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171.
Disturbance and predation in an assemblage of herbivorous Diptera and algae on rocky shores 总被引:1,自引:0,他引:1
Carlos Robles 《Oecologia》1982,54(1):23-31
Summary Speculation about the effects of disturbance in marine benthic communities is often based on competition theory. Disturbances are thought to provision numerically depleted or competitively inferior species with resources associated with open substrate. However, disturbances that remove entire assemblages of sessile species also alter trophic structure, and thereby, influence the outcome of predator/prey relations. Aspects of community structure may be determined by patterns of disturbance and predation.The influence of disturbance and predation on the distribution and seasonality of blooms of ephemeral algae and associated Diptera was investigated with field experiments at several rocky beaches in central California. Blooms of ephemeral algae developed on high intertidal rock faces that were subject to severe seasonal disturbances caused by shifting sediment. These were subsequently colonized by the herbivorous larvae of several Diptera species for predictable periods each year. Other areas, without blooms, were not so disturbed.Experiments were done to determine if seasonal blooms were caused by seasonal disturbances that remove predators which otherwise might prevent the establishment of the Diptera/algae assemblage. The predators were crabs and limpets which eat both algae and larvae while foraging. Blooms of algae and larvae did not develop when limpets were transplanted to disturbed areas in periods between disturbances. Adjacent control areas did support blooms. Transplanted limpets did not survive periods of burial. When both limpets and crabs were excluded from treatment plots in undisturbed areas, blooms developed where they would not otherwise have occurred; controls remaied unchanged. Crabs and limpets differed in their effects on this assemblage. Crabs recruited quickly to the site of a bloom, but did not crop algal cover as closely, nor decrease larval density as much as the slowly recruiting limpets.The results suggest that disturbances favor blooms of some species by reducing predation. Severe localized disturbances increased the variability of the upper shore community by creating a patchwork of differing predator/prey abundances. 相似文献
172.
173.
The recent mathematical formalization of the concepts of matter and extrinsical energy, which are used for the relational
representation of biological systems, is employed in the analysis of the important experimental discoveries of Comorosanet al. related to low energy electromagnetic irradiations on enzyme substrates. By means of the present analysis one of the properties
inherent to the experimental phenomena is more precisely exposed, and theoretical developments corresponding to “energetical
evolutions” in a biological system (Leguizamón, 1976) may now have an experimental basis.
Important limitations are introduced for the validity of the commutativity and associativity of cartesian product of sets,
when they represent matter and its linked extrinsical energy. In connection with this last aspect, new important knowledge
is obtained for the relational mathematical representation of biological systems. 相似文献
174.
Pulmonary insufficiency secondary to outflow tract reconstruction remains an unsolved problem. Although a number of surgical techniques have been designed to avoid or palliate this condition, none so far has been satisfactory. This report describes a new composite stented porcine monocusp patch, which, because of its desirable hemodynamic characteristics, promises to yield stable and reproducible results. The clinical effectiveness of the patch is documented by its successful application in a patient with tetralogy of Fallot. 相似文献
175.
M-mode echocardiograms of two patients with bacterial endocarditis of approximately 4 months' duration showed dense echoes in the area of the aortic valve. In one patient, who had no prior abnormal cardiac findings, the echoes were clearly suggestive of valvular vegetations. The second patient, however, was known to have had aortic valve disease and a systolic murmur for more than a decade; therefore, dense echoes arising from the aortic valve also could have resulted from valvular calcification. In both patients, cross-sectional echocardiography provided important information. In the first patient, retrograde cardiac catheterization was prevented by large and highly mobile masses attached to the aortic cusps that prolapsed into the left ventricular outflow tract during diastole. Aortic valve replacement without further hemodynamic evaluation was recommended. In the second patient, whose blood cultures remained negative after the acute phase of his illness had been treated, cross-sectional echocardiography showed large vegetations on the aortic valve. Intraoperative findings confirmed the echocardiographic interpretation in each case. 相似文献
176.
