Abteilung Fischökologie & Evolution

Quaternary climate fluctuations can affect speciation in regional biodiversity assembly in two non-mutually exclusive ways: a glacial species pump, where isolation in glacial refugia accelerates allopatric speciation, and adaptive radiation in underused adaptive zones during ice-free periods. We detected biogeographic and genetic signatures associated with both mechanisms in the assembly of the biota of the European Alps. Age distributions of endemic and widespread species within aquatic and terrestrial taxa (amphipods, fishes, amphibians, butterflies and flowering plants) revealed that endemic fish evolved only in lakes, are highly sympatric, and mainly of Holocene age, consistent with adaptive radiation. Endemic amphipods are ancient, suggesting preglacial radiation with limited range expansion and local Pleistocene survival, perhaps facilitated by a groundwater-dwelling lifestyle. Terrestrial endemics are mostly of Pleistocene age and are thus more consistent with the glacial species pump. The lack of evidence for Holocene adaptive radiation in the terrestrial biome is consistent with faster recolonization through range expansion of these taxa after glacial retreats. More stable and less seasonal ecological conditions in lakes during the Holocene may also have contributed to Holocene speciation in lakes. The high proportion of young, endemic species makes the Alpine biota vulnerable to climate change, but the mechanisms and consequences of species loss will likely differ between biomes because of their distinct evolutionary histories.

Das Projet Lac war ein grosses Projekt der Eawag und der Universität Bern zur erstmaligen quantitativen Erfassung ganzer Fischgemeinschaften in grossen und tiefen Seen in und um die europäischen Alpen mit standardisierten Probenahmeverfahren. Ab 2010 wurden insgesamt 35 Seen in der Schweiz, Italien, Frankreich, Deutschland und Österreich untersucht und über 106 Fischarten erfasst. Dieser Bericht fasst die wichtigsten Ergebnisse zusammen, vergleicht die Fischgemeinschaften der einzelnen Seen, untersucht ihre Beziehung zu Umweltparametern und gibt einen Überblick über die Faktoren, welche die biologische Vielfalt und die Struktur der Gemeinschaften in diesem wichtigen Ökosystem beeinflussen.

Le Projet Lac était un grand projet de l'Eawag et de l'Université de Berne visant à recenser pour la première fois
de manière quantitative des communautés entières de poissons dans les grands et profonds lacs des Alpes  européennes et de leurs environs, à l'aide de méthodes d'échantillonnage standardisées. A partir de 2010, 35 lacs au total ont été étudiés en Suisse, en Italie, en France, en Allemagne et en Autriche et plus de 106 espèces de poissons ont été recensées. Ce rapport résume les principaux résultats, compare les communautés de poissons des différents lacs, examine leur relation avec les paramètres environnementaux et donne un aperçu des facteurs qui influencent la diversité biologique et la structure des communautés dans cet écosystème important.

Il Projet Lac era un progetto su larga scala dell'Eawag e dell'Università di Berna per la prima indagine quantitativa di intere comunità di pesci in laghi grandi e profondi nelle Alpi europee e dintorni, utilizzando metodi di campionamento standardizzati. A partire dal 2010, un totale di 35 laghi in Svizzera, Italia, Francia, Germania e Austria sono stati studiati e sono state registrate oltre 106 specie di pesci. Questo rapporto riassume i risultati principali, confronta le comunità di pesci di ogni lago, esamina la loro relazione con i parametri ambientali e fornisce una panoramica dei fattori che influenzano la biodiversità e la struttura della comunità in questo importante ecosistema.

Projet Lac was a large project conducted by Eawag and the University of Bern to quantitatively survey, for the
first time, whole-lake fish communities in the large and deep lakes in and around the European Alps using multiple, standardised sampling methods. Starting in 2010, in total 35 lakes were investigated across Switzerland, Italy, France, Germany and Austria, with more than 106 fish species recorded. This report brings together key findings, compares fish communities among lakes, investigates their relationship to environmental parameters, and provides an overview of drivers of biodiversity and community structure in this important ecosystem.

Adaptive radiations in postglacial fish offer excellent settings to study the evolutionary mechanisms involved in the rapid buildup of sympatric species diversity from a single lineage. Here, we address this by exploring the genetic and ecological structure of the largest Alpine whitefish radiation known, that of Lakes Brienz and Thun, using microsatellite data of more than 2000 whitefish caught during extensive species-targeted and habitat-randomized fishing campaigns. We find six strongly genetically and ecologically differentiated species, four of which occur in both lakes, and one of which was previously unknown. These four exhibit clines of genetic differentiation that are paralleled in clines of eco-morphological and reproductive niche differentiation, consistent with models of sympatric ecological speciation along environmental gradients. In Lake Thun, we find two additional species, a profundal specialist and a species introduced in the 1930s from another Alpine whitefish radiation. Strong genetic differentiation between this introduced species and all native species of Lake Thun suggests that reproductive isolation can evolve among allopatric whitefish species within 15,000 years and persist in secondary sympatry. Consistent with speciation theory, we find stronger correlations between genetic and ecological differentiation for sympatrically than for allopatrically evolved species.

