Alien organisms are not only introduced from one biogeographical region to another but also spread within regions. As South Africa shares land borders with six countries, multiple opportunities exist for the transfer of alien species between South Africa and other African countries; however, the direction and importance of intra-regional spread is unclear.
The aim of this study was to gain a greater understanding of the introduction of alien species into Africa and the spread of species between South Africa and other African countries.
We developed scenarios that describe the routes by which alien species are introduced to and spread within Africa and present case studies for each. Using data from literature sources and databases, the relative importance of each scenario for alien birds and insect pests of eucalypts was determined, and the direction and importance of intra-regional spread was assessed.
Alien species from many taxonomic groups have, through various routes, been introduced to and spread within Africa. For birds and eucalypt insect pests, the number of species spreading in the region has recently increased, with South Africa being a major recipient of birds (14 species received and 5 donated) and a major donor of eucalypt insect pests (1 species received and 10 donated). For both groups, many introduced species have not yet spread in the region.
The intra-regional spread of alien species in Africa represents an important and possibly increasing threat to biosecurity. To address this threat, we propose a framework that details how African countries could cooperate and develop a coordinated response to alien species introductions.
The movement of goods and people around the world is facilitating the introduction of organisms to regions where they are not native. Although many alien organisms are introduced directly from one biogeographical region to another (‘inter-regional introduction’), the spread of species within biogeographical regions also contributes to biological invasions (‘intra-regional spread’) (Chiron, Shirley & Kark
The intra-regional spread of species is often asymmetrical [i.e. one country donates more species than it receives (Ferus et al.
Many organisms have been directly introduced to South Africa from other continents [e.g. the Sirex woodwasp (
In an effort to gain a greater understanding of the movements of alien species into and within Africa, we aimed to (1) develop introduction route scenarios that describe how alien species might have been introduced to the region and spread between South Africa and elsewhere in Africa; (2) demonstrate these scenarios using case studies; (3) use the scenarios to quantify, for selected groups, the importance and direction of intra-regional spread; (4) determine if these patterns have changed through time; and (5) propose a framework for trans-boundary collaboration in biosecurity that could address the threat posed to Africa by the intra-regional spread of alien species.
Six introduction route scenarios that describe how alien species might have been introduced to the region and spread between continental South Africa (SA) and elsewhere in continental Africa (AF) were developed and examples identified. In these scenarios, both natural dispersal and the human-aided movement of species within the continent were considered as intra-regional spread. Furthermore, although introduction and spread through all human-related transport vectors were considered (i.e. land, air and sea transport vectors), these vectors were not discriminated in the scenarios. The scenarios describe introduction routes where species have been introduced to SA or AF from other regions, and consider whether subsequent intra-regional spread between SA and AF occurred. Also described are instances where species that are native to either SA or AF have spread between the subregions to areas where they are not native. Details on the introduction route scenarios and examples of species for each scenario are shown in
Introduction route scenarios (indicated using numbers) for alien species in South Africa (SA) and in other parts of Africa (AF), and examples of species which conform to each scenario.
For alien species in SA and AF, information on their native and introduced range (in Africa and elsewhere in the world), descriptions of introduction and spread as well as introduction data (introduction source, number of introductions, pathway of introduction and date of introduction or first record) were used to categorise species in terms of the most likely introduction route scenario that resulted in introduction. As detailed species-level introduction data are often lacking (Faulkner et al.
Re-introductions [e.g. helmeted guineafowl (
While some of the scenarios involve only inter-regional introductions or intra-regional spread, others involve combinations of the two introduction types (i.e. a species is introduced to AF or SA and also spreads between SA and AF; see
A generalised linear model (Poisson error distribution and log link) was used to analyse a two-way contingency table of species counts (Crawley
Birds and eucalypt insect pests have been introduced through various introduction routes (
The number of alien bird and eucalypt insect pest species for which each introduction route scenario was applicable (in black).
The relative importance of inter-regional introduction and intra-regional spread differed for birds and eucalypt insect pests and also varied based on the recipient subregion (
The number of alien bird and eucalypt insect pest species (in black) in South Africa (SA) and elsewhere in Africa (AF) that were introduced through a direct introduction from another region (inter-regional introduction) or through spread between the two subregions (intra-regional spread).
