Abstract
The increased introduction of non-native species to habitats is a characteristic of globalisation. The impact of invading species on communities may be either linearly or non-linearly related to the invaders’ abundance in a habitat. However, non-linear relationships with a threshold point at which the community can no longer tolerate the invasive species without loss of ecosystem functions remains poorly studied. We selected 31 wet meadow sites that encompassed the entire coverage spectrum of invasive goldenrods, and surveyed the abundance and diversity of pollinating insects (bees, butterflies and hover flies) and native plants. The species richness of native plants decreased linearly with goldenrod cover, whereas the abundance and species richness of bees and butterflies decreased non-linearly with increasing goldenrod cover. However, no statistically significant changes across goldenrod cover were noted for the abundance and species richness of hover flies. Because of the non-linear response, goldenrod had no visible impact on bees and butterflies until it reached cover in a habitat of about 50% and 30–40%, respectively. Moreover, changes driven by goldenrod in the plant and pollinator communities were related to species loss rather than species replacement. We demonstrated that the impact of goldenrod cover on a habitat is not instantaneous. Habit management aimed at preventing the invasion process and alleviating its impact should take into account that, for the non-linear relationships, the negative impact can appear rapidly after crossing the threshold point.
Highlights
The introduction of non-native species to habitats increases consistently as a result of globalisation (Amano et al 2016)
Three species made up 36% of the total number of butterflies: Aphantopus hyperantus (13% of the total number of butterflies), Pieris rapae (13%) and Coenonympha pamphilus (10%; ‘‘Appendix 3’’)
We showed that the negative impact of invasive goldenrod cover on bee and butterfly communities is non-linear
Summary
The introduction of non-native species to habitats increases consistently as a result of globalisation (Amano et al 2016). Established alien organisms—invasive species—cause environmental changes that threaten native biodiversity and the human economy (Pejchar and Mooney 2009). The environmental changes induced by invasive species concerns the composition of invaded communities The loss of plant species, primary producers, may impact key ecological processes such as ecosystem productivity (Pysek et al 2012), decomposition (van der Putten et al 2013), or ecosystem resilience to disturbances (Richardson et al 2007). The diversity decline at the level of the primary producers may impact associated arthropod species (Haddad et al 2009). Whether plants and arthropod communities change at all points along the invasion pathway (i.e. a linear response to invasion), or if there is rather a threshold beyond which the communities change as the invasive plant becomes dominant (non-linear response to invasion), remains unclear
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