South Africa. This is not the case in the USA where the species is also highly
invasive. Kudzu Vine flowers are frequently visited by pollinators in both the USA
and South Africa. However, in the USA only 3.3% of pollinated flowers produce
pods, whereas 72% of pollinated flowers do in South Africa (Geerts et al. 2016).
Despite the evident role of selfing in alien plant establishment and invasiveness, it
may come at a cost. Less reliance on pollinators due to high selfing can impede
invasion through higher inbreeding depression. For example, Rodger and Johnson
(2013) found that for the highly invasive Silver Wattle, Acacia dealbata, selfed
seedlings experienced significantly higher inbreeding depression than naturally
cross-pollinated treatments.
Even if an invasive plant species has a negative effect on a specific native plant or
pollinator, the effect on the community may be neutral or positive. This context
dependency is due to factors such as community species richness, and the abundance
of pollinators and flowers (Traveset and Richardson 2014). Further work, using
pollination network analyses, is needed to advance our understanding of the resilience of South African pollinator communities to infiltration by invasive species. We
know of only one non-South African study that has addressed this topic. This study
found that specialist flower-visiting species are lost from pollinator webs in areas
impacted by invasive brambles (Hansen et al. 2018).
Although natural ecosystems in South Africa have a few well-known invasive
insect species (e.g. the Argentine Ant (Linepithema humile) and the European Wasp
(Vespula germanica)), very little is known about invasive invertebrates compared to
other taxonomic groups (McGeoch et al. 2011; Janion-Scheepers and Griffiths 2020,
Chap. 7). Although insects with negative impacts on agricultural production are
generally well-studied, very little is known about alien pollinators. However, there
are some examples of alien pollinators such as the Large Cabbage White Butterflies
(Pieris brassicae) and its association with Devil’s Beard (Centranthus ruber; Geerts
et al. 2017) and Purple Loosestrife (Lythrum salicaria; S. Geerts unpublished data).
14.3.3 Seed Dispersal
As with pollination, alien plants benefit from associations with native seed dispersers, and their successful spread during invasion is often enhanced by these
mutualisms (Richardson et al. 2000a; Traveset and Richardson 2006, 2014). Alien
plants have become thoroughly integrated in seed dispersal networks involving
native birds (Middlemiss 1963; Glyphis et al. 1981; Knight 1986, 1988; Knight
and Macdonald 1991; Dean and Milton 2000; Milton et al. 2007; Underhill and
Hofmeyr 2007; Mokotjomela et al. 2013a, b, 2015; Dlamini et al. 2018) and
mammals (Middlemiss 1963; Kerley et al. 1996; Hill 1999; Lotter et al. 1999;
Richardson et al. 2000b; Foxcroft and Rejmánek 2007; Mokotjomela and Hoffmann
2013; Tew et al. 2018) in South Africa. South Africa has a rich flora of plants
adapted for seed dispersal by animals (e.g. Knight and Siegfried 1983; Knight 1988)
and a rich vertebrate fauna to provide generalist seed-dispersal services.
14 Biotic Interactions as Mediators of Biological Invasions
407
invasive. Kudzu Vine flowers are frequently visited by pollinators in both the USA
and South Africa. However, in the USA only 3.3% of pollinated flowers produce
pods, whereas 72% of pollinated flowers do in South Africa (Geerts et al. 2016).
Despite the evident role of selfing in alien plant establishment and invasiveness, it
may come at a cost. Less reliance on pollinators due to high selfing can impede
invasion through higher inbreeding depression. For example, Rodger and Johnson
(2013) found that for the highly invasive Silver Wattle, Acacia dealbata, selfed
seedlings experienced significantly higher inbreeding depression than naturally
cross-pollinated treatments.
Even if an invasive plant species has a negative effect on a specific native plant or
pollinator, the effect on the community may be neutral or positive. This context
dependency is due to factors such as community species richness, and the abundance
of pollinators and flowers (Traveset and Richardson 2014). Further work, using
pollination network analyses, is needed to advance our understanding of the resilience of South African pollinator communities to infiltration by invasive species. We
know of only one non-South African study that has addressed this topic. This study
found that specialist flower-visiting species are lost from pollinator webs in areas
impacted by invasive brambles (Hansen et al. 2018).
Although natural ecosystems in South Africa have a few well-known invasive
insect species (e.g. the Argentine Ant (Linepithema humile) and the European Wasp
(Vespula germanica)), very little is known about invasive invertebrates compared to
other taxonomic groups (McGeoch et al. 2011; Janion-Scheepers and Griffiths 2020,
Chap. 7). Although insects with negative impacts on agricultural production are
generally well-studied, very little is known about alien pollinators. However, there
are some examples of alien pollinators such as the Large Cabbage White Butterflies
(Pieris brassicae) and its association with Devil’s Beard (Centranthus ruber; Geerts
et al. 2017) and Purple Loosestrife (Lythrum salicaria; S. Geerts unpublished data).
14.3.3 Seed Dispersal
As with pollination, alien plants benefit from associations with native seed dispersers, and their successful spread during invasion is often enhanced by these
mutualisms (Richardson et al. 2000a; Traveset and Richardson 2006, 2014). Alien
plants have become thoroughly integrated in seed dispersal networks involving
native birds (Middlemiss 1963; Glyphis et al. 1981; Knight 1986, 1988; Knight
and Macdonald 1991; Dean and Milton 2000; Milton et al. 2007; Underhill and
Hofmeyr 2007; Mokotjomela et al. 2013a, b, 2015; Dlamini et al. 2018) and
mammals (Middlemiss 1963; Kerley et al. 1996; Hill 1999; Lotter et al. 1999;
Richardson et al. 2000b; Foxcroft and Rejmánek 2007; Mokotjomela and Hoffmann
2013; Tew et al. 2018) in South Africa. South Africa has a rich flora of plants
adapted for seed dispersal by animals (e.g. Knight and Siegfried 1983; Knight 1988)
and a rich vertebrate fauna to provide generalist seed-dispersal services.
14 Biotic Interactions as Mediators of Biological Invasions
407