Temporal changes in the number of alien bird and eucalypt insect pest species in South Africa (a and b) and elsewhere in Africa (c and d) that were introduced through a direct introduction from another region (inter-regional introduction) or through spread between the two subregions (intra-regional spread).
The patterns of movement of alien species are often complex (Hurley et al.
Many birds and eucalypt insect pests have been introduced to either SA or AF but have not yet spread between the two subregions. Similarly, many alien species in other regions [e.g. plants (Lambdon et al.
Although introductions from other regions dominated in most cases, the spread of species between SA and AF has recently increased in importance. This trend might be driven by recent growth in trade between these two subregions (
South Africa is one of a few countries that serve as major introduction points for eucalypt insect pests (Hurley et al.
The results discussed above are based on only two groups for which some historical data could be obtained. Because of data quality issues, using historical data to determine the introduction routes of alien species can lead to imprecise inferences (for information on genetic techniques, see Estoup & Guillemaud
Although inter-regional introductions and intra-regional spread may, in general, be increasing as a result of increased global travel and trade (Hurley et al.
The increasing number of species that have spread between South Africa and the rest of Africa highlights that current efforts in South Africa to prevent or reduce introductions from other African countries are likely insufficient. This potential weakness in South Africa’s biosecurity deserves consideration in the first National Status Report on Biological Invasions, and in any future plans to manage South Africa’s pathways of introduction (Wilson et al.
Unfortunately, preventing intra-regional spread is particularly difficult. Organisms from outside Africa can only be transported directly to South Africa by air or sea, and thus to prevent their introduction, border control only needs to be implemented at 18 official ports of entry (
The modes of transportation, the types of introduction they could facilitate, the number of ports of entry for South Africa and the relative ease of managing introductions.
Mode of transport | Type of introduction | Ports of entry | Management ease |
---|---|---|---|
Sea | Intra-regional spread and inter-regional introduction | 8 | High |
Air | Intra-regional spread and inter-regional introduction | 10 | Medium |
Land | Intra-regional spread | 54 | Low |
Natural dispersal | Intra-regional spread | Anywhere along the 4862-km-long land border | Extremely low |
Only ports of entry where individuals may officially enter or exit the country were considered. Details on the ports of entry were obtained from the website of the South African Department of Home Affairs.
To overcome this problem, and better manage biological invasions in the region, a coordinated regional response is needed. Attempts have been made in other regions to achieve this and, for example, the Chilean and Argentinian governments have developed joint research and control programmes for alien mammals (Jaksic et al.
Framework for a coordinated response to alien species introductions in Africa.
A wide variety of alien species have been introduced to Africa and have spread within the region, with the movement patterns of these species varying across organisms and over time. Although direct introductions from other regions remain a concern, the number of species spreading within the region appears to be increasing, and these species probably pose a particularly high biosecurity threat. As preventing the intra-African spread of species is at best difficult, African countries need to cooperate and coordinate their responses. Achieving this requires communication, the development and implementation of standardised methods and systems, and political will. As the efficacy of a country’s biosecurity greatly influences that of its neighbours, such an endeavour would benefit all of the countries involved.
We thank Georg Goergen, Jesse Kalwij, Ingrid Minnaar and Olaf Weyl for providing photos of example species. We also thank Donald Chungu (Copperbelt University, Zambia), Tembani Mduduzi (Forest Research Centre, Zimbabwe), Peter Kiwuso (Forest Research Institute, Uganda), Gerald Meke (FRIM, Malawi) and Eston Mutitu (KEFRI, Kenya) for providing information on the detection date of eucalypt insect pests in their respective countries.
This work was supported by the South African National Department of Environment Affairs through its funding of the South African National Biodiversity Institute’s Invasive Species Programme. Additional funding was provided by the DST-NRF Centre for Invasion Biology. M.R. acknowledges funding from the South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation of South Africa.
The authors declare that they have no financial or personal relationship(s) that may have inappropriately influenced them in writing this article.
K.T.F., M.P.R. and J.R.U.W. developed the scenarios. K.T.F. identified the examples. K.T.F. and B.P.H. collected the data. K.T.F. analysed the data. K.T.F., B.P.H., M.P.R., M.R. and J.R.U.W. wrote the manuscript.
