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111.
112.
The vertical distribution of Pratylenchus scribneri populations was monitored under irrigated corn and potato grown in loamy sand soil. population estimates were based on the number of nematodes recovered from 100-cm³ soil samples and the roots contained therein. Reproduction was assessed by counting the number of second-stage juveniles. An index of population maturity was computed to evaluate the age structure of populations. At no time were nematodes distributed uniformly among five soil depths from 0 to 37.5 cm deep. During the summer (June-September), changes in the total number of P. scribneri and the number of second-stage juveniles recovered were not consistent among the depths sampled. Early (April-June) and late (September-November) in the season, changes in the abundance, reproduction, and maturity of populations were similar among depths. The timing and pattern of increases in numbers of nematodes suggests that variation in the abundance of P. scribneri in the soil profile beneath potato and corn was caused primarily by reproduction rather than the movement of nematodes. 相似文献
113.
Reproductive ecology of dioecious Siparuna (Monimiaceae) in Ecuador–a case of gall midge pollination
JAN PETER FEIL 《Botanical journal of the Linnean Society. Linnean Society of London》1992,110(3):171-203
The reproductive ecology of the dioecious genus Siparuna , belonging to the primitive family Monimiaceae, was investigated in Ecuador. Thirteen species were studied, and species growing at high altitudes (above 500 m) were compared with species growing at lower altitudes. The genus has specialized flowers pollinated by Cecidomyiidae (Asynapta sp. and other genera) that lay eggs chiefly in male flowers since these are more easily accessible than female flowers due to their morphology. Several traits ensure that pollen transfer is accomplished: 1. long flowering of individuals and single flowers; 2. specific floral morphology (unisexuality, landing platform, restricted pore) allowing the flowers to be visited by Cecidomyiidae seeking egg-laying sites, and 3. a low number of ovules that have to be pollinated in each flower. The low number of ovules per flower results in a high pollen-ovule (P/O) ratio even though pollen production in male flowers is only moderate.
High altitude species had larger flowers, higher pollen-ovule ratios, fewer ovules per female flower, and longer periods of anthesis. Gender differences were seen in the longer functionality of female flowers; the larger numbers of male flowers produced; and the average diameter at breast height (DBH) biased for one of the two sexes depending on the species investigated, with no clear trend in the size distributions of individuals of both sexes. Sex ratios departed significantly from unity both to male and female bias but usually were in favour of males. There were no general differences in the ratio of functional male to female flowers at the time of observation nor in the sizes of male and female flowers. The evolution of unisexual flowers in Siparuna can be explained as a result of the differential predation by larvae: unimportant in male flowers, destructive if occurring in female flowers. 相似文献
High altitude species had larger flowers, higher pollen-ovule ratios, fewer ovules per female flower, and longer periods of anthesis. Gender differences were seen in the longer functionality of female flowers; the larger numbers of male flowers produced; and the average diameter at breast height (DBH) biased for one of the two sexes depending on the species investigated, with no clear trend in the size distributions of individuals of both sexes. Sex ratios departed significantly from unity both to male and female bias but usually were in favour of males. There were no general differences in the ratio of functional male to female flowers at the time of observation nor in the sizes of male and female flowers. The evolution of unisexual flowers in Siparuna can be explained as a result of the differential predation by larvae: unimportant in male flowers, destructive if occurring in female flowers. 相似文献
114.
Conditions for plant regeneration from excised shoot tips of Vigna radiata were studied. Complete plants were regenerated directly without an intervening callus phase from shoot tips on basal medium (MS salts+B5vitamins). Regeneration frequency varied with genotype, explant size and growth regulator combinations in the medium. Addition of cytokinins induced a variable amount of callus at the base of the shoot tip, followed by multiple shoot formation. Benzyladenine (BA), kinetin and zeatin at 5×10-6 M each induced multiple shoots in 100% of the explants but the highest number of regenerants per explant (9) was produced with BA. The efficacy of BA for shoot multiplication was not improved when it was supplemented with naphthaleneacetic acid (NAA) or indoleacetic acid (IAA). NAA or adenine sulphate, when applied alone, induced complete plantlets. The growth regulator requirement of explants for the induction of multiple shoots varied with explant size. The shoot tip explants maintained proliferation ability on subculture. None of the treatments was effective in inducing shoot bud differentiation from callus. Regenerated shoots were rooted on MS basal medium and MS supplemented with either IAA or indolebutyric acid. The rooted plants were transferred to the field; 60% subsequently survived and grew.Abbreviations BM
basal medium [MS (Murashige & Skoog 1962) salts+B5 (Gamborg et al. 1968) vitamins]
- BA
6-benzyladenine
- AdS
adenine sulphate
- IAA
indole-3-acetic acid
- NAA-1
naphthaleneacetic acid
- IBA
indolebutyric acid 相似文献
115.
