Authors:V. J. Debastiani, S. C. Muller, J. M. Oliveira, F. S. Rocha, M. C. Sestren-Bastos, and L. D. S. Duarte
The phylogenetic relationship among species may influence the mechanisms controlling local community assembly in ecological time. We analyzed the degree of recurrence of phylogenetic structure patterns in woody plant communities distributed along grassland-forest ecotones, across different vegetation types in southern Brazil, and the effect of phylogenetic pool size used to assess such patterns. Species frequency in quadrats distributed along grassland-forest ecotones was surveyed in different phytogeographic regions, where forests tend to expand over grasslands. We used principal coordinates of phylogenetic structure (PCPS) to evaluate the structure within vegetation quadrats divided into three habitat categories: grassland, forest edge and forest interior. Furthermore, phylogenetic structure measures were computed using different phylogenetic pool sizes. Our analyses showed consistent patterns in relation to habitat categories and to different phylogenetic pool sizes. Basal clades of angiosperms were associated with forest areas, while late-divergence clades were associated with grasslands. These results suggest that grasslands act as phylogenetic habitat filters to forest woody species, independently of species composition at each site and the phylogenetic pool. Rosanae and Asteranae act as vanguards of forest expansion over grasslands, while Magnolianae species tend to be restricted to forest. Our results shed light on the organization of ecological systems, providing evidence of recurrent phylogenetic structure patterns in ecotone plant communities at regional scale.
Authors:Cs. Tölgyesi, L. Erdős, L. Körmöczi, and Z. Bátori
Ecotones between plant communities have received considerable attention among ecologists in the context of fragmentation, climate change and the management of heterogeneous landscapes. However, the predictability of ecotone dynamics is low and the processes taking place within ecotones are still poorly understood. In this study we aimed to characterize the positional and structural dynamics of thirteen ecotones in an ecotone-rich steppe–wetland landscape of Hungary in relation to the inter-annual fluctuations of water regime and the gradients of elevation and of soil composition. According to our results, the ecotones between steppe and wetland communities were sharp and their positions coincided with those places in the landscape where the rate of change in elevation was the highest, confirming that microtopography is a major determinant of ecotone position. Soil boundaries were also detected, mostly downhill to the ecotones. Interestingly, the fluctuations of the water supply had no effect on the position of the ecotones but significantly influenced a structural ecotone parameter, the compositional contrast bridged by the ecotones. High water supply caused high contrast, while low supply went along with low contrast. We explain these changes by asymmetric sensitivities to edge effects. When the water supply was low, the wetland edges became similar to the steppe edges due to the decrease of wetland specialists and to the increase of steppe specialists, but steppe edges did not exhibit an opposite change in wet years, suggesting that steppe communities dominated over wetland communities. The asymmetry in the interaction between the two communities may have pushed the soil boundaries downhill to the ecotones but the currently steppe-like soil of wetland edges could also make wetland edges more sensitive to edge effects; thus, the cause-effect relationship is difficult to disentangle.
For the correction of losses due to true coincidences summing and edge effect, a simple method which is based on the ratio of a reference single -ray energy to that of cascade energies at near and far geometry is developed. The correction factors for several radioactive sources with simple and complex decay schemes are experimentally determined for three types of germanium detectors. It is shown that coincidence summing can be a complex effect and depends on the individual detector, the counting geometry and on the decay scheme of the radionuclide concerned.
A new concept, the flowing eluent walls (FEW) process, for segmentation of a non-segmented adsorbent bed, has been used for single- and multi-channel on-line overpressured-layer chromatography (OPLC). The FEW process leads to active and non-active regions on the adsorbent layer during the separation process. Mobile phase only is introduced to the non-active part of the layer whereas mobile phase and sample can be admitted to the active part, thus the non-homogeneous part of the adsorbent bed can be excluded from the separation process. The FEW configurations at the inlet side (FEW-I) eliminate the edge effect of OPLC in single-sample injections and the effect of sample-mixing between neighboring lanes in multi-channel separations. The FEW arrangements at the inlet and outlet sides (FEW-I/O) enable separate detection and collection of the components of the separation, and FEW lines solve the problems of joint detection of sample components and contaminants originating from the sealing material. One-channel OPLC with the FEW configuration is suitable for rapid isolation in different preparative ranges. Analytical and preparative TLC plates (20 cm × 20 cm) can be loaded with 5–25 mg and 25–125 mg, respectively. The multi-channel solution will be a tool for high-throughput analysis using efficient fine, superfine, or monolithic layers. The four and eight-channel versions can be used for high-throughput parallel analysis and for micro-preparative parallel isolation. The FEW concept provides the possibility of real multi-channel liquid chromatographic separation on a non-segmented layer and column shaped adsorbent bed.
Authors:M. Petrášová-Šibíková, T. Bacigál, and I. Jarolímek
The present study focuses on how spatial patch characteristics, such as patch area, shape and isolation, affect the natural species composition of hardwood floodplain forests. The natural species composition is defined according to species groups obtained using phytocoenological methods. The aim of the study was to establish the relationship between fragmentation indices and the number and proportion of species in each functional species group stated in this paper. This study is based on a dataset of 118 phytocoenological relevés sampled using the standard methodology of the Zürich-Montpellier School, ordered within the suballiance Ulmenion (mixed oak-elm-ash forests along the great rivers). The study area is situated in Central Europe, in the northern part of the Pannonian biogeographic region. The digital map of hardwood floodplain forests was rasterized to 25 m cell size. The FRAGSTATS software was used to obtain fragmentation indices, and generalised linear models tested the influence of forest patch fragmentation indices on species composition. Our analyses confirm that large hardwood floodplain forests are essential for natural species composition conservation, and that large fragment areas are highly susceptible to non-native species penetration. We also determined that small, compact fragments contain very valuable remnants of well-preserved natural hardwood floodplain forests with a high proportion of specialised Ulmenion species. However, disruption to hardwood floodplain forest natural borders engenders a greater threat to its natural species composition than decline in patch area, because disruption results in increased Shape index, increased contact with the surrounding environment, greater edge effect and a higher proportion of alien species in the forest community.
Bieringer, G. and K.P. Zulka. 2003. Shading out species richness: edgeeffect of a pine plantation on the Orthoptera (Tettigoniidae and Acrididae) assemblage of an adjacent dry grassland.