Cape, and translocated animals from Mpumalanga, with the first records around
1995 (Tolley et al. 2008). Davies et al. (2013) explained how Painted Reed Frogs
have been able to overcome their historical range limits by using a combination
of human-mediated jump dispersal and artificial impoundments. This has allowed
these frogs to expand their niche into novel environmental space, not occupied in
the native range (Davies et al. 2013). The permanence of the dams mitigated the
influence of historical climatic barriers that previously prevented movement into
drier and more thermally variable habitats (Davies et al. 2019). Importantly, their
model suggests that the invasion is ongoing, with only around a quarter of potential
sites occupied, a result that was corroborated in a niche-modelling exercise on the
same species, which signified range disequilibrium (Davies et al. 2019). Painted reed
frogs in their novel range were found to exhibit plasticity of temperature limits
and metabolism, which may provide benefit in drier and more thermally variable
habitats of its novel range (Davies et al. 2015). The painted reed frog poses
considerable risk should its populations be moved to other suitable climates globally.
In the urban environment, age-structured and landscape resistance models suggest
that this species would be able to rapidly colonise garden ponds, quickly saturating
an area of 50 km
2 within 10 years of its introduction to a new site (Vimercati et al.
2017a).
5.6.2 Sclerophrys gutturalis (Guttural Toad)
The Guttural Toad was deliberately introduced to Mauritius and from there to
Reunion in the 1920s as a biological control for mosquitoes (Telford et al. 2019).
The same species was first recorded in Constantia, a suburb of Cape Town, in 2000
(de Villiers 2006), with the presumption that individuals were transferred
unintentionally with a consignment of aquatic plants from Durban (de Villiers
2006; Measey et al. 2017). Genetic investigation into the origin of all three invasions
suggests that all of these explanations are correct. Moreover, invasions into Mauritius and (then) Reunion, also appear to be derived from the Durban area, but have
much greater genetic diversity than the Constantia invasion as a result of the
deliberate introduction (Telford et al. 2019). The rapid movement from Durban, in
South Africa’s summer rainfall zone, to Constantia in the winter rainfall zone (see
Wilson et al. 2020, Chap. 14), and the short period this species has had to adapt, are
of considerable interest. Field data show that Constantia animals are significantly
more dehydrated than Durban populations (Vimercati et al. 2018). However, the
toads were able to withstand dehydration by hunkering down into a waterconserving posture. The invading toads also performed better in endurance trials,
by moving much farther than animals from their native Durban when dehydrated.
Lastly, invading toads were able to withstand cooler conditions than Durban animals
(Vimercati et al. 2018). This rapid adaptation to a novel climate means that Guttural
Toads could invade more areas with a similar climate.
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J. Measey et al.
1995 (Tolley et al. 2008). Davies et al. (2013) explained how Painted Reed Frogs
have been able to overcome their historical range limits by using a combination
of human-mediated jump dispersal and artificial impoundments. This has allowed
these frogs to expand their niche into novel environmental space, not occupied in
the native range (Davies et al. 2013). The permanence of the dams mitigated the
influence of historical climatic barriers that previously prevented movement into
drier and more thermally variable habitats (Davies et al. 2019). Importantly, their
model suggests that the invasion is ongoing, with only around a quarter of potential
sites occupied, a result that was corroborated in a niche-modelling exercise on the
same species, which signified range disequilibrium (Davies et al. 2019). Painted reed
frogs in their novel range were found to exhibit plasticity of temperature limits
and metabolism, which may provide benefit in drier and more thermally variable
habitats of its novel range (Davies et al. 2015). The painted reed frog poses
considerable risk should its populations be moved to other suitable climates globally.
In the urban environment, age-structured and landscape resistance models suggest
that this species would be able to rapidly colonise garden ponds, quickly saturating
an area of 50 km
2 within 10 years of its introduction to a new site (Vimercati et al.
2017a).
5.6.2 Sclerophrys gutturalis (Guttural Toad)
The Guttural Toad was deliberately introduced to Mauritius and from there to
Reunion in the 1920s as a biological control for mosquitoes (Telford et al. 2019).
The same species was first recorded in Constantia, a suburb of Cape Town, in 2000
(de Villiers 2006), with the presumption that individuals were transferred
unintentionally with a consignment of aquatic plants from Durban (de Villiers
2006; Measey et al. 2017). Genetic investigation into the origin of all three invasions
suggests that all of these explanations are correct. Moreover, invasions into Mauritius and (then) Reunion, also appear to be derived from the Durban area, but have
much greater genetic diversity than the Constantia invasion as a result of the
deliberate introduction (Telford et al. 2019). The rapid movement from Durban, in
South Africa’s summer rainfall zone, to Constantia in the winter rainfall zone (see
Wilson et al. 2020, Chap. 14), and the short period this species has had to adapt, are
of considerable interest. Field data show that Constantia animals are significantly
more dehydrated than Durban populations (Vimercati et al. 2018). However, the
toads were able to withstand dehydration by hunkering down into a waterconserving posture. The invading toads also performed better in endurance trials,
by moving much farther than animals from their native Durban when dehydrated.
Lastly, invading toads were able to withstand cooler conditions than Durban animals
(Vimercati et al. 2018). This rapid adaptation to a novel climate means that Guttural
Toads could invade more areas with a similar climate.
140
J. Measey et al.