Ectotherms are considered to be particularly vulnerable to climate warming. Descriptions of habitat temperatures and predicted changes in climate usually consider mean monthly, seasonal or annual conditions. Ectotherms, however, do not simply experience mean conditions, but are exposed to daily fluctuations in habitat temperatures. Here, we highlight how temperature fluctuation can generate ‘realized’ thermal reaction (fitness) norms that differ from the ‘fundamental’ norms derived under standard constant temperatures. Using a mosquito as a model organism, we find that temperature fluctuation reduces rate processes such as development under warm conditions, increases processes under cool conditions, and reduces both the optimum and the critical maximum temperature. Generalizing these effects for a range of terrestrial insects reveals that prevailing daily fluctuations in temperature should alter the sensitivity of species to climate warming by reducing ‘thermal safety margins’. Such effects of daily temperature dynamics have generally been ignored in the climate change literature.

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Temperature variation makes ectotherms more sensitive to climate change.

Over the last two decades, macroecology – the analysis of large-scale, multi-species ecological patterns and processes – has established itself as a major line of biological research. Analyses of statistical links between environmental variables and biotic responses have long and successfully been employed as a main approach, but new developments are due to be utilized. Scanning the horizon of macroecology, we identifi ed four challenges that will probably play a major role in the future. We support our claims by examples and bibliographic analyses. 1) Integrating the past into macroecological analyses, e.g. by using paleontological or phylogenetic information or by applying methods from historical biogeography, will sharpen our understanding of the underlying reasons for contemporary patterns. 2) Explicit consideration of the local processes that lead to the observed larger-scale patterns is necessary to understand the fi ne-grain variability found in nature, and will enable better prediction of future patterns (e.g. under environmental change conditions). 3) Macroecology is dependent on large-scale, high quality data from a broad spectrum of taxa and regions. More available data sources need to be tapped and new, small-grain large-extent data need to be collected. 4) Although macroecology already lead to mainstreaming cuttingedge statistical analysis techniques, we fi nd that more sophisticated methods are needed to account for the biases inherent to sampling at large scale. Bayesian methods may be particularly suitable to address these challenges. To continue the vigorous development of the macroecological research agenda, it is time to address these challenges and to avoid becoming too complacent with current achievements.

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What ' s on the horizon for macroecology?

Climate change is expected to drive species ranges towards the poles and to have a strong influence on species distributions. In this study, we focused on diadromous species that are of economical and ecological importance in the whole of Europe. We investigated the potential distribution of all diadromous fish regularly encountered in Europe, North Africa and the Middle East (28 species) under conditions predicted for twenty-first century climate change. To do so, we investigated the 1900 distribution of each species in 196 basins spread across all of Europe, North Africa and the Middle East. Four levels were used to semiquantitatively describe the abundance of species, that is missing, rare, common and abundant. We then selected five variables describing the prevailing climate in the basins, the physical nature of the basins and reflecting historical events known to have affected freshwater fish distribution. Logistic regressions with a four-level ordinal response variable were used to develop species-specific models. These predictive models related the observed distribution of these species in 1900 to the most explanatory combination of variables. Finally, we selected the A2 SRES scenario and the HadCM3 (Hadley Centre Coupled Model version 3) global climate model (GCM) to obtain climate variables (temperature and precipitation) at the end of this century. We used these 2100 variables in our models and obtained maps of climatically suitable and unsuitable basins, percentages of contraction or expansion for each species. Twenty-two models were successfully built, that is there were five species for which no model could be established because their distribution range was too narrow and the Acipenser sturio model failed during calibration. All the models selected temperature or/and precipitation as explanatory variables. Responses to climate change were species-specific but could be classified into three categories: little or no change in the distribution (five species), expansion of the distribution range (three species gaining suitable basins mainly northward) and contraction of the distribution (14 species losing suitable basins). Shifting ranges were in accordance with those found in other studies and underlined the high sensitivity of diadromous fish to modifications in their environment.

