Studies of the impact of alien species on the environment are increasingly being carried out, and there has been ongoing debate about how to standardise the description of these impacts. This chapter evaluates the state of knowledge on the impacts of alien species on biodiversity in South Africa based on different assessment methods. Despite South Africa being one of the most biologically diverse countries in the world, there have been very few studies that formally document the impacts of alien species on biodiversity. Most of what is known is based on expert opinion, and consequently the level of confidence in the estimates of the magnitude of these impacts is low. However, it is clear that a significant number of alien species cause major negative impacts, and that there is cause for serious concern. There is a growing global effort to assess all alien species with standardised protocols to alleviate the problem of comparing impacts measured using different approaches. Formal assessments have been done for a few alien species in South Africa, but most naturalised and invasive species have not been evaluated, and, we suspect, for most alien species there has been no attempt, as yet, to document their impacts. However, red-listing processes found that alien species were frequently included as a significant extinction risk for several native species of fish, amphibians, and plants. There are very few studies that cover the combined impacts of co-occurring alien species in particular areas, and these studies could provide the rationale for regulation and management, which is often absent. While reductions due to alien species in the value of ecosystem services, the productivity of rangelands, and biodiversity intactness are relatively low at present these impacts are expected to grow rapidly as more invasive species enter a stage of exponential growth.
South Africa occupies only 2% of the world’s land area but it is one of the most biologically diverse countries globally (Mittermeier et al. 1997). For example, it is estimated that 7% of the world’s vascular plants, 5% of mammals and 7% of birds are found in South Africa (Le Roux 2002). In addition, more than half of the plants, butterflies, amphibians and reptiles native to South Africa are endemic (Colville et al. 2014). This is partly because of the country’s diverse environmental conditons that have resulted not only in high species diversity and endemism, but also in a diversity of terrestrial, freshwater and marine ecosystems (van Wilgen et al. 2020a, Chap. 1; Wilson et al. 2020, Chap. 13) . The country’s terrestrial vegetation types can be broadly grouped into nine biomes that range from deserts and Mediterranean-climate shrublands (fynbos) in the west to grasslands and savanna in the eastern interior, and evergreen forests in high rainfall areas along the east coast (Mucina and Rutherford 2006). Three areas within these biomes—the Cape Floristic Region , the Succulent Karoo , and the Maputaland-Pondoland-Albany region—have been designated global biodiversity hotspots (Myers et al. 2000; Mittermeier et al. 2004). The marine realm includes several ecosystems in the surrounding Indian and Atlantic oceans and offshore islands (van Wilgen et al. 2020a, Chap. 1). The marine ecosystems are also diverse with over 12,000 species that represent 15% of all known coastal marine species worldwide (Le Roux 2002; Griffiths et al. 2010).
Alien species can change the composition, structure and functioning of biodiversity in many ways. Examples include hybridisation with native species (e.g. Tracey et al. 2008), extirpation of native species through predation (e.g. Rodda and Fritts 1992) or disease transmission (Hulme 2014), alterations to the structure of vegetation by introducing novel growth forms (van Wilgen and Richardson 1985) , and changes to ecosystem processes like fire (Brooks et al. 2004) and hydrology (Le Maitre et al. 2015). A recent study concluded, based on data from the IUCN Red List, that alien species were the most common threat associated with extinctions of mammals, amphibians and reptiles, and for vertebrate extinctions overall (Bellard et al. 2016a).
In South Africa, a total of 107 alien species are suspected to have major negative impacts on biodiversity, and most (75%) of these are plants (van Wilgen and Wilson 2018). Despite these concerns, there have been relatively few studies that have formally quantified the impacts of alien species on different facets of biodiversity in South Africa. In a review focussing on alien plants, Richardson and van Wilgen (2004) concluded that information on the ecological impacts of alien plants was generally poor, and that the consequences of invasions for the delivery of ecosystem goods and services were, with the notable exception of their influence on water resources , inadequately studied. Since then, the situation has improved to some degree.
This chapter evaluates the state of knowledge on the impacts of alien species on biodiversity in South Africa based on different assessment methods. It focuses mainly on explicit knowledge of impacts of alien species on compositional and structural aspects of biodiversity at a species scale, and less at genetic, community, and ecosystem scales (cf. Noss 1990). Some references are presented that discuss the cumulative impact of all invasions on biodiversity, but how these impacts interact with other global change drivers is not covered.
2 Assessing the Impact of Alien Species on Biodiversity
Different approaches have been used to quantify, assess and summarise the impacts caused by alien species on native biodiversity. Here, we focus on three main methods: impact-scoring schemes, expert opinion assessments, and impacts identified during red-listing processes. Impact scoring schemes such as the Environmental Impact Classification for Alien Taxa (EICAT; Blackburn et al. 2014; Hawkins et al. 2015; see also Box 17.1) and the Socio-Economic Impact Classification of Alien Taxa (SEICAT; Bacher et al. 2018), amongst others, can be used to formally assess and quantify impacts of individual alien species. Impact-scoring schemes are based on published evidence, and aim to make impacts comparable between taxa and regions by assigning them to semi-quantitative classes which are clearly defined to minimise assessor bias. We focus here on the EICAT scheme as it is most relevant for impacts of a particular alien species on native species. Expert opinion studies (e.g. Zengeya et al. 2017) also assess impacts of specific alien species, but use experts rather than published impact evidence to gauge impacts. Expert opinion studies can be done at a species level (impact of a particular alien species on native species) and or on the entirety of invasions on an ecosystem (e.g. ecosystem services; van Wilgen et al. 2008). Lastly, the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species reports threats from a combination of invasions on a particular native species (Mace et al. 2008).
Box 17.1 The Environmental Impact Classification for Alien Taxa (EICAT)
EICAT is a simple, objective and transparent method to classify alien taxa according to the magnitude of environmental impacts caused in their introduced ranges (Blackburn et al. 2014; Hawkins et al. 2015). It assesses impacts caused by a specific alien taxon (mostly a species) on native species in the recipient area and can help identify taxa with different levels of impacts as well as facilitate comparisons of impacts between taxa and regions. Based on published records of impacts, EICAT classifies detrimental impacts based on 12 mechanisms, namely:
Transmission of diseases
Chemical, physical or structural impact on ecosystem
Interaction with other taxa
Furthermore, if records of impact are available, EICAT distinguishes between five impact levels based on the organisational level of the species affected, as follows:
Minimal Concern (MC)—the alien taxon does not affect the performance of any native species it interacts with through any of the above mentioned mechanisms
Minor (MN)—the alien taxon affects the performance of at least one native species through any of the above mentioned mechanisms, but does not affect population size
Moderate (MO)—the alien taxon reduces the population size of at least one native species through any of the above mentioned mechanisms, but the native species is still present in the community
Major (MR)—the alien taxon leads to the local or metapopulation extinction of at least one native species changing the native community, with the impacts being reversible when the alien taxon is no longer present
Massive (MV)—irreversible community changes caused by the alien taxon through the local, sub-population or global extinction of at least one native species
If no data on impacts of the taxon in the alien range is available, it is classified as Data Deficient (DD).
EICAT is in the process of being adopted by the IUCN as a standard system for classifying invasive alien species based on the nature and magnitude of their impacts (see https://www.iucn.org/theme/species/our-work/invasive-species/eicat for more details).
2.1 Impact-Scoring Schemes
The Environmental Impact Classification for Alien Taxa has been applied to various taxa that are known to occur as alien species in South Africa including grasses (Visser et al. 2017; Nkuna et al. 2018; Canavan et al. 2019), amphibians (Kumschick et al. 2017), birds (Evans et al. 2016), mammals (Hagen and Kumschick 2018), fish (Marr et al. 2017), gastropods (Kesner and Kumschick 2018), and some other invertebrates (Nelufule 2018). Most EICAT assessments performed to date have been done at a global scale, i.e. including all records of impact of a given species in its global alien range. It is important to note that although global assessments are comprehensive, there will need to be regularly updated as further assessments are done at national scales. In South Africa, national-level EICAT assessments have been done for some alien grasses (Visser et al. 2017) and fishes (Marr et al. 2017) (Table 17.1).
