Received: 25 March 2020 | Revised: 12 October 2020 | Accepted: 31 October 2020 DOI: 10.1111/gcb.15442

PRIMARY RESEARCH ARTICLE

Two centuries for an almost complete community turnover from native to non-native species in a riverine ecosystem

Phillip J. Haubrock1,2 | Francesca Pilotto3 | Gianna Innocenti4 | Simone Cianfanelli4 | Peter Haase1,5

1Department of River Ecology and Conservation, Senckenberg Research Abstract Institute and Natural History Museum Non-native species introductions affect freshwater communities by changing com- Frankfurt, Gelnhausen, Germany munity compositions, functional roles, trait occurrences and ecological niche spaces. 2Faculty of Fisheries and Protection of Waters, South Bohemian Research Reconstructing such changes over long periods is difficult due to limited data availa- Center of Aquaculture and Biodiversity of bility. We collected information spanning 215 years on fish and selected macroinver- Hydrocenoses, University of South Bohemia in České Budějovice, Vodňany, Czech tebrate groups (Mollusca and Crustacea) in the inner-Florentine stretch of the Arno Republic River (Italy) and associated water grid, to investigate temporal changes. We identified 3Environmental Archaeology Lab, Department of Historical, Philosophical and an almost complete turnover from native to non-native fish (1800: 92% native; 2015: Religious Studies, Umeå University, Umeå, 94% non-native species) and macroinvertebrate species (1800: 100% native; 2015: Sweden 70% non-native species). Non-native fish species were observed ~50 years earlier 4Museo di Storia Naturale ‘La Specola’, Sistema Museale di Ateneo dell'Università di compared to macroinvertebrate species, indicating phased invasion processes. In Firenze, Firenze, Italy contrast, α-diversity of both communities increased significantly following a linear 5Faculty of Biology, University of Duisburg– pattern. Separate analyses of changes in -diversities for native and non-native spe- Essen, Essen, Germany α cies of both fish and macroinvertebrates were nonlinear. Functional richness and di- Correspondence vergence of fish and macroinvertebrate communities decreased non-significantly, as Phillip J. Haubrock, Department of River Ecology and Conservation, Senckenberg the loss of native species was compensated by non-native species. Introductions of Research Institute and Natural History non-native fish and macroinvertebrate species occurred outside the niche space of Museum Frankfurt, Clamecystrasse 12, 63571 Gelnhausen, Germany. native species. Native and non-native fish species exhibited greater overlap in niche Email: [email protected] space over time (62%–68%) and non-native species eventually replaced native spe- cies. Native and non-native macroinvertebrate niches overlapped to a lesser extent (15%–30%), with non-natives occupying mostly unoccupied niche space. These tem- poral changes in niche spaces of both biotic groups are a direct response to the ob- served changes in α-diversity and species turnover. These changes are potentially driven by deteriorations in hydromorphology as indicated by alterations in trait mo- dalities. 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 en- vironmental conditions and that variations in communities are multifaceted requiring more indicators than single metrics.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2020 The Authors. Global Change Biology published by John Wiley & Sons Ltd

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KEYWORDS Arno River, fish, functional redundancy, hydromorphology, invasion, macroinvertebrates, time series analysis, traits

1 | INTRODUCTION role in outlining species-specific behaviours and local adaptations, such as adaptive feeding behaviour due to, for example, emergent Global changes are increasing the spread of non-native species multiple predator effects (e.g. Barrios-O'Neill et al., 2014; Lindqvist & (Capinha, Brotons, et al., 2013; Capinha, Larson, et al., 2013; Mazza Huner, 2017). Of particular interest is the introduction of new traits et al., 2014), often causing irreversible ecological damages (Essl et al., through new species, such as a higher fertility (e.g. Bishai et al., 1974; 2020; Gozlan, 2008; Gozlan & Newton, 2009). Freshwater systems Marchetti et al., 2004; Usher, 1986) elevated abiotic tolerances (Copp have been identified to be particularly vulnerable to invasions (Gherardi, et al., 2009; Gherardi, 2006), novel defences or predation techniques 2007; Ricciardi & Rasmussen, 1999; Sala et al., 2000; Strayer, 2010). (Bosher et al., 2006; Fine et al., 1997; Kimbro et al., 2009). Moreover, Several freshwater species, particularly fish, molluscs and crustaceans, non-native species can alter the trait compositions of native species have been intentionally or unintentionally introduced into lakes and with specific traits potentially disappearing due to increasing compe- rivers by humans (e.g. Haubrock, Kubec, et al., 2019; Mrugała et al., tition (Brown et al., 2002; Mangla et al., 2011) or resource partition- 2015). For example, the introduction of edible non-native crustaceans ing (Haubrock, Azzini, et al., 2019; Jackson et al., 2014). Such studies (e.g. Procambarus clarkii) and molluscs (e.g. Corbicula spp.) has fre- indicated that the analysis of species traits can elucidate important quently been related to cultural introductions (e.g. religious releases or biotic interactions between native and non-native species. However, the introduction­ of species native in the original area of a certain culture the dynamics of trait composition through time have not gained suffi- to mantain traditions, see e.g. Bodon et al., in press; Britton & Morton, cient scientific attention and remain mostly anecdotal (Fox et al., 2007; 1979; Cianfanelli et al., 2017; Counts, 1983; Liu et al., 2013), while the Lindqvist & Huner, 2017). This is particularly true in the context of introduction of a broad spectrum of fish and other macroinvertebrate multiple introduction events (Chapple et al., 2012) and in comparative species is often related to stockings, ballast water of ships, aquaculture analyses across different biotic groups. and recreational angling (Cambray, 2003; Savini et al., 2010). One ecosystem where information on the temporal course of fish According to the invasion meltdown theory (Crane et al., 2020; and macroinvertebrate species introductions does exist is the Arno Simberloff, 2006; Simberloff & Von Holle, 1999), the successive intro- River in Tuscany (Italy), which is known for its anthropogenic usage duction of non-native species can, above a certain threshold, facilitate and economic importance for the development of the city of Florence the introduction of further non-native species, potentially increasing (Masters, 1998; Rinaldi & Simon, 1998; Sznura, 2010). We compiled effects on native communities (Ellender & Weyl, 2014). Investigating presence/absence data for fish and macroinvertebrate species (mol- effects of such frequent non-native species introductions in freshwa- luscs and crustaceans) from the Arno River between ~1800 and 2015, ter ecosystems, however, generally suffers from a lack of appropriate as well as their species-specific trait information and analysed temporal long-term data that are needed to reconstruct introduction events changes in species and trait composition for the two biotic groups. In (Strayer et al., 2006) as well as the resulting changes in the (native) com- particular, we calculated changes in (a) α-diversity and temporal turn- munity (Haubrock, Azzini, et al., 2019; Haubrock, Balzani, et al., 2019). over, (b) trait modalities as a prerequisite to (c) functional composition, Historical notes on the occurrence of non-native species play an im- functional metrics and resulting niche space to understand whether portant role as they can allow to reconstruct a timeline of species intro- non-native species occupy an empty or occupied niche, which would duction and to reliably approximate species population trends (Bried & inform on competition dynamics. Finally, we (d) inferred and discussed Siepielski, 2018; Bucharova & van Kleunen, 2009; Carlton, 2009). Such potential drivers of these changes. For the latter, we faced the com- temporal information retrieved from early natural history collections, mon issue of lacking continuous information on environmental vari- scientific records, surveys or citizen science (Horns et al., 2018) often ables over such a long period of time. We thus compensated for this are based on presence/absence data, which can potentially be used to using changes in traits that reflect changes in certain environmental compare species occurrences over time (Pollock, 2006). Nevertheless, conditions as proxies, and by compiling information on environmental such information must be carefully evaluated due to the often unclear change using historical notes. origin and the sampling method applied. We hypothesized (i) a significant temporal turnover in species Temporal changes in community composition triggered by fre- over the past 215 years driven by the successive introduction of non- quent introductions of non-native species not only affect the tax- native species. We further hypothesized that this turnover is concomi- onomic composition and diversity of a community but also its trait tant with (ii) an identifiable turnover in trait modalities and changes in compositions. Traits at the community level have been used to pre- the niche space of the biotic assemblages. Moreover, we tested two dict and explain species invasions and are argued to indicate com- (partially) competing hypotheses: (iii) non-native species introduced petitive processes through the displacement of native by non-native novel traits, hence occupying empty niche space, or (iv) non-native species in trait-niche space (Blonder, 2018; Lamanna et al., 2014). species did not introduce new traits, resulting in overlapping or par- Moreover, previous studies have shown that traits play an important tially overlapping niche space with native species. 608 | HAUBROCK et al.

