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61.
The effects of visits to nests by researchers interested in quantifying avian nesting success have received considerable attention, as researchers have long been concerned about the possible negative effects of their own activities on the resulting estimates. There is a widely held view that investigator disturbance has an overall negative effect on breeding success by increasing nest predation rates in the nests studied. However, to date no one has statistically assessed the empirical evidence for such a relationship. We undertook a meta‐analysis of published results to assess whether researcher activities increase nest predation in birds. We also assessed the variability in this effect in relation to the traits of the study species and the methodology used. These analyses used data from 18 experimental studies involving 25 species from six avian orders. Our results suggest that, contrary to the traditional view, researcher activities do not generally affect the incidence of nest predation. Moreover, this relationship appears inconsistent among avian orders and, surprisingly, nest survival of passerines increased weakly with researcher activities. We also found significant positive effects of researcher activity on nest survival for species breeding on coastal areas and for species nesting on the ground. The possible explanation for these differences among orders and guilds could be due to different nest predator communities. This new perspective on the effect of investigators could have important implications for bird management and conservation, as well as for other fields of study such as ecology and evolution, in which nest survival rates measured in the field are widely used to test and support a range of hypotheses. 相似文献
62.
Some isolates of ryegrass mosaic virus produced necrosis in Lolium multiflorum much more frequently than others. This frequency could be increased or decreased by selecting plants with or without necrosis, respectively, as sources of inoculum. Infection with the milder, mosaic-inducing isolates which rarely caused necrosis did not protect the plants against subsequent infection with the more severe necrosis-inducing isolates. Oat plants were infected much more readily by isolates which frequently caused necrosis than by the less necrotic isolates, but passage through oat appeared to have no effect on the frequency with which an isolate produced necrosis in ryegrass.
Genotypes of L. multiflorum varied greatly in their tolerance of infection. Their level of tolerance was closely correlated with symptom expression. All genotypes tested were tolerant to a mild, mosaic-inducing, isolate. Two genotypes were tolerant to a severe, necrosis-inducing, isolate and to an original Rothamsted isolate; three genotypes were equally susceptible to both isolates, and two were more susceptible to the necrotic isolate than to the Rothamsted isolate. 相似文献
Genotypes of L. multiflorum varied greatly in their tolerance of infection. Their level of tolerance was closely correlated with symptom expression. All genotypes tested were tolerant to a mild, mosaic-inducing, isolate. Two genotypes were tolerant to a severe, necrosis-inducing, isolate and to an original Rothamsted isolate; three genotypes were equally susceptible to both isolates, and two were more susceptible to the necrotic isolate than to the Rothamsted isolate. 相似文献
63.
DAVID E. WILKINS 《American anthropologist》2004,106(1):205-206
Clearing. Path:Theorizing the Past in Native American Studies. Nancy Shoemaker, ed. New York: Routledge, 2002. 215 pp. 相似文献
64.
ZINC TOLERANCE IN BETULA SPP. 总被引:10,自引:4,他引:6
65.
P. W. WILKINS 《The Annals of applied biology》1987,111(2):409-413
Polygenic resistance to ryegrass mosaic virus (RMV) was transferred from perennial to Italian ryegrass cv. Tribune by repeated cycles of backcrossing, polycrossing and selection. The resulting synthetic variety (Bb 2113) was highly resistant to infection by RMV whereas the Italian ryegrass cultivars Tribune, RvP, Bartolini, Augusta, Wilo and Dalita all were highly susceptible. Leaf width and length of Bb 2113 was similar to that of cv. Tribune and, like Tribune, Bb 2113 had awned florets. In a field trial, Bb 2113 had a similar persistency rating and number of inflorescences in the regrowth to cv. Tribune but produced 11% less dry matter. The results emphasise the need for a more efficient means of transferring small numbers of genes from one species of Lolium to another than backcrossing provides. 相似文献
66.
Movement of Abscisic Acid in <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> Plants 总被引:6,自引:0,他引:6
THE movement of abscisic acid (ABA) in plants seems to have been studied only in isolated segments of tissue1–4. We have used 14C-labelled ABA of relatively high specific activity to investigate its movement in a number of plant species, in both isolated tissue segments and whole plants. The movement of 2-14C-ABA in intact seedlings of Phaseolus vulgaris is described here. 相似文献
67.