The rate of inhibition of cyclic photophosphorylation in chloroplast thylakoids by the arginine reagent phenylglyoxal was enhanced in the light, i.e., under conditions where membrane energization occurred. Uncouplers, but not energy-transfer inhibitors, prevented the effect of light. Chemical modification of chloroplast thylakoids by phenylglyoxal under dark or in light conditions affected differently the light-induced exchange of tightly bound ADP. In both cases the exchange was less inhibited than photophosphorylation. Complete inhibition of ATPase activity of soluble CF1 was correlated with the incorporation of 8 mol [14C]phenylglyoxal per mol enzyme. About 50% of the incorporated radioactivity was lost at different rates depending on the buffer present and suggesting a change in the stoichiometry of the adduct from 2:1 to 1:1. Inhibition of ATPase and photophosphorylating activities of chloroplasts by modification with [14C]phenylglyoxal in the dark was associated with the incorporation of 1 and 2 mol reagent per mol membrane-bound CF1, respectively. In the light the rate of incorporation was enhanced and both reactions were inactivated when 2 mol were bound. In all the labelling experiments the radioactivity was mainly recovered from the α- and β-subunits. 相似文献
177.
Klaas A. Zachariasse Winchil L.C. Vaz Carlos Sotomayor Wolfgang Kühnle 《生物化学与生物物理学报:生物膜》1982,688(2):323-332
Human erythrocyte ghost membranes have been investigated using two intramolecular excimer probes, di(1-pyrenyl)propane and di(1-pyrenylmethyl) ether. Values for the viscosity of the direct probe environment in the ghost membranes range from 76 cP at 37°C to 570 cP at 5°C, as reported for di(1-pyrenyl)propane, with liquid paraffin as the reference solvent. For the activation energy of the excimer formation process, determined here mainly by the viscosity of the medium, a value of 37 kJ/mol is obtained. The other probe molecule reports a higher local viscosity, 133 cP at 37°C, as well as a higher activation energy of excimer formation, 54 kJ/mol. Neither thermotropic phase transitions nor temperature hysteresis effects are observed within the temperature range (0 to 40°C) studied. From the vibrational structure of the fluorescence spectrum of di(1-pyrenylmethyl) ether, a polarity of the probe environment close to that of hexanol () results for the erythrocyte ghost membranes. The polarity measured in egg phosphatidylcholine membranes and in multibilayers of dimyristoylphosphatidylcholine is slightly larger, comparable to that of butanol (), whereas a polarity comparable to that of methanol () is observed for aqueous micellar solutions of sodium dodecyl sulphate. Further, from the wavelength shifts in the absorption spectrum of di(1-pyrenyl)propane and di(1-pyrenylmethyl) ether, the polarizability of the probe surroundings can be determined, leading to a surprisingly high value for the apparent refractive index. This is attributed to a high local density of the direct environment of the probe, for which a location between the membrane/water interface and the unpolar bilayer mid-plane is deduced. 相似文献
178.
Marcia R. Brochetto-Braga Suely Lopes Gomes JoséCarlos Da Costa Maia 《Archives of biochemistry and biophysics》1982,217(1):295-304
Using a combination of Chromatographic and sucrose density gradient techniques under carefully controlled conditions of pH and protease inhibitors, we demonstrate that there is only one form of adenosine 3′,5′-monophosphate-dependent protein kinase in the cytosol fraction of the Blastocladiella emersonii zoospore. If any of these conditions are omitted during extract preparation, one obtains what are apparently multiple forms of the enzyme, which are in reality artifacts due to extensive endogenous proteolytic activity. This endogenous protease is stimulated by alkaline pH and inhibited by antipain. The zoospore protein kinase is similar to type II protein kinase from mammalian cells in several aspects including Chromatographic behavior on DEAE-cellulose column, conditions for subunit dissociation and reassociation, as well as the molecular weight value of the regulatory subunit. 相似文献
179.
The gas-liquid-chromatographic retention-times and the mass-spectral features of partially methylated d-galactononitrile acetates are reported. Distinctive fragmentation of each of the mono-O-methyl derivatives allows their identification, and the results are applicable to the same substituted derivatives of the other aldohexoses. A new fragmentation-pathway, typical of the acetylated and the O-acetyl-O-methylaldononitriles, is proposed in order to justify previously unexplained fragments. This fragmentation competes with the known ones in derivatives that do not carry vicinal methoxyl groups. 相似文献
180.