Bird species introduced to South Africa and/or other parts of Africa.
No | Family | Species | Synonym | Common name |
---|---|---|---|---|
1 | Alaudidae | Bimaculated lark | ||
2 | Anatidae | Mandarin duck | ||
3 | Anatidae | Wood duck | ||
4 | Anatidae | Northern pintail | ||
5 | Anatidae | Northern shoveler | ||
6 | Anatidae | Blue-winged teal | ||
7 | Anatidae | Mallard | ||
8 | Anatidae | Garnaney | ||
9 | Anatidae | American black duck | ||
10 | Anatidae | Common pochard | ||
11 | Anatidae | Tufted duck | ||
12 | Anatidae | Ferruginous duck | ||
13 | Anatidae | Muscovy duck | ||
14 | Anatidae | Ringed teal | ||
15 | Anatidae | Black swan | ||
16 | Anatidae | Mute swan | ||
17 | Anatidae | Black-bellied whistling duck | ||
18 | Anatidae | Red-crested pochard | ||
19 | Anatidae | Ruddy duck | ||
20 | Anatidae | European shelduck | ||
21 | Cacatuidae | Yellow-crested cockatoo | ||
22 | Cacatuidae | Cockatiel | ||
23 | Columbidae | Common pigeon | ||
24 | Columbidae | Inva dove | ||
25 | Columbidae | Diamond dove | ||
26 | Columbidae | Eurasian collared dove | ||
27 | Columbidae | European turtle dove | ||
28 | Columbidae | Mourning dove | ||
29 | Coraciidae | Blue-bellied roller | ||
30 | Corvidae | Rook | ||
31 | Corvidae | Jackdaw | ||
32 | Corvidae | House Crow | ||
33 | Corvidae | Rufous treepie | ||
34 | Emberizidae | Red-crested Cardinal | ||
35 | Estrildidae | Red Avadavat | ||
36 | Estrildidae | Orange-cheeked waxbill | ||
37 | Estrildidae | African silverback | ||
38 | Estrildidae | Java Sparrow | ||
39 | Estrildidae | Zebra finch | ||
40 | Falconidae | Merlin | ||
41 | Fringillidae | Goldfinch | ||
42 | Fringillidae | Common chaffinch | ||
43 | Leiothrichidae | Silver-eared mesia | ||
44 | Meropidae | Rosy beeater | ||
45 | Muscicapidae | Nightingale | ||
46 | Musophagidae | Western gray plaintain-eater | ||
47 | Musophagidae | White-bellied-go-away-bird | ||
48 | Musophagidae | Violet turaco | ||
49 | Passeridae | House sparrow | ||
50 | Phasianidae | Chukar partridge | ||
51 | Phasianidae | Arabian chukar | ||
52 | Phasianidae | Golden pheasant | ||
53 | Phasianidae | Bobwhite quail | ||
54 | Phasianidae | Asian blue quail | ||
55 | Phasianidae | Red jungle fowl | ||
56 | Phasianidae | California quail | ||
57 | Phasianidae | Silver pheasant | ||
58 | Phasianidae | Common peacock | ||
59 | Phasianidae | Common pheasant | ||
60 | Ploceidae | Vieillot’s black weaver | ||
61 | Psittacidae | Madagascar lovebird | ||
62 | Psittacidae | Blue-fronted parrot | ||
63 | Psittacidae | Jandaya conure | ||
64 | Psittacidae | Brown-throated conure | ||
65 | Psittacidae | Dusky-headed conure | ||
66 | Psittacidae | Patagonian conure | ||
67 | Psittacidae | Blue-winged parrotlet | ||
68 | Psittacidae | Budgerigar | ||
69 | Psittacidae | Monk parakeet | ||
70 | Psittacidae | Black-hooded conure | ||
71 | Psittacidae | Ruppell’s parrot | ||
72 | Psittacidae | African orange-bellied parrot | ||
73 | Psittacidae | Rose-ringed parakeet | ||
74 | Psittacidae | Black-capped conure | ||
75 | Psittaculidae | Plum-headed parakeet | ||
76 | Pycnonotidae | Red-whiskered bulbul | ||
77 | Rallidae | American coot | ||
78 | Rallidae | Gough moorhen | ||
79 | Rallidae | Tristan moorhen | ||
80 | Sturnidae | Common myna | ||
81 | Sturnidae | Emerald starling | ||
82 | Sturnidae | Ruppells long-tailed starling | ||
83 | Sturnidae | Superb starling | ||
