Competitive Effects Hinder the Recolonization of Native Species in Environments Densely Occupied by One Invasive Exotic Species

Abstract

The responses of native plants to competition with invasive plants depend mainly on the density of the invasive plants and on the ability of the native plants to compete for resources. In this study, we tested the influence of the invasive exotic Urochloa arrecta (Poaceae) on the early colonization of two native species (Pontederia cordata and Leersia hexandra) of aquatic macrophytes. Our hypotheses were (i) the competitive effects of U. arrecta on the native species P. cordata and L. hexandra are density-dependent and that (ii) these species respond differently to competitive interactions with the invasive species. We conducted the experiments in a greenhouse and in the field, in a tropical reservoir. The biomass of U. arrecta (ranging from 206.2 to 447.1 g) was manipulated in the greenhouse in trays with different densities. After the establishment of the invasive species, we added P. cordata and L. hexandra propagules to each tray. In the field, a propagule of P. cordata was planted in 36 sites with different densities of U. arrecta. The biomass and length of the natives and the biomass of the invasive species were measured in the greenhouse and in the field experiments. The biomass and length of the native plants decreased with increasing biomass of the exotic species in both experiments, showing that the competition between U. arrecta and native species depends on the density of the exotic species. The root:shoot ratio of L. hexandra decreased with increasing U. arrecta biomass, but the opposite occurred for P. cordata. These results indicate that native species exhibit different strategies of biomass allocation when interacting with U. arrecta. The strong competitive effects of U. arrecta and the different responses of the native species help to explain the reduced diversity of native macrophytes observed in sites colonized by U. arrecta. The results also suggest that in a scenario of dominance of exotic species, recolonization by native macrophytes is unlike to occur naturally and without human interventions that reduce the biomass of the exotic species.

Global Change Sharpens the Double-Edged Sword Effect of Aquatic Alien Plants in China and Beyond

“…They also hamper recreational activities and disrupt agricultural production, causing great economic losses (Oreska and Aldridge, 2010; Rumlerova et al, 2016; Keller et al, 2018; Tanveer et al, 2018). Alien aquatic plants often compete for space, nutrients, and sediment fertilities with native macrophytes, thus hindering their re-establishment and decreasing diversity (Michelan et al, 2018; Silveira et al, 2018). Some of them aggravate water loss in invaded habitats through extensive transpiration (Fraser et al, 2016); accelerating water pollution by increasing sedimentary organic matter (Cuassolo et al, 2016; Bertrin et al, 2017); and reducing oxygen diffusion across the water–air interface (Chamier et al, 2012), etc.…”

Interactive effects of climate change and plant invasion on alpine biodiversity and ecosystem dynamics

“…However, the effect of invasive species is commonly driven by density (Bradley 2013, Michelan et al 2018, and this is supported by the analysis presented here. We find that the consequences of invasive species on SAR are non-linear in response to both biomass and canopy cover.…”

“…The presence of invasive plant species often reduces the abundance and diversity of native plants (Nielsen et al 2015, Fox 2018, Michelan et al 2018) and may increase the risk of extinctions (He and Hubbell 2011), however, the effects of invasive species on native plant richness typically vary with the scale of investigation (Powell et al 2013, Case et al 2016, Socolar et al 2016. It is expected that climate change may alter the impact of invasive species on ecosystems (Brooker 2006) by modifying competitive conditions between native and invasive species (Schweiger et al 2010).…”

Community stability and seasonal biotic homogenisation emphasize the effect of the invasive tropical tanner grass on macrophytes from a highly dynamic neotropical tidal river

“…Yet, the decomposition of U. arrecta biomass and the diminished circulation of water between its stems, could favour an accumulation of nutrients in the adjacent water, allowing the free-floating plants to prosper after ending up trapped by the extensive U. arrecta macrophyte beds (e.g., Dainez-Filho et al 2019 ). Furthermore, the dominance of the established U. arrecta can hamper the recolonization of other species (Michelan et al 2018 ), promoting a positive feedback.…”