Efeito da densidade de povoamento na produtividade final em carpas (Cyprinus carpio var specularis) em fase de engorda, durante o verão Effect of population density on the productivity of carp (Cyprinus carpio var specularis), in the fattening stage, during the summer

O objetivo desta pesquisa foi estudar o efeito da densidade de povoamento na produtividade final, em carpas na fase de engorda, no período de verão. O delineamento foi inteiramente casualizado com três tratamentos (1; 0,5; e 0,33 peixes/m²) e três repetições. Os peixes foram estocados com peso e comprimento médios de 2,40 g e 5,35; 5,40 e 5,39 cm, respectivamente, nos tratamentos 1, 2 e 3, com 45 dias de idade. As dietas foram formuladas com 27% PB e 2925 kcal/kg de ração, sendo fornecidas diariamente, na quantidade de 3% do peso vivo. O comportamento dos tratamentos foi estudado por intermédio da análise de regressão. Os resultados para o comprimento e peso dos peixes foram 25,68; 28,66; e 31,21 cm e 255,00; 424,00; e 519,66 g, respectivamente. Os tratamentos 1 e 3 apresentaram modelo de regressão linear diferente do tratamento 2, que apresentou modelo quadrático. Na biomassa total, os resultados foram 1881; 1512; e 1302 kg/ha/período e os modelos de regressão significativos para os tratamentos 1e 3 foram lineares e para o tratamento 2 quadrático. A conversão alimentar apresentou modelo de regressão linear para todos tratamentos. Em condições similares, podem-se recomendar todas densidades sugeridas, com base na produção final e sobrevivência.<br>This study aimed to evaluate impact of stocking density on final productivity in the production of mirror common carp in fattening stage, during the summer. A completely randomized design with three treatments (1, .5, .33 fishes/m²) and three replicates was used. The fish were stocked with an average weight of 2.40 g and average length of 5.35, 5.40 and 5.39 cm, respectively, in the treatments 1, 2 and 3, with 45 days of age. The diets were formulated with 27% CP and 2925 kcal/kg of diet and supplied daily at a rate of 3% of body weight. Regression analysis was used to evaluate the behavior of each treatment. For the fish lengths, the results were 25.68, 28.66 and 31.21 cm, respectively. For the fish weights, the results were 255.00, 424.00, and 519.66 g. The treatments 1 and 3 showed a linear regression model, different from the treatment 2, that showed quadratic model. In the total biomass, the results were 1881, 1512 and 1302 kg/ha•period and the significant regression model were linear for treatments 1 and 3 and quadratic for treatment 2. The feed: gain showed a linear regression model for all treatments. In similar condition, it could be recommended all suggested densities, based on the final production and survival

Ecology and conservation status of endemic freshwater crabs in Lake Tanganyika, Africa

Sedimentation resulting from riparian deforestation has a wide range of detrimental effects on aquatic biodiversity, but predicting the full consequences of such disturbances requires an understanding of the ecosystem’s key functional components. We investigated the ecology and response to sedimentation of the diverse, endemic freshwater crabs of Lake Tanganyika, which may occupy important positions in littoral foodwebs. Our surveys revealed crab distribution patterns to be patchy, and that crabs can be locally abundant (0-28 individuals m−2). Crab densities decreased with depth and the dry mass of crab assemblages ranged from 0.0 to 117.7 g m−2. Comparisons among sites revealed significant effects of sedimentation on crab assemblage evenness, but provided no evidence that sedimentation has altered densities, incidence or species richness. The resilience of crabs to sedimentation might be related to their intraspecific dietary breadth. Stable isotope data (δ13C and δ15N) from crabs and their potential food resources indicated differences in trophic roles among endemic crab species. Overall, crabs occupy higher trophic positions than most other invertebrates, and they draw upon both benthic and planktonic energy pathways. The high biomass and top-predator status of some crab species suggests the potential for cascading effects on organisms lower in the food web

Milieux naturels, espaces sociaux

Robert Delort se distingue par l'ampleur et l'originalité du champ de sa réflexion historique. Il a abordé, grâce à sa maîtrise des méthodes de la recherche historique les plus diversifiées, de la linguistique à l'archéologie, des statistiques à l'analyse littéraire et iconographique, aussi bien l'histoire économique, sociale et politique du Moyen Âge, que celle des comportements ou encore de la biologie des espèces animales. Il n'est donc pas étonnant que Robert Delort ait orienté ses recherches et celles de ses élèves vers l'histoire des relations de l'homme avec son environnement, histoire dont il fut l'un des pionniers. Il a donné en particulier une impulsion décisive à l'histoire du monde animal. De plus, en élargissant la réflexion à la fois sur le plan chronologique et géographique bien au-delà de la période médiévale et de l'Occident européen, il propose une investigation globale du devenir historique qui séduit ses auditeurs et ses lecteurs en France comme à l'étranger. Le volume des études présentement offertes à Robert Delort par ses amis et élèves, s'ouvrant sur une préface de Jacques Le Goff, veut témoigner de la globalité méthodologique, thématique, chronologique et géographique de sa pensée historique

Landscape potential for pollen provisioning for beneficial insects favours biological control in crop fields

International audienceContext: The importance of landscape complexity for biological control is well-known, but its functional roles are poorly understood.Objectives: We evaluated the landscape capacity to provide floral resources for beneficial insects and its consequences for biological control in fields.Methods:The gut contents of adult hoverflies sampled in 41 cereal fields were analysed to determine which plant species are exploited. The relative value of each habitat in providing adequate pollen resources was evaluated by vegetation survey. Then 15 cereal fields were selected along a gradient of landscape complexity, where the abundance of aphids, hoverfly larvae and aphid parasitism was monitored. The habitat’s proportions in landscape buffers surrounding these fields were used as landscape descriptors and to assess the potential level of pollen resources provision (LP index).Results: Aphid abundance significantly decreased with an increase of the LP index mainly sustained by grassy strips and weeds in fields. However, hoverfly larvae abundance also decreased with the increasing LP index. The enhancement of the aphid parasitism rate with the LP index suggests that aphid parasitoids may benefit from the same floral resources as hoverflies. Their crop habitat specialism may give them a competitive advantage in fields where both aphid and floral resources are abundant.Conclusions: Complex interaction networks involved in biological control may disrupt the expected direct effects of floral resource provisioning for a focal beneficial species. We highlighted fields and grassy strips as habitats provisioning floral resources for which the LP index could be very helpful to optimize agroecological management strategies