2 | METHODS our analyses to crustaceans and molluscs (hereafter, ‘macroinver- tebrates’). The available data covered the years prior to ~1800, 2.1 | Study site years within the periods of 1850–1900, 1900–1950, 1950–2000 and lastly the year 2015. Hence, for our analysis, we chose these The Arno River is the second largest river in Central Italy with a length time slices as they corresponded adequately with the available of 241 km and a watershed of approximately 8,200 km2. Its cultural information. usage is tightly linked with the history and development of the city Presence/absence data can be used as an indicative proxy to de- of Florence (Supplement 1). It has a mean annual discharge of about tect shifts over time. This is, because changes in abundance are often 110 m3/s (Nocita & Zerunian, 2007) and a typical Mediterranean seen as ‘early’ signs of community change as abundance data can hydrological regime with severe flow reductions during summer. In track smaller and initial stages of change (Bried & Siepielski, 2018; Florence, the Arno River (Figure 1) is sectioned by various weirs and Horns et al., 2018). However, if changes are visible with presence/ exhibits a high density of aquatic vegetation during spring, but a sparse absence data, these are indicators of more profound differences riparian vegetation along the riverbanks. With the use of floodgates, within a community (Bried & Siepielski, 2018). We thus compiled the water regime is controlled during winter periods to prevent floods presence/absence data on 38 fish species (12 native, 26 non-native), and to regulate water levels during dry periods in summer. Mean sum- 15 molluscs (9 native, 6 non-native) and 8 crustaceans (6 native, 2 mer and winter water temperatures of the Arno River in the city of non-native) species (Table 1). Florence are 29.6°C and 11.1°C, respectively (Supplement 1). To analyse changes in trait composition during the transition from native to non-native communities in the Arno River, we downloaded the species- and genera-specific traits for the studied fish and mac- 2.2 | Collection of species presence data and trait roinvertebrates species from www.fresh​water​ecolo​gy.info (Schmidt- information Kloiber & Hering, 2015; Supplement 3). Specifically, we compiled different traits on habitat and region preference for fish species. Single We collected historic and contemporary literature, as well as mu- fish traits were checked or completed using www.fishb​ase.org (Froese seum records, on the presence and absence of fish and macroin- & Pauly, 2010) and Kottelat & Freyhof (2007). For macroinvertebrates, vertebrates within the inner Florentine stretch of the Arno River we compiled trait information covering habitat, region and saprobic (Figure 1). Moreover, we consulted local historians, naturalists and preference parameters and life-history parameters. Missing values at experts (Elena Tricarico, Nicola Fortini, Annamaria Nocita) to iden- the species level were supplemented using information from the genus tify suitable literature to complete the datasets (Supplement 2). The level averaging the available species information. To every trait modal- collected records and the samples of the historical collections kept ity, an integer is assigned describing the affinity of each taxon to the at the Natural History Museum of Florence included information on specific trait modality. If the affinity of a species to a trait modality native species as well as the time of introduction in the Arno River was not identified and there was no information available for the eval- and the directly associated water grid (stream and spring tributar- uation, a score of 0 was given for the respective modalities. In total, ies). The information on aquatic insects was insufficient (Ruffo & we analysed 19 traits with 65 modalities for fish and 25 traits with Stoch, 2005). Therefore, among macroinvertebrates, we restricted 146 modalities for macroinvertebrates (Supplement 4).

(b) (a)

(c)

FIGURE 1 Map showing (a) Italy, (b) Tuscany and (c) the municipality of Florence (beige), indicating the past city centre (black line), the considered stretch of the Arno River (blue) and weirs (red) HAUBROCK et al. | 609

TABLE 1 Taxonomic groupings, species, common names of fish and macroinvertebrates listed for the Arno River between 1800 and 2015, as well as native/non-native status (native, blue; non-native, red) and known occurrences

