Global Invader Research Articles

The cane toad's ( Chaunus [ Bufo ] marinus ) increasing ability to invade Australia is revealed by a dynamically updated range model

Invasive species threaten biological diversity throughout the world. Understanding the dynamics of their spread is critical to mitigating this threat. In Australia, efforts are underway to control the invasive cane toad (Chaunus [Bufo] marinus). Range models based on their native bioclimatic envelope suggest that the cane toad is nearing the end of its invasion phase. However, such models assume a conserved niche between native and invaded regions and the absence of evolution to novel habitats. Here, we develop a dynamically updated statistical model to predict the growing extent of cane toad range based on their current distribution in Australia. Results demonstrate that Australian cane toads may already have the ability to spread across an area that almost doubles their current range and that triples projections based on their native distribution. Most of the expansion in suitable habitat area has occurred in the last decade and in regions characterized by high temperatures. Increasing use of extreme habitats may indicate that novel ecological conditions have facilitated a broader realized niche or that toad populations at the invasion front have evolved greater tolerance to extreme abiotic conditions. Rapid evolution to novel habitats combined with ecological release from native enemies may explain why some species become highly successful global invaders. Predicting species ranges following invasion or climate change may often require dynamically updated range models that incorporate a broader realization of niches in the absence of natural enemies and evolution in response to novel habitats.

Global Invasive Potential of 10 Parasitic Witchweeds and Related Orobanchaceae

The plant family Orobanchaceae includes many parasitic weeds that are also impressive invaders and aggressive crop pests with several specialized features (e.g. microscopic seeds, parasitic habits). Although they have provoked several large-scale eradication and control efforts, no global evaluation of their invasive potential is as yet available. We use tools from ecological niche modeling in combination with occurrence records from herbarium specimens to evaluate the global invasive potential of each of 10 species in this assemblage, representing several of the worst global invaders. The invasive potential of these species is considerable, with all tropical and subtropical countries, and most temperate countries, vulnerable to invasions by one or more of them.

NATURALIZED POPULATIONS OF OYSTERS, CRASSOSTREA GIGAS ALONG THE SOUTH AFRICAN COAST: DISTRIBUTION, ABUNDANCE AND POPULATION STRUCTURE

Abstract The Japanese oyster Crassostrea gigas forms the mainstay of the South African oyster farming industry. Despite having been cultured along the South African coast for 30 years, this is the first record of naturalized populations of this well known global invader from the region. DNA sequence data confirmed the presence of C. gigas in the Breede and Goukou estuaries. Populations of 184,206 ± 21 058.9 (SE), 876 ± 604.2 (SE) and 1 228 ± 841.8 (S.E.) individuals were recorded in the Breede, Goukou and Knysna estuaries respectively. No C. gigas were recorded from the open coast. The condition index of oysters in the Goukou and Knysna estuaries differed significantly from those in the Breede Estuary (Kruskal-Wallis ANOVA H = 48.249, P 0.05). The lower condition index recorded in the Breede Estuary is believed to reflect decreased food supply as a result of the large C. gigas population prese...

Invasion of Langebaan Lagoon, South Africa, by Mytilus galloprovincialis – effects on natural communities

In 1992 the invasive mussel Mytilus galloprovincialis began establishing beds on the centre sandbanks of Langebaan Lagoon. This global invader had previously been restricted to rocky shores along the South African coastline. In order to investigate the effect of the invasion on naturally-occurring communities, a comparative study between invaded areas and areas clear of invasion was conducted. Communities in these areas differed significantly (ANOSIM, R = 0.685, P < 0.01). The biomass supported in invaded areas (53 262 g/m2), was significantly greater than that in clear areas (1133 g/m2), (Mann-Whitney, U = 225, P < 0.001). Invertebrate densities supported in invaded (6780.1 individuals/m2) and clear areas (835 individuals/m2) were also significantly different, (Mann-Whitney, U = 219, P < 0.001). Of the 66 species recorded, only 33 % occurred in both clear and invaded areas (often in very different densities), 41 % occurred exclusively in invaded areas, and 26 % were restricted to non-invaded areas. These figures indicate a replacement of the naturally-occurring sandbank communities by those more typical of rocky shores. It is thus recommended that the invasive mussel beds be removed to conserve the natural biota of the centre banks, which lie within a national park.