Abstract
Non-native species of aquatic plants may become invasive and affect native communities, reducing the diversity of plants and other organisms. In general, the successful colonization of new habitats by macrophytes depends first on their dispersion ability and second on the existence of favorable abiotic conditions. In this investigation, we used a transplant experiment to test the effects of habitat water (main river channel versus lake) and habitat sediment (river sediment versus lake sediment) on the growth of two species, the non-native Hydrilla verticillata and the native macrophyte Egeria najas . We tested the hypothesis that the non-native species is more successful when it grows in the river channel with river sediment as substrate, whereas the native E. najas is more successful when it grows in the lake with lake sediment as substrate. Fragments of both species were planted in river and lake sediment and transported to the main river channel and a lake for the growing period. The field experiment results demonstrated that H. verticillata did not grow in either river or lake sediment when planted in the lake. However, this species developed higher root biomass than E. najas in the main river channel, which explains its predominance in this type of habitat. The results support the view that habitat characteristics are determinants of the successful or unsuccessful growth of H. verticillata in our study sites. Finally, H. verticillata invasiveness may improve after certain lag times in response to alterations in habitat, as observed for several other non-native species. Thus, future invasions of floodplain lakes by this species cannot be discarded.
Highlights
Non-native invasive species have attracted considerable attention due to their potential impacts on natural ecosystems (MACK et al, 2000) and their relevance for testing ecological theories (TILMAN, 1997; SAX et al, 2007).In general, the successful colonization of new habitats by organisms depends primarily on the dispersion ability of species (SAX et al, 2007; VAN DER VALK et al, 2009)
The results demonstrated that the river sediment had significantly lower N, P and OM concentrations than the lake sediment (Table 2)
The results indicate that Egeria performs better than Hydrilla in lentic, shallow and turbid habitats, corroborating our hypothesis
Summary
Non-native invasive species have attracted considerable attention due to their potential impacts on natural ecosystems (MACK et al, 2000) and their relevance for testing ecological theories (TILMAN, 1997; SAX et al, 2007).In general, the successful colonization of new habitats by organisms (including macrophytes) depends primarily on the dispersion ability of species (SAX et al, 2007; VAN DER VALK et al, 2009). In Brazil, this species is found in reservoirs (THOMAZ et al., 2009) and recently invaded the Upper Parana River (SOUSA et al, 2009), a strategic ecosystem for biodiversity conservation in Brazil. Since it has rapidly spread along the Upper Parana River, infesting large areas with high biomass production and causing problems related to navigation, fishing and recreation activities.
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