Search

We studied fish size structure by using mean size, size diversity, and the slope of linear size spectra of six common European fish species along large-scale environmental gradients. We further analyzed the response of these three size metrics to environmental variables and to density-dependent effects, i.e., relative estimates of abundance (catch per unit effort, CPUE). We found differences in the strength of main predictors of size structure between the six species, but the direction of the response was relatively similar and consistent for most of the size metrics. Mean body size was negatively related to temperature for perch (Perca fluviatilis), roach (Rutilus rutilus), and ruffe (Gymnocephalus cernuus). Lake productivity (expressed as total phosphorus concentration) and lake depth were also predictors of size structure for four of six species. Moreover, we found a strong density dependence of size structure for all species, resulting in lower mean body size and size diversity and steeper size spectra slopes when density dependence increases. This suggests that density dependence is a key driver of fish size structure. Nous avons etudie la structure de tailles des poissons en utilisant la taille moyenne, la diversite des tailles et la pente des distributions lineaires des tailles de six especes communes de poissons europeens sur des gradients environnementaux a large echelle. Nous avons ensuite analyse la reponse de ces trois metriques de tailles aux variables environnementales et a des mesures de densite-dependances, i.e. estimations relatives de l'abondance (captures par unite d'effort, CPUE). Nous avons decele des differences quant a l'importance des principales variables explicatives de la structure de taille entre les six especes, mais le sens de la reponse etait relativement comparable et coherent pour la plupart des parametres associes a la taille. La taille moyenne du corps presentait une relation negative avec la temperature pour la perche (Perca fluviatilis), le gardon (Rutilus rutilus) et la gremille (Gymnocephalus cernuus). La productivite du lac (representee par la concentration de phosphore total) et la profondeur du lac etaient egalement des variables explicatives de la structure de tailles pour quatre des six especes. En outre, nous avons constate une forte densite dependance de la structure de tailles de toutes les especes qui se traduit par des tailles du corps moyennes et une diversite de tailles plus faibles, ainsi que des pentes plus grandes des distributions de tailles avec l'augmentation de la densite. Ces resultats donnent a penser que la densite dependance est un facteur cle de la structure de tailles des poissons., Introduction Size structure has traditionally been used for elucidating trophic interactions and patterns of energy transfer through trophic levels (Jennings et al. 2002; Woodward et al. 2005; Trebilco et al. [...]

Planktivorous and benthivorous fish have been documented to influence the density and size structure of their prey communities in lakes. We hypothesized that piscivorous fish modify their prey fish communities in the same way and sought to find evidence for such predation effects from a comparison across 356 lakes located in nine European ecoregions. We categorized individual fish as being piscivore, nonpiscivore, or prey of piscivores, depending on species and individual size. We calculated piscivore, nonpiscivore, and piscivore prey densities, respectively, and fit linear abundance size spectra (SS) on lake-specific piscivore, nonpiscivore, and piscivore-prey size distributions. Multiple linear regressions were calculated to quantify the effect of piscivore density and SS slopes on nonpiscivore and piscivore-prey densities and SS slopes by accounting for potentially confounding factors arising from lake morphometry, productivity, and local air temperature. Piscivore density correlated positively with piscivore-prey density but was uncorrelated with density of nonpiscivores. Across a subset of 76 lakes for which SS slopes of piscivores were statistically significant, SS slopes of piscivores were uncorrelated with SS slopes of either nonpiscivores or piscivore prey. However, densities of piscivores, nonpiscivores, or piscivore prey were a significant negative predictor of SS slopes of the respective groups. Our analyses suggest that direct predation effects by piscivorous fish on density and size structure of prey fish communities are weak in European lakes, likely caused by low predator-prey size ratios and the resulting size refuges for prey fish. In contrast, competition may substantially contribute to between-lake variability in fish density and size. Il est documente que les poissons planctonivores et benthivores influencent la densite et la structure de taille des communautes de leurs proies dans les lacs. Nous avons postule que les poissons piscivores modifient leurs communautes de poissons-proies de la meme maniere et tente de trouver des indices de tels effets de la predation en comparant 356 lacs situes dans neuf ecoregions europeennes. Nous avons classe chaque poisson en tant que piscivore, non piscivore ou proie de piscivores, selon son espece et sa taille. Nous avons calcule les densites des poissons piscivores, non piscivores et proies de piscivores, respectivement, et cale les spectres lineaires d'abondance selon la taille (SS) sur les distributions de tailles des poissons piscivores, non piscivores et proies de piscivores propres a chaque lac. Des regressions lineaires multiples ont ete calculees pour quantifier l'effet de la densite de poissons piscivores et des pentes des SS sur les densites des poissons non piscivores et des proies de piscivores et de leurs pentes des SS, en tenant compte de facteurs de confusion potentiels decoulant de la morphometrie et de la productivite du lac et de la temperature locale de l'air. La densite des piscivores etait positivement correlee a la densite des proies de piscivores, mais non correlee a la densite des non-piscivores. Pour un sous-ensemble de 76 lacs dont les pentes de SS des piscivores etaient statistiquement significatives, ces dernieres n'etaient pas correlees aux pentes de SS des non-piscivores, ni des proies de piscivores. Les densites des piscivores, des non-piscivores et des proies de piscivores constituaient toutefois une variable explicative negative significative des pentes de SS de leurs groupes respectifs. Nos analyses donnent a penser que les effets directs de la predation par les poissons piscivores sur la densite et la structure de taille des communautes de poissons-proies sont faibles dans les lacs europeens, probablement en raison de faibles rapports des tailles de predateurs et proies et des tailles-refuges qui en resultent pour les poissons-proies. En revanche, la concurrence pourrait contribuer de maniere sensible aux variations de la densite et de la taille des poissons entre les lacs. [Traduit par la Redaction], Introduction Following two seminal papers on the effect of predation by planktivorous fish on zooplankton communities (Hrbacek et al. 1961; Brooks and Dodson 1965), pelagic food webs have long been [...]