Hugh J. Barclay 《Population Ecology》1992,34(1):131-141
A methodology is developed to assess the effects of spatial distribution on the efficiency of insect pest control. This methodology is especially applicable to pest control methods whose efficiency of action depends either positively or negatively on pest density It is applied here to the sterile insect technique and pheromone trapping for male annihilation, which both depend negatively on density. This methodology relies on quantifying clumps of various size and then relating this to efficiency of control and predicting the total pest production given the information on clump sizes and efficiency of control for each clump size. It is found that control is about four times as difficult for a population that is highly clumped (k of the negative binomial distribution=0.25) as for a regularly dispersed population. 相似文献
116.
Gerhard Maier 《Hydrobiologia》1990,206(1):11-18
The spatial distribution of dormant copepodids of 3 species of cyclopoid copepods — Cyclops vicinus, Mesocyclops leuckarti and Thermocyclops crassus — was studied in 4 small lakes in South Germany. The rate of emergence from diapause and times from the resting stage to adulthood and from adulthood to the appearance of the first clutch was studied at 4 constant temperatures (5, 10, 15, 20 °C) in the laboratory. Resting stages of C. vicinus were always concentrated in the deepest parts of the lakes and were found relatively deep in the mud. M. leuckarti- and T. crassus-copepodids preferred shallow areas in deep lakes but were concentrated in the deep areas in shallow lakes. Copepodids of both species were always concentrated in the uppermost mud layers.Rate of emergence from diapause was strongly temperature-dependent. At high temperatures (20 °C) copepodids of all species under study emerged within 2 weeks. At lower temperatures C. vicinus copepodids showed the highest rate of emergence. At 5 to 10 °C only few M. leuckarti- and T. crassus-copepodids had emerged after the investigation period (7 weeks). Both C. vicinus and T. crassus showed the highest rate of emergence at the natural end of diapause but even at that time only few T. crassus-copepodids emerged at 5 °C. Times to adulthood at 5 °C were shortest in C. vicinus. At higher temperatures this species was passed by M. leuckarti. Times from adulthood to the appearance of the first clutch at 5–15 °C were shortest in C. vicinus. T. crassus produced no clutch at 5 and 10 °C. 相似文献
117.
Observations on morphological characters of milk and permanent teeth, based on 648 pairs of dental casts of 356 male and 292 female Jat children of Haryana (India) are reported. Deciduous teeth show high frequencies of bilateral winging of maxillary central incisor, Carabelli's cusp of maxillary second molar, and deflecting wrinkle of mandibular second molar. Reduction of maxillary molar cusps is more marked in males than in females. Y pattern is very common in deciduous molars. Permanent teeth have high frequencies of grooved cingulum of incisors, cingular nodule of lateral incisors and canines, and distal accessary ridge of canines. Low frequencies of Carabelli's cusp and winging are also common. The tendency towards faintly developed shovelling in milk incisors occurs more often than in the permanent teeth. 相似文献
118.
119.
N. Collins 《Hydrobiologia》1980,68(2):99-112
The population of Ephydra cinerea was studied during three summers when dissolved solids levels were about 130 g/l. All life stages are present year-round, but there is apparently some coordination of the initial pulse of adult emergence in June. There are probably 1–2 generations per year.Eggs are deposited on the water surface; inputs to three locations were similar. Larvae successfully avoid the large benthic area covered by an anaerobic monimolimnion. They tend to immigrate from substrates where they grow relatively poorly, and to remain on substrates where they grow better. Consequently, larval densities are more than ten times higher on reef and shallow water mud substrates than on sand. This marked spatial specialization in the absence of substrate-specific predators or competitors illustrates the power of habitat quality by itself in determining spatial patterns of abundance in a lake.Experiments showed larval growth on the reef was inversely related to density, and the lake as a whole produced relatively larger flies in a year when larval and pupal densities were relatively low. Yearly production by E. cinerea is roughly 50 g/m2, about 88% of which comes from reefs and shallow water mud areas covering only 18% of the bottom area.Past studies indicate that blue-green algae dominate the lake's benthic flora when salt concentrations are high (due to low lake levels), and diatoms take over when salt concentrations are low. Fly abundance appears to be inversely related to salinity.The lake's present high planktonic primary production is equal to that of eutrophic freshwater lakes, yet it has water clarity more characteristic of an oligotrophic lake. The high water clarity (which makes possible the high benthic production) probably depends on the absence of phytoplankters that can both tolerate the high salinity and avoid being eaten by Artemia salina. Continued dilution of the lake will probably upset this situation and result in reorganization of the lake's energy flow pattern. 相似文献
120.
Impoundment behavior was determined for alkalinity, temperature, dissolved oxygen, and conductivity from stations located along the length of a bottom-draining, oligo-mesotrophic, hardwater, deep-storage reservoir located in central Texas. The epilimnion deepened the length of the reservoir throughout the summer as a result of drawdown. Bicarbonate alkalinity and conductivity exhibited both longitudinal and vertical stratification. Alkalinity and conductivity in the epilimnion decreased from the riverine reach downreservoir to the dam. This longitudinal progression was attributed to inflow and photosynthetically induced epilimnetic decalcification.Hypolimnetic anoxic conditions first occurred in the sedimentation zone in the upreservoir and riverine reaches and then developed in a downreservoir pattern as summer progressed as a result of drawdown. Alkalinity and conductivity in the hypolimnion increased during anoxic conditions and consequently increased in a downreservoir progression. 相似文献