Group Subgroup Species Common name Distribution status Range

Fish Acipenser sturio European sea sturgeon Native 180 0–1950 Alosa fallax Twait shad Native 180 0–1950 Anguilla anguilla European eel Native 1800–2000 Barbus tyberinus Horse barbell Native 180 0–1950 Cottus gobio European bullhead Native 180 0–1950 Esox lucius European pike Native 1800–2000 Padogobius nigricans Arno goby Native 1800–2000 Rutilus rubilio South European roach Native 1800–1900 Scardinius Common rudd Native 1800–1900 erythrophthalmus Squalius squalus Italian chub Native 1800–2000 Telestes muticellus Vairone Native 1800 Tinca tinca Tench Native 1800–2015 Abramis brama Common bream Non-native 2015 Alburnus alburnus Bleak Non-native 2015 Ameiurus nebulosus Brown bullhead Non-native 1950–2000 Barbus barbus Common barbell Non-native 2000–2015 Barbus plebejus Italian barbell Non-native 1950–2000 Blicca bjoerkna white bream Non-native 2000 Carassius auratus Goldfish Non-native 1950–2000 Carassius carassius Crucian carp Non-native 2015 Chondrostoma soetta Italian nase Non-native 1950 Cobitis taenia spined loach Non-native 1800–2000 Ctenopharyngodon Grass carp Non-native 1950–2000 idella Cyprinus carpio Common carp Non-native 1800–2015 Gambusia holbrooki Eastern mosquitofish Non-native 1950–2015 Gobio gobio Gudgeon Non-native 2000 Ictalurus punctatus Channel catfish Non-native 2015 Lepomis gibbosus Pumpkinseed Non-native 1950–2015 Micropterus salmoides Black bass Non-native 2000 Padogobius bonelli Padanian goby Non-native 2015 Perca fluviatilis European perch Non-native 2000 Pseudorasbora parva Topmouth gudgeon Non-native 2015 Rutilus pigus Pigo Non-native 1950–2000 Rutilus rutilus Roach Non-native 2015 Sander lucioperca Zander Non-native 2000–2015 Scardinius hesperidicus Rudd Non-native 1950–2000 Silurus glanis European catfish Non-native 2000–2015 Squalius cephalus European chub Non-native 2015 Macroinvertebrates Molluscs Gastropoda Belgrandia thermalis Native 1800–2000 Physa fontinalis Common bladder snail Native 1800–1900 Planorbarius corneus Great Ramshorn Native 1800–1900 Planorbis carinatus Native 1800–1900 Stagnicola fuscus Native 1800 (Continues) 610 | HAUBROCK et al.

TABLE 1 (Continued)

Group Subgroup Species Common name Distribution status Range

Theodoxus fluviatilis River nerite Native 1800–2015 Viviparus contectus Lister's river snail Native 1800–1900 Ferrissia californica Non-native 2000–2015 Gyraulus chinensis Non-native 2015 Physella acuta Tadpole snail Non-native 1950–2015 Potamopyrgus New Zealand mudsnail Non-native 2000–2015 antipodarum Bivalvia Anodonta exulcerata Native 1800–2000 Unio mancus Native 180 0–1950 Unio elongatulus Non-native 1950–2000 Sinanodonta woodiana Chinese pond mussel Non-native 2000–2015 Crustaceans Proasellus banyulensis Native 1800–2000 Echinogammarus veneris Native 1800–2000 Orchestia cavimana Native 180 0–1950 Atyaephyra desmarestii Native 1800–2000 Palaemon antennarius Grass shrimp Native 1800–2015 Potamon fluviatile European river crab Native 1800–2015 Dikerogammarus villosus Killer shrimp Non-native 2015 Procambarus clarkii Red swamp crawfish Non-native 2015

2.3 | Changes in taxonomic composition and 2.5 | Changes in functional composition, alpha diversity metrics and resulting niche space

