Abstract
Non-native species introductions affect freshwater communities by changing community compositions, functional roles, trait occurrences and ecological niche spaces. Reconstructing such changes over long periods is difficult due to limited data availability. We collected information spanning 215years on fish and selected macroinvertebrate groups (Mollusca and Crustacea) in the inner-Florentine stretch of the Arno River (Italy) and associated water grid, to investigate temporal changes. We identified an almost complete turnover from native to non-native fish (1800: 92% native; 2015: 94% non-native species) and macroinvertebrate species (1800: 100% native; 2015: 70% non-native species). Non-native fish species were observed ~50years earlier compared to macroinvertebrate species, indicating phased invasion processes. In contrast, α-diversity of both communities increased significantly following a linear pattern. Separate analyses of changes in α-diversities for native and non-native species of both fish and macroinvertebrates were nonlinear. Functional richness and divergence of fish and macroinvertebrate communities decreased non-significantly, as the loss of native species was compensated by non-native species. Introductions of non-native fish and macroinvertebrate species occurred outside the niche space of native species. Native and non-native fish species exhibited greater overlap in niche space over time (62%-68%) and non-native species eventually replaced native species. Native and non-native macroinvertebrate niches overlapped to a lesser extent (15%-30%), with non-natives occupying mostly unoccupied niche space. These temporal changes in niche spaces of both biotic groups are a direct response to the observed changes in α-diversity and species turnover. These changes are potentially driven by deteriorations in hydromorphology as indicated by alterations in trait modalities. Additionally, we identified that angling played a considerable role for fish introductions. Our results support previous findings that the community turnover from native to non-native species can be facilitated by, for example, deteriorating environmental conditions and that variations in communities are multifaceted requiring more indicators than single metrics.
Highlights
Global changes are increasing the spread of non-native species (Capinha, Brotons, et al, 2013; Capinha, Larson, et al, 2013; Mazza et al, 2014), often causing irreversible ecological damages (Essl et al, 2020; Gozlan, 2008; Gozlan & Newton, 2009)
Non-native fish species were observed ~50 years earlier compared to macroinvertebrate species, indicating phased invasion processes
The introduction of edible non-native crustaceans (e.g. Procambarus clarkii) and molluscs (e.g. Corbicula spp.) has frequently been related to cultural introductions, while the introduction of a broad spectrum of fish and other macroinvertebrate species is often related to stockings, ballast water of ships, aquaculture and recreational angling (Cambray, 2003; Savini et al, 2010)
Summary
Global changes are increasing the spread of non-native species (Capinha, Brotons, et al, 2013; Capinha, Larson, et al, 2013; Mazza et al, 2014), often causing irreversible ecological damages (Essl et al, 2020; Gozlan, 2008; Gozlan & Newton, 2009). Historical notes on the occurrence of non-native species play an important role as they can allow to reconstruct a timeline of species introduction and to reliably approximate species population trends (Bried & Siepielski, 2018; Bucharova & van Kleunen, 2009; Carlton, 2009) Such temporal information retrieved from early natural history collections, scientific records, surveys or citizen science (Horns et al, 2018) often are based on presence/absence data, which can potentially be used to compare species occurrences over time (Pollock, 2006). We tested two (partially) competing hypotheses: (iii) non-native species introduced novel traits, occupying empty niche space, or (iv) non-native species did not introduce new traits, resulting in overlapping or partially overlapping niche space with native species
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