DOI: 10.5061/dryad.msbcc2g08
title: Non-native species drive biotic homogenization, but it depends on the realm, beta diversity facet and study design: A meta-analytic systematic review

description: While reducing the species richness of invaded communities is a well-known
 consequence of biological invasions, non-native species can also reduce
 variability between communities over time (i.e., beta diversity) in a
 process known as biotic homogenization. Although biotic homogenization due
 to non-native species is a common topic of theoretical reviews, we believe
 no global meta-analysis on the effect of non-native species on beta
 diversity has been carried out yet. Here, we systematically show that
 non-native species drive biotic homogenization, but it depends on the
 realm, beta diversity facet and study design. Biotic homogenization was
 more intense in marine and freshwater ecosystems than in terrestrial
 ecosystems. We also found that non-native species reduced both taxonomic
 and phylogenetic beta diversity, but not the functional beta diversity.
 Finally, we observed more intense effects using “before vs. after
 invasion” followed by “uninvaded vs. invaded sites” while the effect size
 of studies using “communities associated with native vs. non-native
 species” did not differ from zero. Our findings highlight that non-native
 species contribute to biotic homogenization as a prevalent pattern in
 communities worldwide, and that biodiversity conservation strategies
 should go beyond investigating the reduction in the number of species by
 also taking into account beta diversity in its multiple facets.
description: <em>Data
 sampling</em><br> <br> We performed a systematic search
 on the Web of Science (WoS) on March 2020 using the following combination
 of keywords and Boolean arguments: ("invas*" OR "biological
 invas*" OR "non-native" OR "exotic" OR
 "alien*") AND ("beta diversit*" OR "β
 diversit*" OR "dissimilar*" OR "bio* homog*"). We
 used this keyword combination because it is comprehensive enough regarding
 literature on biotic homogenization due to non-native species and it
 returned a viable number of studies for screening. The search was made on
 “Topic” and considering WoS main collection. We found a total of 1,468
 studies in our WoS search. We excluded the non-primary studies (e.g.,
 theoretical reviews or simulation-based studies), out of scope studies
 (those that did not assess the effect of non-native species on beta
 diversity or similarity) and duplicates. We retained only studies that
 planned to compare with and without non-native species effect. When
 evaluating the abstracts, 1,018 articles were excluded. Consequently, we
 evaluated 450 full-texts. Of these, 407 articles were excluded because
 they were out of scope, were not primary studies, did not present enough
 data (e.g., lack of dispersion measures, control and treatment mean beta
 diversity), the design was not appropriate (e.g., the effect of non-native
 species confused with other variables), or the control was not adequate
 (e.g., sampling native and non-native species in the same sampling units
 and then splitting the dataset in native and non-native species to
 estimate their respective beta diversities). Therefore, we included a
 total of 43 articles in our systematic review (see Figure 1 and Table
 S1). From the
 selected studies, we extracted sample size, measures of central tendency
 (mean and median) and dispersion (standard deviation, standard error,
 confidence intervals and amplitude) for both control (without non-native
 species effect) and treatment (with non-native species effect) (Borenstein
 et al. 2009). For studies that did not provide mean and standard
 deviation, we estimated these values from medians and amplitudes according
 to Hozo et al. (2005) or from standard errors and confidence intervals
 according to Lajeunesse (2013). We also obtained information about the
 realm (terrestrial, freshwater or marine), taxa of the non-native species
 and from the resident community (algae, higher plants, fungi,
 invertebrates, or vertebrates), type of study (experimental, field
 sampling or species list), beta diversity facet (taxonomic, functional or
 phylogenetic), and study design. We also extracted spatial extent (largest
 distance between the farthest sample sites, in km) from maps, text or
 coordinates provided by each study. Regarding studies design, we
 classified studies sampling the same sites before and after a non-native
 species invasion as “before vs. after invasion”. Comparisons “before vs.
 after invasion” assume that differences in beta diversity between the
 periods are due to the non-native species. We classified studies that
 conducted a spatial sampling with sites with and without non-native
 species as “uninvaded vs. invaded sites”. In those cases, researchers
 assume that invaded sites had comparable beta diversity to uninvaded sites
 in the same region, and everything being equal, changes in beta diversity
 were due to non-native species. We classified studies that sampled a set
 of sites with the presence of both a native and non-native species which
 were used as habitat for other communities as “communities associated with
 native vs. non-native species”. Examples of such experimental designs are
 aquatic fungi decomposing native or non-native vegetal material (Biasi et
 al. 2020) or arthropods exploring native or non-native trees (Buchholz et
 al. 2015). In those studies, differences in beta diversity of associated
 communities may arise due to the new features provided by the non-native
 species or because non-native species do not share evolutionary history
 with native communities. Finally, we classified studies that quantified
 beta diversity in communities from the native and non-native area of
 occurrence of a given non-native species as “native vs. invaded range”.
 These studies assume that beta diversity in both regions is comparable,
 and changes observed in the invaded range are due to unshared evolutionary
 history with the resident native community.