Diversity and biomass of native macrophytes are negatively related to dominance of an invasive Poaceae in Brazilian sub-tropical streams

Abstract

Diversity and biomass of native macrophytes are negatively related to dominance of an invasive Poaceae in Brazilian sub-tropical streamsA diversidade e a biomassa de macrófitas nativas são negativamente relacionadas com a dominância de uma Poaceae invasora em riachos sub-tropicais Abstract: Besides exacerbated exploitation, pollution, flow alteration and habitats degradation, freshwater biodiversity is also threatened by biological invasions. This paper addresses how native aquatic macrophyte communities are affected by the non-native species Urochloa arrecta, a current successful invader in Brazilian freshwater systems. We compared the native macrophytes colonizing patches dominated and non-dominated by this invader species. We surveyed eight streams in Northwest Paraná State (Brazil). In each stream, we recorded native macrophytes' richness and biomass in sites where U. arrecta was dominant and in sites where it was not dominant or absent. No native species were found in seven, out of the eight investigated sites where U. arrecta was dominant. Thus, we found higher native species richness, Shannon index and native biomass values in sites without dominance of U. arrecta than in sites dominated by this invader. Although difficult to conclude about causes of such differences, we infer that the elevated biomass production by this grass might be the primary reason for alterations in invaded environments and for the consequent impacts on macrophytes' native communities. However, biotic resistance offered by native richer sites could be an alternative explanation for our results. To mitigate potential impacts and to prevent future environmental perturbations, we propose mechanical removal of the invasive species and maintenance or restoration of riparian vegetation, for freshwater ecosystems have vital importance for the maintenance of ecological services and biodiversity and should be preserved.Keywords: signal grass, nvasive macrophytes, freshwater, biodiversity.Resumo: Juntamente com a exploração exacerbada, poluição, alteração de regime hidrológico e degradação de habitas as invasões biológicas são consideradas uma ameaça à biodiversidade dos ecossistemas aquáticos continentais. Nesse sentido, a Poaceae Urochloa arrecta é reconhecida como uma invasora bem sucedida em ambientes aquáticos brasileiros. Nós comparamos bancos de macrófitas dominados e não-dominados por esta invasora. Foram amostrados oito córregos no noroeste do Estado do Paraná (Brasil). Em cada córrego registramos a riqueza e a biomassa de macrófitas nativas em locais onde U. arrecta era dominante e em locais onde ela não dominava ou era ausente. Em sete dos oito locais onde U. arrecta dominava, não haviam macrófitas nativas. Assim, encontramos maiores riqueza de espécies nativas, índice de Shannon e biomassa nativa nos locais não dominados por U. arrecta com relação aos locais dominados. Apesar da dificuldade em se extrair conclusões sobre as causas dessas diferenças, inferimos que a elevada biomassa da invasora pode ser a principal fonte de altera...

Biotic resistance buffers the effects of nutrient enrichment on the success of a highly invasive aquatic plant

“…The global history of U. arrecta invasion is uncertain, but it was probably introduced in Brazil and in the U.S.A. as a forage crop (Wipff & Thompson, 2003). This species can be considered invasive because it has colonised and developed high biomasses in streams, lakes, wetlands and reservoirs, where it reduced the diversity and changed the composition of native macrophytes (Pott et al, 2011;Fernandes, Teixeira & Thomaz, 2013;Amorim et al, 2015) and fishes (Carniatto et al, 2013). Thus, the factors that regulate the invasion success of this grass are worthy of investigation, and may offer a model to understand and predict invasions by other aquatic Poaceae (e.g.…”

Influence of an exotic grass on benthic macroinvertebrate communities in a tropical rural landscape

“…Colonization and development of grasses can occur both along stream bank margins (Menninger & Palmer, 2007;Casatti et al, 2009) and within the stream channel, where they grow as macrophytes (Bunn et al, 1998;Fernandes et al, 2013). Grasses rooted on stream banks can reduce margin erosion (Davies-Colley, 1997) and contribute with allochthonous resources and habitats for both macroinvertebrates (Menninger & Palmer, 2007) and fish (Casatti et al, 2009).…”

“…On the other hand, grasses that grow as dominant macrophytes in the stream channel can reduce the water quality by reducing the availability of dissolved oxygen (Bunn et al, 1997) and affect channel morphology and hydrology, reducing the effective channel capacity by sediment accumulation (Davies-Colley, 1997;Bunn et al, 1998). Biological effects of exotic grasses on the streambed include dominance of the stream channel in macrophyte-poor streams or stream reaches (Urochloa arrecta: Fernandes et al, 2013;Michelan et al, 2013), homogenization of macroinvertebrate communities (Glyceria maxima: Clarke et al, 2004), increased local macroinvertebrate abundances (U. mutica: Douglas & O'Connor, 2003), possible negative effects on fish due to changes in habitat structure, water quality, and food web structure (Pusey & Arthington, 2003), low contribution of basal resources to detrital food webs, although breakdown of these plants may occur through physical or microbial action (Clapcott & Bunn, 2003; but see Menninger & Palmer, 2007).…”

“…In Brazil, streams in pasture and agriculturedominated watersheds are mostly deforested, so that grasses of the genus Urochloa such as U. arrecta are increasingly common in streambeds and wetlands (Pott et al, 2011;Fernandes et al, 2013). In this study, we evaluated whether patches of an exotic grass (Urochloa sp.)…”

Crescimento e nutrição mineral de Urochloa arrecta

“…Segundo Kissmann & Groth (2007) e Lorenzi (2008), sua adaptabilidade a solos úmidos e alagados permitiu a invasão de áreas cultivadas com arroz irrigado, canais de irrigação e beiras de corpos d'água, sendo inclusive classificada como planta daninha macrófita aquática de reservatórios (Carniatto et al, 2013;Fernandes et al, 2013;Moura Junior et al, 2013).…”