A global effort is in progress to use EICAT to assess all species in their alien ranges, and researchers from South Africa have contributed many assessments to date. Evidence-based assessments are also needed in South Africa for regular reporting on the status of biological invasions (van Wilgen and Wilson 2018; Wilson et al. 2018; van Wilgen et al. 2020a, Chap. 1). Moreover, the risk analysis framework currently used as evidence to support listing of alien species in South Africa (Kumschick et al. 2018) requires impact assessments analogous to EICAT (Kumschick et al. 2020, Chap. 20). However, while some progress has been made, there is still a very large number of species that have to be formally assessed in South Africa.
There are six grass species that have had EICAT assessments done at a national scale for South Africa, with Arundo donax (Giant Reed) and Glyceria maxima (Reed Meadow Grass) evaluated as having major impacts (Visser et al. 2017; Nkuna et al. 2018; VK Nkuna, unpublished data). These two species have been implicated in competitively displacing native species; A. donax, for example, dominates riparian areas and can locally exclude native plants (Holmes et al. 2005; Guthrie 2007), while G. maxima has locally displaced some native wetland species (Mugwedi 2012).
Thirty-four gastropod species alien to South Africa have formal global EICAT assessments. Four of these—Helisoma duryi (Seminole Rams-Horn), Tarebia granifera (Quilted Melania Snail), Oxychilus draparnaudi (Drapanaud’s Glass Snail) and Theba pisana (White Garden Snail)—are known to change community structures in their global invaded range (Kesner and Kumschick 2018). For example, H. duryi outcompetes and displaces native snail species (e.g. Christie et al. 1981), T. granifera has been implicated in causing local extinctions of native snails in wetlands (e.g. Karatayev et al. 2009 ) and O. draparnaudi is a predator that causes the local disappearance of prey species (e.g. Frest and Sanders Rhodes 1982).
In South Africa, the only documented impacts are for Tarebia granifera and Theba pisana. The former was accidentally introduced into South Africa through the aquarium trade and has since invaded several rivers, lakes, wetlands and estuaries in the eastern and northern parts of the country (Appleton et al. 2009). It can reach high population densities, and has been implicated in displacing native snails and becoming the dominant component of invertebrate assemblages in invaded areas (Miranda and Perissinotto 2014). Theba pisana can reach high densities on the west and south coast of South Africa, with the potential to impact on native fauna and flora (Odendaal et al. 2008).
No fish species have been globally assessed with EICAT to date, but an assessment of alien fish species naturalised in South Africa identified five species that have negative impacts (Marr et al. 2017). Micropterus dolomieu (Smallmouth Bass), M. salmoides (Largemouth Bass), Oncorhynchus mykiss (Rainbow Trout), Salmo trutta (Brown Trout) and Oreochromis niloticus (Nile Tilapia) are known to have adverse impacts in South Africa that span all levels of biological organisation from gene to ecosystem (Ellender and Weyl 2014). On a genetic level, the integrity of native Oreochromis mossambicus (Mozambique Tilapia) is under threat from hybridisation with O. niloticus, a species introduced for aquaculture (Firmat et al. 2013). Evidence of species and population-level impacts are mainly linked to direct predation by O. mykiss, S. trutta and Micropterus species (Black Basses), which have resulted in local extirpations of native fishes and invertebrates (Ellender and Weyl 2014; van der Walt et al. 2016; Shelton et al. 2018).
Oncorhynchus mykiss and S. trutta are cold water species that, as a result of stocking for sport fishing, have naturalised in many cool, well-oxygenated headwater streams in the country (Ellender et al. 2017; Weyl et al. 2017a). They are generalist predators that feed primarily on aquatic invertebrates, but will also opportunistically prey on terrestrial invertebrates, fish and amphibians. Their impacts therefore span numerous trophic levels, and in South Africa include the decline, and in some cases local extirpation, of native invertebrates, frogs and fish (Karssing et al. 2012; Rivers-Moore et al. 2013; Jackson et al. 2016). Oncorhynchus mykiss and S. trutta have also been implicated in the decline of populations of Hadromophryne natalensis (Natal Cascade Frog) in a streams in the uKhahlamba Drakensberg Park (Karssing et al. 2012). The two trout species have aslo been implicated in the extirpation of the endangered fish Amatolacypris trevelyani (Border Barb) in headwater streams of the Keiskamma River in the Eastern Cape . In the Breede River system, Shelton et al. (2015b) demonstrated that the abundance (mean density and biomass) of native fish species—Pseudobarbus burchelli (Breede River Redfin), Sandelia capensis (Cape Kurper) and Galaxias zebratus (Cape Galaxias), were 5–40 times lower where O. mykiss was present, and that invertebrate species assemblages in streams with O. mykiss were distinctly different from those found in streams without O. mykiss . In addition, Shelton et al. (2015a) observed that O. mykiss had a weaker predation effect on aquatic invertebrates relative to the native fishes that it had replaced. As a result, there was also evidence of cascading effects, with algal biomass being significantly lower when O. mykiss was present because of higher abundance of herbivorous invertebrates relative to uninvaded sites. In the Drakensberg, and the Keiskamma River system, O. mykiss and S. trutta also share emerging insects as a food resource with riparian spiders, causing a decline in spider abundance at invaded sites (Jackson et al. 2016).
Black bass is the collective name for species of the genus Micropterus which, in South Africa, includes M. salmoides, M. dolomieu, M. punctulatus (Spotted Bass) and M. floridanus (Florida Bass) (Weyl et al. 2017b). As warm water species, Black Bass were introduced for sport fishing in the lower reaches of rivers and impoundments (see Khosa et al. 2019). Their impacts are similar to those documented for O. mykiss and S. trutta , and include the alteration of invertebrate communities (Weyl et al. 2010) and local extirpations and fragmentation of native fish populations (e.g. Kimberg et al. 2014; van der Walt et al. 2016; Ellender et al. 2018). A quantitative assessment of aquatic invertebrates in the Wit River, Eastern Cape , found that M. salmoides changed relative abundance and community structure (Weyl et al. 2010). In sections with M. salmoides, several members of large or conspicuous taxa (Odonata, Hemiptera and Coleoptera) were significantly reduced or even absent, while members of cryptic/inconspicuous taxa (Trichoptera, Leptoceridae, Mollusca, and Physidae) were significantly more abundant. In the headwaters of the Swartkops River system in the Eastern Cape, for example, M. salmoides predation has fragmented populations of the now endangered Pseudobarbus afer (Eastern Cape Redfin) (Ellender et al. 2018). Similarly, in the Olifants River system in the Western Cape, M. dolomieu and M. punctulatus invasions have restricted native Cedercypris calidus (Clanwilliam Redfin) and Pseudobarbus phlegethon (Fiery Redfin) to headwater reaches above physical barriers to invasion (van der Walt et al. 2016) and in the Marico River in the North West, M. salmoides and M. punctulatus have depleted mainstream Enteromius motebensis (Marico Barb) populations (Kimberg et al. 2014).
Trout and black bass often act synergistically on native fish populations. Trout are cold water species that are established in cooler headwater reaches of rivers (Ellender et al. 2016; Shelton et al. 2018), from which they exclude native fishes through predation and competition . Downstream trout populations are limited by temperature, which also mediates their predatory impacts (Shelton et al. 2018). Black bass, on the other hand, are warm water species that invade up rivers from mainstream source populations, and their penetration of headwaters is limited only by physical barriers such as waterfalls or gradients (see van der Walt et al. 2016; Ellender et al. 2018). This has resulted in an increasing compression of native fish populations between these two invaders, a situation which has resulted in the loss of more than 80% of habitat in some catchments (van der Walt et al. 2016).
A total of 104 species of alien amphibians globally have been assessed with EICAT (Kumschick et al. 2017), of which 21 are alien species in South Africa (van Wilgen and Wilson 2018). Duttaphrynus melanostictus (Asian Common Toad) is the only one of these species with major impacts globally that also occurs as an alien in South Africa, but there is no evidence for it having any impact in the country to date, probably due to its lack of establishment within the country (Measey et al. 2017). The only cases of documented impacts in the country are restricted to native species. Xenopus laevis (African Clawed Toad), native to South Africa but traded intensively globally, hybridises with the endemic X. gilli (Cape Platanna) (Picker 1985), but importantly there is no evidence of introgression (Furman et al. 2017). Even though these two species might have likely overlapped for millennia (Schreiner et al. 2013), densities of X. leavis have probably been artificially increased in the last 400 years (Measey et al. 2017), leading to intense competition and predation (Vogt et al. 2017; de Villiers et al. 2016). Sclerophrys gutturalis (Guttural Toad), native to much of the country but introduced to a peri-urban area of Cape Town (Vimercati et al. 2017), could potentially threaten the native endangered Sclerophrys pantherina (Western Leopard Toad), but no evidence of the extent of this threat has been reported to date (Measey et al. 2017). Hyperolius marmoratus (Painted Reed Frog) is also native to some parts of South Africa but has become invasive in other areas of the country that are outside its natural range (Tolley et al. 2008; Davies et al. 2013). No studies on its impacts on biodiversity have been conducted to date, but it is suspected that it may impact the endemic Hyperolius horstocki (Arum Lily Frog) (Measey et al. 2017).
