar	Black Rat?	[143]
Nesomys rufus	Island Mouse	Nesomyidae	E, LC	C *	Madagascar	Black Rat?	[143]
Eliurus tanala	Tanala Tufted-tailed Rat	Nesomyidae	E, LC	C *	Madagascar	Black Rat?	[143]
Eliurub webbi	Webbie’s Tufted-tailed Rat	Nesomyidae	E, LC	C *	Madagascar	Black Rat?	[143]
Pachylemur insignis	Giant Lemur	Lemuridae	E, EX c.1500	P *	Madagascar	Dog	[144,145]
Eulemur fulvus	Common Brow Lemur	Lemuridae	E, VU	P *	Madagascar Mayotte (introduced)	Dog	[66]
Propithecus verreauxi	Verreaux’s Sifaka	Indridae	E, CR	P *	Madagascar	Dog	[66]
Archaeolemur majori	Baboon Lemur	Archaeolemuridae	E, EX 1100–700 BP	P *	Madagascar	Dog	[66]
Archeolemur edwardsi	Monkey Lemur	Archaeolemuridae	E, EX, 500 BP	P *	Madagascar	Dog)	[146]
Hadropithecus stenognathus	Monkey Lemur	Archaeolemuridae	E, EX 444–772	P, H **	Madagascar	Feral cattle, pig and dog	[146]
Megaladapsis madagascariens.	Koala Lemur	Megaladapidae	E, EX 500–600 BP	P *	Madagascar	Dog?	[144]
Megaladapsis grandidieri	Koala Lemur	Megaladapidae	E, EX 500–600 BP	P *	Madagascar	Dog?	[144]
Megaladapsis edwardsi	Koala Lemur	Megaladapidae	E, EX 500–600 BP	P *	Madagascar	Dog?	[144]
Palaeopropithecus ingens	Sloth Lemur	Palaeopropi-thecidae	E, EX 1100–700 BP	P *	Madagascar	Dog	[66]
Mesopropithecus pithecoides	Sloth Lemur	Palaeopropi-thecidae	E, EX 570–679 CE	P *	Madagascar	Dog	[144]
Mesopropithecus globiceps	Sloth Lemur	Palaeopropi-thecidae	E, EX 570–679 CE	P *	Madagascar	Dog	[144]
Mesopropithecus dolichobrachion	Sloth Lemur	Palaeopropi-thecidae	E, EX 570–679 CE	P *	Madagascar	Dog	[144]
Babakotia radofilai	Sloth Lemur	Palaeopropi-thecidae	E, EX c.1000 BC	P *	Madagascar	Dog	[66]
Daubentonia robusta	Giant Aye-aye	Daubentonidae	E, EX 900–1150 CE	P *	Madagascar	Dog	[147]
Daubentonia madagascarensis	Aye-aye	Daubentoniidae	E, EN	P *	Madagascar	Black Rat?	[64]
Cryptoprocta ferax	Fossa	Eupleridae	E, VU	P, C *	Madagascar	Dog	[66]
Felis silvestris lybica	African Wild Cat	Felidae	LC	P *	Namibia, Botswana, SA	Feral Cat	[14]
Equus zebra	Mountain Zebra	Equidae	VU	H *	SA: N Cape; Namibia	Feral Donkey	[14]
Equus quagga quagga	Quagga	Equidae	EX, c.1878	G *	SA: Cape, Free State	Feral donkey?	[72]
Equus africanus africanus	Nubian wild ass	Equidae	EX	G **	Ethiopia; Eritrea: Nubian Desert	Feral Donkey	[148]
Hippopotamus laloumena	Malagasy Hippo	Hippopotamidae	E, EX 1670–1950 AD	P, H *	Madagascar	Dog, feral goat	[147,149]
Hippopotamus lemerlei	Lemerle’s Dwarf Hippopotamus	Hippopotamidae	E, EX 670–836 AD	P, H *	Madagascar	Dog, feral goat?	[147,149]
Hippopotamus madagascariensis	Madagascar Dwarf Hippopotamus	Hippopotamidae	E, EX 687–880 CE	P, H *	Madagascar	Dog, feral goat?	[147,149]
Hippotragus leucophaeus	Bluebuck	Bovidae	EX c.1800	H *	SA: W Cape	Feral goat, deer	[150]

