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81.
The energy and nutrient content of most agricultural crops are as good as or superior to natural foods for wild geese and they tend to be available in agricultural landscapes in far greater abundance. Artificial grasslands (fertilised native swards and intensively managed reseeds) offer far superior quality forage and higher intake rates than seminatural or natural grasslands. The availability of such abundant artificial food explains the abandonment of traditional habitats for farmland by geese over the last 50–100 years and favours no reduction in current levels of exploitation of agriculture. Continental scale spatial and temporal shifts among geese undergoing spring fattening confirm their flexibility to respond rapidly to broadscale changes in agriculture. These dramatic changes support the hypothesis that use of agricultural landscapes has contributed to elevated reproductive success and that European and North American farmland currently provides unrestricted winter carrying capacity for goose populations formerly limited by wetlands habitats prior to the agrarian revolution of the last century. 相似文献
82.
Osnat Malka Shiri Shnieor Abraham Hefetz Tamar Katzav-Gozansky 《Behavioral ecology and sociobiology》2007,61(3):465-473
In most social insects, worker sterility is reversible, and in the absence of the queen, at least some workers develop ovaries and lay male-destined eggs. In the honeybee, reproductive workers also produce queen-characteristic mandibular and Dufour’s pheromones. The evolution of worker sterility is still under debate as to whether it is caused by queen manipulation (queen-control hypothesis) or represents worker fitness maximization (worker-control hypothesis). In this study, we investigated whether worker fertility and royal pheromone production are reversible under the queen influence. To that effect, we induced ovary activation and queen pheromone production in workers by rearing them as queenless (QL) groups. These workers were subsequently reintroduced into queenright (QR) microcolonies for 1 week, and their ovary status and queen pheromone levels were monitored. Workers reintroduced into QR, but not QL colonies, showed a clear regression in ovary development and levels of the queen pheromones. This is the first demonstration that worker sterility and/or fertility is reversible and is influenced by the queen. These results also emphasize the robustness of the coupling between ovary activation and royal pheromone production, as well as lending credence to the queen-control hypothesis. The dynamics of queen pheromone production in QL workers supports the role of Dufour’s gland pheromone as a fertility signal and that of the mandibular gland pheromone in dominance hierarchies.The two authors, Osnat Malka and Shiri Shnieor, contributed equally to this work. 相似文献
83.
84.
The vertical diffusion of NaI solution from a horizontal fracture into and within the surrounding matrix was tracked and quantified over time using an artificially fractured chalk core (30x5 cm) and a second-generation X-ray computed tomography (CT) scanner. The different tracer-penetration distances imaged in the matrix above and below the horizontal fracture are indicative of a greater tracer mass penetrating into the lower matrix. The enhanced transport in the matrix below the fracture was related to the Rayleigh-Darcy instability induced by the density differences between the heavier tracer solution in the fracture (1.038) and the distilled water that had initially resided in the matrix. Our observations suggest that below the fracture, the tracer is propagated by an advection-diffusion process that is characterized by both higher rates and higher concentrations relative to its propagation by diffusion above the fracture. The experimental results suggest that the prediction of contaminant migration in a rock intersected by both vertical and horizontal (e.g. along bedding planes) fractures is difficult because of density effects that result in different solute-penetration rates. 相似文献
85.
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87.
Abraham H. Parola Daniel Kost Gila Katsir Edna Ben-Izhak Monselise Rivka Cohen-Luria 《The Environmentalist》2005,25(2-4):103-111
Summary In previous publications, we reported that sinusoidal varying magnetic fields (SVMF) modify the activity and dynamics of the
malignancy marker adenosine deaminase, and enhance the proliferation of chick embryo fibroblasts (CEF). While the SVMF examined
by us (50, 60 & 100 Hz / 0.06–0.7 mT) were all below kT, they may have the potential of altering chemical processes in which
excited radicals are involved.