There are 415 alien bird species that have been assessed with EICAT at a global scale (Evans et al. 2016), of which 37 occur as aliens in South Africa (van Wilgen and Wilson 2018). Two species, Anas platyrhynchos (Mallard) and Pycnonotus jocosus (Red-Whiskered Bulbul) are known to cause major impacts in their global invasive range (Evans et al. 2016). Anas platyrhynchos threatens the genetic integrity of native congeners through hybridisation (e.g. Tracey et al. 2008). In southern Africa A. platyrhynchos hybridises with endemic species such as Anas undulata (Yellow-billed Duck), but currently there are low levels of introgression of A. platyrhynchos genes into A. undulata (Stephens et al. 2020). Introgression could become more extensive in the future if A. platyrhynchos populations are not controlled (Stephens et al. 2020; Davies et al. 2020, Chap. 22). Pycnonotus jocosus have been shown to damage crops, spread weeds, prey on native species and compete with them elsewhere (Mo 2015), but their impact in South Africa is unknown. Similarly, Psittacula krameri (Ring-necked Parakeet) is thought to compete for breeding holes with bats and other birds in other alien ranges leading to population declines of affected species. It has a very limited but expanding distribution in South Africa, and only ancedotal observations of impacts have been reported so far (Hart and Downs 2014). The species is a conflict species because it has both societal benefits (as a pet) and negative impacts (see Zengeya et al. 2017; Shackleton et al. 2020, Chap. 25).
There are 42 alien mammal species that have been recorded outside of captivity in South Africa (van Wilgen and Wilson 2018), eleven of which have formal global-scale EICAT assessments. All of these species cause large impacts in their invasive range globally (Hagen and Kumschick 2018). For example, several alien rodent species such as Rattus rattus (Black Rat), Rattus norvegicus (Norwegian Rat) and Mus musculus (House Mouse) 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. Steadman 1995; Marris 2000; Courchamp et al. 2003). The feral species Capra hircus (Goat), Equus asinus (Donkey) and Sus scrofa (Pig) cause massive impacts through competition with native species for food, altering the structure and composition of plant communities by grazing and rooting (e.g. Kurdila 1998; Campbell and Donlan 2005; Means and Travis 2007). This has led to habitat loss, resulting in local extinction of some native species and accelerated soil erosion. Other domestic species such as Felis catus (Cat) can cause major impacts through predation leading to population declines, and in some cases local extirpation, of native mammals, reptiles, and birds (Fitzgerald and Veitch 1985; Winter and Wallace 2006).
For a few species, impacts have been recorded in South Africa. For example, M. musculus and F. catus have caused major impacts on offshore islands (Berruti 1986; Greve et al. 2017, 2020, Chap. 8). Mus musculus was introduced on Marion Island before 1818, likely as a stowaway on ships whose crews were engaged in seal hunting (Watkins and Cooper 1986). On the island, it preys on invertebrates (Jones and Ryan 2010; Dilley et al. 2016) and this changed the population densities, reproduction strategies and growth rates of some invertebrates on the island (Treasure and Chown 2014) . Similarly, declines in albatross populations have been ascribed to predation of chicks by M. musculus (Dilley et al. 2016). Felis catus was introduced onto Marion Island in 1949 to control M. musculus (Bester et al. 2002). Although F. catus fed on M. musculus, it also preyed on seabirds and this severely affected seabird populations, especially burrowing species such as petrels (Procellariidae), leading to decreased breeding success, population declines and the local extinction of at least one species (van Rensburg 1983; Bester et al. 2002). Felis catus was eventually eradicated from the island in 1991 (Bester et al. 2002; Davies et al. 2020, Chap. 22), but the population of summer-breeding burrowing petrels is still to recover (Cerfonteyn and Ryan 2016).
Rattus norvegicus, R. rattus, S. scrofa and C. hircus have all caused massive impacts in other alien ranges (Hagen and Kumschick 2018), but their impacts in South Africa have not been studied apart from a few unpublished reports on wild boar impacts on vegetation and soil erosion (as mentioned in Spear and Chown 2009) . The two rat species were unintentionally introduced into South Africa through the shipping trade (Long 2003). These two species are amongst the most invasive Rattus species with a global distribution in urban areas (Aplin et al. 2011). Rattus rattus is believed to be widely distributed but restricted by the drier parts of South Africa, while R. norvegicus is assumed to be limited to coastal areas of the country (De Graaf 1981). 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. Jassat et al. 2013; Julius et al. 2018; Potgieter et al. 2020, Chap. 11). Sus scrofa damages some critically endangered plants in the Western Cape , affecting succession and facilitating alien plant spread (Picker and Griffiths 2011). Capra hircus grazing has reduced the cover and density of endemic geophytes and succulents shrubs in thicket vegetation, and conservation of this endemic-rich flora is seriously threatened (Moolman and Cowling 1994).
2.2 Expert Opinion Assessments
Given that few taxa have been formally evaluated for the impacts using EICAT in South Africa, a classification based on expert opinion rather than on published literature was used as an interim measure in South Africa’s first national status report on biological invasions (van Wilgen and Wilson 2018). Here, experts scored species according to their perceived ecological impacts and their socio-economic impacts (separately for negative and positive impacts) (see Zengeya et al. 2017 for more details). Using this scheme, 25 species were assessed as having severe impacts, and 82 as having major impacts (Table 17.2), the majority of these being terrestrial and freshwater plants (80 species). Here, using selected examples we highlight impacts on biodiversity of some of these alien species.
There are 893 alien plants species that are known to occur outside of cultivation in South Africa (van Wilgen and Wilson 2018). For a majority (56%) of these plant species, their impact on biodiversity has not been evaluated (Table 17.2). Of the 379 species that have been assessed by expert opinion, the majority (33%) were categorised as low-impact species (i.e. species with negligible, few or some impacts). Only 80 plants were classified as having major and severe impacts, 17 of which had severe impacts, most of them Australian wattles (genus Acacia) and mesquite trees (genus Prosopis).
Prosopis are some of the few alien plants whose impacts (ecological and economic) have been examined in some detail in South Africa. The genus consists of several species and their hybrids that are regarded among some of the world’s most damaging invasive plants. They were introduced to South Africa to provide supplemaneraty feed and shade for livestock, but similar to other countries where they have been introduced in the world, they have become invasive, generating negative impacts. In South Africa they have been found to have pronounced effects on insects, birds, and plants. Steenkamp and Chown (1996) found that invasion reduced the abundance and diversity of dung beetles. Native bird communities in invaded sites were found to be less diverse; some feeding guilds such as raptors were eliminated, and there was a marked decline in the abundance of frugivores and insectivorous species (Dean et al. 2002). However, other guilds such as nectarivores and seedeaters were less affected. Invasion also reduced the abundance and diversity of native plants. For example, in some plots the number of native tree species declined by 37% (n = 8) when the denstity of Prosopis doubled, while native perennial grasses and herbaceous plants were eliminated (Shackleton et al. 2015). Invasive Prosopis competes with the native Vachellia erioloba (Camel Thorn) for groundwater, increasing the likelihood of competive exclusion of Camel Thorn trees when water resources are limiting (Schachtschneider and February 2013).
