Invasion by an exotic grass species homogenizes native freshwater plant communities

Abstract

A growing body of evidence has shown that biological invasions cause shifts in species composition of communities in space and time. Although biological invasions are considered a major driver of biotic homogenisation worldwide, most previous studies were conducted at small spatial scales and over short time periods, which may have underestimated the impacts of exotic species on native communities. Using a unique dataset of aquatic plants sampled in 235 sites over 12 years (2007–2010 and 2015–2019) in a large reservoir (Itaipu Reservoir; 1350 km2), we analysed how the invasion of a non‐native grass Urochloa arrecta affects the species richness, ecological uniqueness (i.e. local contribution to beta diversity—LCBD) and temporal β–diversity of native plant communities. From 3934 surveyed plant communities, U. arrecta was recorded in 2888 samples and it was absent from 1046 samples. Overall, species richness and ecological uniqueness of native plant communities were markedly lower in sites invaded than non‐invaded by U. arrecta. From 2007 to 2019, the ecological uniqueness of native plants was 60% lower in the invaded than non‐invaded sites. Whereas in invaded sites species loss was the dominant process driving native communities over time, in non‐invaded sites gain of new native species was the primary process underlying community trajectories. Moreover, comparing native plant communities before and after the invasion of U. arrecta, species richness, ecological uniqueness and species gains of native plant communities decreased, whereas species losses increased after the invasion of U. arrecta. Finally, the positive relationship between native biodiversity and precipitation was stronger in non‐invaded than invaded sites. Synthesis. Our findings provide comprehensive evidence that an invasive plant is decreasing the spatial and temporal β–diversity of native plant communities through declining species richness, rather than simply correlating with them. This suggests that U. arrecta is driving native plants to become less diverse and homogeneous after the invasion, both spatially and temporally. Our findings illustrate that at broad scales, aquatic plant communities may become increasingly homogeneous with the increasing number of biological invasion events taking place worldwide.

Tolerance to drought and flooding events provides a competitive advantage for an invasive over a native plant species

“…Consequently, drought and flooding events result in a dominance of U. mutica . This is concerning as droughts and flooding events are becoming more frequent worldwide (Romero et al., 2020), and opportunistic invasive plants adapted to extreme water levels, such as U. mutica , can occupy sites that become vacant through the disappearance of native plants, causing widespread harm to native biodiversity (Bando et al., 2023). As Urochloa species grow rapidly after establishment and accumulate high biomass (Carniatto et al., 2013), controlling these species during extreme climatic events will be an increasing challenge.…”

“…For example, plant species with the potential to be invasive often have a higher adaptability and tolerance to some environmental disturbances than non‐invasive species (Diez et al., 2012; Leal et al., 2022; Meisner et al., 2013). As a result, such highly tolerant species are able to colonise environments beyond their native area (Bando et al., 2023). Invasive plants also have been found to recover faster after periods of drought (Barros et al., 2020; Leal et al., 2022) and flooding (Vivian et al., 2014).…”

Analysing spatio‐temporal patterns of non‐native fish in a biodiversity hotspot across decades

“…Freshwater ecosystems are particularly vulnerable to invasion by non-native animals and plants (Bando et al, 2023;Moorhouse & Macdonald, 2015). Because of economic and recreational purposes, fish species, in particular, are frequently introduced into freshwater ecosystems globally, resulting in their widespread establishments and often leading to freshwater biodiversity declines and, in the worst case, ecosystem collapses (Cucherousset & Olden, 2011;Muñoz-Mas et al, 2023;Su et al, 2021).…”