Effects: H—habitat destruction, P—predation, C—competition, G—hybridization; ***—the only cause, **—additional main cause underlined in some cases to distinguish among few species), *—additional minor cause. RDB: EX—extinct, CR—critically endangered, EN—endangered, VU—vulnerable, NT—near-threatened. Endemicity: E—endemic, NE—near-endemic. Alien mammals: in bracket—additional, but often ultimate/final cause of extinction. Internet sources: a—www.aniamlia.bio/comoros (accessed on 2 April 2025); b—www.aniamlia.bio/socotra (accessed on 2 April 2025); c—www.birdlife.datazone (accessed on 2 April 2025), Otus pauliani.

).

In continental Africa, only seven vertebrate species were negatively affected by alien mammals, including three extinct species (bluebuck, quagga zebra and African ass). All the other affected vertebrates occur on islands (

Table 4. Familiar affinities of threatened species. Ex—extinct, En—threatened (in RDB), O—declining, rare, etc., but not in RDB.

Taxa	Ex	En	O	Total
	n	n	n	n	%
PISCES	0	0	0	0	0.0
AMPHIBIA	0	3	0	3	2.1
Sooglossidae	3	0	0	3	2.1
REPTILIA	10	9	4	23	16.0
Bolyeriidae	1	0	0	1	0.7
Typhlopidae	1	0	0	1	0.7
Scincidae	4	3	4	11	7.6
Gekkonidae	0	3	0	3	2.1
Phyllodactylidae	0	1	0	1	0.7
Testudinidae	4	2	0	6	4.2
AVES	37	31	21	89	61.8
Aepyornithidae	3	0	0	3	2.1
Phaethontidae	0	0	2	2	1.4
Sulidae	0	0	2	2	1.4
Hydrobatidae	0	1	0	1	0.7
Procellariidae	0	3	6	9	6.3
Phalacrocoracidae	1	2	0	3	2.1
Diomedeidae	0	5	0	5	3.5
Laridae	0	0	3	3	2.1
Spheniscidae	0	0	2	2	1.4
Anatidae	3	0	0	3	2.1
Threskiornithidae	1	1	0	2	1.4
Ardeidae	2	0	0	2	1.4
Pelecanidae	0	1	0	1	0.7
Rallidae	7	1	0	8	5.6
Columbidae	8	1	0	9	6.3
Psittaculidae	4	1	0	5	3.5
Strigidae	3	2	0	5	3.5
Falconidae	0	1	0	1	0.7
Accipitridae	0	1	0	1	0.7
Hirundinidae	0	1	0	1	0.7
Monarchidae	0	1	0	1	0.7
Muscicapidae	0	2	0	2	1.4
Campephagidae	0	1	0	1	0.7
Zosteropidae	1	2	0	3	2.1
Acrocephalidae	1	1	0	2	1.4
Ploceidae	1	2	0	3	2.1
Sturnidae	1	0	1	2	1.4
Nectariniidae	0	0	1	1	0.7
Pycnonotidae	1	0	0	1	0.7
Cisticolidae	0	0	2	2	1.4
Passeridae	0	0	1	1	0.7
Emberizidae	0	1	0	1	0.7
Fringillidae	0	0	1	1	0.7
MAMMALIA	18	5	6	29	20.1
Nesomyidae	0	0	5	5	3.5
Lemuridae	1	1	0	2	1.4
Indrididae	0	1	0	1	0.7
Archeolemuridae	3	0	0	3	2.1
Megaladapidae	3	0	0	3	2.1
Palaeopropithecidae	5	0	0	5	3.5
Daubentonidae	1	1	0	2	1.4
Eupleridae	0	1	0	1	0.7
Felidae	0	0	1	1	0.7
Equidae	1	1	0	2	1.4
Hippopotamidae	3	0	0	3	2.1
Bovidae	1	0	0	1	0.7
Total number of species	65	45	31	144	100.0

and

Table 5. Geographical distribution of the impacts. Ex—extinct, En—threatened (in RDB), O—declining, rare, etc., but not in RDB.