Other than for the genus Prosopis, there are very few studies that have quantified the impact of alien plants on biodiversity in South Africa. Richardson et al. (1989) reviewed published and unpublished data on plant species richness in the Fynbos Biome with different levels of invasion by alien trees and shrubs in the genera Pinus, Hakea and Acacia. They found significant declines in native plant species richness at the scale of the sample quadrats used in their study (4–256 m2), notably when the cover of alien plants exceeded 50%. Similarly, Yapi et al. (2018) recorded marked declines in the cover of native grass species with increases in the canopy cover of alien Acacia mearnsii (Black Wattle) trees in the Eastern Cape . Such declines in the abundance and richness of native plant species, and associated faunal species, are likely to take place where any alien plant species becomes dominant. Given that many alien plant species have recently entered a phase of rapid spread, it can be expected that these kinds of impacts will increase. For example, Henderson and Wilson (2017) showed that the number of quarter degree grid cells occupied by alien plants in South Africa increased by ~50% between 2000 and 2016, with at least nine species having expanded rapidly over the past decade (see also van Wilgen et al. 2020a, Chap. 21).
Besides trees, some grasses have been shown to affect native biodiversity in South Africa. In addition to the examples mentioned earlier, Ammophila arenaria (European Beach Grass) has changed native dune communities (Hertling and Lubke 1999). Avena barbata (Slender Wild Oat) has invaded some lowland fynbos and can dominate old field habitats (Heelemann et al. 2013), and a recent study on Paspalum quadrifarium (Tussock Paspalum) showed its ability to affect native species communities (Nkuna 2018).
Many alien invertebrates are major pests of agriculture, but here we focus on taxa that have negatively impacted native biodiversity. There are 629 alien freshwater and terrestrial invertebrates that are known to occur outside of captivity in South Africa (van Wilgen and Wilson 2018). For a majority (74%) of these, their impacts on biodiversity have not been evaluated. Of the remainder, 25% were assessed using expert opinion as low-impact species, and less than 2% had major to severe impacts (Table 17.2). Five species of terrestrial invertebrates that purportedly have major to severe impacts include Cornu aspersum (Common Garden Snail), Deroceras invadens (Tramp Slug), Linepithema humile (Argentine Ant), Thebia pisana and Trogoderma granarium (Khapra Beetle). Linepithema humile has invaded fynbos, where it displaces native ants. The displacement of native ants is a direct impact on biodiversity, but the role that native ant species play in the dispersal of the seeds of fynbos plants has also been disrupted. Bond and Slingsby (1984) found that L. humile differed from native ants in moving seeds shorter distances, and in failing to store them in nests below the soil. The seeds were left on the soil surface, where they were eaten by vertebrate and invertebrate seed predators. Bond and Slingsby (1983) estimated that L. humile displacement of native ants could threaten the long-term survival of approximately 1000 fynbos plant species that were dependent on native ants for the dispersal and protection of their seeds.
Among the marine invertebrates, Mytilus galloprovincialis (Mediterranean Mussel) has had significant impacts in South African marine environments (Robinson et al. 2020, Chap. 9). First recorded in South Africa in the late 1970s, it presently occurs along the whole of the west coast and as far east as East London (approx. 2000 km of coastline) (Robinson et al. 2005). Within its invaded range, it has been implicated in causing impacts on native species and altering the structure of rocky shore communities. Along the west coast, M. galloprovincialis competively excludes native species such as mussels and limpets from prime habitas (Robinson et al. 2007), while along the south coast it co-exists with the native Perna perna (Brown Mussel) (Bownes and McQuaid 2006). Interestingly, M. galloprovincialis forms complex mussel beds that have increased habitat availability leading to an increase in the diversity and abundance of native fauna on invaded shores (Sadchatheeswaran et al. 2015).
Of the 42 alien mammal species that have been recorded in South Africa, 8 species have been assessed using expert opinion as causing major impacts in South Africa (van Wilgen and Wilson 2018). Six of these (R. rattus, R. norvegicus, F. catus, M. musculus, S. scrofa and C. hircus) cause massive impacts in the country, in similar ways to those identifed by formal global EICAT assessments (see Sect. 18.104.22.168). For the remainder, Hippotragus equinus koba (Western Roan) has been implicated in hybridising with local sub-species (Mathee and Robinson 1999; Alpers et al. 2004; van Wyk et al. 2019) and the impacts of Macaca fascicularis (Crab-Eating Macaque) are not well documented in South Africa, so their potential impacts can only be inferred from their global invasive range.
Five fish species were classified by experts as causing major to severe impacts in invaded catchments in South Africa (Zengeya et al. 2017). Micropterus dolomieu, M. salmoides, O. mykiss and S. trutta had major impacts through mainly competition and predation. Oreochromis niloticus was assessed as having severe impacts mainly through hybridisation with congeneric native species.
2.3 Impacts Identified During Red-Listing Processes
Some recent studies have used data from the IUCN Red List of Threatened Species (Mace et al. 2008) to assess the role of alien species as drivers of recent extinctions (Bellard et al. 2016a), and global patterns of threats to vertebrates posed by biological invasions (Bellard et al. 2016b). In South Africa, several taxa have undergone formal red list assessments and these include plants, dragonflies, freshwater fishes, amphibians, reptiles, birds and mammals (Child et al. 2015; Taylor et al. 2015; IUCN 2018; SANBI 2019) . Following a similar approach as Bellard et al. (2016b), we assessed whether and how species listed under the IUCN Red List in South Africa were affected by alien species. We calculated the proportion of threatened native species, i.e. those in the upper tier of extinction risk (Vulnerable, Endangered, and Critically endangered), where alien species were indicated as a threat (Table 17.3).
A total of 23,609 native species were assessed, of which 17% had alien species as a major threat to their extinction risk. The proportion of threatened species that are imperilled by alien species varied across threat categories, being higher for Endagered (60%, N = 609 out of 1007) and Vulnerable species (48%, N = 788 out of 1641) and lower for Critically Endangered (40%, N = 276 out of 688) (Table 17.3). This trend is also reflected when comparions are made across taxa in each threat category (Table 17.3). More than half of the taxa assessed as Endangered (five out of eight), Critically Endangered (three out of five) and Vulnerable (three out of five) were threatened by alien species. Across all three threat categories, the proportion of species that are being threatened by alien species was highest for fishes, amphibians and plants. The Red List assessments identified and classified 12 major threats to the persistence of a species, and alien species were rarely considered to be the sole extinction risk for most species. For example, most of the fish and amphibian species listed as Critically Endangered have small distributional ranges, experience a continuous decline in habitat quality through several anthropogenic activities (e.g. pollution, excessive water abstraction and altered flow regimes), and are additionally threatened by invasive species through predation, competition and physical alteration of ecosystems (van Wilgen et al. 2020b, Chap. 29) .
2.4 Impacts on Biodiversity at a Biome Scale
A limited number of studies have quantifed the impact of invasive species on ecosystem services at a landscape scale. Several studies have either focused on a particular ecosystem service (e.g. surface water supplies, Le Maitre et al. 2000), or on a single species (e.g. A. mearnsii, De Wit et al. 2001). This has led to problems in extraplolating the results generated by the different studies to make broad conclusions about the entirety of impacts of invasions on an ecosystem. Van Wilgen et al. (2008), however, assessed current and potential impacts of alien plants on selected ecosystem services (surface water runoff, ground water recharge, livestock production and biodiversity) in five terrestrial biomes (Savanna, Fynbos, Grasslands, Succulent Karoo and Nama Karoo) in South Africa. With the exception of the fynbos, the current invasions had no measurable impact on biodiversity intactness (an estimate of impact of land-use changes on populations of various taxa such as plants, mammals, birds, reptiles and amphibians in a particular area, see Scholes and Biggs 2005) at a landscape scale. While the current impacts of alien plants were relatively low, the future impacts were predicted to be very high. In addition, while the errors in these estimates are likely to be substantial, the predicted impacts were sufficiently large to suggest that there is cause for serious concern. De Lange and van Wilgen (2010) used the above estimates of intactness to estimate the economic value of ecosystem services based on biodiversity. It was estimated that the reduction in value of selected ecosystem services due to invasive alien plants was the highest for fynbos, but still substantial for others like savanna, thicket, grassland, succulent karoo and Nama karoo. Overall, terrestrial ecosystems in South Africa would deliver biodiversity-based ecosystem services valued at ZAR 22.1 billion per annum if no invasions were present. The estimated value of the annual flow of these services was reduced by 2% (ZAR 428 million) each year due to alien plant invasions at current levels; under a scenario where alien plants are allowed to invade all available habitat, these losses were estimated to increase to more than 50% (ZAR 12.9 billion) annually. Other studies have also estimated the total value of ecosystem services in South Africa (Anderson et al. 2017; Turpie et al. 2017). Anderson et al. (2017) estimated this value to be about ZAR 8 trillion per year—this is nearly double that of South Africa’s gross domestic product of ZAR 4.7 trillion for the same period. Turpie et al. (2017) estimated the value of ecosystem services provided by terrestrial, freshwater and estuarine ecosystems to be at ZAR 245 billion annually. The differences in the estimates between these assessments reflect methodological differences and the general challenges associated with attempts to monetise the values of biodiversity. Nevertheless, they highlight that ecosystem services make a substantial contribution to the economy.
