Amphipods are a highly diverse group of aquatic invertebrates with >10,000 described species globally. About 20% of these are freshwater species, with half of them found in the West Palaearctic. Amphipods inhabit almost all freshwater ecosystems, including lakes, rivers, streams, as well as cave and groundwater systems, and can be the dominant macroinvertebrates in these habitats. They exhibit essential roles in the functioning of aquatic ecosystems, contributing to leaf litter breakdown and serving as important prey for fish. Furthermore, they are commonly used as indicator taxa for biomonitoring and in ecotoxicological studies. Many amphipod communities are currently undergoing rapid changes due to various drivers of global change, and some amphipod species are among the most successful nonnative invasive invertebrates.
Despite their ecological and economic significance, the knowledge on amphipods in Switzerland was hitherto limited, and until now no checklist, distribution maps, or broadscale estimates on genetic, functional, and morphological diversity of all amphipod species in Switzerland existed. All hitherto available literature on the ecology, faunistics, and taxonomy of amphipods in Central Europe is either outdated by many decades (Chevreux & Fage, 1925; Schellenberg, 1942), does not cover all species (Ginet, 1995; Eggers & Martens, 2001, Piscart & Bollache, 2012), or is only targeting neighboring countries (Vornatscher, 1965; Karaman, 1993; Eggers & Martens, 2001; Piscart & Bollache, 2012, Zettler & Zettler, 2017). This lack of appropriate baseline information on the ecology, distribution and faunistics of amphipods in Switzerland is a serious limitation for fundamental ecological research, impedes appropriate conservation strategies, and limits the use and application of amphipods as indicator taxa.

Alpine landscapes are being transformed through the rapid recession of glaciers, resulting in the development of numerous non-glacial headwater streams inhabited by a diverse assemblage of macroinvertebrates. We examined spatial patterns in biodiversity and rarity of macroinvertebrates in 41 non-glacial streams from five glacierized catchments in the Swiss Alps undergoing rapid glacial recession over the last decades. Water physico-chemistry and food resources (periphyton, benthic organic matter) varied widely among streams within each catchment, while no significant differences occurred among catchments. Variability in community composition was similar among streams within each catchment but differed among catchments, reflecting differences in catchment-scale species pools due to biogeographical context and season. Overall, 101 taxa from ca 33,000 individuals collected were identified in the streams with 7–33 taxa found in individual streams. Some 64% of the taxa comprised less than 5% of the total abundances at the streams (rare in abundance) with 78% of the taxa being represented by less than 5% of the most common taxon (Baetis sp.), whereas 47% of the taxa were found in less than 10% of the streams (rare in distribution). No taxon was found at all sites (maximum presence at 85% of the sites), while 15% of the taxa were found at 50% of the sites or more. However, analyzing the rank-abundance distribution showed that rarity was less prevalent than previously shown in other ecosystems. The results indicated that community assembly of alpine headwater streams is a complex interaction between environmental properties (habitat filtering), habitat stability coupled with dispersal (source sink dynamics), and time since deglaciation (island biogeography). Integrating these processes is essential towards understanding ongoing colonization events in headwater streams of alpine catchments as glaciers continue to recede.

Habitat connectivity crucially influences dispersal of organisms. It is especially seen as an important driver of the spatial structuring of biological communities in ecosystems that have intrinsic and general connectivity patterns, such as the universal dendritic structure of fluvial networks. These networks not only define dispersal of native species, but also represent corridors of biological invasions, making understanding network topology effects on invasion dynamics and subsequent diversity patterns of high interest. We studied amphipod community diversity and structure in the upper 27,882-km² drainage basin of the river Rhine in Central Europe, focusing on differences between native and non-native species. Overall, species richness increased along the network from headwaters to the outlet nodes. We found, however, contrasting patterns of native and non-native amphipod richness along the network, with headwater nodes representing refugia for native species and more downstream nodes being hotspots of biological invasions. Importantly, while species turnover (b-diversity) of native species increased with distance between nodes in the network, this was not the case for non-native species, indicating a much lower dispersal limitation of the latter. Finally, the overall amphipod community structure closely mirrored the topological modularity of the network, highlighting the network’s imprint on community structure. Our results underpin the importance of connectivity for community formation and the significance of rivers for biological invasions and suggest that empirically observed matches of diversity patterns in rivers predicted by null models are the long-term outcome of species invasions and species sorting.

Amphipods are keystone species in many freshwater ecosystems. Understanding their distribution and diversity is crucial to ensure and preserve freshwater ecosystem functioning, particularly in the northern hemisphere. For the European Alps information on amphipods has been relatively limited until recently. We describe a new, widely distributed amphipod species, Gammarus alpinus sp. nov., found across the Alps and analyse its distribution, biogeography as well as genetic and morphological differentiation. Until now, this species has been reported as Gammarus lacustris. Based on genetic and morphometric measurements, we show that G. alpinus is highly divergent from G. lacustris. The latter has a circumpolar distribution, but may be absent from the Alps. The observed occurrence pattern of G. alpinus might be explained by a Pliocene range expansion and vicariance due to climate warming following the Quaternary glaciation. Historical drainage divides suggest a single recolonization route from a distinct southern refugium. While G. lacustris is widely distributed and not endangered at a global scale, G. alpinus is endemic to the Alps and its habitat is negatively affected by eutrophication, non-native species and possibly climate change.