Impact of twenty-first century climate change on diadromous fish spread over Europe, North Africa and the Middle East

Diadromous fish conservation plans need to consider global warming issues: An approach using biogeographical models

Disruption to migration is a growing problem for conservation and restoration of animal populations. Anthropogenic barriers along migration paths can delay or prolong migrations, which may result in a mismatch with migration-timing adaptations. To understand the interaction of dams (as barriers along a migration path), seasonally changing environmental conditions, timing of Atlantic salmon (Salmo salar) downstream migration, and ultimate migration success, we used 10 years of river temperature and discharge data as a template upon which we simulated downstream movement of salmon. Atlantic salmon is a cool-water species whose downstream migrating smolts must complete migration before river temperatures become too warm. We found that dams had a local effect on survival as well as a survival effect that was spatially and temporally removed from the encounter with the dam. While smolts are delayed by dams, temperatures downstream can reach lethal or near-lethal temperatures; as a result, the match between com...

Migration delays caused by anthropogenic barriers: modeling dams, temperature, and success of migrating salmon smolts

Global warming impacts and conservation responses for the critically endangered European Atlantic sturgeon.

– The aim of this study was to analyse the distribution of 14 diadromous fish at the beginning of the 20th century in western Europe. This study was conducted on a set of 41 water basins. Five environmental variables were selected and we used generalised additive models for explaining the presence–absence of species. The richest basins were located in the centre of the study area. Six main assemblage types were identified along a latitudinal gradient; they were constituted of a common species basis but differed by the absence or presence of other species. The 10 single species models produced have moderate to very good discrimination level and they can correctly predict both absence and presence. Temperature is included in all but one model, response curves vary according to the species; surface area is included in six models.

Distribution and richness of diadromous fish assemblages in Western Europe: large-scale explanatory factors

In the mid-nineteenth century, the European sturgeon (Acipenser sturio L, 1758) was proved to have been present in a significant proportion of the Western Palearctic region, i.e., Europe and North Africa. Of the 196 basin units investigated, 24 were selected for spawning by sexually mature individuals, and 44 were frequented by occasional vagrants. Its spatial distribution did not follow the classic “core–periphery” model noted for most European diadromous fish. Spawning basins were generally separated one from another by hundreds or even thousands of kilometers of coast. In these gaps, sturgeon were totally absent from inland waters, or occasionally migrants entered rivers, sometimes traveling far above the tidal limit, for exploration and feeding activities. Because of diverse anthropogenic regional pressures, the sturgeon’s range decreased drastically, and population disappearances were reported earlier in the twentieth century in the northern part of its range.

An Overview on Geographical Distribution from Past Descriptions

Summary

The objective of this paper was to understand trends in modelling over time within sturgeon research and the effects of modelling applications on the scientific community using a bibliometric approach on articles from the ISI Web of Knowledge online database between 1996 and 2012. The results indicate an increasing contribution of modelling within the general field of sturgeon research. The population models analyzed mainly focused upon the impacts of fisheries, dams, stocking, genetics and elasticity/sensitivity analyses. Habitat suitability models, hydrodynamic models, bioenergetic models and general statistical models focused on the effects of habitat availability, species distribution, survival, growth and spawning migrations. The largest number of publications originated from North America, with a regional focus on the West Coast and Mississippi/Great Lakes regions. In contrast, model development and application was lacking for the Aral Sea region and Siberia. Moreover, thus far there were no published population models for north-western European and Mediterranean sturgeon populations. The models have only been applied to a limited number of species and, with an increased Red List status of a species, the number of publications decreased substantially. Such results should be considered as a warning sign with regard to the effective implementation of conservation strategies for endangered species, given that the development of models is considered a key tool for the optimization of management and protection measures.

E. Rochard

Papers

Diadromous fish conservation plans need to consider global warming issues: An approach using biogeographical models

Global warming impacts and conservation responses for the critically endangered European Atlantic sturgeon.

Distribution and richness of diadromous fish assemblages in Western Europe: large-scale explanatory factors

An Overview on Geographical Distribution from Past Descriptions

Modelling attempts utilized in sturgeon research: a review of the state‐of‐the art