The issue of quantifying the impacts of alien species on biodiversity remains a major challenge, both globally and in South Africa. For the majority of species found in South Africa, there are no studies documenting impacts, and there has been no formal assessment of impacts at a national scale. Evidence-based impact assessments are needed to support calls for management interventions. For example, in South Africa 556 taxa are listed as invasive, and landowners have an obligation to manage them (van Wilgen et al. 2020a, Chap. 1, Box 1.2). However, the regulations should arguably focus on priority species because not all of the listed species are necessarily harmful to the extent that would justify management especially when the current capacity to manage and to regulate them is limited (Zengeya et al. 2017). The use of expert opinion and or formal assessments such as EICAT could help to identify and priotise those species that should be targeted for management.
Alpers DL, van Vuuren BJ, Arctander P, Robinson TJ (2004) Population genetics of the roan antelope (Hippotragus equinus) with suggestions for conservation. Mol Ecol 13:1771–1784. https://doi.org/10.1111/j.1365-294X.2004.02204.x
Anderson S, Ankor BL, Sutton PC (2017) Ecosystem service valuations of South Africa using a variety of land cover data sources and resolutions. Ecosyst Serv 27:173–178. https://doi.org/10.1016/j.ecoser.2017.06.001
Aplin K, Suzuki H, Chinen CH et al (2011) Multiple geographic origins of commensalism and complex dispersal history of black rats. PLoS One 6:1–20. https://doi.org/10.1371/journal.pone.0026357
Appleton CC, Forbes AT, Demetriades NT (2009) The occurrence, bionomics and potential impacts of the invasive freshwater snail Tarebia granifera (Lamarck, 1822) (Gastropoda: Thiaridae) in South Africa. Zool Med Leiden 83:525–536.
Bacher S, Blackburn TM, Essl F et al (2018) Socio-economic impact classification of alien taxa (SEICAT). Methods Ecol Evol 9:159–168
Bellard C, Cassey P, Blackburn TM (2016a) Alien species as a driver of recent extinctions. Biol Lett 12:20150623. https://doi.org/10.1098/rsbl.2015.0623
Bellard C, Genovesi P, Jeschke JM (2016b) Global patterns in threats to vertebrates by biological invasions. Proc R Soc B-Biol Sci 283:20152454. https://doi.org/10.1098/rspb.2015.2454
Berruti A (1986) The predatory impact of feral cats Felis catus and their control on Dassen Island. S Afr J Antarct Res 16:123–127
Bester MN, Bloomer JP, van Aarde RJ et al (2002) A review of the successful eradication of feral cats from sub-Antarctic Marion Island, southern Indian Ocean. S Afr J Wildl Res 32:65–73
Blackburn TM, Essl F, Evans T et al (2014) A unified classification of alien species based on the magnitude of their environmental impacts. PLoS Biol 12:e1001850. https://doi.org/10.1371/journal.pbio.1001850
Bond WJ, Slingsby P (1983) Seed dispersal by ants in shrublands of the Cape Province and its evolutionary implications. S Afr J Sci 79:231–233
Bond WJ, Slingsby P (1984) Collapse of an ant-plant mutalism: the Argentine Ant (Iridomyrmex humilis) and myrmecochorous Proteaceae. Ecology 65:1031–1037. https://doi.org/10.2307/1938311
Bownes SJ, McQuaid CD (2006) Will the invasive mussel Mytilus galloprovincialis lamark replace the indigenous Perna perna L. on the south coast of South Africa? J Exp Mar Biol Ecol 338:140–151. https://doi.org/10.1016/j.jembe.2006.07.006
Brooks ML, D’antonio CM, Richardson DM et al (2004) Effects of invasive alien plants on fire regimes. Bioscience 54:677–688. https://doi.org/10.1641/0006-3568(2004)054[0677:EOIAPO]2.0.CO;2
Campbell K, Donlan CJ (2005) Feral goat eradications on Islands. Conserv Biol 19:1362–1374. https://doi.org/10.1111/j.1523-1739.2005.00228.x
Canavan S, Kumschick S, Le Roux JJ et al (2019) Does origin determine environmental impacts? Not for bamboos. Plants People Planet 1:119–128. https://doi.org/10.1002/ppp3.5
Cerfonteyn M, Ryan PG (2016) Have burrowing petrels recovered on Marion Island two decades after cats were eradicated? Evidence from sub-Antarctic skua prey remains. Antarct Sci 28:51–57. https://doi.org/10.1017/S0954102015000474
Child MF, Roxburgh L, Do Linh San E et al (eds) (2015) The red list of mammals of South Africa, Swaziland and Lesotho. South African National Biodiversity Institute; Endangered Wildlife Trust, Pretoria; Lethabong
Christie JD, Edward J, Goolaman K et al (1981) Interactions between St. Lucian Biomphalaria glabrata and Helisoma duryi, a possible competitor snail, in a semi-natural habitat. Acta Trop 38:395–417
Colville JC, Potts AJ, Bradshaw PL et al (2014) Floristic and faunal Cape biochoria: do they exist? In: Allsopp N, Colville JF, Verboom GA (eds) Fynbos: ecology, evolution, and conservation of a megadiverse region. Oxford University Press, Oxford, pp 73–93. https://doi.org/10.1093/acprof:oso/9780199679584.003.0004
Courchamp F, Pascal M, Chapuis JL (2003) Mammal invaders on islands, impact, control and control impact. Biol Rev 78:347–383. https://doi.org/10.1017/S1464793102006061
Davies SJ, Clusella-Trullas S, Hui C, McGeoch MA (2013) Farm dams facilitate amphibian invasion. Austral Ecol 38:851–863. https://doi.org/10.1111/aec.12022
Davies SJ, Jordaan MS, Karsten M et al (2020) Experience and lessons from alien and invasive animal control projects in South Africa. In: van Wilgen BW, Measey J, Richardson DM, Wilson JR, Zengeya TA (eds) Biological invasions in South Africa. Springer, Berlin, pp 625–660. https://doi.org/10.1007/978-3-030-32394-3_22
De Graaf G (1981) The rodents of southern Africa: notes on their identification, distribution, ecology and taxonomy. Butterworth, Durban
De Lange WJ, van Wilgen BW (2010) An economic assessment of the contribution of biological control to the management of invasive alien plants and to the protection of ecosystem services in South Africa. Biol Invasions 12:4113–4124
de Villiers FA, de Kock M, de Measey GJ (2016) Controlling the African clawed frog Xenopus laevis to conserve the Cape platanna Xenopus gilli in South Africa. Conserv Evid 13:17
De Wit M, Crookes D, van Wilgen BW (2001) Conflicts of interest in environmental management: estimating the costs and benefits of a tree invasion. Biol Invasions 3:167–178. https://doi.org/10.1023/A:1014563702261
Dean WRJ, Anderson MD, Milton SJ, Anderson TA (2002) Avian assemblages in native Acacia and alien Prosopis drainage line woodland in the Kalahari, South Africa. J Arid Environ 51:1–19. https://doi.org/10.1006/jare.2001.0910
Dilley BJ, Schoombie S, Schoombie J, Ryan PG (2016) “Scalping” of albatross fledglings by introduced mice spreads rapidly at Marion Island. Antarct Sci 28:73–80. https://doi.org/10.1017/S0954102015000486
Ellender BR, Weyl OLF (2014) A review of current knowledge, risk and ecological impacts associated with non-native freshwater fish introductions in South Africa. Aquat Invasions 9:117–132. https://doi.org/10.3391/ai.2014.9.2.01
Ellender BR, Rivers-Moore NA, Coppinger CR et al (2016) Towards using thermal stress thresholds to predict salmonid invasion potential. Biol Invasions 18:513–3525. https://doi.org/10.1007/s10530-016-1244-9
Ellender BR, Wasserman RJ, Chakona A et al (2017) A review of the biology and status of Cape Fold Ecoregion freshwater fishes. Aquat Conserv 27:867–879
Ellender BR, Weyl OLF, Alexander ME et al (2018) Out of the pot and into the fire: explaining the vulnerability of an endangered small headwater stream fish to black-bass Micropterus spp. invasion. J Fish Biol 92:1035–1050. https://doi.org/10.1111/jfb.13562
Evans T, Kumschick S, Blackburn TM (2016) Application of the environmental impact classification for Alien Taxa (EICAT) to a global assessment of alien bird impacts. Divers Distrib 22:919–931
Firmat C, Alibert P, Losseau M et al (2013) Successive invasion-mediated interspecific hybridizations and population structure in the endangered cichlid Oreochromis mossambicus. PLoS One 8:e63880. https://doi.org/10.1371/journal.pone.0063880
