Theoretical studies claim that if co-occurring species have very different mobilities this will result in greater small-scale
species richness, but empirical evidence is still lacking. We measured horizontal vegetative mobility (VM) of 48 herbaceous
understory species and estimated small-scale species richness in early and late successional boreonemoral herb-rich coniferous
forests in central Estonia. VM of erosulate growth forms was significantly higher than that of hemi-rosette and rosette growth
forms. Erosulate species exhibited higher mobility in young stands, but their relative and total cover was considerably higher
in old stands. Local plant richness (in 1 × 1 m plots) correlated positively with the variability of VM of species in a plot—larger
differences in VM resulted in a higher number of coexisting species. Our results thus suggest that species differences in
VM can contribute to small-scale coexistence by providing different ways to colonise empty space.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
PtdIns and PtdInsP kinases from normal erythrocyte (AA) membranes and sickle cell anaemia erythrocyte (SS) membranes have been characterized. PtdIns kinase was studied in native membranes under conditions in which PtdInsP kinase and PtdInsP phosphatase do not express any activity. Kinetic analysis of the AA and SS PtdIns kinases indicate similar Km values for PtdIns and ATP but higher Vmax values for SS PtdIns kinase. PtdInsP kinase was partially purified from erythrocyte ghosts by NaCl extraction. The kinetic parameters of PtdInsP kinase determined under these conditions were similar in AA and SS NaCl extracts. These data suggest the presence of some effector of PtdIns kinase in SS cell membranes, resulting in a greater activity of the enzyme. This leads consequently, to increase the PtdInsP pool and to activate PtdInsP kinase, in agreement with our previous observations of a greater [32P]Pi incorporation in both polyphosphoinositides in SS cells relatively to AA cells. 相似文献
The ability of embryonating eggs of Ascaris lumbricoides to avoid desiccation by reducing the loss of water through the egg shell was investigated. When exposed to desiccation the eggs lost water at a rate dependent upon the relative humidity and ambient temperature, eventually resulting in the collapse of the eggs and the death of the enclosed embryo. The eggs are small with a large surface to volume ratio. A low permeability to gaseous exchange thus restricts water loss while still ensuring an adequate supply of oxygen for embryonic development. Relative humidity did not appear to affect the rate of development. In eggs exposed to desiccation at various constant temperatures, the rate of water loss increased as an exponential function of increasing temperature. When eggs were exposed to various temperatures before exposure to desiccation at 22 C, the rate of water loss increased as a function of increasing pretreatment temperature. After exposure to 63–65 C, the ability of the egg shell to slow down the loss of water was destroyed. These phenomena suggest that there is not a simple “critical” or “transition” temperature, but a gradual melting of the complex mixture of components forming the lipid layer. 相似文献
The impact of the micropore width, external surface area, and meso‐/macropore size on the charging performance of electrochemical double‐layer capacitor (EDLC) electrodes is systematically investigated. Nonactivated carbon xerogels are used as model electrodes in aqueous and organic electrolytes. Monolithic porous model carbons with different structural parameters are prepared using a resorcinol‐formaldehyde‐based sol–gel process and subsequent pyrolysis of the organic precursors. Electrochemical properties are characterized by utilizing them as EDLC half‐cells operated in aqueous and organic electrolytes, respectively. Experimental data derived for organic electrolytes reveals that the respective ions cannot enter the micropores within the skeleton of the meso‐ and macroporous carbons. Therefore the total capacitance is limited by the external surface formed by the interface between the meso‐/macropores and the microporous carbon particles forming the xerogel skeleton. In contrast, for aqueous electrolytes the total capacitance solely depends on the total surface area, including interfaces at the micropore scale. For both types of electrolytes the charging rate of the electrodes is systematically enhanced when increasing the diameter of the carbon xerogel particles from 10 to 75 nm and the meso‐/macropore size from 10 to 121 nm. 相似文献
Addition of 15L-hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HPETE) to human leukocytes led to the formation of a novel series of compounds containing four conjugated double bonds. The yield of tetraenes was increased approx. 100-fold when ionophore A23187 (5 μM) was added simultaneously with 15-HPETE. The structure of the major tetraene was established by physical methods as well as by chemical degradation and found to be 5,6,15L-trihydroxy-7,9,11,13-eicosatetraenoic acid. 相似文献
Nymphs of Rhipicephalus appendiculatus and Hyalomma anatolicum anatolicum were fed on rabbits and maintained in the laboratory to allow moulting and further development. At specified time intervals from 0 to 500 days after engorgement, samples of ticks were ground individually in distilled water within the wells of an agglutination plate. A 0.1 ml aliquot was removed from each and levels of haemin and protein assessed from optical density values at specific wavelengths in a spectrophotometer.
Both protein and haemin levels showed an initial rapid decrease after engorgement; values did not fall to zero in either case but showed marked fluctuation throughout the study period. These fluctuations combined with the high standard errors of the results, made assessments of the physiological age of individual ticks impossible.
Such fluctuating values, however, suggested the possibility that haem biosynthesis might be taking place, and this was tested by injecting the radioactively-labelled haem precursor [4-14C]δ-amino laevulinic acid into engorged nymphs, immediately following their detachment. Both tick species revealed an incorporation of this compound into their haematin content, although neither incorporated the non-haem precursor [1-14C]2-amino isobutyric acid. These results indicate an ability of ticks to synthesize haem in vivo, although the underlying reasons for such a mechanism remain unknown. 相似文献