Transformation of the natural land cover is one of the most important global changes. Changes in land use may strongly affect ecosystem functions and biodiversity by directly or indirectly modifying key structural properties. Here, we examined the effects of land use on the size structure of fish communities in subtropical Uruguayan streams. We analysed the suitability of non-taxonomic, size-related variables as a tool to elucidate shifts in stream fish assemblages along a gradient in land use change. We also tested some taxonomic variables (e.g., species richness and species diversity) to compare their response with size-related variables. In the more anthropogenic disturbed basins (i.e., dominance of urban and agricultural land use), we found higher size diversity, slope of size spectrum (flatter slopes) and total range of fish length, whereas higher species richness, fish abundance and species diversity were detected in more pristine stream basins (i.e., dominance of rangelands). In combination with traditional taxonomic variables, size-related variables of fish communities in streams may be effective tools in evaluating the changes occurring in freshwater ecosystems associated with anthropogenic changes in land use. La transformation de la couverture naturelle des sols est un des changements planetaires les plus importants. Les changements d'utilisation du sol peuvent avoir une grande incidence sur les fonctions et la biodiversite des ecosystemes en modifiant directement ou indirectement des proprietes structurales cles. Nous examinons les effets de l'utilisation du sol sur la structure selon la taille des communautes de poissons dans des cours d'eau uruguayens subtropicaux. Nous avons analyse l'adequation de variables non taxonomiques reliees a la taille comme outil pour elucider les modifications des assemblages de poissons lotiques le long d'un gradient de changement de l'utilisation du sol. Nous avons egalement teste certaines variables taxonomiques (p. ex. richesse et diversite specifiques) pour comparer leur reaction a celle de variables reliees a la taille. Dans les bassins les plus perturbes par l'activite humaine (c.-a-d. oU dominent des utilisations urbaines et agricoles des sols), nous avons constate une plus grande diversite de tailles, des pentes moins inclinees du spectre de tailles et une plus grande fourchette totale de longueurs des poissons, alors qu'une plus grande richesse specifique, une plus grande abondance de poissons et une plus grande diversite specifique ont ete observees dans les bassins de cours d'eau moins perturbes (c.-a-d. oU dominent les parcours naturels). Combinees a des variables taxonomiques traditionnelles, les variables reliees a la taille des communautes de poissons dans les cours d'eau pourraient constituer des outils efficaces pour evaluer les modifications aux ecosystemes d'eau douce associees aux changements d'utilisation des sols d'origine humaine. [Traduit par la Redaction], 1. Introduction A key driver of global change is the transformation of the natural land cover, with half of the terrestrial surface of the Earth already being transformed by human [...]

Body size is a master trait in aquatic ecosystems to complement traditional taxonomic diversity measures. Based on a dataset of fish communities from 40 Turkish lakes covering a wide environmental gradient and continental to dry cold steppe to Mediterranean climates, we elucidated the key variables controlling size diversity, geometric mean length and number of size classes in the fish community. We further examined how these three size measures were related to species diversity and species richness. A GLM analysis revealed that both size diversity and the number of sizes were strongly related to taxonomic diversity and richness. Furthermore, fish size diversity decreased with decreasing annual precipitation, while the number of size classes increased with increasing lake area but decreased with increasing salinity. The geometric mean length of fish decreased with total nitrogen and increased with altitude. The inter-relatedness between the number of size classes and lake area suggests an increase in fish niches with increasing ecosystem size, while fish are smaller and have fewer size classes in lakes with higher salinity. We conclude that size measures provide valuable integrating information on lake fish diversity; thus, they may complement, but not replace, more traditional taxonomic fish measures. [ABSTRACT FROM AUTHOR]