84 | Sturnidae | Common starling | ||
85 | Threskiornithidae | Scarlet ibis | ||
86 | Turdidae | Blackbird | ||
87 | Turdidae | Song thrush |
Insect pests of
No | Family | Species | Common name |
---|---|---|---|
1 | Adelgidae | Pine woolly aphid | |
2 | Aphididae | Black pine aphid | |
3 | Aphididae | Pine needle aphid | |
4 | Cerambycidae | Eucalyptus longhorn beetle | |
5 | Cerambycidae | Eucalyptus longhorn beetle | |
6 | Chrysomelidae | Eucalyptus tortoise beetle | |
7 | Curculionidae | Eucalyptus snout beetle | |
8 | Curculionidae | Pine weevil | |
9 | Eulophidae | Bluegum chalcid | |
10 | Eulophidae | Eucalyptus gall wasp | |
11 | Psyllidae | Eucalyptus psyllid | |
12 | Psyllidae | Bluegum psyllid | |
13 | Psyllidae | Redgum lerp psyllid | |
14 | Psyllidae | Shell lerp psyllid | |
15 | Scolytidae | Pine bark beetle | |
16 | Scolytidae | Red-haired pine bark beetle | |
17 | Scolytidae | Mediterranean pine engraver beetle | |
18 | Siricidae | Sirex woodwasp | |
19 | Thaumastocoridae | Bronze bug |
Bird species introduced to South Africa and/or other parts of Africa categorised in terms of the most likely introduction route scenario that resulted in introduction, and our confidence in each designation. For some species data were insufficient to make a designation.
Species | Common name | Scenario | Confidence |
---|---|---|---|
Mute swan | 1 | High | |
California quail | 1 | High | |
Red jungle fowl | 1 | High | |
Madagascar Lovebird | 1 | High | |
Budgerigar | 1 | High | |
Common Chaffinch | 1 | High | |
Red-crested Cardinal | 1 | High | |
Common peacock | 1 | High | |
Silver pheasant | 1 | High | |
Common pheasant | 1 | High | |
Asian blue quail | 1 | High | |
Black-bellied whistling duck | 1 | High | |
Black swan | 1 | High | |
Mandarin duck | 1 | High | |
Wood duck | 1 | High | |
Blue-winged teal | 1 | High | |
Yellow-crested cockatoo | 1 | High | |
Cockatiel | 1 | High | |
Diamond dove | 1 | High | |
Mourning dove | 1 | High | |
Zebra finch | 1 | High | |
Golden pheasant | 1 | High | |
Brown-throated conure | 1 | High | |
Black-hooded conure | 1 | High | |
Blue-winged parrotlet | 1 | High | |
Blue-fronted parrot | 1 | High | |
Plum-headed Parakeet | 1 | High | |
Red-whiskered bulbul | 1 | High | |
Tristan moorhen | 1 | High | |
Scarlet ibis | 1 | High | |
European shelduck | 1 | High | |
Ringed teal | 1 | High | |
American black duck | 1 | High | |
Ferruginous duck | 1 | High | |
Inva dove | 1 | High | |
Rufous treepie | 1 | High | |
Silver-eared mesia | 1 | High | |
Black-capped conure | 1 | High | |
Jandaya conure | 1 | High | |
Dusky-headed conure | 1 | High | |
Patagonian conure | 1 | High | |
American coot | 1 | High | |
Gough moorhen | 1 | High | |
Rose-ringed Parakeet | 1 | Low | |
Nightingale | 1 | Low | |
Blackbird | 1 | Low | |
Song Thrush | 1 | Low | |
Red Avadavat | 1 | Low | |
Java Sparrow | 1 | Low | |
Goldfinch | 1 | Low | |
red-crested Pochard | 1 | Low | |
Common pochard | 1 | Low | |
Tufted duck | 1 | Low | |
Muscovy duck | 1 | Low | |
Rook | 1 | Low | |
Eurasian collared dove | 1 | Low | |
Bimaculated lark | 1 | Low | |
Merlin | 1 | Low | |
Northern shoveler | 1 | Low | |
Northern pintail | 1 | Low | |
Garnaney | 1 | Low | |
House Crow | 2 | High | |
Blue-bellied roller | 3 | High | |
White-bellied-go-away-bird | 3 | High | |
Western gray plaintain-eater | 3 | High | |
Violet turaco | 3 | High | |
