Natives out of place: management of freshwater aquatic plants isolated from their natural enemies

CABRERA WALSH GUILLERMO; M.C.HERNÁNDEZ; F. MCKAY; A.J. SOSA; M. GUALA

Buenos Aires

Congreso; Marine & Freshwater Invasive Species: Ecology, Impact and Management; 2016

Native species can become invasive under several circumstances, for instance when they move to a new habitat within or close to their distribution range, where they are isolated from their natural enemies, and when human-mediated habitat modifications stimulates expansion of opportunistic species. And although this situation leads to reconsider the concept of native, it mainly reflects a common problem with within and trans-frontier movement of organisms. At FuEDEI we have studied and attacked three such invasions (water hyacinth -Eichhornia crassipes- in Dique los Sauces, La Rioja Province, and Laguna del Ojo, San Vicente, Buenos Aires; and water lettuce -Pistia stratiotes- in the Reserva de Vicente Lopez, Buenos Aires) by means of the introduction of specific herbivores from close-by habitats. The study sites shared four characteristics: they were man-made or strongly modified habitats, the ecological niche (floating macrophytes) taken by the invasive was vacant, they were isolated from nearby sources of natural enemies, and human impact (i.e. nutrient input) was high. The native weevils Neochetina bruchi and N. eichhorniae controlled waterhyacinth in Dique los Sauces and seem to be on the way of doing so in El Ojo lake. The weevil Neohydronomus affinis and the planthopper Lepidelphax pistiae controlled the water lettuce invasion and contributed to a drastic increase in plant species richness in the Vicente Lopez lake. Two post-release effects are currently under study: the establishment and impact of other herbivores released against water hyacinth in El Ojo, and the replacement of water lettuce by other floating macrophytes in Vicente Lopez.