Places	Reptilia			Aves			Mammalia			Total
	Ex	En	O	Ex	En	O	Ex	En	O	Ex	En	O
AFRICA: continent	1	1	0	0	1	0	3	1	1	3	3	1
Ethiopia/Eritrea	0	0	0	0	0	0	1	0	0	1	0	0
Southern Africa	0	0	0	0	0	0	0	1	1	0	1	1
South Africa	0	1	0	0	1	0	2	0	0	2	2	0
AFRICA: islands	9	10	2	42	29	24	16	4	5	68	43	32
Cape Verde	1	1	0	0	3	5	0	0	0	1	4	5
Gulf of Guinea islands	0	0	0	0	1	0	0	0	0	0	1	0
Marion Isl.	0	0	0	0	6	4	0	0	0	0	6	4
Madagascar	1	0	0	3	1	0	16	4	5	20	5	5
Mauritius	3	9	0	11	7	2	0	0	0	14	16	2
Reunion	2	0	0	12	1	2	0	0	0	14	1	2
Rodrigues	2	0	0	12	1	0	0	0	0	14	1	1
Other Mascarenes	0	0	0	1	1	1	0	0	0	1	1	1
Comoros	0	0	1	0	3	0	0	0	0	0	3	1
Seychelles	1	0	0	3	5	3	0	0	0	4	5	3
Socotra	0	0	1	0	1	7	0	0	0	0	1	8
Total	10	11	2	42	30	24	19	5	6	71	46	33

, Figure 3). However, while islands in the Atlantic Ocean witnessed only one extinction (Cape Verde), all the others died out on islands in the Indian Ocean. An especially high rate of the extinction caused by alien mammals was recorded in the Mascarenes, mainly birds (35 species), with a few mammals (n = 7) and no amphibian and fish species. In contrast, only four species (three birds and one reptile) became extinct in the Seychelles. It is probably because the Mascarenes were occupied and transformed by humans much earlier than the Seychelles. In Madagascar, most extinct species were among mammals (n = 16), with three birds and one reptile species.

6. Impact of Alien Mammals on Islands

6.1. Cape Verde

The archipelago Cape Verde (4033 km², 538 thousand people) is part of a larger archipelago, Macaronesia, which also includes the Canary Islands, Madeira and Azores. Cape Verde is an independent state, which encompasses 10 larger and 16 small islands. The vertebrate fauna is represented by 130 bird species (including 40 breeding species), only 3 mammals (all bats), and 15 reptiles (including 12 endemics) (https://en.wikipedia.org/wiki/Wildlife_of_Cape_Verde; accessed on 2 April 2025). In addition, there is only one invasive fish species, the Guppy Poecilia reticulata [151].

Seabirds suffered extinctions after the arrival of humans and the introduction of alien species by humans. On one of Cape Verde’s islands, Santa Luzia, an uninhabited island of 35 km², the following main bird species were extirpated: the white-faced storm petrel Pelagodroma marina eadesorum, Boyd’s shearwater Pufinus lherminieri boydi, Cape Verde storm Petrel Hydrobates jabejabe, Cape Verde shearwater Calonectris edwardsii. The recent extinction of these species on Santa Luzia might be a consequence of the arrival of humans and their domestic animals (mainly cats) [152].

Currently, the breeding seabird community in Cape Verde is composed of Bulwer’s petrel Bulweria bulwerii, white-faced storm-petrel Pelagodroma marina aedesorum, Cape Verde shearwater Calonectris edwardsii, Cape Verde storm-petrel, Cape Verde petrel, Boyd’s shearwater Puffinus lherminieri boydi, brown booby Sula leucogaster, and red-billed tropicbird Phaethon aethereus. One breeding species is currently extinct, the magnificent frigatebird Fregata magnificens [153]. Cape Verde petrel is currently considered near threatened, and cats are the main problem [140].

6.2. São Tomé e Principe and Other Islands in the Gulf of Guinea

There are four islands in the Gulf of Guinea in the Atlantic Ocean, the south-west of Cameroon: two islands forming an independent state, São Tomé (854 km², 193 thousands people in 2018) and Principe (136 km², 5000 people in 2017), and two islands belonging to Equatorial Guinea, Bioko (2017 km², 335 thousands people in 2015) and Annabon (17 km², 5323 people in 2013). Most of the islands were not inhabited before the Portuguese conquest in 1493, while Bioko has been occupied by the Bantu people since the 7th century.

