AimMetacommunities are assembled through a combination of local and regional processes, with the relative importance of the drivers of assembly depending on ecological context. Global change can alter community assembly at both local and regional levels, potentially shifting communities into disequilibrium with their local environmental conditions. In this study, we evaluated the spatial variation in environmental filtering and habitat matching of 1078 riverine macroinvertebrate communities distributed across nine ecoregions within the conterminous United States.LocationConterminous United States.TaxonFreshwater macroinvertebrates.MethodsWe first quantified spatial patterns in environmental filtering, habitat matching, and functional trait diversity. We then used boosted regression trees to identify (1) functional trait predictors of environmental filtering and habitat match and (2) environmental, landscape, and network variables that predict functional trait abundances.ResultsOur results demonstrated that environmental filtering but not habitat matching varied strongly by ecoregion. We also found that functional trait diversity varied by ecoregion, but not as strongly as the signatures of environmental filtering. We did not identify consistent functional trait predictors for both environmental filtering and habitat matching, with trait predictors instead varying by individual traits, trait categories, and ecoregions. Notwithstanding inconsistent trait predictors, environmental filtering was primarily influenced by habitat preference traits while habitat matching was primarily influenced by both habitat preference and dispersal traits. Predictors of functional traits also varied by trait category and ecoregion, with habitat preference and dispersal traits primarily influenced by network variables.Main conclusionsOur study demonstrates the contingent patterns and drivers of environmental filtering and habitat matching on a macroecological scale. We aim for this work to provide the foundation on which trait-environment relationships can be further quantified and causal explanations established in the context of community disequilibrium and applied to conservation and management of freshwater systems.
Aim Metacommunities are assembled through a combination of local and regional processes, with the relative importance of the drivers of assembly depending on ecological context. Global change can alter community assembly at both local and regional levels, potentially shifting communities into disequilibrium with their local environmental conditions. We evaluated the spatial variation in environmental filtering and habitat matching of 1078 riverine macroinvertebrate communities distributed across nine ecoregions. Location Conterminous United States. Taxon Freshwater macroinvertebrates. Methods Patterns in environmental filtering, habitat matching and functional trait diversity were compared among ecoregions. Boosted regression trees were used to identify (1) functional trait predictors of environmental filtering and habitat matching and (2) environmental, landscape and network variables that predict functional trait abundances. Results Environmental filtering but not habitat matching varied strongly by ecoregion. Functional trait diversity varied by ecoregion, but not as strongly as the signatures of environmental filtering. Functional trait predictors of environmental filtering and habitat matching were not consistent, with trait predictors instead varying by individual traits, trait categories and ecoregions. Notwithstanding inconsistent trait predictors, environmental filtering was primarily influenced by habitat preference traits, whereas habitat matching was primarily influenced by both habitat preference and dispersal traits. Predictors of functional traits also varied by trait category and ecoregion, with habitat preference and dispersal traits primarily influenced by network variables. Main conclusions Our study demonstrates the contingent patterns and drivers of environmental filtering and habitat matching on a macroecological scale. We provide the foundation on which trait–environment relationships can be further quantified and causal explanations established in the context of community disequilibrium and applied to conservation and management of freshwater systems.
Seismic vibrator is one of the most widely used equipments in exploration field. In recent years, with the development of exploration field, as well as the growing needs of high quality seismic data, the seismic vibrator's tonnage has increased a lot, which makes the stress of the vehicle frame very complicated in working state. And some local structure of the vehicle frame often appears crack phenomenon in working state. Therefore, the dynamic characteristic analysis is essential to the Seismic vibrator. In this paper, the finite element model of vehicle frame is established by ANSYS software. Through the modal analysis, the natural frequencies are obtained, and each vibration modes are analyzed. On the basis of the modal analysis, the modal neutral file of the vehicle frame is established. Using the data transfer function between ANSYS and ADAMS, the rigid-flexible coupling multi-body model is built for the dynamics simulation of the seismic vibrator. In this model, the stiffness and damping of air springs, hydraulic oil and soil are simulated by the spring-damper in the ADAMS software. The dynamic characteristics of vehicle frame under excited forces with different amplitude are obtained and analyzed. The stresses for some of the hot spots of the vehicle frame are extracted, which can be used to analyze the dynamic failure of the vehicle frame.
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