We tested this hypothesis in two experimental systems: CEF in culture and Spirodela oligorrhiza (Lemnaceae) (a small aquatic plant, commonly known as Duckweed). CEF were exposed to SVMF of 100 Hz/0.7 mT for 24 h. The addition of
the exogenous radical scavengers catalase, superoxide dismutase or vitamin E to the cells during exposure significantly suppressed
enhancement of cell proliferation caused by the field (by 79, 67 and 82%, respectively, as evaluated by the MTT colorimetric
assay). 15N NMR analysis of Duckweed plants fed by 15N-labeled ammonium chloride and exposed to SVMF at 60 and 100 Hz/0.7 mT for 24 h, revealed augmented alanine production. Alanine
did not accumulate in the absence of SVMF. The addition of vitamin C, a radical scavenger, reduced alanine production by 82%.
Exposure to SVMF resulted in specific metabolic stress effects in Duckweed plants and enhanced proliferation of CEF. In both
cases, it is suggested that free radicals are involved. 相似文献
88.
Harmonizing water management and social needs: a necessary condition for sustainable development. The case of Israel's coastal aquifer 总被引:3,自引:0,他引:3
This study focuses on the problem of most efficiently fulfilling the water requirements of society for sustainable water resources management. The goal is to coordinate effectively the social needs of the resident population with operational water resources management planning.The proposed approach consists of a pyramidal hierarchy of water resource management needs, similar to that suggested by psychologist Abraham Maslow for human social needs. The two pyramidal hierarchies can be simultaneously employed to delineate guidelines to synchronize planning for sustainable water resources development with the concerns and expectations of the resident population. In both hierarchies, higher level needs remain irrelevant and difficult to attain until lower level needs of the resident population have been fulfilled.Management planning measures employed with regard to Israel's coastal aquifer have been used to illustrate this approach. Observation of Israel's experience indicates markedly reduced effectiveness where such measures have failed to be properly synchronised with societal needs. Conversely, where hydrological management measures were successfully synchronized with societal concerns, increased efficiency towards attaining sustainable groundwater management was evident. 相似文献
89.
A study has been made regarding the action of the hydrocortisone, testosterone and 17β-estradiol on isolated liver and spleen tissue homogenates or slices of male and female adults of the fish Trachurus mediterraneus ponticus. The results showed a decrease of the oxygen uptake and of the cytochrome oxydase and succinic dehydrogenase activity of the liver homogenate after hydrocortisone administration, while this hormone increased significantly the lactic acid production in both tissues. Testosterone acted in an opposite manner to hydrocortisone by increasing the intensity of oxygen consumption and the succinic dehydrogenase activity, but decreased the lactic acid production of the liver and spleen tissue preparations. Estradiol decreased the oxygen consumption of the liver, the cytochrome oxydase activity and the lactic acid production in both tissues of female Trachurus mediterraneus ponticus. 相似文献
90.
Christine Errard Francisca Ruano Freddie-Jeanne Richard Alain Lenoir Alberto Tinaut Abraham Hefetz 《Chemoecology》2006,16(4):235-240
Summary. Proformica longiseta exists as two populations in the Sierra Nevada Mountains in Spain, only one of which is parasitized by the slave-maker ant
Rossomyrmex minuchae. To investigate the possible effect of co-evolutionary pressures on cuticular hydrocarbon (CHC) profiles (the presumed nestmate
recognition cues), we performed a comparative analysis of the CHC of R. minuchae and P. longiseta colonies from both the allopatric and sympatric populations; the latter includes samples of enslaved as well as free-living
workers. Discriminant analyses based on these chemical profiles showed two clear profile groups: the first comprised R. minuchae and both enslaved and free-living P. longiseta from the sympatric population; and the second the allopatric P. longiseta workers. As expected, the profiles of the two sympatric P. longiseta groups (enslaved and free-living) were distinct; but, interestingly, those of the enslaved P. longiseta and its parasite R. minuchae were also distinguishable. This indicates that despite their cohabitation each species maintains its own chemical identity.
Profile similarity between the sympatric free-living P. longiseta and its parasite may explain the lower than expected aggression observed during raids. We further speculate that in view
of the differences between the sympatric and allopatric population of P. longiseta, co-evolutionary pressures have driven changes in the profile of the former to better match that of its parasite R. minuchae. Such an adjustment may have enabled nests of the sympatric P. longiseta to endure multiple raids by the parasite (due to the reduced aggression) and thus to continue to reproduce despite the damage
inflicted by the raids. 相似文献