Browsing by Autor "Nicolas Lamouroux"

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Convergence of temperate and tropical stream fish assemblages
(Wiley, 2009) Carla Ibañez; Jérôme Belliard; Robert M. Hughes; Pascal Irz; André Kamdem‐Toham; Nicolas Lamouroux; Pablo A. Tedesco; Thierry Oberdorff
The hypothesis of convergence takes the deterministic view that community (or assemblage) structure can be predicted from the environment, and that the environment is expected to drive evolution in a predictable direction. Here we present results of a comparative study of freshwater fish assemblages from headwater streams in four continents (Europe, North America, Africa and South America), with the general objective of testing whether these assemblages display convergent structures under comparable environmental conditions (i.e. assemblage position in the stream longitudinal continuum). We tested this hypothesis by comparing species richness and trophic guilds of those stream fish assemblages represented in available data from multiple sites on each continent. Independent of phylogenetic and historical constraints, fish assemblage richness and trophic structure in the four continents converged along the stream continua to a substantial degree. For the four continents, assemblage richness increased, the proportion of invertivorous species decreased, and the proportion of omnivorous species increased from upstream to downstream, supporting theoretical predictions of the river continuum concept. However, the herbivore/detritivore and piscivore guilds were virtually absent from our small European and North American stream sites, unlike our African and South American stream sites. This divergence can be linked to differences in energy availability between temperate and tropical systems.
Fish habitat preferences in large streams of southern France
(Wiley, 1999) Nicolas Lamouroux; Hervé Capra; Marc Pouilly; Yves Souchon
1. Relationships between fish and their habitat over whole geographic regions, which are evident from studies of many streams and species, can improve understanding of lotic communities and provide reliable management tools. Nevertheless, most habitat preference studies have been based on single sites, and confined to small streams and to game species. 2. Regional habitat preference models, based on local velocity, depth and roughness, were developed for twenty‐four species and their size classes commonly found in large European streams. Fish surveys were conducted in six large streams in southern France over an 8‐year period. To limit the influences of habitat variables other than those studied, we estimated fish preferences within each survey and averaged this information across surveys. Preferences were fitted with confidence intervals and their sensitivity to field uncertainty was evaluated. 3. Most species and size classes had significant preferences for local habitat conditions which were consistent across the region. Habitat preferences predominant in the region overall were not always observed at any one site, but habitat conditions preferred on average in the region were never actually avoided locally. These results support the use of regional preference models for fish and the development of similar models for other lotic groups whose sensitivity to local habitat conditions has been reported elsewhere.
Predicting habitat suitability for lotic fish: linking statistical hydraulic models with multivariate habitat use models
(Wiley, 1998) Nicolas Lamouroux; Hervé Capra; Marc Pouilly
Quantitative estimates of habitat suitability in a stream reach generally result from coupling a hydraulic habitat model with a biological model of habitat use. The choice of each of these models has led to much controversy and discussion. Nevertheless, most habitat studies of lotic fish use a deterministic hydraulic model and univariate suitability curves. The objective of this contribution is to present a new, alternative method, which relates statistical hydraulic models to multivariate habitat use models. Our statistical hydraulic models predict the frequency distributions of hydraulic variables such as velocity or water depth within stream reaches. Their main advantage is the simplicity of their input variables (mainly discharge and average characteristics of the reach). Our multivariate formulation of habitat use models takes into account the local variability of fish habitat, predicting habitat suitability as a function of the frequency distribution of hydraulic variables within the local fish habitat. We demonstrate how these two model types can be linked to estimate habitat suitability in a stream reach as a function of discharge, focusing on two fish species (barbel, chub) in a regulated reach of the French Rhône River. The main limitations of this new method are a result of mathematical constraints associated with the linkage of the two modelling approaches and to uncertainties in transferring biological models from one stream to another because of insufficient data. Despite these limitations, the method provides solutions to several critical problems facing existing approaches and the simplicity of its input variables can accelerate the validation process of habitat models. Therefore, our first simulations strongly encourage: (i) the use of statistical approaches to describe hydraulic variables; and (ii) the study of multivariate habitat use models that apply to a large variety of streams. © 1998 John Wiley & Sons, Ltd.
Predicting habitat suitability for lotic fish: linking statistical hydraulic models with multivariate habitat use models
(Wiley, 1998) Nicolas Lamouroux; Hervé Capra; Marc Pouilly
Quantitative estimates of habitat suitability in a stream reach generally result from coupling a hydraulic habitat model with a biological model of habitat use. The choice of each of these models has led to much controversy and discussion. Nevertheless, most habitat studies of lotic fish use a deterministic hydraulic model and univariate suitability curves. The objective of this contribution is to present a new, alternative method, which relates statistical hydraulic models to multivariate habitat use models. Our statistical hydraulic models predict the frequency distributions of hydraulic variables such as velocity or water depth within stream reaches. Their main advantage is the simplicity of their input variables (mainly discharge and average characteristics of the reach). Our multivariate formulation of habitat use models takes into account the local variability of fish habitat, predicting habitat suitability as a function of the frequency distribution of hydraulic variables within the local fish habitat. We demonstrate how these two model types can be linked to estimate habitat suitability in a stream reach as a function of discharge, focusing on two fish species (barbel, chub) in a regulated reach of the French Rhône River. The main limitations of this new method are a result of mathematical constraints associated with the linkage of the two modelling approaches and to uncertainties in transferring biological models from one stream to another because of insufficient data. Despite these limitations, the method provides solutions to several critical problems facing existing approaches and the simplicity of its input variables can accelerate the validation process of habitat models. Therefore, our first simulations strongly encourage: (i) the use of statistical approaches to describe hydraulic variables; and (ii) the study of multivariate habitat use models that apply to a large variety of streams. © 1998 John Wiley & Sons, Ltd.