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10.1007/s10750-012-1182-1Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. form, nor will it be during the first three months after its submission to Hydrobiologia."Corresponding author: Erik Jeppesen (ej@dmu.dk)We dedicate this paper to the late Prof. Jürgen Benndorf, a true pioneer and mentor in lake and reservoir management oriented research, who inspired a number of us to initiate longterm comprehensive experimental ecological studies on lakes and reservoirs. AbstractFish play a key role in the trophic dynamics of lakes. With climate warming, complex changes in fish assemblage structure may be expected owing to direct effects of temperature and indirect effects operating through eutrophication, water level changes, stratification and salinisation. We reviewed published and new long-term (10-100 years) fish data series from 24 European lakes (area: 0.04-5648 km 2 ; mean depth: 1-177m; a north-south gradient from 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 4 Sweden to Spain). Along with an annual temperature increase of about 0.15-0.3 °C per decade profound changes have occurred in either fish assemblage composition, body size and/or age structure during recent decades and a shift towards higher dominance of eurythermal species.These shifts have occurred despite a reduction in nutrient loading in many of the lakes that should have benefited the larger-sized individuals and the fish species typically inhabiting cold-water, low-nutrient lakes. The cold-stenothermic Arctic charr has been particularly affected and its abundance has decreased in the majority of the lakes where its presence was recorded. The harvest of cool-stenothermal trout has decreased substantially in two southern lakes. Vendace, whitefish and smelt show a different response depending on lake depth and latitude. Perch has apparently been stimulated in the north, with stronger year classes in warm years, but its abundance has declined in the southern Lake Maggiore, Italy. Where introduced, roach seems to take advantage of the higher temperature after years of low population densities. Eurythermal species such as common bream, pike-perch and/or shad are apparently on the increase in several of the lakes. The response of fish to the warming has been surprisingly strong and fast in recent decades, making them ideal sentinels for detecting and documenting climate-induced modifications of freshwater ecosystems.

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To evaluate the roles of extinction and isolation in predicting richness and composition of fish assemblages in small forest lakes of Finland and Wisconsin, we analyzed data from 114 Finnish and 55 Wisconsin lakes 0.2–86.9 ha in area. Six isolation variables characterized properties of stream corridors, land barriers, and source pools of invading species; four extinction variables were related to habitat severity, lake area, and productivity. Two types of multivariate analyses were used: the nonparametric classification and regression trees (CART) and the parametric linear discriminant analysis (LDA). Both types of analyses showed that extinction variables were collectively more important than isolation variables in predicting richness and composition both in Finland and Wisconsin. We interpret that the greater importance of extinction vs. isolation results, not because isolation is unimportant, but because the probability of an arrival of a new species is much less than that of an extinction. Thus, the time after an extinction event before a subsequent invasion is long relative to the time after an invasion event before a subsequent extinction; consequently, fish assemblages sampled at a given point in time more likely represent the stamp of the extinctions than of the invasions. This conclusion was robust to the differences in the geomorphic settings and fish faunas of Finland and Wisconsin. However, the importance of individual isolation and extinction variables in determining richness and composition differed between the two regions, apparently more from differences in geomorphic settings than from differences in fish faunas. Influences of horizontal rather than vertical barriers over land and water were more apparent in Wisconsin, with its lower relief and higher incidence of lakes without stream connections; influences of the area of the nearest lake (representing the size of the available species pool) and stream gradient were more important in Finland, with its higher relief and higher incidence of lakes with stream connections. The importance of individual extinction variables also differed between the two regions, again reflecting differences in the geomorphic settings of the two lake districts and the strong influence that lake position in the landscape has in determining limnological features of the lake.

Summary We aimed to distinguish the relative contributions of natural and anthropogenic local factors on patterns of fish diversity in European lakes at different geographical scales. We compiled data from standardised fish monitoring using multimesh benthic gill nets, information on lake morphometry and on geographical, climatic and anthropogenic pressure variables from 1632 lakes in 11 European countries. By means of regression trees, we determined those natural and anthropogenic factors and their thresholds that best predicted local fish diversity, density and mean size. Generalised linear models were used to assess the influence of anthropogenic factors at smaller geographical and morphometric scales. Local fish species richness and diversity were related mainly to morphometric and (bio)geographical/climatic variables. Larger and deeper lakes in warm areas tended to be the most species rich and diverse. Fish density was related mainly to anthropogenically driven productivity but also was sensitive to geographical/climatic factors. Thus, warmer and shallower lower‐altitude European lakes, which are usually more eutrophic, had higher fish densities than cold and deeper higher‐altitude lakes. Fish size increased with altitude and declined with increasing seasonality and temperature. After controlling for the natural factors, productivity had a positive effect on fish species richness and diversity, whereas it negatively influenced fish size. Our results suggest that macroecological patterns of lake fish diversity across Europe are best predicted by natural factors. The contribution of anthropogenic factors to fish diversity was evident only via the effect of eutrophication at smaller geographical scales, whereas no effect could be found from hydromorphological pressures. From an applied perspective, these results suggest that bioassessment and biodiversity evaluation might be most effectively conducted and interpreted locally, where anthropogenic effects on biodiversity become more apparent. At a macroecological scale, the strong effect of environmental temperature on most components of fish diversity suggests future changes in fish diversity as a consequence of climate change.