We investigated patterns of trait-based community assembly in grasslands sampled along a moisture gradient (216 species) using three continuous species-level traits (maximum species height, minimum species height, seed mass), as well as seven nominal traits (flowering phenology, fruit type, pollen vector, clonal growth organs – CGOs, branching type, leaf distribution, lateral spread), some of which are unusual in that a species may possess more than one state per trait simultaneously (e.g. CGO). Additionally, this study tests whether patterns of assembly vary with plot biomass and moisture using both presence-absence and abundance-weighted analyses (two plot sizes: 25 × 25 cm, 75 × 75 cm). Plant species in these grasslands were randomly organized with respect to both maximum and minimum species height; however, coexisting plant species had a significantly smaller mean seed mass than expected by chance, and were significantly convergent in seed mass, consistent with observations from one previous study, and with theory related to environmental or competitive filtering. These patterns were consistent across plot sizes, and were similar whether analyses were abundance-weighted or not, although partitioned analyses show that these patterns are most pronounced in wet grasslands. Grasslands were non-randomly assembled with respect to five of our ten traits including seed mass, fruit type, CGO, branching type and leaf distribution. Among these, only patterns of branching type clearly conformed to the predictions from Limiting Similarity Theory, suggesting that variation in this trait may contribute to species coexistence in these grasslands. In two cases (fruit type, branching type), results differed in significance depending on whether analysis used presence-absence or abundance data; incorporating abundance may be more relevant, however, cover-based abundance measures in small plots can bias trait representation in favour of size over ramet number. In general, patterns were consistent across the two plot sizes. For four traits (seed mass, flowering phenology, leaf distribution and lateral spread) plot-level effect sizes of our tests varied significantly with plot-level biomass production; the slope of these relationships was positive for seed mass, but negative for flowering phenology, leaf distribution and lateral spread. For seven of ten traits, plot-level effect sizes varied significantly with plot-level soil moisture, with positive regression slopes for some traits (flowering phenology, leaf distribution), and negative slopes for others (minimum height, seed mass, fruit type, pollen vector, CGO). These results indicate that community assembly rules related to different functional traits can be responsive to variation in either biomass or soil moisture, or both.
Low detectability of small nocturnal carnivores and biases associated to different census methods hamper the interpretation and reliability of the results of censuses and habitat studies of many cryptic and elusive species, especially because of false-negatives and/or lack of negatives. In order to overcome this problem, methodologies based on the use of presence-only data have been used to predict distribution of species. In this paper, we used presence data of two abundant nocturnal carnivores to test for segregation in their habitat. We compared niche overlap between the common genet and the stone marten at two different spatial scales, home range scale and landscape scale, through logistic regression analyses using presence-only data from Biscay, an area in which both species are common and widespread. We found great niche overlap at both spatial scales, but in spite of it logistic regression analyses found statistically significant differences in the predictor values of some variables. Habitat of genets and stone marten was differentiated by areas with dense vegetation that were of importance for genets, and open areas that were characteristic of stone marten habitat. We suggest that competition between the two species causes the observed segregation.
The aim of the paper is further presentation of some destructive and non-destructive methods for investigation of mechanical properties of natural stone quarried and used as a building material in Bohemia in the past. Tested samples were made both from virgin material from existing quarries (e.g. sandstone from Hořice) and from material acquired from historical constructions (various sandstones from the Charles Bridge in Prague), which was built-in for a long time. The flexural strength, the compressive strength and Young modulus were obtained from basic destructive tests. Before performing these tests the identical samples were investigated non-destructively by ultrasound and so called peeling test so that the two ways of testing could be compared in the end. and Obsahuje seznam literatury
The intra- and interspecific variability in the West Palaearctic tibialis-group species of the subgenus Pandasyopthalmus (Diptera: Syrphidae: Paragus) was analysed. Novel immature and molecular characters were studied and the traditionally used adult characters reviewed with the aim of establishing the status of the most widespread taxa of the tibialis-group in the Palaearctic region. Moreover, a review of the morphology of the larvae of the subgenus Pandasyopthalmus is also presented and includes the first description of the chaetotaxy of the larval head of Syrphidae. The larval morphology showed a continuum between two extremes. There is intraspecific variability in the male genitalia characters typically used for diagnostic species identification in this group. Molecular characters of the mitochondrial cytochrome c-oxidase subunit I (COI) was invariant for the West Palaearctic Pandasyopthalmus taxa analysed. Despite the fact that no great differences were found when compared with Afrotropical tibialis-group individuals (uncorrected pairwise divergence 0.17-0.35%), the divergences of the West Palaearctic vs. Nearctic and Austral-Oriental tibialis-group taxa varied between 1.15-2.75% (uncorrected pairwise divergence). Molecular characters of the nuclear ribosomal internal transcribed spacer region (ITS2) revealed several molecular haplotypes of a dinucleotide repeat that was not constrained to morphospecies or to populations of the same geographic origin. The closely related and morphologically similar species of the tibialis-group known from the West Palaearctic region are separable in most cases only by the shape and size of male postgonites. The results of this study support the presence of a single polymorphic taxon in the West Palaearctic region (or a very recent origin of the taxa studied). Moreover larval morphology and the lack of a clear relation between ITS2 haplotypes and the geographic distribution or adult morphology, support the taxonomic implications of barcode taxonomy based on mitochondrial DNA for this species-group of Syrphidae.
Inspired by Rakonczai et al. [8], we use autocopulas for the testing of linearity against Markov-switching type of nonlinearity and remaining nonlinearity. They applied this autocopula approach to testing heteroscedasticity in AR-ARCH model. Given a strictly stationary time series Yt, a k-lag autocopula is a bivariate joint distribution function of the random vector (Yt, Yt-k). Our contribution is in extending the idea to test the linearity against Markov-switching type of nonlinearity and remaining nonlinearity [5,6] in order to avoid classical, time-consuming tests.
The dynamics of the mistuned model of the tests bladed disc with double perodicity was experimentally investigated. The mistuning arised due to the implemantation of two bunches of blades with damping heads fixed on opposite ends of the diameter. The dry friction effect in the heads was treated. The scale for measurement of the electromagnetic force acting on the disc was designed. It enables to analyse the real electromagnetic excitation of the disc under rotation and evaluation of the FRF characteristics from measured blade responses under rotation. The identified eigenfrequencies and damping constan ts served as indicators for assessment of stiffening and damping effects of the friction couplings in the heads. and Obsahuje seznam literatury
The aim of this paper is the analysis of temporal changes in multipath propagation errors on the pseudorange GNSS signal used for positioning, and its behavior during the calendar year (the quality of signal depends on e.g. foliage of trees, changes reflectivity surfaces due to rain or snow, etc.). The analysis was performed on data measured on a stationary point at Geodetic Observatory Pecný at Ondřejov, where one day was chosen as a constant time unit. Given the relatively highly unfavorable configuration of the experiment, RMS value of multipath is up to 60 cm on C1 and 40 cm on C2. These values vary with different weather conditions between 10 and 20 cm.