In this study, we computed two common community metrics to in- We used changes in functional metrics to describe changes in the vestigate the changes within the fish and macroinvertebrate com- Hutchinsonian niche space (n-dimensional hypervolume, with munities over the investigated period. These were the species n being equal to the axes corresponding to species-specific re- richness (α-diversity), which is expressed as the total number of quirements; Blonder, 2018), that is, niche differentiation (Blonder species per period and the temporal species turnover (estimated et al., 2018; D'Andrea & Ostling, 2016). In this context, different as the proportion of species gained, i.e. ‘appearances’, or lost i.e. trait spaces reflect different community niches, and are hereafter ‘disappearances’, between two observations, using the R package referred to as niche space. The display of trait-based niche space can ‘codyn’; Hallett et al., 2014), which characterizes temporal shifts in hence indicate an ecological differentiation among species, attribut- the identities of occurring species and thus, community composition able to processes such as competition (Blonder, 2018). over time. Furthermore, we tested if the percentage of non-native Therefore, we quantified changes in community niche space fish and macroinvertebrates increased significantly over time using a within the individual biotic groups, using four metrics: functional correlation analysis (Spearman correlation). Spearman was preferred trait divergence (FDiv; measure of variance of the species func- as it is a nonparametric test, which does not require data normality tion, whereby clustering extent indicates niche differentiation; assumptions. Mason et al., 2005), functional dispersion (FDis; overall convex hull volume occupied by all occurring traits in multidimensional space), functional richness (FRic; descriptor of how much niche 2.4 | Changes in trait modality compositions space is occupied by present species, measured as the number of unique trait value combinations in each period; see Supplement 4), Considering the identified turnover in species composition due to and functional evenness (FEve; measure of nearest neighbour the introduction of non-native species and the decrease or extirpa- distance among species, indicating the regular distribution of tion of native species, we investigated the changes in the proportion species in occupied niche space; Schleuter et al., 2010; Villéger of individual fish and macroinvertebrate trait modalities during the et al., 2008). Together, these metrics can depict shifting trends in study period. For this purpose, we tested for significant correlations a communities' occupied niche space when displayed over time. (Spearman correlation) between the increase in the number of non- Each metric was computed for a community's respective time slice native species and the changing proportions of trait modalities for using the ‘dbFD.function()’ of the R-package ‘FD’ (Laliberté et al., fish and macroinvertebrate species. 2014) after ‘fuzzy coding’ standardization (Chevenet et al., 1994) HAUBROCK et al. | 611 of the traits using the ‘prep.fuzzy.var.function()’ of the same in the community increased further throughout the studied pe- package. We repeated this procedure for native and non-native riod (Figure 2a,b; Table 1). The observed nonlinear change in non- species independently. To test for significant changes in these native α-diversity (overall increasing towards 2000, followed by a metrics, we applied a correlation (Spearman correlation) of the slight decrease in 2015, Supplement 5) was identified as significant individual functional metrics over time. To display changes in na- (Spearman correlation rSp > .7; p < .05). In contrast, native species tive and non-native species' niche space over time, we used a ca- decreased continuously with only the common tench Tinca tinca nonical analysis of principal coordinates (CAP; R-package ‘vegan’; remaining until 2015. The overall temporal turnover (0.71) in all Oksanen, 2007; Oksanen et al., 2019), which was run on ‘Gower’ fish species indicated a directional change in community composi- dissimilarity (Gower, 1971) for native and non-native species' tion towards non-native species (rSp > .7; p < .05; Figure 2a). This traits and ‘Jaccard’ distance for information regarding the oc- change was reflected by more gains than losses in non-native spe- currence of species as it is adequate for presence/absence data cies (Figure 2b). (Anderson & Willis, 2003). The α-diversity of macroinvertebrates decreased nonlinearly with an initial drop in 1900–1950, followed by an increase in 1950–2000 and another decrease in 2015 (Figure 2). These un- 2.6 | Identification of potential drivers derlying changes in the macroinvertebrate community occurred in a two-step process: In 1800, the macroinvertebrate community Changes in specific trait modalities over time can reflect a re- consisted exclusively of native species. By 1900–1950, various sponse to external stressors. Therefore, we conducted another native species had already disappeared (loss of 17%; Figure 2a) CAP with the same specifications as before, but pooling native while the majority of non-native macroinvertebrates appeared and non-native species. Upon this ordination, we fitted trait after 1900–1950 (1950–2000: 43%). Similar to the non-native modalities that had nonlinear relationships with the principal fish species, the percentage of non-native macroinvertebrates coordinates to identify those modalities that correlated signifi- increased significantly (rSp > .7; p < .05, Supplement 5). Both tem- cantly with the ordination axes. Trait modalities included into this poral turnover and gains of non-native macroinvertebrate species analysis were selected using backward selection until the minimal increased significantly over time (rSp > .7; p < .05), indicating a Akaike's information criterion (AIC) was obtained. All analyses directional change in community composition (turnover = 0.77; were initiated with a model containing all traits and second- Figure 2a). degree interactions and conducted using the R-package ‘vegan’ For both, native fish and macroinvertebrate species, only losses (Oksanen et al., 2019). but no gains were observed. For non-native fish and macroinverte- Environmental data (i.e. on changes in hydromorphology, cli- brate species, both gains and losses occurred, although gains domi- mate, land use and pollution) were not available for the entire period; nated in the fish community (39 gains and 33 losses over the entire monitoring of climate data sparsely covered the time since the mid- period) and losses dominated in the macroinvertebrate community 1940s (www.regio n​ e . t o s c a na.it/docum​ ents/10180/​ 2​ 3 1 0 1 / C​ a m b i ​ (16 gains and 27 losses over the entire period; Figure 2b). As a con- ament​i+clima​tici+in+T o s c a n​ a +1990-2015/). However, we were able sequence, the continuous increase in non-native species over time, to compile data on the growth of the city area of Florence (1800: 54 fostered by introductions of non-native macroinvertebrate and fish km2; 1900: 61.8 km2; 2015: 102.3 km2; www.istat.it), human popu- species and paralleled by the decrease or extirpation of native spe- lation growth (1900: 205.589; 1950: 374.625; 1970: 460.912; 2000: cies, led to an almost entire turnover in the investigated communi- 356.172; 2015: 377.207; www.istat.it) and historical changes in the ties (Figure 2; Table 1). use of the Arno River as an additional resource (Supplement 1). We matched and discussed available historical notes on changes in the river's hydromorphology and angling use in relation to the results 3.2 | Changes in trait modality compositions obtained from the CAP. We recorded a change in the proportion of several trait modali- ties through time (fish: 19; macroinvertebrates: 24). The majority 3 | RESULTS of trait modalities correlated significantly with the increase in non- native fish and macroinvertebrate species (Supplements 6 and 7). 3.1 | Changes in taxonomic composition and alpha Accordingly, 13 fish and 12 macroinvertebrate traits changed sig- diversity nificantly due to changing trait modalities over time. For the fish community, these, for instance, indicated an increase in eurytopic Over time, the α-diversity of fish increased (Figure 2a). The first rheophily but also significant changes in the utilized reproductive non-native fish species, the common carp Cyprinus carpio, was al- habitat, feeding habitat and diet, body length, fecundity (relative ready present in ~1800 (Fortini, 2018) and it has often been consid- and female), parental care, shape and swimming factor (Figure 3). ered as naturalized or even native (Vilizzi et al., 2015). Many other The macroinvertebrate community expressed comparably more non-native fish species occurred in 1900–1950 and their proportion diverse trait modalities compared to the fish community. These 612 | HAUBROCK et al.

(a) FIGURE 2 Changes in (a) α-diversity and (b) temporal turnover (displaying gains and losses of species) for the fish (left) and macroinvertebrate community (right) of the Arno River from ~1800 to 2015

(b)

FIGURE 3 Changing fish trait modalities over time. Eight (out of the thirteen) fish traits that significantly changed over time are shown (r > .7; p < .05). The remaining traits are given in the Supplement 8. The y-axes correspond to the proportional occurrence of each trait showed variations in ecological preferences (hydrological habitat, 3.3 | Changes in functional composition, current and substrate preferences), saprobity, species maximum metrics and resulting niche space size, reproductive cycles per year, feeding habit and resistance form (Figure 4). Additionally, reproductive behaviour changed, indicating Changes in functional metrics were identified (Table 2). While the the loss of polyvoltine species and an increase in univoltine species. overall functional richness of the entire fish community did not HAUBROCK et al. | 613

FIGURE 4 Changing macroinvertebrate trait modalities over time. Eight (out of twelve) macroinvertebrate traits that significantly changed over time are shown (r > .7; p < .05). The remaining traits are given in Supplement 9. The y-axes correspond to the proportional occurrence of each trait