Fitzgerald BM, Veitch CR (1985) The cats of Herekopare Island, New Zealand: their history, ecology and effects on birdlife. New Zeal J Zool 12:319–330. https://doi.org/10.1080/03014223.1985.10428285
Frest TJ, Sanders Rhodes R (1982) Oxychilus draparnaldi in Iowa. Nautilus 96:36–39
Furman B, Cauret C, Colby G et al (2017) Limited genomic consequences of hybridization between two African clawed frogs, Xenopus gilli and X. laevis (Anura: Pipidae). Sci Rep 7:1091. https://doi.org/10.1038/s41598-017-01104-9
Greve M, Mathakutha R, Steyn C, Chown SL (2017) Terrestrial invasions on sub-Antarctic Marion and Prince Edward Islands. Bothalia 47:a2143. https://doi.org/10.4102/abc.v47i2.2143
Greve M, von der Meden CEO, Janion-Scheepers C (2020) Biological invasions in South Africa’s offshore sub-Antarctic territories. In: van Wilgen BW, Measey J, Richardson DM, Wilson JR, Zengeya TA (eds) Biological invasions in South Africa. Springer, Berlin, pp 205–226. https://doi.org/10.1007/978-3-030-32394-3_8
Griffiths CL, Robinson TB, Lange L, Mead A (2010) Marine biodiversity in South Africa: an evaluation of current states of knowledge. PLoS One 5:e12008. https://doi.org/10.1371/journal.pone.0012008
Guthrie G (2007) Impacts of the invasive reed Arundo donax on biodiversity at the community-ecosystem level. MSc Thesis. University of the Western Cape
Hagen BL, Kumschick S (2018) The relevance of using various scoring schemes revealed by an impact assessment of feral mammals. NeoBiota 38:37–75. https://doi.org/10.3897/neobiota.38.23509
Hart LA, Downs CT (2014) Public surveys of rose-ringed parakeets, Psittacula krameri, in the Durban Metropolitan area, South Africa. Afr Zool 49:283–289. https://doi.org/10.1080/15627020.2014.11407644
Hawkins CL, Bacher S, Essl F et al (2015) Framework and guidelines for implementing the proposed IUCN Environmental Impact Classification for Alien Taxa (EICAT). Divers Distrib 21:1360–1363. https://doi.org/10.1111/ddi.12379
Heelemann S, Krug CB, Esler KJ et al (2013) Soil seed banks of remnant and degraded Swartland Shale Renosterveld. Appl Veg Sci 16:585–597. https://doi.org/10.1111/avsc.12026
Henderson L, Wilson JRU (2017) Changes in the composition and distribution of alien plants in South Africa: an update from the Southern African Plant Invaders Atlas. Bothalia 47:a2172
Hertling UM, Lubke RA (1999) Indigenous and Ammophila arenaria-dominated dune vegetation on the South African Cape coast. Appl Veg Sci 2:157–168. https://doi.org/10.2307/1478979
Holmes PM, Richardson DM, Esler KJ et al (2005) A decision-making framework for restoring riparian zones degraded by invasive alien plants in South Africa. S Afr J Sci 101:553–564
Hulme PE (2014) Invasive species challenge the global response to emerging diseases. Trends Parasitol 30:267–270. https://doi.org/10.1016/j.pt.2014.03.005
IUCN (2018) The IUCN red list of threatened species. Version 2018-1. www.iucnredlist.org. Downloaded 01 Oct 2018
Jackson MC, Woodford DJ, Bellingan TA et al (2016) Trophic overlap between fish and riparian spiders: potential impacts of an invasive fish on terrestrial consumers. Ecol Evol 6:1745–1752. https://doi.org/10.1002/ece3.1893
Jassat W, Naicker N, Naidoo S, Mathee A (2013) Rodent control in urban communities in Johannesburg, South Africa: from research to action. Int J Environ Health Res 23:474–483
Jones MGW, Ryan PG (2010) Evidence of mouse attacks on albatross chicks on sub-Antarctic Marion Island. Antarct Sci 22:39–42. https://doi.org/10.1017/S0954102009990459
Julius RS, Schwan EV, Chimimba CT (2018) Molecular characterization of cosmopolitan and potentially co-invasive helminths of commensal, murid rodents in Gauteng Province, South Africa. Parasitol Res 117:1729. https://doi.org/10.1007/s00436-018-5852-4
Karatayev AY, Burlakova LE, Karatayev VA, Padilla DK (2009) Introduction, distribution, spread, and impacts of exotic freshwater gastropods in Texas. Hydrobiologia 619:181–194. https://doi.org/10.1007/s10750-008-9639-y
Karssing RJ, Rivers-Moore NA, Slater K (2012) Influence of waterfalls on patterns of association between trout and Natal cascade frog Hadromophryne natalensis tadpoles in two headwater streams in the Ukhahlamba Drakensberg Park World Heritage Site, South Africa. Afr J Aquat Sci 37:107–112. https://doi.org/10.2989/16085914.2012.666381
Kesner D, Kumschick S (2018) Gastropods alien to South Africa cause severe environmental harm in their global alien ranges across habitats. Ecol Evol 8:8273–8285. https://doi.org/10.1002/ece3.4385
Khosa D, Marr SM, Wasserman RJ et al (2019) An evaluation of the current extent and potential spread of Black Bass invasions in South Africa. Biol Invasions 21:1721. https://doi.org/10.1007/s10530-019-01930-0
Kimberg PK, Woodford DJ, Roux H, Weyl OLF (2014) Species-specific impact of introduced largemouth bass Micropterus salmoides in the Groot Marico Freshwater Ecosystem Priority Area, South Africa. Afr J Aquat Sci 39:451–458. https://doi.org/10.2989/16085914.2014.976169
Kumschick S, Vimercati G, de Villiers FA et al (2017) Impact assessment with different scoring tools: how well do alien amphibian assessments match? NeoBiota 33:53–66. https://doi.org/10.3897/neobiota.33.10376
Kumschick S, Wilson JR, Foxcroft LC (2018) Framework and guidelines for conducting risk analyses for alien species. Preprints. https://doi.org/10.20944/preprints201811.0551.v1
Kumschick S, Foxcroft LC, Wilson JR (2020) Analysing the risks posed by biological invasions to South Africa. In: van Wilgen BW, Measey J, Richardson DM, Wilson JR, Zengeya TA (eds) Biological invasions in South Africa. Springer, Berlin, pp 569–592. https://doi.org/10.1007/978-3-030-32394-3_20
Kurdila J (1998) The introduction of exotic species into the United States: there goes the neighborhood! BC Envtl Aff L Rev 16:95–119
Le Maitre DC, Versfeld DB, Chapman RA (2000) The impact of invading alien plants on surface water resources in South Africa: a preliminary assessment. Water SA 26:397–408
Le Maitre DC, Gush MB, Dzikiti S (2015) Impacts of invading alien plant species on water flows at stand and catchment scales. AoB Plants 7:plv043. https://doi.org/10.1093/aobpla/plv043
Le Roux J (2002) The biodiversity of South Africa 2002: indicators, trends and human impacts. World Wildlife Fund, Endangered Wildlife Trust and Nedbank Green. Struik Publishers, Cape Town
Long J (2003) Introduced mammals of the world: their history, distribution and influence. CSIRO, Melbourne. https://doi.org/10.1071/9780643090156
Mace GM, Collar NJ, Gaston KJ et al (2008) Quantification of extinction risk: IUCN’s system for classifying threatened species. Conserv Biol 22:1424–1442. https://doi.org/10.1111/j.1523-1739.2008.01044.x
Marr SM, Ellender BR, Woodford DJ et al (2017) Evaluating invasion risk for freshwater fishes in South Africa. Bothalia 47:a2177. https://doi.org/10.4102/abc.v47i2.2177
Marris JWM (2000) The beetle (Coleoptera) fauna of the Antipodes Islands, with comments on the impact of mice; and annotated checklist of the insect and arachnid fauna. J R Soc N Z 30:169–195. https://doi.org/10.1080/03014223.2000.9517616
Mathee CA, Robinson TJ (1999) Mitochondrial DNA population structure of roan and sable antelope: implications for the translocation and conservation of the species. Mol Ecol 8:227–238. https://doi.org/10.1046/j.1365-294X.1999.00556.x
Means DB, Travis J (2007) Declines in ravine-inhabiting dusky salamanders of the southeastern US coastal plain. Naturalist 6:83–96. https://doi.org/10.1656/1528-7092(2007)6[83:DIRDSO]2.0.CO;2
Measey J, Davies SJ, Vimercati G et al (2017) Invasive amphibians in southern Africa: a review of invasion pathways. Bothalia 47:a2117. https://doi.org/10.4102/abc.v47i2.2117
Miranda NAF, Perissinotto R (2014) Effects of an alien invasive gastropod on native benthic assemblages in coastal lakes of the iSimangaliso Wetland Park, South Africa. Afr Invertebr 55:209–228.
