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Ants of the speciesMessor arenariusandM. ebeninusare known as common granivores in the deserts of the Middle East and North Africa. The relationship between the spatial distribution of nests of these ant species and the distribution of vegetation was examined in the Negev highlands. Using the method of nearest neighbour analysis, it was found that nests ofM. arenariusare evenly dispersed while the dispersion of nests ofM. ebeninusdoes not differ from a random distribution. It is suggested that in desert surroundings there is a connection between the distribution pattern of nests of harvester ants and their foraging type. It seems that nests of individually foraging ants are usually evenly dispersed while nests of trunk-trail foraging ants are usually distributed in a random or aggregated dispersion. 相似文献
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G. F. Gentile G. Bressan L. Burlini & R. De Franco 《Geophysical Journal International》2000,141(2):457-478
3-D images of P velocity and P - to S -velocity ratio have been produced for the upper crust of the Friuli area (northeastern Italy) using local earthquake tomography. The data consist of 2565 P and 930 S arrival times of high quality. The best-fitting V P and V P / V S 1-D models were computed before the 3-D inversion. V P was measured on two rock samples representative of the investigated upper layers of the Friuli crust. The tomographic V P model was used for modelling the gravity anomalies, by converting the velocity values into densities along three vertical cross-sections. The computed gravity anomalies were optimized with respect to the observed gravity anomalies. The crust investigated is characterized by sharp lateral and deep V P and V P / V S anomalies that are associated with the complex geological structure. High V P / V S values are associated with highly fractured zones related to the main faulting pattern. The relocated seismicity is generally associated with sharp variations in the V P / V S anomalies. The V P images show a high-velocity body below 6 km depth in the central part of the Friuli area, marked also by strong V P / V S heterogeneities, and this is interpreted as a tectonic wedge. Comparison with the distribution of earthquakes supports the hypothesis that the tectonic wedge controls most of the seismicity and can be considered to be the main seismogenic zone in the Friuli area. 相似文献
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Nest and feeding behaviour patterns were compared between two sympatric species, the bushy-tailed gerbilSekeetamys calurusand the golden spiny mouseAcomys russatus, in order to assess nest site and food as possible resources of competition. The way the species interact under laboratory conditions was also compared. WhileS. calurusused a nest into which they removed bedding material, only two out of sixA. russatusdid so, while in at least half of the studied cases they were found roosting outside of the nest inside the enclosure. When introduced into the same enclosure,S. caluruswas the dominant species and in five out of 12 casesS. calurusinhabited the nest abandoned byA. russatus, and in seven casesA. russatuswas found resting in the enclosure. UnlikeA. russatus,S. calurusaccumulated food inside its nest and also protected the food resource in the enclosure againstA. russatus. It seems that different nest and feeding behavioural patterns can reduce competition between these two sympatric species. 相似文献
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Mark A. Riedesel Duncan Agnew Jon Berger Freeman Gilbert 《Geophysical Journal International》1980,62(2):457-471
Summary. Using nine IDA records for the Indonesian earthquake of 1977 August 19, we have formed an optimal linear combination of the records and have measured the frequency and Q of 0 S 0 and 1 S 0 . The frequency was measured using the moment ratio method. The attenuation was measured by the minimum width method and by the time-lapse method. The frequency and attenuation were measured simultaneously by varying them to obtain a best fit to the data. A 2000-hr stack, the sum of nine individual records, for 0 S 0 gave a frequency of 0.814664 mHz±4 ppm. The values for the Q of 0 S 0 for the three different methods of measurement were 5600,5833 and 5700, respectively. The error in the estimates of Q -1 is about 5 per cent for the minimum power method. For 1 S 0 a 300-hr stack yielded a frequency of 1.63151 mHz±30 ppm. The values of Q for this mode were 1960, 1800 and 1850, respectively, with an error in Q -1 of about 12 per cent for the minimum power method. 相似文献
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All A. Nowroozi 《Geophysical Journal International》1986,86(2):687-699
Summary. The statistical capability of the m b : M s discriminant for the discrimination of earthquake and explosion populations is examined by application of discriminant functions to a group of 83 explosions and 72 earthquakes in Eurasia. Equations are derived for the probability that an event is an earthquake or an explosion. The positive sign of DIS in the decision index equation, DIS i = 34.3383 – 11.9569 mb t + 7.1161 M si , indicates that the event i is an earthquake. Its negative sign indicates that event i is an explosion. The probability of correct classification for an event, P i , is related to its DIS i value, by P i = [1-exp (DIS i )]−1 , where a large, positive DIS indicates a high probability that an event is an earthquake and a large, negative DIS indicates a high probability that an event is an explosion. The discrimination line M s = 1.680 m b – 4.825, or m b = 0.595 M s + 2.872 very successfully separates the explosion population from the earthquake population. The points on this line have an equal chance of being an earthquake or an explosion; moreover, for any event, the distance parallel to the M s -axis from the point representing that event in the m b : M s plane to this line is a measure of the probability for the correct classification of that event. 相似文献
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Extensive areas of low lying coastal plains on Santiago Island, Republic of Cape Verde, are virtually devoid of natural vegetation. Of many introduced trees and shrubs, onlyAtriplexspecies have been found to thrive. Several plantations have been established during the past 15 years by the Cape Verde Government, FAO and other agricultural development groups. Results from these, together with local perceptions, indicate that although growth and survival are good, the primary objective of providing forage is not being met, owing to the unpalatability ofAtriplexto local stock. In recent field trials, severalAtriplexspecies showed good growth, but none were browsed and survival was quite poor, with onlyA. undulata(65%) andA. canescens(100%) exceeding 60% survival. Forage analysis identified high salt content in all species tested, and the highest protein content was found inA. glauca(16%),A. vesicaria(17%) andA. canescens(20%), which also had the lowest salt levels.Atriptex canescenswas identified as worthy of further introduction. An establishedA. halimusplantation that was observed to be browsed was compared to unbrowsed stands in terms of forage, soil and local drinking water analyses. Possible reasons for the unpalatability ofAtriplexto local stock and its resolution are discussed, along with the potential future ofAtriplexon the Cape Verde Islands. 相似文献
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