change significantly over time (rSp > .7; p > .05), the functional There are two main differences in changes in niche space pat- richness of native fish species decreased significantly (rSp = −.924; terns observed in fish and macroinvertebrates: First, non-native p = .025). Simultaneously, functional richness and functional even- macroinvertebrate species occurred about 50–100 years later than in ness of non-native fish species increased significantly (rSp > .7; fish and the replacement process from natives to non-natives lagged p < .05). The functional metrics estimated for the macroinverte- accordingly. Second, the replacement process itself differed. As for brate community varied similarly, with no overall significant changes fish, a much higher overlap in niche space among native and non- over time (rSp = .62; p > .05). However, while the functional richness native species was observed than in macroinvertebrates. In macro- of native macroinvertebrates decreased significantly (rSp = .977; invertebrates, this overlap was much lower, as native and non-native p = .004), no other metric changed significantly for non-native mac- macroinvertebrate species occupied different niche spaces. roinvertebrates (rSp = .43; p > .05). The niche space of the only non-native fish species (C. carpio; Linnaeus, 1758) present in the Arno River before ~1800 and 3.4 | Identification of potential drivers 1850–1900 was outside the niche space occupied by native spe- cies (Figure 5). In the period 1900–1950, already 61.7% of the The canonical analysis of principal coordinates (CAP) identified five overall niche space (occupied by native or non-native species) trait modalities for fish as ordination defining (females maturity; overlapped between natives and non-natives. By 1950–2000, this protection with nester or egg hiders; spawning in winter time; re- overlap increased to 67.9%. From 2015, the only native species production habitat of rock and gravel spawners with benthic larvae; present (T. tinca; Linnaeus, 1758) was outside the non-native spe- and reproduction habitat of non-obligatory plant spawner; Figure 6). cies' niche space. This pattern thus reflects a complete reversal Littoral species that spawn on gravel during winter were character- of the state in ~1800 (Figure 5). As with fish, the niche space of istic for the native communities before 1900–1950 and decreased the two non-native macroinvertebrate species that were first re- after 1950. These were replaced by non-obligatory plant spawners. corded in 1900–1950 were outside the niche space of the native Coinciding with a decrease in winter spawning species, later matura- macroinvertebrate species. By 1950–2000, 29.8% of the overall tion and nest guarding were traits introduced by, and characteristic niche space (occupied by native or non-native species) overlapped for, non-native species communities after 1900–1950. between natives and non-natives. In 2015, this overlap decreased For macroinvertebrates, we identified seven modalities as being to 15.3% (Figure 5). characteristic for changes among community compositions of 614 | HAUBROCK et al.

different time slices (hydrological preference for main channel and side arms; no preference for a certain current velocity; predatory Non- native - 0.0000 - 0.0000 na 0.236 0.170 0.250 0.142 0.246 feeding habit; substrate preference mud; sprawling or walking ac- tively with legs, pseudopods or on mucus; feeding preference of liv- ing microinvertebrates; maximal potential size > 4–8 cm; Figure 6). Macroinvertebrate species with a preference for muddy substrates Native 0.153 0.243 0.155 0.246 0.182 0.242 0.161 0.244 0.132 0.000 decreased in 1900–1950 and increased again towards 2015, while the preference for main channels and side arms increased between 2000 and 2015. Predatory and larger species also increased through- All 0.154 Functional dispersion Functional 0.242 0.155 0.247 0.165 0.256 0.172 0.256 0.148 0.248 out the time period, while species with a feeding preference for

1800 to 2015; ‘na’ indicates that the living microinvertebrates were at their highest between 1900 and 1950. Species with the ability to actively sprawl or walk were highest Non- native - na - na na 0.9499 0.9516 0.9684 0.9607 0.9801 in the beginning and end of the investigated period (Figure 6).

4 | DISCUSSION Native 0.936 0.978 0.936 0.982 0.923 0.998 0.992 0.983 0.962 na 4.1 | Changes in alpha diversity and temporal turnover All Functional evenness Functional 0.9362 0.9784 0.9358 0.9820 0.9291 0.9748 0.9270 0.9761 0.9609 0.9788

Studies investigating biodiversity change at several locations around the globe have found no consistent local decrease in α-diversity across Non- native - na - na na 0.860 0.763 0.877 0.849 0.860 locations, despite local changes in community composition (Dornelas et al., 2014; Pilotto et al., 2020). The introduction of non-native spe- cies, which is among the leading causes of native biodiversity decline (Pyšek et al., 2020), might affect α-diversity at local scales by keeping it Native 0.731 0.829 0.731 0.840 0.778 0.807 0.818 0.831 0.756 na either constant or even increasing it as invaders replace native species (Hermoso et al., 2011). In the case of the Arno River, we confirmed our hypothesis (i) that a temporal turnover occurred in the past 215 years. All 0.840 Functional divergence Functional 0.923 0.841 0.929 0.833 0.941 0.880 0.941 0.888 0.925 This turnover from native to non-native species was, however, accom- panied by opposite temporal trends in α-diversity for the two biotic groups. For fish, we found that the successive introduction of non- native fish species compensated the loss of native species richness. Non- native - na - na na 8.54e-04 0.0197 1.70e-03 0.0153 2.25e-03 In contrast, the loss of native macroinvertebrates overweighed the gains from non-native species, and therefore α-diversity decreased. Our results, therefore, confirm previous considerations that variations in species composition are more informative indicators of changes in Native 0.334 2.39e-03 0.334 2.21e-03 0.021 1.33e-03 0.021 8.10e-05 0.002 na biotic communities than α-diversity metrics (Pilotto et al., 2020). Considering that past monitoring methods were likely less effi- cient than modern approaches, it also is possible that several native 9.45e-16 1.51e-12 1.03e-14 1.01e-12 4.31e-12 1.29e-11 3.81e-15 All Functional richness Functional 6.39e-13 2.24e-12 2.42e-12 species present in the early time periods may have been overlooked. This would result in a greater initial number of native species, and thus an even higher temporal turnover rate. Nevertheless, introduc- tions for both groups started mostly after 1900 and the introduction history is known for several species that were introduced for spe- 1800 1800 ~ Time slice Time ~ 1850–190 0 1850–190 0 1900–1950 1900–1950 1950–2000 1950–2000 2015 2015 cific purposes (see C. carpio: Balon, 1995; Silurus glanis: Economidis et al., 2000; P. clarkii: Kouba et al., 2014). Therefore, we are confi- dent that our reconstruction of the freshwater communities of the Arno River for the studied periods is reliable. Nonetheless, past and current species introductions are not suf- ficient to explain the ongoing biotic homogenization (i.e. spatially distributed communities becoming increasingly similar over time) of Group Macroinvertebrates Fish TABLE 2 TemporalTABLE changes in functional richness, divergence, evenness and dispersion of fish and macroinvertebrate species of the Arno River from ~ number of native or non-native species was not sufficient for the estimation, indicates while ‘-’ that no native or non-native species were present over that time aquatic ecosystems. For instance, downstream sections of rivers are HAUBROCK et al. | 615

FIGURE 5 Occupied niche space of the investigated native (blue) and non-native (red) fish and macroinvertebrate communities for the respective periods. Circles indicate the standard error of the (weighted) average of scores around the centroid of occupied niche space; the polygonized area represents the overall occupied niche space as the smallest convex hull volume occupied by all occurring traits in reference to species in multidimensional space

Fish Macroinvertebrates pnh 4.2 | Changes in trait modality compositions ma4 2015 pli 1900–1950 lmic 1850–1900 mud The information provided by the trait composition of communi- eup 1950–2000 ~1800

2 1950–2000

P ties is increasingly valued (Pyšek et al., 2009; Thuiller et al., 2006).