Mittermeier RA, Robles-Gil P, Mittermeier CG (1997) Megadiversity: Earth’s biologically wealthiest nations. CEMEX, Conservation International, Arlington
Mittermeier RA, Robles-Gil P, Hoffmann M et al (2004) Hotspots revisited: Earth’s biologically richest and most endangered terrestrial ecoregions. CEMEX, Mexico City
Mo M (2015) The red-whiskered bulbul Pycnonotus jocosus in Australia – a global perspective, history of introduction, current status and potential impacts. Aust Zool 37:461–471. https://doi.org/10.7882/AZ.2015.014
Moolman HJ, Cowling RM (1994) The impact of elephant and goat grazing on the endemic flora of South Africa succulent thicket. Biol Conserv 68:53–61. https://doi.org/10.1016/0006-3207(94)90546-0
Mucina L, Rutherford MC (eds) (2006) The vegetation of South Africa. Lesotho and Swaziland, South African National Biodiversity Institute
Mugwedi LF (2012) Invasion ecology of Glyceria maxima in KZN Rivers and wetlands. MSc Thesis, University of the Witwatersrand
Myers N, Mittermeier RA, Mittermeier CG et al (2000) Biodiversity hotspots for conservation priorities. Nature 403:853–858. https://doi.org/10.1038/35002501
Nelufule T (2018) An assessment of alien terrestrial invertebrate species in the pet trade in South Africa. MSc Thesis, University of Pretoria
Nkuna VK (2018) Risk analysis of alien grasses occurring in South Africa. MSc Thesis, Stellenbosch University
Nkuna VK, Visser V, Wilson JRU, Kumschick S (2018) Global environmental and socio-economic impacts of selected alien grasses as a basis for ranking threats to South Africa. NeoBiota 41:19–65. https://doi.org/10.3897/neobiota.41.26599
Noss RF (1990) Indicators for monitoring biodiversity: a hierarchical approach. Conserv Biol 4:355–364. https://doi.org/10.1111/j.1523-1739.1990.tb00309.x
Odendaal LJ, Haupt TM, Griffiths CL (2008) The alien invasive land snail Theba pisana in the West Coast National Park: is there cause for concern? Koedoe 50:93–98. https://doi.org/10.4102/koedoe.v50i1.153
Picker MD (1985) Hybridization and habitat selection in Xenopus gilli and Xenopus laevis in the south-western Cape Province. Copeia 1985:574–580. https://doi.org/10.2307/1444746
Picker M, Griffiths C (2011) Alien & invasive animals: a South African perspective. Struik Nature, Cape Town
Potgieter L, Douwes E, Gaertner M et al (2020) Biological invasions in South Africa’s urban ecosystems: patterns, processes, impacts and management. In: van Wilgen BW, Measey J, Richardson DM, Wilson JR, Zengeya TA (eds) Biological invasions in South Africa. Springer, Berlin, pp 273–310. https://doi.org/10.1007/978-3-030-32394-3_11
Richardson DM, van Wilgen BW (2004) Invasive alien plants in South Africa: how well do we understand the ecological impacts? S Afr J Sci 100:45–52
Richardson DM, Macdonald IAW, Forsyth GG (1989) Reductions in plant species richness under stands of alien trees and shrubs in the Fynbos biome. South Afr For J 149:1–8. https://doi.org/10.1080/00382167.1989.9628986
Rivers-Moore NA, Fowles B, Karssing RJ (2013) Impacts of trout on aquatic macroinvertebrates in three Drakensberg rivers in KwaZulu–Natal, South Africa. Afr J Aquat Sci 38:93–99. https://doi.org/10.2989/16085914.2012.750592
Robinson TB, Griffiths CL, McQuaid CD, Rius M (2005) Marine alien species of South Africa – status and impacts. Afr J Mar Sci 27:297–306. https://doi.org/10.2989/18142320509504088
Robinson TB, Branch GM, Griffiths CL et al (2007) Effects of the invasive mussel Mytilus galloprovincialis on rocky intertidal community structure in South Africa. Mar Ecol Prog Ser 340:163–171. https://doi.org/10.3354/meps340163
Robinson TB, Peters K, Brooker B (2020) Coastal invasions: the South African context. In: van Wilgen BW, Measey J, Richardson DM, Wilson JR, Zengeya TA (eds) Biological invasions in South Africa. Springer, Berlin, pp 227–246. https://doi.org/10.1007/978-3-030-32394-3_9
Rodda GH, Fritts TH (1992) The impact of the introduction of the colubrid snake Boiga irregularis on Guam’s lizards. J Herpetol 26:166–174. https://doi.org/10.2307/1564858
Sadchatheeswaran S, Branch GM, Robinson TB (2015) Changes in habitat complexity resulting from sequential invasions of a rocky shore: implications for community structure. Biol Invasions 17:1799–1816. https://doi.org/10.1007/s10530-014-0837-4
SANBI (2019) Statistics: red list of South African plants version 2019.1. Downloaded Redlist.sanbi.org on 2019/01/22
Schachtschneider K, February EC (2013) Impact of Prosopis invasion on a keystone tree species in the Kalahari Desert. Plant Ecol 214:597–605. https://doi.org/10.1007/s11258-013-0192-z
Scholes RJ, Biggs R (2005) A biodiversity intactness index. Nature 434:45–49. https://doi.org/10.1038/nature03289
Schreiner C, Rödder D, Measey GJ (2013) Using models to test Poynton’s predictions. African. J Herpetol 62:49–62. https://doi.org/10.1080/21564574.2013.794865
Shackleton RT, Le Maitre DC, Richardson DM, van Wilgen BW (2015) The impact of invasive alien Prosopis species (mesquite) on native plants in different environments in South Africa. S Afr J Bot 97:25–31. https://doi.org/10.1016/j.sajb.2014.12.008
Shackleton RT, Novoa A, Shackleton CM et al (2020) The social dimensions of biological invasions in South Africa. In: van Wilgen BW, Measey J, Richardson DM, Wilson JR, Zengeya TA (eds) Biological invasions in South Africa. Springer, Berlin, pp 697–726. https://doi.org/10.1007/978-3-030-32394-3_24
Shelton JM, Samways MJ, Day JA (2015a) Non-native rainbow trout change the structure of benthic communities in headwater streams of the Cape Floristic Region, South Africa. Hydrobiologia 745:1–15. https://doi.org/10.1007/s10750-014-2067-2
Shelton JM, Samways MJ, Day JA (2015b) Predatory impact of non-native rainbow trout on endemic fish populations in headwater streams in the Cape Floristic Region of South Africa. Biol Invasions 17:365–379. https://doi.org/10.1007/s10530-014-0735-9
Shelton JM, Weyl OLF, Esler KJ et al (2018) Temperature mediates the impact of non-native rainbow trout on native freshwater fishes in South Africa’s Cape Fold Ecoregion. Biol Invasions 20:2927–2944. https://doi.org/10.1007/s10530-018-1747-7
Spear D, Chown SL (2009) Non-indigenous ungulates as a threat to biodiversity. J Zool 279:1–17. https://doi.org/10.1111/j.1469-7998.2009.00604.x
Steadman DW (1995) Prehistoric extinctions of Pacific Island birds’ biodiversity meets zooarchaeology. Science 267:1123–1131. https://doi.org/10.1126/science.267.5201.1123
Steenkamp HE, Chown SL (1996) Influence of dense stands of an exotic tree Prosopis glandulosa Benson, on a savanna dung beetle (Coleoptera: Scarabeidae) assemblage in southern Africa. Biol Conserv 78:305–311. https://doi.org/10.1016/S0006-3207(96)00047-X
Stephens K, Measey J, Reynolds C et al (2020) Occurrence and extent of hybridization between the invasive Mallard Duck and native Yellow-billed Duck in South Africa. Biol Invasions 22:693–707. https://doi.org/10.1007/s10530-019-02122-6