Effects of combinations of insecticides and herbicides on the growth and yield of cauliflower plants (cvs No. 110, Garant and Strong) were determined in two field experiments with seed drilled to give a stand of c. 300000 plants/ha. Granular formulations of chlorfenvinphos or fonofos were applied by the bow-wave method at 2 kg a.i./ha to control cabbage root fly (Delia brassicae). Weeds were successfully controlled with combinations of trifluralin, incorporated into the soil at 0·6 or 1·2 kg a.i./ha before drilling, and propachlor, applied pre-emergence at 2·2 or 4·4 kg a.i./ha. Fonofos, with and without herbicides, significantly lessened (P < 0·01) numbers of seedlings that would survive to harvest. Herbicides and chlorfenvinphos generally did not significantly affect the emergence of healthy seedlings of any cultivar. Combinations of herbicides and chlorfenvinphos were compatible for control of target species. Chlorfenvinphos reduced root damage by at least 50% but did not significantly increase (P > 0·05) the total or marketable weight of curds. Numbers of curds were not usually affected and consistent effects of treatments on maturation periods of the three cultivars were not detected. 相似文献
68.
P. W. WILKINS 《The Annals of applied biology》1978,89(3):429-434
After exposure to infection in the field, the proportion of plants showing distinct symptoms of ryegrass mosaic virus (RMV) was less in perennial than in Italian ryegrass. The perennial ryegrass cv. Mascot had a smaller proportion of plants with symptoms than cv. S.23. Far milder symptoms were induced in test plants by RMV from naturally infected perennial ryegrass plots than from Italian ryegrass plots. Within perennial ryegrass, RMV from cv. Mascot caused milder symptoms than that from cv. S.23. Severe RMV isolated from Italian ryegrass cv. Trident (RMVT) became milder after one passage through cv. Mascot, although not as mild as RMV obtained from field plots of cv. Mascot (RMVM). Families from two highly resistant perennial ryegrass clones and two randomly selected clones of cv. S.23 crossed in all possible combinations varied in symptom severity when inoculated with RMVT but not when inoculated with RMVM. Families inoculated with RMVT also yielded virus which varied in the severity of symptoms induced in test plants, families with severe symptoms yielding severer virus. Thus, much of the variation in the resistance of these clones could be attributed to infection with RMV of differing severity. Resistance was controlled by several genes which were mainly additive in their effect. 相似文献
69.
The circadian rhythm of CO2 output in leaves of Bryophyllumfedtschenkoi damps out after 34 d in continuous darknessand a CO2-free air stream at 15°C. The rhythm is reinitiatedafter a single exposure to white light of 2, 4, 6 or 8 h duration,damps out again after a further 34 d and can be reinitiatedfor a second time by a further exposure to light. During the exposure to light there is a burst of CO2 outputconsistent with the decarboxylation of malate, and the rhythmbegins afterwards with an initial high rate of CO2 fixation.Malate gradually accumulates in the leaves in continuous darknessto attain a maximum value (35 mol m3) at the time whenthe circadian rhythm disappears, and decreases to a low value(19 mol m3) after a 4 h exposure to light which reinitiatesrhythmicity. These results support the hypothesis that damping of the rhythmof CO2 output in continuous darkness is due to the accumulationof malate in the leaf cells, eventually reaching such a levelthat its removal from the cytoplasm into the vacuole cannottake place, with the result that PEPc activity, upon which therhythm of CO2 output depends, remains allosterically inhibited. Key words: CAM, circadian rhythm, Bryophyllum, CO2-fixation, malate metabolism 相似文献
70.
Genomic signatures of ancient asexual lineages 总被引:9,自引:0,他引:9
BENJAMIN B. NORMARK OLIVIA P. JUDSON NANCY A. MORAN 《Biological journal of the Linnean Society. Linnean Society of London》2003,79(1):69-84
Ancient asexuals – organisms that have lived without sex for millions of years – offer unique opportunities for discriminating among the various theories of the maintenance of sex. The last few years have seen molecular studies of a number of putative ancient asexual lineages, including bdelloid rotifers, Darwinulid ostracods, and mycorrhizal fungi. To help make sense of the diverse findings of such studies, we present a review and classification of the predicted effects of loss of sex on the eukaryotic genome. These include: (1) direct effects on the genetic structure of individuals and populations; (2) direct effects on the mutation rate due to the loss of the sexual phase; (3) decay of genes specific to sex and recombination; (4) effects of the cessation of sexual selection; (5) dis-adaptation due to the reduced efficiency of selection; and (6) adaptations to asexuality. We discuss the utility of the various predictions for detecting ancient asexuality, for testing hypotheses of the reversibility of a transition to asexuality, and for discriminating between theories of sex. In addition, we review the current status of putative ancient asexuals. © 2003 The Linnean Society of London. Biological Journal of the Linnean Society 2003, 79 , 69–84. 相似文献