A

C For instance, Dencker et al. (2017) similar to Beukhof et al. (2019) spw ~1800 lit st1 ind used a limited selection of traits to investigate temporal and spa- 1900–1950 1850–1900 size (4–8cm) pre 2015 tial incongruences to infer the effect of environmental drivers on the North Sea fish community. Despite the increasing appre- CAP1 CAP1 ciation and consideration of such trait information for temporal FIGURE 6 Canonical analysis of principal coordinates for processes, traits have not been used to investigate the effect of significant traits of both fish and macroinvertebrate communities. species introductions on native communities over the entire inva- Blue arrows indicate the respective time slice ordered according sion process (Theoharides & Dukes, 2007). In fact, the response to community similarity. Black arrows describe significant traits of native species to non-native species introductions has rather (r > .7; p < .05) in relation to the time slices; (Fish: ma4—females mature ≤ 4 and 5 years; pnh—protection with nester or eggs being neglected (Buckwalter, 2016). The investigation of single hiders; st1—fish spawn in winter time; lit—reproduction habitat of snapshots in time (García-Berthou, 2007) results in an overall lack rock and gravel spawners with benthic larvae; pli—reproduction of information on other phases during the introduction or estab- habitat of non-obligatory plant spawner; Macroinvertebrates: lishment of introduced species (Buckwalter, 2016; Theoharides & eup—hydrological preference for main channel and side arms; Dukes, 2007). Furthermore, several biological traits, particularly ind—no preference for a certain current velocity; pre: predatory those indicating ‘euryoeciousness’ (i.e. the ability to live under feeding habit; mud—mud substrate preference; spw—sprawling or walking actively with legs, pseudopods or on mucus; lmic—feeding variable conditions), were proclaimed to concur with the suc- preference of living microinvertebrates; size (4–8 cm)—maximal cess of non-native species, despite not being tested using tem- potential size > 4–8 cm). Orange trait modalities indicate an poral datasets (Cuthbert et al., 2020; Devin & Beisel, 2007; Kolar increasing trend, while red trait modalities indicate a decline of the & Lodge, 2001; Ricciardi & Rasmussen, 1998). In this study, we respective modality over time tackle this obvious gap for the first time, investigating chang- ing trait modality occurrences and interactions in niche space. more affected by non-native species than upstream sections. This Following our hypothesis (ii), we concur that changes in trait mo- is because many successful non-native species are more tolerant dalities were identified as a direct response to the observed sig- towards wider ranges of environmental conditions than native spe- nificant temporal species turnover. cies (Früh et al., 2012a, 2012b) and disturbances are occurring more The concurred temporal changes in fish traits indicate an in- frequently in larger rivers than in upper river sections. This further crease in previously proclaimed euryoecious species. Euryoecious indicates interactive effects between biotic invasions and other an- non-native fish species can adapt to various environmental condi- thropogenic pressures in shaping freshwater communities. tions (Lenz et al., 2011; Marchetti et al., 2004), which often gives 616 | HAUBROCK et al. them a competitive advantage over native species. Recently, Su retreat of their niche space. Unlike fish, macroinvertebrates showed et al. (2006, 2019), showed that established non-native fish spe- less overlap in niche space. This suggests the possibility of (a) direct cies in various biogeographic regions were characterized by ‘ex- competition that resulted in the retreat of native species, or (b) that treme morphological traits’ and thereby differed from native but changes in the environment created vacant niches, which were then also non-established non-native species. In this regard, we also occupied by non-native species. These observed changes in niche identified that a higher fecundity was expressed in successfully space for the two studied biotic groups confirm hypothesis (ii) that established non-native species (especially observed in fish spe- a turnover in species is reflected in shifting niche space. These ob- cies; Howeth et al., 2016). Exemplary species that represent these servations also partially confirm hypotheses (iii) and (iv) as changes modalities are, for instance, Pseudorasbora parva (Temminck & in niche space reflected progressing invasions that were initiated Schlegel, 1846) or S. glanis (Copp et al., 2009; Gozlan, Andreou, by introductions into un-occupied space. However, this has to be et al., 2010). These results therefore confirm findings from Vila- taken with caution as the underlying trait information did not cover Gispert et al. (2005), who stated that successful non-native fish novel traits (i.e. traits that are entirely unknown to the new system species especially differ from native species in the expression of such as anti-predator defensive spines in Lepomis sp., Januszkiewicz life-history and ecological traits. & Robinson, 2007; or poisonous pectoral spines used for defence Similar to fish, changes in macroinvertebrate traits also reflect and stridulation in Ictalurus punctatus, Fine et al., 1997), but rather a shift towards more euryoecious species (e.g. without preference showed differences in expressed trait modalities among native and for current velocities). Typical representatives are, for instance, non-native species. Gyraulus chinensis (Dunker, 1848) or Sinanodonta woodiana (I. Lea, One possibility to explain the observed occurrence of non- 1834) (Ohta et al., 2011; Spyra et al., 2012), which are generally native species outside the native species' niche space is that an out- less specialized with a tendency towards eutrophic rivers. In past side position facilitates its establishment and population growth studies, the effect of pesticides (Chiu et al., 2016) and increased due to a lower degree of overlap (i.e. competition) with native spe- fine sedimentation (Mathers et al., 2017) on macroinvertebrate cies. It can also be assumed that these pioneering non-native spe- traits were investigated. Both concluded that the complex expres- cies introduced new trait modalities. However, it is not yet clear sion in macroinvertebrate traits was adequate to mirror changes if they facilitated other non-natives by affecting native species in communities or signal external stressors. Furthermore, we (Simberloff, 2006) and lowering the communities' ‘biotic resis- identified significant changes in all trait groups (region-related tance’ (Alofs & Jackson, 2014; Cuthbert et al., 2018) or by other parameters, habitat preferences, saprobic preferences and life facilitating interactions (Adams et al., 2003; Crane et al., 2020). parameters), underlining the versatility of macroinvertebrate trait The principle of functional redundancy (Rosenfeld, 2002) argues information. that if a species declines in its abundance, another species ‘takes over’. Therefore, the changing niche space might have made the community more ‘invadable’, because ecological functions within 4.3 | Changes in functional composition, the community could have become vacant, thus ‘opening up’ space metrics and resulting niche space that could be more easily claimed by a non-native species due to the limited degree of competition (Pyron et al., 2017). Species in- Changes in niche space have been used to infer competition arising troductions can also lead to top-down or bottom-up effects that, from species introductions at the community scale (Blonder, 2018; in turn, could initiate trophic cascades (Walsh et al., 2016). As such, Lamanna et al., 2014), suggesting that in the presented study com- it is possible that biotic homogenization as a process following suc- petitive processes between native and non-native fish and mac- cessive introductions will also be echoed within niche space given roinvertebrates species led to a displacement of native species. sufficient time. However, recent advances in trait-based ecology indicate that, in some cases, differences among species traits can make competition stronger and increase the difficulty of coexistence (Blonder, 2018; 4.4 | Identification of potential drivers Mayfield & Levine, 2010). Our analysis cannot discriminate between competing or coexisting species but the use of abundance data The turnover within the two biotic groups and the niche spaces might help in future studies. This is because in presence/absence occupied by native and non-native species have severe ecological data only major changes over time, that is, the loss of a species with implications: introduced non-native species may compete with na- its species-specific traits, result in visible changes. With our pres- tive counterparts, but with deteriorating environmental conditions ence/absence data, we could thus show an almost complete turno- over time certain combinations of traits might become inadequate. ver in community composition of both biotic groups, paralleled by In turn, this generates a feedback-loop on prevalent competitions an almost complete turnover in niche space. The niche space of na- (MacDougall & Turkington, 