Search results for "niche"
showing 10 items of 1201 documents
Variations spatiales et temporelles des communautés adventices des cultures annuelles en France
2007
Although arable weed species are particularly well adapted to habitats characterised by high levels of disturbance(ploughing, harvest), the degree and rate at which agro-ecosytems have been transformed in the last 50 years in Europe(use of chemicals, changes in crop rotations) has led to profound changes in the composition and diversity of arable weedcommunities. This thesis provides an update on the composition and diversity of weed communities that can be foundacross the main crop types and regions of France. It also addresses two objectives i) applying (community) ecologytheories for the analysis and interpretation of spatial and temporal variations in weed communities and ii) using the …
Differing trophic niches of three French stygobionts and their implications for conservation of endemic stygofauna
2019
1. Groundwater ecosystems represent the greatest proportion of unfrozen freshwa- ter on Earth and harbour high numbers of rare taxa with restricted distributions. Stygofaunal abundance, species richness, and ecology play essential roles in groundwater ecosystem services and functioning, as well as providing an impor- tant contribution to global biodiversity. However, as global depletion and contam- ination of groundwater pose serious and often irreversible threats to stygofauna, more information is urgently needed about the ecology of rare groundwater spe- cies to guide effective strategies for their conservation or restoration. 2. In this study, analyses of carbon and nitrogen stable isoto…
The effect of fish life-history structures on the topologies of aquatic food webs
2021
Biological organisms can vastly change their ecological functionality due to changes in body size and diet across their life. Consequently, it has been increasingly recognized that to attain sufficient biological realism, food webs may need to include life-history structures. The objective of the work is to study theoretically whether and how the inclusion of life-history structures affects the food web topology. Topological research was done by applying network theory metrics for three different food web types with two different sizes that were generated by using the niche-model. The dynamical modeling was performed by using an allometric trophic network modeling approach. The different ty…
Species composition modulates seedling competitiveness of temperate tree species under hemiboreal conditions
2020
Abstract Mixed stands are advised for reduction of impacts of natural hazards, and species composition can largely affect sustainability and productivity of the stands. Early development of a stands after a stand-replacing disturbance can have considerable legacy effects on growth via alterations in the diversity-productivity relationships. Accordingly compatibility of growth and competitiveness of different species is one of the key issues for susceptibility of mixed stands. A two-year chamber experiment was conducted to assess early growth and intra- and inter-specific competition for light and soil resources among the seedlings of temperate tree species simulating the predicted effect of…
Testing macroecological abundance patterns:the relationship between local abundance and range size, range position and climatic suitability among Eur…
2020
Aim A fundamental question in macroecology centres around understanding the relationship between species' local abundance and their distribution in geographical and climatic space (i.e. the multi-dimensional climatic space or climatic niche). Here, we tested three macroecological hypotheses that link local abundance to the following range properties: (a) the abundance-range size relationship, (b) the abundance-range centre relationship and (c) the abundance-suitability relationship. Location Europe. Taxon Vascular plants. Methods Distribution range maps were extracted from the Chorological Database Halle to derive information on the range and niche sizes of 517 European vascular plant speci…
Community structure affects trophic ontogeny in a predatory fish.
2016
While most studies have focused on the timing and nature of ontogenetic niche shifts, information is scarce about the effects of community structure on trophic ontogeny of top predators. We investigated how community structure affects ontogenetic niche shifts (i.e., relationships between body length, trophic position, and individual dietary specialization) of a predatory fish, brown trout (Salmo trutta). We used stable isotope and stomach content analyses to test how functional characteristics of lake fish community compositions (competition and prey availability) modulate niche shifts in terms of (i) piscivorous behavior, (ii) trophic position, and (iii) individual dietary specialization. …
Resource availability and competition shape the evolution of survival and growth ability in a bacterial community
2013
Resource availability is one of the main factors determining the ecological dynamics of populations or species. Fluctuations in resource availability can increase or decrease the intensity of resource competition. Resource availability and competition can also cause evolutionary changes in life-history traits. We studied how community structure and resource fluctuations affect the evolution of fitness related traits using a two-species bacterial model system. Replicated populations of Serratia marcescens (copiotroph) and Novosophingobium capsulatum (oligotroph) were reared alone or together in environments with intergenerational, pulsed resource renewal. The comparison of ancestral and evol…
Macrophytes shape trophic niche variation among generalist fishes.
2017
Generalist species commonly have a fundamental role in ecosystems as they can integrate spatially distinct habitats and food-web compartments, as well as control the composition, abundance and behavior of organisms at different trophic levels. Generalist populations typically consist of specialized individuals, but the potential for and hence degree of individual niche variation can be largely determined by habitat complexity. We compared individual niche variation within three generalist fishes between two comparable lakes in the Czech Republic differing in macrophyte cover, i.e. macrophyte-rich Milada and macrophyte-poor Most. We tested the hypothesis that large individual niche variation…
Were climatic changes a driving force in hominid evolution?
2000
International audience; A comparison of externalist and internalist approaches in hominid evolution shows that the externalist approach, with its claim that climate was responsible for the appearance of bipedalism and hominization, now seems to be ruled out by the biological, palaeogeographical, palaeontological and palaeoclimatic data on which it was based. Biological data support the embryonic origin of cranio-facial contraction, which determined the increase in cranial capacity and the shift in the position of the foramen magnum implying bipedalism. In the internalist approach, developmental biology appears as the driving force of hominid evolution, although climate exerts a significant …
Are there so many congeneric species of chironomid larvae in a small stream?
2018
The co-occurrence of larvae of congeneric chironomid species is common in natural stream assemblages, and raises the problem of finding mechanisms to explain the co-existence of species with similar ecological requirements. In this contribution, we explored the co-occurrence of chironomid larvae belonging to congeneric species within four genera of chironomids: Cricotopus, Eukiefferiella, Orthocladius and Rheocricotopus (with 2, 7, 2 and 4 species, respectively) in the headwaters of a small Mediterranean calcareous stream. Due to the intrinsic, natural spatial and temporal variability in these habitats, we studied three different sites at two different seasons within the annual hydrological…