Box 14.1 (continued)
and the Asian House Rat (Rattus tanezumi) (Richardson et al. 2011; Measey et
al. 2020, Chap. 5). Many widespread alien plants also seem to be confined to
human-dominated ecosystems, for example Tree of Heaven (Ailanthus
altissima; Walker et al. 2017) and Red Valerian (Centranthus ruber; Geerts
et al. 2017; Holmes et al. 2018). Urban areas provide important habitats for
many other alien plants, and may act as beachheads for invasion into natural
systems; they provide opportunities for species to accumulate high propagule
pressure to drive invasions beyond the urban-wildland interface (e.g. Alston
and Richardson 2006; Foxcroft et al. 2008; Donaldson et al. 2014). Urban
invasion ecology has only recently begun to be studied in South Africa and
much more work remains to be done to elucidate the ecology of urban invaders
(see Potgieter et al. 2020, Chap. 11).
14.2 Parasitism
14.2.1 Plants
As mentioned above, phylogenetic similarity of recipient communities to alien
species may impact on the rate and nature of interaction reassembly. Under ecological fitting, recipient communities harbouring phylogenetically closely related taxa,
or alien species with high eco-evolutionary experience, could possibly facilitate
spillovers of enemies from the recipient community onto the alien species, except
if these lack high eco-evolutionary experience to the invader. Evidence for such
spillover in South Africa comes from Crous et al. (2017). These authors found that,
irrespective of residence time, pathogen accumulation of alien pines (genus Pinus),
Australian wattles (genus Acacia), and eucalypts (genus Eucalyptus) was highest in
taxa most closely related to the South African flora. That is, pines, with no
confamilial relatives in South Africa, have acquired only one highly polyphagous
pathogen despite the long residence time of the genus in the country (>300 years).
On the other hand, wattles and eucalypts, both with confamilial relatives in
South Africa have accumulated many pathogens since their introduction (Crous
et al. 2017). For example, the fungus Chrysoporthe austroafricana, a pathogen of
the South African Water Berry Tree, Syzygium cordatum (Heath et al. 2006), has
caused serious stem canker disease on introduced eucalypts (Wingfield et al. 1989).
In contrast, patterns of accumulation of insect pests in these three plant genera do not
seem to be associated with the phylogenetic relatedness of these genera to
South African plants. In line with the New Associations Hypothesis, these associations appear random and exclusively involve generalist (highly polyphagous) insect
pests (Crous et al. 2017). Despite this, high abundances of South African herbivores
14 Biotic Interactions as Mediators of Biological Invasions
397
and the Asian House Rat (Rattus tanezumi) (Richardson et al. 2011; Measey et
al. 2020, Chap. 5). Many widespread alien plants also seem to be confined to
human-dominated ecosystems, for example Tree of Heaven (Ailanthus
altissima; Walker et al. 2017) and Red Valerian (Centranthus ruber; Geerts
et al. 2017; Holmes et al. 2018). Urban areas provide important habitats for
many other alien plants, and may act as beachheads for invasion into natural
systems; they provide opportunities for species to accumulate high propagule
pressure to drive invasions beyond the urban-wildland interface (e.g. Alston
and Richardson 2006; Foxcroft et al. 2008; Donaldson et al. 2014). Urban
invasion ecology has only recently begun to be studied in South Africa and
much more work remains to be done to elucidate the ecology of urban invaders
(see Potgieter et al. 2020, Chap. 11).
14.2 Parasitism
14.2.1 Plants
As mentioned above, phylogenetic similarity of recipient communities to alien
species may impact on the rate and nature of interaction reassembly. Under ecological fitting, recipient communities harbouring phylogenetically closely related taxa,
or alien species with high eco-evolutionary experience, could possibly facilitate
spillovers of enemies from the recipient community onto the alien species, except
if these lack high eco-evolutionary experience to the invader. Evidence for such
spillover in South Africa comes from Crous et al. (2017). These authors found that,
irrespective of residence time, pathogen accumulation of alien pines (genus Pinus),
Australian wattles (genus Acacia), and eucalypts (genus Eucalyptus) was highest in
taxa most closely related to the South African flora. That is, pines, with no
confamilial relatives in South Africa, have acquired only one highly polyphagous
pathogen despite the long residence time of the genus in the country (>300 years).
On the other hand, wattles and eucalypts, both with confamilial relatives in
South Africa have accumulated many pathogens since their introduction (Crous
et al. 2017). For example, the fungus Chrysoporthe austroafricana, a pathogen of
the South African Water Berry Tree, Syzygium cordatum (Heath et al. 2006), has
caused serious stem canker disease on introduced eucalypts (Wingfield et al. 1989).
In contrast, patterns of accumulation of insect pests in these three plant genera do not
seem to be associated with the phylogenetic relatedness of these genera to
South African plants. In line with the New Associations Hypothesis, these associations appear random and exclusively involve generalist (highly polyphagous) insect
pests (Crous et al. 2017). Despite this, high abundances of South African herbivores
14 Biotic Interactions as Mediators of Biological Invasions
397