to the developing field of invasion science, arising from a small, well-connected, and
highly collaborative research community.
Part II (Chaps. 3–11) deals with the current situation. The first chapters focus on
specific taxa—terrestrial plants (Richardson et al. 2020b), aquatic plants (Hill et al.
2020a), terrestrial vertebrates (Measey et al. 2020a), terrestrial invertebrates (JanionScheepers and Griffiths 2020), and pathogens that affect mammals, including
humans (van Helden et al. 2020). The ecology of diseases, such as those covered
by van Helden et al. (2020), has not yet been integrated within the invasion science
agenda in South Africa. It is hoped that the inclusion of this chapter will stimulate
further work to explore the links between disease ecology and invasion science (cf.
Ogden et al. 2019). The remaining chapters focus on specific areas that are
invaded—freshwater ecosystems (Weyl et al. 2020), coastal marine ecosystems
(Robinson et al. 2020), offshore sub-Antarctic islands (Greve et al. 2020), and
urban settings (Potgieter et al. 2020). Most invasive alien species in South Africa
are plants (Table 1.1), and these are consequently best understood. Invertebrates are
also important, but are less well documented. Other groups (e.g. birds, reptiles and
amphibians) have markedly fewer invasive species, and our understanding of marine
and microbial species is still very limited.
Part III (Chaps. 12–14) details the underlying factors influencing invasions—
how species arrived in South Africa, and how they were dispersed once they got here
(Faulkner et al. 2020); the environmental factors, including geomorphology, soils,
climate, extreme events (specifically droughts and floods), fire, and land uses that
influence the success of alien species (Wilson et al. 2020a); and the role of symbiotic
interactions in affecting biological invasions in South Africa (Le Roux et al. 2020).
Many early introductions were deliberate, but accidental introductions are increasing
in importance. The high diversity of alien plants that have established is in part due
to the wide range of environmental conditions across the country, but successful
establishment can be limited by fire and aridity. Biotic interactions also play a role,
with examples documented of parasitism and mutualism and how these relate to
various ecological and evolutionary hypotheses aimed at explaining invasions. But it
is clear there is much scope for further research.
Part IV (Chaps. 15–17) addresses why invasive species are important in the
South African context, dealing with water resources (Le Maitre et al. 2020), rangeland productivity (O’Connor and van Wilgen 2020), and biodiversity (Zengeya et al.
2020). As in the rest of the world, the impacts of invasive species have not been
adequately documented, but enough research has been done to examine particular
aspects. Invasive trees and shrubs are estimated to be reducing the national mean
annual runoff by almost 3%, and reductions in some key catchments are much
higher. The productivity of rangelands has been reduced by about 1%, but this
will almost certainly increase as aggressive invasive plants spread. Formal assessments of the impact of individual alien species on biodiversity have only recently
been initiated, but red-listing processes suggest that alien species constitute a
significant extinction risk for several native species of fish, amphibians and plants.
Part V (Chaps. 18–25) covers aspects of the management of invasions in
South Africa. The first traces the development of policy from the first legislation
passed in 1861 to the current day (Lukey and Hall 2020). The next charts progress
1 Biological Invasions in South Africa: An Overview
23
highly collaborative research community.
Part II (Chaps. 3–11) deals with the current situation. The first chapters focus on
specific taxa—terrestrial plants (Richardson et al. 2020b), aquatic plants (Hill et al.
2020a), terrestrial vertebrates (Measey et al. 2020a), terrestrial invertebrates (JanionScheepers and Griffiths 2020), and pathogens that affect mammals, including
humans (van Helden et al. 2020). The ecology of diseases, such as those covered
by van Helden et al. (2020), has not yet been integrated within the invasion science
agenda in South Africa. It is hoped that the inclusion of this chapter will stimulate
further work to explore the links between disease ecology and invasion science (cf.
Ogden et al. 2019). The remaining chapters focus on specific areas that are
invaded—freshwater ecosystems (Weyl et al. 2020), coastal marine ecosystems
(Robinson et al. 2020), offshore sub-Antarctic islands (Greve et al. 2020), and
urban settings (Potgieter et al. 2020). Most invasive alien species in South Africa
are plants (Table 1.1), and these are consequently best understood. Invertebrates are
also important, but are less well documented. Other groups (e.g. birds, reptiles and
amphibians) have markedly fewer invasive species, and our understanding of marine
and microbial species is still very limited.
Part III (Chaps. 12–14) details the underlying factors influencing invasions—
how species arrived in South Africa, and how they were dispersed once they got here
(Faulkner et al. 2020); the environmental factors, including geomorphology, soils,
climate, extreme events (specifically droughts and floods), fire, and land uses that
influence the success of alien species (Wilson et al. 2020a); and the role of symbiotic
interactions in affecting biological invasions in South Africa (Le Roux et al. 2020).
Many early introductions were deliberate, but accidental introductions are increasing
in importance. The high diversity of alien plants that have established is in part due
to the wide range of environmental conditions across the country, but successful
establishment can be limited by fire and aridity. Biotic interactions also play a role,
with examples documented of parasitism and mutualism and how these relate to
various ecological and evolutionary hypotheses aimed at explaining invasions. But it
is clear there is much scope for further research.
Part IV (Chaps. 15–17) addresses why invasive species are important in the
South African context, dealing with water resources (Le Maitre et al. 2020), rangeland productivity (O’Connor and van Wilgen 2020), and biodiversity (Zengeya et al.
2020). As in the rest of the world, the impacts of invasive species have not been
adequately documented, but enough research has been done to examine particular
aspects. Invasive trees and shrubs are estimated to be reducing the national mean
annual runoff by almost 3%, and reductions in some key catchments are much
higher. The productivity of rangelands has been reduced by about 1%, but this
will almost certainly increase as aggressive invasive plants spread. Formal assessments of the impact of individual alien species on biodiversity have only recently
been initiated, but red-listing processes suggest that alien species constitute a
significant extinction risk for several native species of fish, amphibians and plants.
Part V (Chaps. 18–25) covers aspects of the management of invasions in
South Africa. The first traces the development of policy from the first legislation
passed in 1861 to the current day (Lukey and Hall 2020). The next charts progress
1 Biological Invasions in South Africa: An Overview
23