Vieillot’s black weaver | 3 | High | |
African orange-bellied parrot | 3 | High | |
Ruppell’s parrot | 3 | High | |
Emerald starling | 3 | High | |
Ruppells long-tailed starling | 3 | High | |
Superb starling | 3 | High | |
Rosy beeater | 3 | High | |
Orange-cheeked waxbill | 3 | Low | |
African silverback | 3 | Low | |
Arabian Chukar | 4 | High | |
House Crow | 4 | High | |
Jackdaw | 4 | High | |
House Sparrow | 4 | High | |
Java Sparrow | 4 | High | |
Ruddy duck | 4 | High | |
Monk parakeet | 4 | High | |
Mallard | 4 | Low | |
Rose-ringed Parakeet | 4 | Low | |
Common Myna | 4 | Low | |
Red Avadavat | 4 | Low | |
Muscovy duck | 4 | Low | |
Common starling | 5 | High | |
Common Myna | 5 | High | |
House Sparrow | 5 | High | |
Mallard | 5 | Low | |
Chukar partridge | 5 | Low | |
Bobwhite quail | Insufficient data | ||
Common pigeon | Insufficient data | ||
European turtle dove | Insufficient data |
Insect pests of
Species | Common name | Scenario | Confidence |
---|---|---|---|
Pine weevil | 1 | High | |
Eucalyptus tortoise beetle | 1 | High | |
Sirex woodwasp | 1 | High | |
Shell lerp psyllid | 1 | High | |
Bluegum psyllid | 1 | Low | |
Eucalyptus psyllid | 1 | Low | |
Eucalyptus gall wasp | 1 | Low | |
Bluegum chalcid | 2 | High | |
Eucalyptus longhorn beetle | 4 | Low | |
Eucalyptus longhorn beetle | 4 | Low | |
Bluegum psyllid | 4 | Low | |
Black pine aphid | 4 | Low | |
Pine woolly aphid | 4 | Low | |
Eucalyptus psyllid | 4 | Low | |
Redgum lerp psyllid | 4 | Low | |
Eucalyptus gall wasp | 4 | Low | |
Eucalyptus snout beetle | 5 | High | |
Pine bark beetle | 5 | High | |
Red-haired pine bark beetle | 5 | Low | |
Eucalyptus longhorn beetle | 5 | Low | |
Eucalyptus longhorn beetle | 5 | Low | |
Mediterranean pine engraver beetle | 5 | Low | |
Black pine aphid | 5 | Low | |
Pine woolly aphid | 5 | Low | |
Bronze bug | 5 | Low | |
Redgum lerp psyllid | 5 | Low | |
Pine needle aphid | Insufficient data |
The number of alien bird and eucalypt insect pest species for which each introduction route scenario was applicable (in black). Scenario designations with only high certainty were included. Details of the scenarios are provided in
The number of alien bird and eucalypt insect pest species (black) in South Africa (SA) and elsewhere in Africa (AF) that were introduced through a direct introduction from another region (inter-regional introduction) or through spread between the two subregions (intra-regional spread). Scenario designations with only high certainty were included and expected values are shown in white. The association between introduction type, organism type and recipient sub-region was not significant: χ2 = 1.5,
Direction of trade statistics from the International Monetary Fund showing temporal changes in the contribution of (a) Africa (black) and other regions (grey) to South African imports and (b) South Africa (black) and other regions (grey) to African imports.
Recent temporal changes in the value of merchandise exports from South Africa to elsewhere in Africa (black) and from elsewhere in Africa to South Africa (grey). Data were obtained from the International Monetary Fund.
Details on the introduction and spread of
Details on the introduction and spread of
Details on the introduction and spread of
Details on the introduction and spread of
Details on the introduction and spread of
Details on the introduction and spread of