2005; Pyšek et al., 2010, 2020). Thus, tive and non-native fish species overlapped substantially, suggest- environmental conditions can affect the outcome of the introduc- ing a potential increase in competition, eventually having resulted tion of non-native species. Such disturbance-induced changes may (among other possible factors) in the demise of native species and generate an equilibrium in traits despite the presence of non-native HAUBROCK et al. | 617 species which can be explained by the principle of functional redun- Fish traits can also respond to the introduction of weirs and thus a dancy. However, as direct measurements of environmental variables slower flow through changes in the traits ‘shape’ or swimming factor. over the entire study period were unfortunately unavailable, model- Indeed, we observed a significant increase in shorter species with ling their effects on the observed temporal turnover and changes in higher depth (shape factor 1) and consequently a decrease in lon- trait modality occurrences was not possible. We therefore infer the ger species with higher shape factors. Furthermore, we identified effects of environmental change on the biota by analysing histori- a decrease in strong swimmers (swimming factor 1) and increase in cal reconstructions of the studied system and, indirectly, by discuss- other classes (particularly swimming factor 3) as defined by the ratio ing the changes in species trait modalities as a response to land use of minimum depth of the caudal peduncle to the maximum caudal change (i.e. observed city and population growth, changing angling fin depth in centimetre (Poff & Allan, 1995). In accordance with the activities) and altered hydromorphology. observed increase in bad swimmers (swimming factor 3) within fish, Non-native fish introductions generally relate to changing cus- the maximal potential size of macroinvertebrates and species with toms and angling use (Gozlan, Britton, et al., 2010). This is particu- the ability to move on legs increased. These trait modalities can po- larly true for the Arno River that has long been used as a food source tentially be advantageous when competing with native counterparts and later for recreational activities (Zagli, 2003). The introduction of in a slow flowing river, as observed by Vila-Gispert et al. (2005) in fish species between 1900 and 1950 matches the strong increase small Mediterranean streams. Furthermore, these traits can underlie in the city area of Florence and its human population. Accordingly, the ability to spread, which can be a prerequisite for the invasiveness local fishing associations were founded in that period, introduc- of non-native species (Ricciardi & Cohen, 2007). ing non-native fish species to increase angling activities—not pri- The introduction of weirs, but also the associated straighten- marily by authorized stockings, but intentional and illegal releases ing of the riverbed and removal of riparian vegetation, can induce by citizens (Bianco, 1995; Bianco & Ketmaier, 2001). Several non- particular changes in hydrological and substrate preference traits native fish species introduced after 1950 were not able to sustain (Autorità di Bacino dell'Arno, 1996; Becchi & Paris, 1989; Billi & stable populations and vanished again as, for example, species like Rinaldi, 1997; Menduni, 2017). Such hydromorphological alter- Micropterus salmoides (Lacépède, 1802) are bound to certain envi- ations, but also increased anthropogenic activities and wastewater ronmental conditions (i.e. turbidity for predation; Reid et al., 1999). management due to increasing populations (Karatayev et al., 2009) The increase of non-native fish species can therefore be linked to are commonly associated with an increase in pollution, low oxy- the aforementioned intentional introductions (Su et al., 2019). It is gen levels or an unnatural enrichment with nutrients (Klein, 1979; therefore likely that the concomitant observed decline in native fish Wilson, 2015). Such conditions may be exacerbated by climate species was at least partially linked to the increasing presence of change that has increased the frequency of years with extreme non-native fish species (Albins, 2015), indicated by the overlap into water scarcity and low precipitation since the mid-1940s. Indeed, niche space. Non-native macroinvertebrate species introductions we observed an increase in α-mesosaprobic and polysaprobic mac- in the Arno River were, on the other hand, reported to have origi- roinvertebrate species, underlining the effect of changes in the nated from accidental introductions, downstream spread (Tricarico saprobity of the Arno River over time and reflecting ongoing envi- et al., 2010) or cultural releases to practice native customs (Bodon ronmental degradation. This was further mirrored in the retreating et al., 2020; Gherardi et al., 1999; Gravili et al., 2010; Occhipinti- native macroinvertebrate' niche space. The changes in trait modality Ambrogi et al., 2011) and traditional cuisine (Cianfanelli et al., 2017; occurrences as a response to changes in the hydromorphology of Pfeiffer & Voeks, 2008). the ecosystem are mirrored in the disappearance of a major part of With the growth of the city of Florence in the past ~215 years, the occupied macroinvertebrate niche space without being replaced the hydromorphology of the Arno River changed significantly to- by non-native species. Compared to fish species, the higher variabil- wards a deeper and more channelized river with increased turbid- ity in traits and modalities of macroinvertebrates, paired with the ity and sediment transportation (e.g. impoundments; Adamek & higher number of ecological preference traits as opposed to biolog- Jurajda, 2001; bed material mining and loss of aquatic vegetation; Billi ical traits (e.g. stream zonation, hydrological preferences, substrate & Rinaldi, 1997). These changes, accompanied by the construction of and current preferences, saprobity) led to a better representation of weirs, continuously contributed to this change in hydromorphology environmental changes in the macroinvertebrate niche space. This over time accompanied by shifts in trait modalities and community leads to the conclusion that macroinvertebrates are more adequate niche space. Non-native fish have likely been favoured by the new to infer environmental changes from changes in community com- hydromorphological conditions, for example, a decrease in stream positions and trait occurrences, while fish traits might not reflect velocity and reduced competitiveness of native species (Leavy & environmental conditions sufficiently. Bonner, 2009). This was echoed by a decrease in rheophilic and in- In summary, whereas recreational activities and the use as a crease in limnophilic species. This increase in non-native fish spe- food source may be a substantial factor for introduced fish species cies and the consequent incoming transport of larvae of non-native globally and even on local scales, it does not suffice to explain species or of specimens from other populations could have further the turnover in the macroinvertebrate community. The demise compromised the genetic identity and survivability of native species of native macroinvertebrate species might, aside from changes (Manganelli et al., 2000; Marrone et al., 2019; Stoch & Bodon, 2014). in hydromorphology and an increase in pollution, relate to biotic 618 | HAUBROCK et al. interactions or the loss thereof. For instance, the demise of na- evolve or learn mechanisms surrounding invasions, ultimately persist- tive fish species, and thus the reproductive dependency of var- ing on their own within a few generations (Carroll et al., 2007; Wallach ious native molluscs (e.g. Anodonta exulcerata Porro, 1838 and et al., 2015). Although rarely observed, such a case was described by species of the genus Unio sp.) was shown to lead to the decline Letnic et al. (2008), after 50 years and Kiesecker & Blaustein (1997) of the latter (McNichols et al., 2010). Furthermore for Unionidae, after 70 years. A further step, consisting in the temporary reduction of the introduction of fish, and the consequent incoming transport the invaders' abundance, should be carefully considered to avoid the of larvae of native species or of specimens from other popula- ecological release of nontarget species (Bissattini et al., 2018). tions, can further compromise the genetic identity of autochtho- Our study shows that historical notes can be used to track and nous species (Manganelli et al., 2000; Marrone et al., 2019; Stoch explain species replacement dynamics. We further show the worth & Bodon, 2014). Given that notable changes in the community in considering multiple indicators for the assessment of biodiversity occurred earlier for fish than for macroinvertebrate species, it is change rather than few selective metrics like α-diversity or biomass likely that the macroinvertebrate community will display higher due to the multifaceted nature of community changes over time. For non-native species gains than native species losses in the future, the future, we urgently need harmonized long-term ecosystem mon- as observed from the fish community. itoring schemes that capture changes in biodiversity and environ- mental conditions (Haase et al., 2018; Mirtl et al., 2018).

