The Constantia population has been subjected to control measures (see Davies
et al. 2020, Chap. 22) and is also mentioned in the context of urban invasions
(Potgieter et al. 2020, Chap. 11). Modelling of the Guttural Toad invasion has
provided insight into population dynamics, which translate into practical implications for control. For example, the density-dependent nature of tadpoles and
metamorphs (Vimercati et al. 2017a, b) means that contracted workers can concentrate on removing adults and juveniles, saving considerable expense and time spent
in private properties.
5.7 Future Perspectives for Invasive Vertebrates
Our cumulative records for terrestrial vertebrates look unlike those reported by
Picker and Griffiths (2017) (Fig. 5.2a), most likely as they were missing some
introduction dates and ‘domestic exotics’ such as the geckos and frogs. Their
inclusion here suggests that contrary to the conclusion of Picker and Griffiths
(2017), terrestrial vertebrate invasions in South Africa have seen the biggest rise
during the last 150 years. We found that the proportion of deliberate to accidental
introductions was skewed toward deliberate introductions, although the trend is
moving from deliberate to accidental (Fig. 5.2b). Similarly, species in the last
150 years have Asia as the most common donor region. However, most recently,
is the arrival of ‘domestic exotics’ (Guo and Ricklefs 2010), species that have part of
their native and introduced range within South Africa. Studies to date (Telford et al.
2019; Tolley et al. 2008) suggest that all invasions originate from populations within
the country.
Many of the species reviewed here still have the capacity to increase their
distribution and invasive impact in South Africa, and so reports of low or no impacts
mentioned above are probably not static. Although it is encouraging that only a
single successful twenty-first century invasion is recorded here (Asian House Rat,
R. tanezumi), this situation may reflect a level of invasion debt in vertebrate species
(Rouget et al. 2016), commensurate with the increased levels of trade (Faulkner et al.
2017). Many of the impact levels (EICAT and SEICAT, see Blackburn et al. 2014;
Bacher et al. 2018) noted above have not been assessed in the South African context,
but this is required for high-ranking species such as feral pigs, donkeys, feral cats,
horses, fallow deer, goats and house crows. This sets an important research agenda
for the region.
Interactions between invasive vertebrates (and other invasive species) are not well
documented in South Africa, but have been implicated with the term ‘invasion
meltdown’ when facilitation occurs. Conversely, some invasive species can repel
others or simply have negative impacts, such as Rose-ringed Parakeets attacking and
killing House Rats (Hernández-Brito et al. 2014).
There are also signs that the numbers of invasive vertebrate species are rising
(Fig. 5.2a). Of concern is the growing demand for ornamental and caged birds in
5 Terrestrial Vertebrate Invasions in South Africa
141
et al. 2020, Chap. 22) and is also mentioned in the context of urban invasions
(Potgieter et al. 2020, Chap. 11). Modelling of the Guttural Toad invasion has
provided insight into population dynamics, which translate into practical implications for control. For example, the density-dependent nature of tadpoles and
metamorphs (Vimercati et al. 2017a, b) means that contracted workers can concentrate on removing adults and juveniles, saving considerable expense and time spent
in private properties.
5.7 Future Perspectives for Invasive Vertebrates
Our cumulative records for terrestrial vertebrates look unlike those reported by
Picker and Griffiths (2017) (Fig. 5.2a), most likely as they were missing some
introduction dates and ‘domestic exotics’ such as the geckos and frogs. Their
inclusion here suggests that contrary to the conclusion of Picker and Griffiths
(2017), terrestrial vertebrate invasions in South Africa have seen the biggest rise
during the last 150 years. We found that the proportion of deliberate to accidental
introductions was skewed toward deliberate introductions, although the trend is
moving from deliberate to accidental (Fig. 5.2b). Similarly, species in the last
150 years have Asia as the most common donor region. However, most recently,
is the arrival of ‘domestic exotics’ (Guo and Ricklefs 2010), species that have part of
their native and introduced range within South Africa. Studies to date (Telford et al.
2019; Tolley et al. 2008) suggest that all invasions originate from populations within
the country.
Many of the species reviewed here still have the capacity to increase their
distribution and invasive impact in South Africa, and so reports of low or no impacts
mentioned above are probably not static. Although it is encouraging that only a
single successful twenty-first century invasion is recorded here (Asian House Rat,
R. tanezumi), this situation may reflect a level of invasion debt in vertebrate species
(Rouget et al. 2016), commensurate with the increased levels of trade (Faulkner et al.
2017). Many of the impact levels (EICAT and SEICAT, see Blackburn et al. 2014;
Bacher et al. 2018) noted above have not been assessed in the South African context,
but this is required for high-ranking species such as feral pigs, donkeys, feral cats,
horses, fallow deer, goats and house crows. This sets an important research agenda
for the region.
Interactions between invasive vertebrates (and other invasive species) are not well
documented in South Africa, but have been implicated with the term ‘invasion
meltdown’ when facilitation occurs. Conversely, some invasive species can repel
others or simply have negative impacts, such as Rose-ringed Parakeets attacking and
killing House Rats (Hernández-Brito et al. 2014).
There are also signs that the numbers of invasive vertebrate species are rising
(Fig. 5.2a). Of concern is the growing demand for ornamental and caged birds in
5 Terrestrial Vertebrate Invasions in South Africa
141