The number and status of alien species in south africa

In document The sTaTus of biological invasions and Their managemenT in souTh africa 2017 (Page 73-76)

4. the StatuS of aLieN SPeCieS

4.2. The number and status of alien species in south africa

The introduction status of alien species can be assessed at different levels, depending on the availability of data (Table 4.3). for many species it was only possible to either determine whether or not it was present in south africa, while for others it was possible to assess whether the species was absent, introduced but not naturalised, naturalised but not invasive, or invasive. There are very few studies on specific groups that provide data at the third and highest level of resolution, i.e. a breakdown of introduction status according to the unified framework of blackburn et al. (2011), as was done, for example, by Jacobs et al. (2017). full details of all species are provided in appendix 3.

tABle 4.3 The relationship between the three levels of resolution that can be used to describe introduction status. Species are placed as far along the introduction-naturalisation-invasion continuum as they can be with the available evidence (e.g. there has to be reported evidence that a species is invasive for it to be classed as such).

preSenCe BASiC introduCtion

StAtuS StAtuS AdApted FroM tHe uniFied FrAMework For BiologiCAl invASionS (BlACkBurn et Al., 2011) ABSent not present a0 (never introduced beyond limits of indigenous range to the region in

question, i.e. south africa)

a1 (has been introduced beyond limits of indigenous range to south africa, but no longer present)

preSent introduced but not naturalised

B1 (in captivity or quarantine)

B2 (in cultivation but no measures in place to prevent escape) B3 (released outside of captivity or cultivation)

C0 (some escape from captivity or cultivation, but survival limited)

C1 (escape and survival outside of captivity or cultivation, but no reproduction) C2 (escape, survival, and reproduction outside of captivity or cultivation, but

not clear whether the population is self-sustaining) naturalised but not

invasive C3 (escape, survival, and reproduction outside of captivity or cultivation;

population self-sustaining but not spreading)

invasive d1 (escape, survival, reproduction and spread outside of captivity or cultivation; though no evidence of reproduction post-dispersal)

d2 (escape, survival, reproduction, spread, and subsequent reproduction outside of captivity or cultivation; though spread as yet limited to a few localities) e (invasive at multiple localities)

4.2.1. Number of alien species in South africa

a total of 2033 alien species were found to be present in south africa (Table 4.4). all of the species listed as prohibited in the a&is regulations were assumed to be absent from south africa, except for eight prohibited species that are known to have been introduced. These include one bird, one reptile, two amphibians, one microbial species and three invertebrates.

Tus of biological invasions and Their managemenT in souTh africa2017

4.2.2. Status of alien species in South africa

of the 2033 alien species recorded (or assumed to be present) outside of cultivation or captivity in south africa, 775 are known to be invasive, 388 are known to be naturalised but not invasive, and 355 are present, but not naturalised. There are a further 516 species where there is insufficient information on which to assign them to one of the basic introduction status categories. for terrestrial and freshwater plants, the assessment relied heavily on the saPia dataset [see henderson & Wilson (2017) for a recent analysis of the database]. unless explicitly stated elsewhere, the assumptions were made that all taxa recorded in saPia were naturalised and all taxa in two or more quarter degree grid cells (Qdgcs) were invasive. This is not strictly correct, as for a species to be recorded in saPia there is no formal assessment of naturalisation, or whether a population is invasive or not, but the assumption will hold for the majority of records. for the other taxa, the determination of a species as invasive was based on expert opinion where available, otherwise the species was not classed as naturalised or invasive (recorded as na – not assessed – in appendix 3).

about one third of the alien species found outside of captivity or cultivation in south africa are known to have become invasive in south africa. The proportion differed among taxa, with terrestrial, freshwater and marine plants having relatively high proportions (55 – 64%), while reptiles and microbes had no known invasive species (though in the case of microbes this is undoubtedly a classification error). The proportion of all introduced species (for example of a genus or family) that are invasive will be lower than the above estimates, because the estimates express the proportion in terms of species that are already present outside of captivity or cultivation.

reliable estimates of the proportion of species within a genus are only available for some genera of plants, where the proportion of introduced species that becomes invasive ranges from 2% to 22%. at least 36 species in the genus Melaleuca (bottlebrushes) have been introduced to south africa, and 10 of these have naturalised, including 5 (14%) that are invasive (Jacobs et al. 2017). more than 80 species of the genus Acacia (australian wattles) have been introduced to south africa, and 18 (22%) have been recorded as naturalised (richardson, le roux & Wilson 2015). at least 68 species of the genus Pinus (pine trees) have been introduced to south africa, where eight species have become invasive (12%), and a further 26 species are regarded as potentially invasive (van Wilgen & richardson, 2012). such analyses have the potential to inform risk analyses by identifying high-risk groups (diez, hulme & duncan 2012), but should be moderated by an assessment of whether introduced taxa had an opportunity to become invasive or not (moodley et al., 2014).

facility for mass-rearing biological control agents – Kim Weaver facility for mass-rearing biological control agents – Kim Weaver

tHe SituAtion

alien species have established populations outside

of cultivation or captivity in South Africa

2033

of t hese are invasi 775 ve

ChaPter 4IThe sTaTus of alien sP

tABle 4.4 The number of alien species known to occur in South Africa, assigned to various categories of introduction status. The categories under “NeM:BA” refer to species listed in the Alien and Invasive Species Regulations under the National environmental Management: Biodiversity Act; “context-specific” refers to species that are listed in different categories depending on their location or habitat. See Table 4.3 for definitions of status.

tAxon legAl

CAtegory

StAtuS

occurs in sa, but insufficient

data to assign status = na

present in south africa, but not established outside of captivity or cultivation =

b1, b2, b3, c0, c1, c2

naturalised

= c3 invasive

d1, d2, e Total

terrestrial and

freshwater plants listed 29 4 34 315 382

unlisted 3 68 181 259 511

Marine plants listed 0 0 1 2 3

unlisted 0 0 2 3 5

Mammals listed 34 1 4 1 40

unlisted 2 0 0 0 2

Birds Prohibited 0 1 0 0 1

listed 7 3 5 8 23

unlisted 41 8 13 6 68

reptiles Prohibited 0 1 0 0 1

listed 22 5 2 0 29

unlisted 81 16 0 1 98

Amphibian Prohibited 0 2 0 0 2

listed 0 3 1 2 6

unlisted 0 11 1 1 13

Freshwater fish listed 2 7 6 0 15

unlisted 6 4 1 0 11

terrestrial

invertebrates Prohibited 0 1 0 0 1

listed 13 2 8 0 23

unlisted 262 133 73 107 575

Freshwater

invertebrates Prohibited 0 0 0 1 1

listed 4 2 0 3 9

unlisted 1 2 2 14 19

Marine invertebrates Prohibited 0 0 1 0 1

listed 0 0 3 9 12

unlisted 0 4 31 37 72

Microbial species Prohibited 0 1 0 0 1

listed 7 0 0 0 7

unlisted 1 76 19 6 102

total 516 355 388 775 2033

Tus of biological invasions and Their managemenT in souTh africa2017

In document The sTaTus of biological invasions and Their managemenT in souTh africa 2017 (Page 73-76)