Wilgen and Wilson 2018 for the raw data and details on the methodology followed).
In this chapter, we present these historical and socio-economic data as well as
additional information, and discuss how alien taxa have been introduced to and
dispersed within (referred to in this chapter as ‘pathways of dispersal’) South Africa.
We demonstrate how these pathways have changed over time and discuss the socioeconomic factors that have driven these changes. The pathways that are currently
facilitating the introduction and within-country dispersal of alien taxa are addressed,
and how the pathways might change in the future are discussed. While the pathways
of introduction and dispersal are discussed broadly, more detail is provided for some
pathways that demonstrate important aspects or trends.
12.2 How Have Taxa Been Introduced to and Dispersed
Within South Africa?
12.2.1 Importance of the Pathways of Introduction
and Dispersal
Alien taxa have been introduced to South Africa through a wide variety of pathways
(Fig. 12.1). Many plant taxa have been intentionally imported by the ornamental
plant trade, or have been introduced for agriculture (Fig. 12.1). These plants have
subsequently escaped from gardens or cultivation, and many have become invasive
(Faulkner et al. 2016). Several vertebrates have been imported intentionally and
released for purposes like fishing (Figs. 12.1 and 12.2, also see Box 12.1; Weyl et al.
2020, Chap. 6), and most of these introductions have resulted in invasions (Faulkner
et al. 2016). A large number of invertebrates have been released as biological control
agents (Figs. 12.1 and 12.2; Hill et al. 2020, Chap. 19), and none of the agents
released to control alien plants in South Africa in the last 100 years have been
reported to cause negative impacts (Moran et al. 2013). While many alien taxa have
been intentionally imported into the country, alien organisms have also entered the
country accidentally (Fig. 12.2). For example, as contaminants on imported goods
like plants or parts thereof (e.g. wood or fruit), or as stowaways on transport vessels
such as ships (Fig. 12.1). The majority of taxa that are known to have been
accidentally introduced are invertebrates (Fig. 12.2), and several of these taxa have
subsequently become invasive (Faulkner et al. 2016). Some organisms that have
been introduced to neighbouring countries have also spread unaided into
South Africa; however, no alien taxa are known to have spread into the country
through human-built corridors that connect previously unconnected regions
(Fig. 12.2). Information on the pathways of introduction for many of the taxa
introduced to South Africa is not available (Fig. 12.2), with these data more likely
available for taxa that are well known or widespread and those that are intentionally
introduced (Faulkner et al. 2016). Additionally, there may be many taxa that have
been introduced but that have not been recorded (McGeoch et al. 2012). It is likely
12 Pathways of Introduction and Dispersal
319
In this chapter, we present these historical and socio-economic data as well as
additional information, and discuss how alien taxa have been introduced to and
dispersed within (referred to in this chapter as ‘pathways of dispersal’) South Africa.
We demonstrate how these pathways have changed over time and discuss the socioeconomic factors that have driven these changes. The pathways that are currently
facilitating the introduction and within-country dispersal of alien taxa are addressed,
and how the pathways might change in the future are discussed. While the pathways
of introduction and dispersal are discussed broadly, more detail is provided for some
pathways that demonstrate important aspects or trends.
12.2 How Have Taxa Been Introduced to and Dispersed
Within South Africa?
12.2.1 Importance of the Pathways of Introduction
and Dispersal
Alien taxa have been introduced to South Africa through a wide variety of pathways
(Fig. 12.1). Many plant taxa have been intentionally imported by the ornamental
plant trade, or have been introduced for agriculture (Fig. 12.1). These plants have
subsequently escaped from gardens or cultivation, and many have become invasive
(Faulkner et al. 2016). Several vertebrates have been imported intentionally and
released for purposes like fishing (Figs. 12.1 and 12.2, also see Box 12.1; Weyl et al.
2020, Chap. 6), and most of these introductions have resulted in invasions (Faulkner
et al. 2016). A large number of invertebrates have been released as biological control
agents (Figs. 12.1 and 12.2; Hill et al. 2020, Chap. 19), and none of the agents
released to control alien plants in South Africa in the last 100 years have been
reported to cause negative impacts (Moran et al. 2013). While many alien taxa have
been intentionally imported into the country, alien organisms have also entered the
country accidentally (Fig. 12.2). For example, as contaminants on imported goods
like plants or parts thereof (e.g. wood or fruit), or as stowaways on transport vessels
such as ships (Fig. 12.1). The majority of taxa that are known to have been
accidentally introduced are invertebrates (Fig. 12.2), and several of these taxa have
subsequently become invasive (Faulkner et al. 2016). Some organisms that have
been introduced to neighbouring countries have also spread unaided into
South Africa; however, no alien taxa are known to have spread into the country
through human-built corridors that connect previously unconnected regions
(Fig. 12.2). Information on the pathways of introduction for many of the taxa
introduced to South Africa is not available (Fig. 12.2), with these data more likely
available for taxa that are well known or widespread and those that are intentionally
introduced (Faulkner et al. 2016). Additionally, there may be many taxa that have
been introduced but that have not been recorded (McGeoch et al. 2012). It is likely
12 Pathways of Introduction and Dispersal
319