Synergistic impact of invasive alien plants and the alien Argentine ant on local ant assemblages in the Western Cape

[摘要] ENGLISH ABSTRACT: Alien trees, Pinus spp. and Eucalyptus spp., affect ants negatively in the Cape FloristicRegion (CFR), a global biodiversity hotspot in South Africa. They reduce ant abundanceand species richness, thus also changing ant assemblage structure. This is alarming,because almost 1300 species of plant species in the CFR are dispersed by certainindigenous ants, and thus there is concern for an indirect effect on indigenous plantassemblages. One of the most impacting ant species on seed dispersal is the invasiveArgentine ant (Linepithema humile (Mayr)), which discards seeds outside its nest, wherethey do not germinate. Ten sites, on Vergelegen Wine Estate, were selected to explorethese effects of alien plants. These varied from invaded to non-invaded sites. Each siteconsisted of six sampling points, which in turn consisted of four pitfall traps left out forseven days, during December 2005, February 2006, May 2006 and September 2006.Forty species of ant were sampled, and various analyses used to illustrate the comparativeeffects of plant invasion. All analytical methods showed that invasive alien plants had asignificant impact on the abundance and richness of the ant species assemblage, bycreating a dense canopy cover that changed the abiotic environment of the epigaeic ants'habitat. Furthermore, increased alien tree invasion correlated significantly with Argentineant abundances. The Argentine ant displaced Pheidole capensis and Camponotus spp.,while it decreased the abundances of commonly-occurring indigenous ants, such asLepisiota capensis and Plagiolepis spp. Displacement by the Argentine ant may be aresult of indirect competition for food resources. The effects of invasive aliens aresynergistic in that there is a cascade effects from initial plant invasions to subsequentanimal invasion.

[发布机构] Stellenbosch University