The vertebrate fauna is composed of 143 bird species (including 23 endemics), 15 mammals (including 7 endemics), 14 reptiles (all endemics), 9 amphibians (all endemics), and 6 fish species (including 1 introduced, the Nile Tilapia Oreochromis niloticus niloticus).

The International Action Plan is designed for the conservation of the three critically endangered bird species, endemic to the island of São Tomé: the dwarf olive ibis Bostrychia bocagei, the São Tomé fiscal Lanius newtoni and the São Tomé grosbeak Neospiza concolor [154]. Predation on adults, juveniles and nests by introduced mammal species could be a potential threat to all three species and, in particular, to the olive ibis, although there are no recorded predation events. The introduced black rat, mona monkey, African civet, cat and least weasel are all potential predators. Rats and the African civets have both colonized primary forests or certainly the edges of this vegetation and are very likely to have had a deleterious effect upon nesting birds. However, civets and weasels have been observed to prefer plantations [155].

6.3. Madagascar

Madagascar is the fourth largest island in the world (592,796 km²), with a population of 32 million in 2024. The island was permanently colonized by Austronesians about 2000 years ago. It is a megadiverse country with about 90% of endemic fauna: 241 mammal species (99% endemics), 280 bird species (including 200 breeding species, and c. 100 endemics), 280 reptile species (>90% endemics), 290 amphibian species (99% endemics) and 150 freshwater fish species (99% endemics) (https://en.wikipdia.org/wiki/Fauna_of_Madagascar; accessed on 2 April 2025).

By 600 AD, people began clearing the forests of the central highlands. About 1000 years ago, they were joined by the Bantu people from eastern Africa, who brought the zebu Bos taurus indicus, Sanga Bos taurus africanus cattle, and dog Canis familiaris. Since then, devastation of the natural vegetation has been greatly accelerated. The extinction event that wiped out much of the endemic megafauna on Madagascar, such as the two elephant birds, giant fossa Cryptoprocta spelea, seventeen species of giant lemurs and three hippopotamuses species, followed the arrival of humans to Madagascar around 2000 years ago and dogs about 1000 years ago [141,148]. This megafauna was intensively hunted by humans, accompanied by the dog, for meat and eggs (elephant birds), and, to a lesser extent, by feral dogs. Their extinction was also caused by habitat loss and fragmentation through the slash-and-burn techniques of early farmers. Habitats were also changed due to climate change [147,156,157,158,159,160].

6.4. Mascarenes

Mascarenes is an archipelago of the independent state Mauritius (2040 km², and 1.2 million people in 2020; including Rodrigues: 108 km², Agalega: 24 km² and St. Brandon: 1.3 km²) and a few French overseas dependencies, including Reunion (2511 km², settled in 17th century) and Mayotte (374 km²; 257 thousand people in 2020). The dependencies include four small uninhabited coral islands, named Iles esparses (Dispersed Islands) in Mozambique Chanel (Europa: 28 km², Glorieuses: 7 km², Juan de Nova: 5 km² and Bassa da India: atoll 0.2 km²) and Tormeli Island (0.8 km²) east of Madagascar. All these islands constitute a part of French Southern and Antarctic Territories.

Mascarenes fauna has been threatened since the 17th century, when humans began to settle on the islands, transforming forests into cultivated fields and pastures. The domestic mammal species, such as cats, pigs, and also rats and monkeys, further accelerated the erosion of local biodiversity. Mauritius and Reunion were especially severely impacted. In Mauritius, 18 species became extinct in the course of the 17th–20th centuries. On various islands of Mauritius, Rodrigues, Mayotte, and Seychelles, the successful eradication of alien mammals took place in 1990–2010. The following species were targeted: feral goat, rats, cats, common tenrec and house mouse [125,134,136].

6.5. Comoros

Comoros is an archipelago of four islands (and independent state Comoros with three islands, and Mayotte which is a French overseas department), with a total surface area of 2235 km². It was settled by Austronesian people in the 9th century and later also by Arab and Bantu people. There are 15 threatened bird species and 2 species of terrestrial mammals, viz. the common brown lemur Eulemur fulvus (only in Mayotte, where it is classified as ‘vulnerable’) and the mongoose lemur Eulemur mongoz. Although the latter is in the ‘critically endangered’ category in Comoros, it is regarded as a probably alien species, introduced to Comoros from Madagascar [161,162]. Among birds, two Otus owl species and the Humbold’s flycatcher Humboldia flavirostris are threatened by rats. The Comorian skink Trachylepis comorensis is threatened by feral dogs.