Amphipods are key organisms in many freshwater systems and contribute substantially to the diversity and functioning of macroinvertebrate communities. Furthermore, they are commonly used as bioindicators and for ecotoxicological tests. For many areas, however, diversity and distribution of amphipods is inadequately known, which limits their use in ecological and ecotoxicological studies and handicaps conservation initiatives. We studied the diversity and distribution of amphipods in Switzerland (Central Europe), covering four major drainage basins, an altitudinal gradient of>2,500 m, and various habitats (rivers, streams, lakes and groundwater). We provide the first provisional checklist and detailed information on the distribution and diversity of all amphipod species from Switzerland. In total, we found 29 amphipod species. This includes 16 native and 13 non-native species, one of the latter (Orchestia cavimana) reported here for the first time for Switzerland. The diversity is compared to neighboring countries. We specifically discuss species of the genus Niphargus, which are often receiving less attention. We also found evidence of an even higher level of hidden diversity, and the potential occurrence of further cryptic species. This diversity reflects the biogeographic past of Switzerland, and suggests that amphipods are ideally suited to address questions on endemism and adaptive radiations, post-glaciation re-colonization and invasion dynamics as well as biodiversity-ecosystem functioning relationships in aquatic systems.

Background: Worldwide, natural communities are invaded by non-native species, with potentially devastating effects on the native communities. A large part of past research aimed at finding traits and characteristics of the invading species or the invaded community explaining observed invasions. Only recently, the focus shifted on the spatial patterns during invasions per se. Empirical data, however, are limited, as invasions are often unique incidences of a complex spatio-temporal process. In order to identify generalities of invasion patterns, we studied 13 naturally replicated tributary streams draining into Lake Constance, and studied the occurrence of native and non-native amphipods along linear transects from the stream outlets to the upstream headwater reaches.
Results: We found repeated spatial patterns of community composition and the occurrence of native and non-native amphipod species across two different years. Specifically, occurrence as well as abundance of two non-native amphipod species decreased from the stream outlets at the lake site towards upstream headwater reaches. Populations of the most common native amphipod species were largest at the uppermost headwater reaches. All populations of this native species, however, showed significant signals of recent genetic bottlenecks, irrespective of the stream position and occurrence of non-native species. Contrary to our expectations, this native species also showed no longitudinal genetic differentiation within individual tributaries as postulated for headwater versus outlet populations.
Conclusions: Our results indicate that invasions of river-systems may overall follow predictable patterns on the level of spatial distributions and community composition. However, effects of invading organisms on the genetic diversity and genetic structure of native populations observed at larger scales may not necessarily be directly reflected at the scale of smaller tributaries.

The amphipod genus Niphargus (Amphipoda: Niphargidae Bousfield, 1977) is the most species-rich genus of freshwater amphipods in the World. Species of this genus, which live almost exclusively in subterranean water, offer an interesting model system for basic and applied biodiversity science. Their use, however, is often limited due to the hitherto unresolved taxonomy within the whole genus. As a comprehensive taxonomic revision of the currently >425 Niphargus species is too demanding, it has been suggested that the taxonomy of the genus could be advanced in smaller steps, by reviewing regional faunas, that would eventually integrate into a global revision. In this study, we provide such a revision of Niphargus in Switzerland. First, we molecularly delimited, morphologically diagnosed, and formally described two new species, namely Niphargus luchoffmanni sp. n. and Niphargus tonywhitteni sp. n. Second, we updated and revised a checklist of Niphargus in Switzerland with new findings, and prepared a list of reference sequences for routine molecular identification, available at BOLD and GenBank. All available specimens of 22 known species from the area were morphologically examined, and their morphological variation was compiled in a data file of DEscription Language for TAxonomy, which can be used for automated generation of dichotomous or interactive keys. The data file is freely available at the World Amphipoda Database. Together, the checklist, the library of reference sequences, the DELTA file, but also a list of hitherto unresolved aspects are an important step towards a complete revision of the genus within a well-defined and biogeographically interesting area in Central Europe.