4.5 | Management implications ACKNOWLEDGEMENTS We truly acknowledge the contribution of Elena Tricarico, Nicola In our study, we suggest that the combined effect of non-native Fortini, Annamaria Nocita and Fabio Stoch, who contributed to the species' introductions and stream degradation (i.e. hydromor- reconstruction of the investigated communities and history informa- phology, increased pollution) led to the dominance of non-native tion on the Arno River. We also thank two anonymous reviewers for species (in line with Früh et al., 2012a, 2012b) and the demise of their very constructive criticism and efforts to improve this manu- native species at the Arno River, which underlines the complexity script. Additionally, we acknowledge the thorough proof reading and of non-native species management. Indeed, Pyšek & Richardson language editing by Ross N. Cuthbert and Nathan J. Baker. Open ac- (2010) highlighted that the management of non-native species cess funding enabled and organized by Projekt DEAL. has to face various emergent problems. These are (a) ‘secondary introductions’, that is, the rapid replacement of non-native spe- DATA AVAILABILITY STATEMENT cies by other non-native species, (b) the ‘legacy effects’, mean- The data that support the findings of this study are available in the ing the long-lasting effects of environmental degradation caused supplementary material of this article. by introduced species due to a measurable impact (e.g. elevated nitrogen levels in the soil following invasions by nitrogen-fixing ORCID plants; Yelenik et al., 2004) and (c) the negative effects of non- Phillip J. Haubrock https://orcid.org/0000-0003-2154-4341 native species control attempts on native species (e.g. mesopreda- Francesca Pilotto https://orcid.org/0000-0003-1848-3154 tor releases as biocontrol agents leading to increased densities of Gianna Innocenti https://orcid.org/0000-0002-4504-0765 intermediate predators with cascading down effects; Bergstrom Simone Cianfanelli https://orcid.org/0000-0001-6058-4958 et al., 2009). Peter Haase https://orcid.org/0000-0002-9340-0438 In the light of the identified changes in niche space that accompa- nied the demise of native and rise of non-native species in the Arno REFERENCES River, we suggest that water managers should address the identi- Adamek, Z., & Jurajda, P. (2001). Stream habitat or water quality-what fied stressors to develop tailored mitigation measures. Management influences stronger fish and macrozoobenthos biodiversity? International Journal of Ecohydrology and Hydrobiology, 3, 305–311. efforts could target environmental and biological conditions as in- Adams, M. J. (1999). Correlated factors in amphibian decline: Exotic dicated by the changes in trait space to promote the long-term sur- species and habitat change in western Washington. The Journal vival of both native and non-native species (Laha & Mattingly, 2006) of Wildlife Management, 63, 1162–1171. https://doi.org/10.2307/ because these are more likely to coexist when they differ in natural 3802834 Adams, M. J., & Pearl, C. A. (2007). Problems and opportunities managing history and microhabitat preferences (Adams & Pearl, 2007). In partic- invasive bullfrogs: Is there any hope? In F. Gherardi (Ed.), Biological in- ular, the maintenance or restoration of suitable habitats may support vaders in inland waters: Profiles, distribution, and threats (pp. 679–693). the recovery of native species and limit the distribution of invaders Springer. (Adams, 1999; Adams & Pearl, 2007). The increase in habitat diver- Adams, M. J., Pearl, C. A., & Bruce Bury, R. (2003). Indirect facilitation of sity, through the creation of temporal and spatial refugia, may mediate an anuran invasion by non-native fishes. Ecology Letters, 6, 343–351. https://doi.org/10.1046/j.1461-0248.2003.00435.x the interactions between native and non-native species by reducing Albins, M. A. (2015). Invasive Pacific lionfish Pterois volitans reduce competition pressure on native species and eventually favouring their abundance and species richness of native Bahamian coral-reef long-term survival (Adams & Pearl, 2007; Schlaepfer et al., 2005). In fishes. Marine Ecology Progress Series, 522, 231–243. https://doi.org/ areas with refugium and non-refugium habitats, native species could 10.3354/meps1​1159 HAUBROCK et al. | 619

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