Taylor MR, Peacock F, Wanless RM (eds) (2015) The Eskom red data book of birds of South Africa, Lesotho and Swaziland. BirdLife South Africa, Johannesburg
Tolley KA, Davies SJ, Chown SL (2008) Deconstructing a controversial local range expansion: conservation biogeography of the painted reed frog (Hyperolius marmoratus) in South Africa. Divers Distrib 14:400–411. https://doi.org/10.1111/j.1472-4642.2007.00428.x
Tracey JP, Lukins BS, Haselden C (2008) Hybridisation between mallard (Anas platyrhynchos) and grey duck (A. superciliosa) on Lord Howe Island and management options. Notornis 55:1–7
Treasure AM, Chown SL (2014) Antagonistic effects of biological invasion and temperature change on body size of island ectotherms. Divers Distrib 20:202–213. https://doi.org/10.1111/ddi.12153
Turpie JK, Forsythe KK, Letley GK et al (2017) Mapping and valuation of South Africa’s ecosystem services: a local perspective. Ecosyst Serv 27:179–192. https://doi.org/10.1016/j.ecoser.2017.07.008
van der Walt JA, Weyl OLF, Woodford DJ, Radloff FGT (2016) Spatial extent and consequences of black bass (Micropterus spp.) invasion in a Cape Floristic Region river basin. Aquat Conserv 26:736–748. https://doi.org/10.1002/aqc.2589
van Rensburg PJJ (1983) The feeding ecology of a decreasing feral house cat, Felis catus, population at Marion Island. In: Siegfried WR, Condy PR, Laws RM (eds) Antarctic nutrient cycles and food webs. Springer, Berlin, pp 620–624. https://doi.org/10.1007/978-3-642-82275-9_84
van Wilgen BW, Richardson DM (1985) The effects of alien shrub invasions on vegetation structure and fire behaviour in South African fynbos shrublands: a simulation study. J Appl Ecol 22:955–966. https://doi.org/10.2307/2403243
van Wilgen BW, Wilson JR (eds) (2018) The status of biological invasions and their management in South Africa in 2017. South African National Biodiversity Institute, Kirstenbosch and DST-NRF Centre of Excellence for Invasion Biology, Stellenbosch
van Wilgen BW, Reyers B, Le Maitre DC et al (2008) A biome-scale assessment of the impact of invasive alien plants on ecosystem services in South Africa. J Environ Manag 89:336–349. https://doi.org/10.1016/j.jenvman.2007.06.015
van Wilgen BW, Measey J, Richardson DM et al (2020a) Biological invasions in South Africa: an overview. In: van Wilgen BW, Measey J, Richardson DM, Wilson JR, Zengeya TA (eds) Biological invasions in South Africa. Springer, Berlin, pp 3–30. https://doi.org/10.1007/978-3-030-32394-3_1
van Wilgen NJ, van Wilgen BW, Midgley GF (2020b) Biological invasions as a component of South Africa’s global change research effort. In: van Wilgen BW, Measey J, Richardson DM, Wilson JR, Zengeya TA (eds) Biological invasions in South Africa. Springer, Berlin, pp 851–874. https://doi.org/10.1007/978-3-030-32394-3_29
van Wyk AM, Dalton DL, Kotzé A et al (2019) Assessing introgressive hybridization in roan antelope (Hippotragus equinus): lessons from South Africa. BioRxiv 569830. https://doi.org/10.1101/569830
Vimercati G, Hui C, Davies SJ, Measey GJ (2017) Integrating age structured and landscape resistance models to disentangle invasion dynamics of a pond-breeding anuran. Ecol Model 356:104–116. https://doi.org/10.1016/j.ecolmodel.2017.03.017
Visser V, Wilson JRU, Canavan K et al (2017) Grasses as invasive plants in South Africa revisited: patterns, pathways and management. Bothalia 47:a2169. https://doi.org/10.4102/abc.v47i2.2169
Vogt S, de Villiers FA, Ihlow F et al (2017) Competition and feeding ecology in two sympatric Xenopus species (Anura: Pipidae). PeerJ 5:e3130. https://doi.org/10.7717/peerj.3130
Watkins BP, Cooper J (1986) Introduction, present status and control of alien species at the Prince Edward Islands. S Afr J Antarct Res 16:86–94
Weyl PSR, de Moor FC, Hill MP, Weyl OLF (2010) The effect of largemouth bass Micropterus salmoides on aquatic macro-invertebrate communities in the Wit River, Eastern Cape, South Africa. Afr J Aquat Sci 35:273–281. https://doi.org/10.2989/16085914.2010.540776
Weyl OLF, Ellender BR, Ivey P et al (2017a) Africa: brown trout introductions, establishment, current status, impacts and conflicts. In: Lobón-Cerviá J, Sanz N (eds) Brown trout: biology, ecology and management. Wiley-Blackwell, Hoboken, pp 623–639. https://doi.org/10.1002/9781119268352.ch24
Weyl OLF, Schirrmann MK, Hargrove JS et al (2017b) Invasion status of Florida bass Micropterus floridanus (Lesueur, 1822) in South Africa. Afr J Aquat Sci 42:359–365
Wilson JRU, Faulkner KT, Rahlao SJ et al (2018) Indicators for monitoring biological invasions at a national level. J Appl Ecol 55:2612–2620. https://doi.org/10.1111/1365-2664.13251
Wilson JR, Foxcroft LC, Geerts S et al (2020) The role of environmental factors in promoting and limiting biological invasions in South Africa. In: van Wilgen BW, Measey J, Richardson DM, Wilson JR, Zengeya TA (eds) Biological invasions in South Africa. Springer, Berlin, pp 353–384. https://doi.org/10.1007/978-3-030-32394-3_13
Winter L, Wallace GE (2006) Impacts of feral and free-ranging cats on bird species of conservation concern. A report from the American Bird Conservancy. Accessed at: ww.abcbirds.org/newsandreports/NFWF.pdf
Yapi TS, O”Farrell PJ, Dziba LE et al (2018) Alien tree invasion into a South African montane grassland ecosystem: impact of Acacia species on rangeland condition and livestock carrying capacity. Int J Biodivers Sci Ecosyst Serv Manage 14:105–116. https://doi.org/10.1080/21513732.2018.1450291
Zengeya T, Ivey P, Woodford DJ et al (2017) Managing conflict-generating invasive species in South Africa: challenges and trade-offs. Bothalia 47:a2160. https://doi.org/10.4102/abc.v47i2.2160
BvW, TAZ, OLFW thank the DSI-NRF Centre for Invasion Biology and the South African National Research Foundation (Grants 109467, 103602, 109015, 110507) for support. SK acknowledges support from the South African National Department of Environmental Affairs through its funding of the South African National Biodiversity, and the DSI-NRF Centre of Excellence for Invasion Biology. John Measey and John Wilson provided useful comments on an earlier draft of this chapter. The South African Department of Environment, Forestry, and Fisheries (DEFF) are thanked for funding the South African National Biodiversity Institute noting that this publication does not necessarily represent the views or opinions of DEFF or its employees.
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Zengeya, T.A., Kumschick, S., Weyl, O.L.F., van Wilgen, B.W. (2020). An Evaluation of the Impacts of Alien Species on Biodiversity in South Africa Using Different Assessment Methods. In: van Wilgen, B., Measey, J., Richardson, D., Wilson, J., Zengeya, T. (eds) Biological Invasions in South Africa. Invading Nature - Springer Series in Invasion Ecology, vol 14. Springer, Cham. https://doi.org/10.1007/978-3-030-32394-3_17
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