Groundwater belongs to the spatially most extensive, but least explored freshwater systems. On a global scale, the species richness of several subterranean invertebrate taxa parallels species richness found in surface waters, while on a local scale species richness hardly exceeds 20 species. This results in a high contribution of groundwater ecosystems to regional β- and γ-diversity, and to a smaller degree to α-diversity, and deserves focused attention. In general, more species are to be found in large cave systems. The second largest cave system in Europe is Hölloch in Switzerland. In this paper we revised the taxonomic, phylogenetic and ecological diversity of the amphipod community in the Hölloch cave system. While previous records listed five geographically widespread species of the genus Niphargus for this cave system, we could not confirm the presence of any of those species, but rather found three highly distinct species new to science. In this paper we describe Niphargus styx sp. nov., Niphargus murimali sp. nov., and Niphargus muotae sp. nov., and suggest that previous records from that cave were probably misidentificationsf. Although amphipod species richness in this cave system seems to be lower than previously thought in terms of absolute numbers, the cave retained its regional and international importance in terms of nature conservation for multiple reasons. First, all newly described species are probably endemic to this cave system. Second, they are phylogenetically distantly related and exhibit moderate to high phylogenetic diversity. Third, the species, as inferred from their functional morphology, are also ecologically highly divergent. Based on geographic distribution of their nearest relatives, we hypothesize that the cave system was most likely independently colonized from North, West and South and that the pre-adapted ancestors occupied different ecological niches within the system.

Losses and gains in species diversity affect ecological stability^1–7 and the sustainability of ecosystem functions and services^8–13. Experiments and models have revealed positive, negative and no effects of diversity on individual components of stability, such as temporal variability, resistance and resilience^{2,3,6,11,12,14}. How these stability components covary remains poorly understood¹⁵. Similarly, the effects of diversity on overall ecosystem stability¹⁶, which is conceptually akin to ecosystem multifunctionality^17,18, remain unknown. Here we studied communities of aquatic ciliates to understand how temporal variability, resistance and overall ecosystem stability responded to diversity (that is, species richness) in a large experiment involving 690 micro-ecosystems sampled 19 times over 40 days, resulting in 12,939 samplings. Species richness increased temporal stability but decreased resistance to warming. Thus, two stability components covaried negatively along the diversity gradient. Previous biodiversity manipulation studies rarely reported such negative covariation despite general predictions of the negative effects of diversity on individual stability components³. Integrating our findings with the ecosystem multifunctionality concept revealed hump- and U-shaped effects of diversity on overall ecosystem stability. That is, biodiversity can increase overall ecosystem stability when biodiversity is low, and decrease it when biodiversity is high, or the opposite with a U-shaped relationship. The effects of diversity on ecosystem multifunctionality would also be hump- or U-shaped if diversity had positive effects on some functions and negative effects on others. Linking the ecosystem multifunctionality concept and ecosystem stability can transform the perceived effects of diversity on ecological stability and may help to translate this science into policy-relevant information.

Chironomids generally dominate macroinvertebrate assemblages in alpine streams. This study compared chironomid assemblages inhabiting 51 non-glacial streams in six alpine catchments in the Swiss Alps in 2012. Total abundances ranged from 3 to ca. 1900 individuals per sample with 42 taxa identified overall. Common taxa differed among catchments and among streams within a catchment (5 taxa comprised > 95 % of the total abundances among streams). Taxon richness varied from 18 to 29 between catchments and between 2 and 16 between individual streams. Beta diversity (B_w) ranged from 1.27 to 3.03 between streams within catchments. The most common taxa included Diamesa spp. (mostly D. zernyi-cinerella group), Pseudodiamesa spp. (mostly P. branickii), Pseudokiefferiella parva, Corynoneura sp, Eukiefferiella spp., Orthocladius frigidus, Parametriocnemus stylatus, and Micropsectra spp. Nineteen taxa (45 %) were found at < 5 % of the streams and 8 taxa (19 %) were exclusive to one stream alone. These results indicate a highly diverse and spatially-structured chironomid assemblage with a prevalence towards rarity in these high elevation alpine catchments.

We investigated environmental characteristics and macroinvertebrate trophic structures of alpine streams in the glaciated Dinwoody catchment of the Wind River Range, Wyoming, USA. Study sites were above 3100 m a.s.l. and all above treeline except for one site representing a forested headwater stream. Physico-chemistry grouped sites by sub-basin and glacial influence. Seston levels were higher in the forested stream and a side-slope tributary (> 227 mg m^-3) than the other streams (< 100 mg m^–3). Periphyton levels were higher (> 2.7 mg m^–2) in streams in the Heap Steep sub-basin fed by a remnant hanging glacier (active ice field) than in the other streams (< 1.0 mg m^–2). Macroinvertebrate abundances (range = 140 – 2400 individuals per 5-min kick sample) and taxa richness were generally low (2–8 taxa at most sites), although being higher in lower-basin sites and the forested stream than at sites nearest the glaciers. Macroinvertebrate trophic structures were simple, consisting of primary consumers and predators, including two riparian spiders. Macroinvertebrate δ¹⁵N values ranged from ca. –2.54 to –5.41, whereas δ¹³C values ranged from –24.23 to –16.08. Individual taxa varied widely in δ¹³C among sites, suggesting carbon sources differed among sites. Carbon isotope ratios also increased from upper sites to lower sites in the same subbasin, suggesting a glacial carbon source at sites near the glacier to an instream carbon source at lower glacial sites lacking substantial riparian inputs. The upper glacial sites also had carbon isotope ratios similar to that of the forested headwater stream. These data suggest a highly heterogeneous spatial structure in alpine landscapes concomitant with the longitudinal development of glacial streams that is reflected in the trophic structure of local macroinvertebrates.