The invasive tropical tanner grass decreases diversity of the native aquatic macrophyte community at two scales in a subtropical tidal river

Rayana Yumi Sato,Ana Paula Lula Costa,Andre Andrian Padial

doi:10.1590/0102-33062020abb0360

Rayana Yumi Sato, Ana Paula Lula Costa + Show 1 more

Open Access

https://doi.org/10.1590/0102-33062020abb0360

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Abstract

The tropical tanner grass, Urochloa arrecta, is one of the worst aquatic plant invaders in Brazilian freshwater ecosystems. This study aimed to compare beds of macrophytes dominated and without U. arrecta in the Guaraguaçu River, a subtropical tidal river in South Brazil, to analyze effects that this invasive grass has on the biodiversity of native macrophytes at two spatial scales. We compared macrophyte beds dominated by tanner grass to macrophyte beds without, considering species richness, composition, and beta diversity at two scales of variation: among-beds and within-beds. We expected that beds dominated by tanner grass would have lower biodiversity, thus promoting macrophyte biotic homogenization. Our results confirmed our hypotheses, highlighting the lower species richness in beds dominated by tanner grass. Species composition differed among beds. In general, nestedness among beds dominated by U. arrecta was more related to variation in species composition. Beds dominated by tanner grass had lower turnover and higher nestedness within beds. This study indicates a prominent sign of biotic homogenization promoted by U. arrecta, and highlights the degree of biotic homogenization among and within beds.

Highlights

The introduction and establishment of exotic invasive species often leads to species loss and imbalance in natural ecosystems (Simberloff et al 2013)
Turnover refers to dissimilarity given species substitution amongst local communities; nestedness refers to the compositional changes due to the differences between species richness amongst local communities, i.e., the local communities with lower species richness is a subset of the local communities with higher species richness in a nested meta-community (Baselga 2012).The aim of our study was to analyze the effect of the invasive macrophyte U. arrecta on the native biodiversity of the Guaraguaçu River by comparing beds either dominated by or without the presence of tropical tanner grass
A pattern of local increase in species richness and decrease in regional biodiversity is common as a result of biotic homogenization phenomenon driven by invasive species (e.g., Vellend 2010; Peoples et al 2020)

Summary

Introduction

The introduction and establishment of exotic invasive species often leads to species loss and imbalance in natural ecosystems (Simberloff et al 2013). Environmental changes due to invasive species result in the ‘Biotic Homogenization’ process, a complex phenomenon of increasing similarity amongst communities due to biological invasions and extinctions of species in which few winner species replace many losers in the mass extinction event (McKinney & Lockwood 1999). This phenomenon, not formally defined, was first described by the prominent Charles Elton’s book The Ecology of Invasion by Animals and Plants (published in 1958) and it is suggested that an occurrence at a global scale will cause an intense decrease in the beta diversity of natural ecosystems (Olden et al 2018). Aquatic macrophytes are among the worst invasive species in the aquatic realm (Mormul et al 2011; Hussner et al 2017)

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