Tahr; Hemitragus jemlahicus on Table Mountain and Fallow Deer; Dama dama).
See Measey et al. (2020, Chap. 5) for detailed accounts of the above species.
Urbanisation in Johannesburg and the Gauteng metropolis has transformed large
tracts of grassland to urban woodland over the past 150 years. This has resulted in a
positive relationship between the number of invasive species, the proportion of
transformed land and the land-use heterogeneity index, as well as a shift in local species
composition (Symes et al. 2017). For example, the distribution and population densities
of the Common Myna Sturnus tristis, independently introduced to South Africa on at
least two occasions since the late nineteenth century, are closely tied to that of people
and are associated with highly transformed land (Peacock et al. 2007).
Urbanisation has also contributed to major range expansions of several native
South African species. For example, the Hadeda Ibis (Bostrychia hagedash) and
Speckled Pigeon (Columba guinea) are now common in nearly all South African
cities (Duckworth et al. 2012). Hadedas rely on (many alien) trees in which to nest,
and irrigated lawns (mainly alien grass species) for foraging (Macdonald et al.
1986b). Similarly, Guttural Toads (Sclerophrys gutturalis) translocated from their
native range in Durban to a peri-urban area of Cape Town have become established
(Telford et al. 2019), as this area of the city has low-density, high-income housing
with frequent water features in which the animals could breed (Measey et al. 2017).
Although movement from the summer rainfall area of South Africa into the winter
rainfall zone would normally result in failure to establish (Vimercati et al. 2018), the
availability of garden ponds meant that this species expanded rapidly over 15 years
to cover much of the suburb (~5 km
2 Measey et al. 2017; Vimercati et al. 2017a).
Moreover, attempts to control the population were severely hampered by restricted
access to the properties of multiple private landowners, enabling the spread to
continue (Vimercati et al. 2017b).
The desire to have gardens with trees, lawns and ponds has facilitated many of the
invasions of alien vertebrates in urban areas of South Africa. The desire to emulate a
European garden is normally only enacted in the most affluent suburbs. Invasions in
these areas are clearly mediated by factors such as changes in gardening practices or
the densification of human settlements which alters the extent of suitable habitat and
the effectiveness of dispersal corridors (Moodley et al. 2014). Rivers are key
dispersal conduits for alien plant dispersal in South African towns and cities
(e.g. Kaplan et al. 2012).
11.3 Positive and Negative Effects of Invasive Alien Species
in Urban Areas
In some instances, the introduction of alien species results in a novel set of ecosystem services (ES) and ecosystem disservices (EDS) for urban residents. For example,
many alien trees were introduced into towns and cities situated within the Fynbos
284
L. J. Potgieter et al.
See Measey et al. (2020, Chap. 5) for detailed accounts of the above species.
Urbanisation in Johannesburg and the Gauteng metropolis has transformed large
tracts of grassland to urban woodland over the past 150 years. This has resulted in a
positive relationship between the number of invasive species, the proportion of
transformed land and the land-use heterogeneity index, as well as a shift in local species
composition (Symes et al. 2017). For example, the distribution and population densities
of the Common Myna Sturnus tristis, independently introduced to South Africa on at
least two occasions since the late nineteenth century, are closely tied to that of people
and are associated with highly transformed land (Peacock et al. 2007).
Urbanisation has also contributed to major range expansions of several native
South African species. For example, the Hadeda Ibis (Bostrychia hagedash) and
Speckled Pigeon (Columba guinea) are now common in nearly all South African
cities (Duckworth et al. 2012). Hadedas rely on (many alien) trees in which to nest,
and irrigated lawns (mainly alien grass species) for foraging (Macdonald et al.
1986b). Similarly, Guttural Toads (Sclerophrys gutturalis) translocated from their
native range in Durban to a peri-urban area of Cape Town have become established
(Telford et al. 2019), as this area of the city has low-density, high-income housing
with frequent water features in which the animals could breed (Measey et al. 2017).
Although movement from the summer rainfall area of South Africa into the winter
rainfall zone would normally result in failure to establish (Vimercati et al. 2018), the
availability of garden ponds meant that this species expanded rapidly over 15 years
to cover much of the suburb (~5 km
2 Measey et al. 2017; Vimercati et al. 2017a).
Moreover, attempts to control the population were severely hampered by restricted
access to the properties of multiple private landowners, enabling the spread to
continue (Vimercati et al. 2017b).
The desire to have gardens with trees, lawns and ponds has facilitated many of the
invasions of alien vertebrates in urban areas of South Africa. The desire to emulate a
European garden is normally only enacted in the most affluent suburbs. Invasions in
these areas are clearly mediated by factors such as changes in gardening practices or
the densification of human settlements which alters the extent of suitable habitat and
the effectiveness of dispersal corridors (Moodley et al. 2014). Rivers are key
dispersal conduits for alien plant dispersal in South African towns and cities
(e.g. Kaplan et al. 2012).
11.3 Positive and Negative Effects of Invasive Alien Species
in Urban Areas
In some instances, the introduction of alien species results in a novel set of ecosystem services (ES) and ecosystem disservices (EDS) for urban residents. For example,
many alien trees were introduced into towns and cities situated within the Fynbos
284
L. J. Potgieter et al.