Eutrophication increases primary production and changes the relative abundance, taxonomic composition and spatial distribution of primary producers within an aquatic ecosystem. The changes in composition and location of resources alter the distribution and flow of energy and biomass throughout the foodweb. Changes in productivity also alter the physico-chemical environment, which has further effects on the biota. Such ecological changes influence the direction and strength of natural and sexual selection experienced by populations. Besides altering selection, they can also erode the habitat gradients and/or behavioural mechanisms that maintain ecological separation and reproductive isolation among species. Consequently, eutrophication of lakes commonly results in reduced ecological specialization as well as genetic and phenotypic homogenization among lakes and among niches within lakes. We argue that the associated loss in functional diversity and niche differentiation may lead to decreased carrying capacity and lower resource-use efficiency by consumers. We show that in central European whitefish species radiations, the functional diversity affected by eutrophication-induced speciation reversal correlates with community-wide trophic transfer efficiency (fisheries yield per unit phosphorus). We take this as an example of how evolutionary dynamics driven by anthropogenic environmental change can have lasting effects on biodiversity and ecosystem functioning.
This article is part of the themed issue ‘Human influences on evolution, and the ecological and societal consequences’.

The European standard for gillnet sampling to characterize lake fish communities stratifies sampling effort (i.e., number of nets) within depth strata. Nets to sample benthic habitats are randomly distributed throughout the lake within each depth strata. Pelagic nets are also stratified by depth, but are set only at the deepest point of the lake. Multiple authors have suggested that this design under-represents pelagic habitats, resulting in estimates of whole-lake CPUE and community composition which are disproportionately influenced by ecological conditions of littoral and benthic habitats. To address this issue, researchers have proposed estimating whole-lake CPUE by weighting the catch rate in each depth-compartment by the proportion of the volume of the lake contributed by the compartment. Our study aimed to assess the effectiveness of volume-weighting by applying it to fish communities sampled according to the European standard (CEN), and by a second whole-lake gillnetting protocol (VERT), which prescribes additional fishing effort in pelagic habitats. We assume that convergence between the protocols indicates that volume-weighting provides a more accurate estimate of whole-lake catch rate and community composition. Our results indicate that volume-weighting improves agreement between the protocols for whole-lake total CPUE, estimated proportion of perch and roach and the overall fish community composition. Discrepancies between the protocols remaining after volume-weighting may be because sampling under the CEN protocol overlooks horizontal variation in pelagic fish communities. Analyses based on multiple pelagic-set VERT nets identified gradients in the density and biomass of pelagic fish communities in almost half the lakes that corresponded with the depth of water at net-setting location and distance along the length of a lake. Additional CEN pelagic sampling effort allocated across water depths and distributed throughout the lake would therefore help to reconcile differences between the sampling protocols and, in combination with volume-weighting, converge on a more accurate estimate of whole-lake fish communities.

Ecological research and monitoring of lacustrine ecosystems often requires a whole-lake assessment of fish communities. Gillnet sampling offers an efficient means of estimating abundance, biomass and fish community composition. However the choice of gillnet sampling protocol may influence lake characterization via physical properties of the nets and allocation of sampling effort between littoral, benthic and pelagic habitats. This paper compares two commonly used, whole-lake sampling protocols applied across 17 prealpine, subalpine and alpine European lakes ranging widely in size, depth and altitude to determine their relative strength for research and management applications. Effort-corrected estimates of abundance, biomass and species richness were correlated between the protocols and both distinguished the trout-dominated alpine communities from subalpine and prealpine lakes dominated by whitefish and perch. A considerable amount of variance remained unexplained between the two protocols however, which seemed to correspond with differences in the proportion of effort among benthic and pelagic habitats. We suggest that both the European standard (CEN) and vertical (VERT) netting protocols are suitable for assessing ecological status and monitoring changes in lake fish communities through time. However the details of each protocol should be kept in mind when comparing fish communities between lakes. Mesh sizes used in CEN nets produce a more even size frequency distribution, suggesting that this protocol is most appropriate for assessing size structure of fish assemblages. The high proportion of netting effort in benthic habitats shallower than 70 m depth under the CEN protocol means that, particularly in larger lakes, outcomes will be disproportionately influenced by the ecological condition of this habitat. The VERT protocol presumably provides a more accurate estimate of whole-lake CPUE and community composition because effort, in terms of net area, is more evenly distributed across the entire volume of the lake. This is particularly important in large and deep lakes where pelagic habitats occupy a high proportion of the lake volume.

Die grossen Seen des Alpenraums weisen eine einzigartige und bisher nur unvollständig bekannte Fischartenvielfalt auf. Mit dem Projet Lac wurden erstmals systematisch die Fischbestände in 35 Seen des Alpenraums aufgenommen. Die standardisierte Erfassung der Fischgemeinschaften, die Charakterisierung aller Arten und deren korrekte Bestimmung, das Wissen über ihre Ökologie sowie die rechtliche Verankerung ihres Schutzes bilden die Grundlage für deren langfristigen Erhalt.

Mit dem «Projet Lac» wurden erstmals systematisch die Fischbestände in 35 Seen des Alpenraums aufgenommen. Die Ergebnisse zeigen: Die vorherrschenden Umweltbedingungen beeinflussen die Artenzusammensetzung und die Häufigkeiten der Fischgemeinschaften massgeblich. Menschliche Einflüsse verändern diese Umweltbedingungen, mit einschneidenden Konsequenzen für die Fischgemeinschaften. Der Schutz und die Wiederherstellung von wichtigen Lebensräumen von einheimischen Arten, insbesondere in der Tiefe, bei Flussmündungen und am Ufer der Seen muss deshalb vorangetrieben werden.