6.6. Seychelles

The Seychelles is an archipelago (and independent state) of 155 small islands, with a total surface area of only 457 km² (the biggest: Mahe: 157 km², Praslin: 39 km² and La Digue: 10 km²) and a population of 100,600 in 2022. Permanent settlements on the islands began with the Portuguese colonization as late as in the 1770s. The vertebrate fauna includes 285 bird species (11 extinct or extirpated, 14 endemic, 16 globally endangered), only 9 terrestrial mammals (6 species of bats and 3 introduced spp.), 14 amphibian (13 endemic), 20 lizard (>3 endemic) and 3 snake (2 endemic) species (https://en.wikipedia.org; accessed on 2 April 2025). Rats and cats threaten several endemic species in the Seychelles, namely Seychelles black paradise flycatcher Terpsiphone corvina, Seychelles magpie robin Copsychus sechellarum, Seychelles White-eye Zosterops modestus, Seychelles Warbler Acrocephalus seychellensis, Seychelles fody Foudia sechellarum, Wedged-tailed shearwater Ardenna pacifica, white-tailed tropicbird Phaethon lepturus, masked booby Sula dactylatra [163]. Six bird species became extinct in the Seychelles, e.g., Marianne white-eye, Seychelles parakeet, Aldabra brush warbler. In addition to these, the saltwater crocodile Crocodilus porosus and most of the giant tortoises from the 40 granitic islands also became extinct. However, the total number of extinct species was, by far, much lower in the Seychelles than in Mauritius, partly due to a shorter period of human occupation of the previous one.

6.7. Socotra

After Madagascar, it is the second largest African island, with a surface area of 3625 km² and c. 60 thousand people. It is situated in the Gulf of Aden between the Horn of Africa and the Arabian Peninsula. No later than 2000 years ago, the island was permanently settled by Arab and Indian people. Today, it is administered by Yemen. Socotra is home to 180 species of birds (41 breeding, and 10 endemic), 14 species of mammals, including domesticated species, and the only indigenous mammals, bats, and 22 reptile species (including 19 endemic) (https://www.welcometosocotra.com/fauna-and-flora; accessed on 2 April 2025). Some vertebrate species are negatively affected due to habitats destroyed by feral mammals [74]. One of the reptile species, Trachylepis socotrana skink, is threatened by invasive species [163].

6.8. Prince Edward Islands

These two uninhabited sub-Antarctic volcanic islands, Marion (279 km²) and Prince Edward (46 km²), harbor a wealth of sub-Antarctic seabirds and marine mammals. Both islands are administered by South Africa. The islands constitute breeding grounds of millions of seabirds from 29 species: 4 penguins, 5 albatrosses, 2 giant petrels, 7 petrels, 2 prions, 2 diving-petrels, at least 2 storm-petrels, and 2 terns and brown skua, kelp gull and Crozet shag [32,76,92]. About 800,000 pairs of the king and the macaroni penguin nest in colonies on the islands [164]. The most abundant birds on the islands are burrow-nesting petrels. The numbers of burrowing petrels were greatly reduced by cats that roamed Marion Island from 1948 to 1991. The density of burrows on Marion Island is much lower than on the neighboring Prince Edward Island, where there are no introduced mammals. The eradication of cats led to some recovery in petrel numbers, but this has been slower than expected due to predation by mice, introduced to the islands before cats [51,165,166,167].

7. Conclusions

As in other parts of the world, feral cats, dogs, mice and rats are the most destructive alien mammal species in the Afrotropical Region. While their negative impact is low on the continent, it is very high on islands around Africa, especially in the Indian Ocean. Ideally, they should be totally eradicated from these islands. Most other alien mammals do not pose serious threats to vertebrate fauna on the continent but can still be destructive on islands. Alien mammals in sub-Saharan Africa are most destructive to birds, less so to mammals, much less to reptiles and amphibians and have almost no effect on fish. A new threat has emerged through the release of pet species (mainly rodents) to nature. The mammal pet trade should be strictly controlled and prohibited. The status of alien species in sub-Saharan Africa is rather poorly investigated, but knowledge on the distribution, numbers and population dynamics is essential for effective control of this invasion.