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821.
822.
Walter Gross 《Die Naturwissenschaften》1939,27(14):226-227
823.
824.
Ingrid Langer Doris Krpata Walter J. Fitz Walter W. Wenzel Peter F. Schweiger 《Environmental pollution (Barking, Essex : 1987)》2009,157(10):2871-2877
The effect of increasing soil Zn concentrations on growth and Zn tissue concentrations of a metal-accumulating aspen clone was examined in a dose–response study. Plants were grown in a soil with a low native Zn content which was spiked with Zn salt solutions and subsequently aged. Plant growth was not affected by NH4NO3-extractable soil Zn concentrations up to 60 μg Zn g?1 soil, but it was completely inhibited at extractable concentrations above 90 μg Zn g?1 soil. From these data an effective concentration of 68.5 μg extractable Zn g?1 soil was calculated at which plant growth was reduced by 50%. The obtained information on toxicity threshold concentrations, and the relation between plant Zn accumulation and extractable soil Zn concentrations may be used to assess the suitability of the investigated Populus canescens clone for various phytoremediation strategies. The potential risk of metal transfer into food webs associated with P. canescens stands on Zn-polluted sites may also be estimated. 相似文献
825.
Walter R. Tschinkel 《Behavioral ecology and sociobiology》1998,43(4-5):247-257
Many benefits and risks of cooperative colony founding (pleometrosis) have been identified, but rarely have the proximate
factors that lead to association been considered. This study examined the choices queens make during the first few hours after
mating, and some of the correlates of those choices. Queens had a strong affinity for preformed holes in the soil and readily
used these as their initial founding chambers. This affinity was so strong that in a field experiment, the dispersion pattern
of preformed holes controlled the final dispersion of colony-founding queens. Attraction to partially formed holes is thus
an important cause of pleometrosis. The excavation of complete founding chambers incurred no measurable cost on the subsequent
reproductive output of queens, suggesting that the primary benefit of using preformed holes is to remove the queen quickly
from exposure to predation and desiccation. In the field, pairs of queens offered five equivalent preformed holes in soil
were more likely to share the same hole if the holes were shallow and close together. In these experiments, queens modified
preformed soil holes so that the test holes were no longer equivalent, causing the choice of queen and hole to become confounded.
Laboratory experiments in plaster arenas with unmodifiable holes confirmed the field experiments: queens were more likely
to share a hole when the holes were shallow than when they were deep. Because queens entering adequately deep holes seldom
reemerged, this suggested that the likelihood of sharing increased with increasing contact between queens, that is, when queens
were readily and frequently detected. Such contacts will also predict the future competitive environments to be experienced
by incipient colonies, and may temper the tendency of queens to associate. However, experiments in which queens were exposed
to high and low densities before pairing in the choice arenas failed to show an effect on the choice to join the resident
queen. Queens that joined a resident queen differed in their robustness from queens that did not join. Queens choosing their
own partners did no better reproductively than those assigned partners at random. Overall, this study suggests that (1) newly
mated queens are under strong selection to leave the soil surface and do so by using any available holes, whether dug by another
queen or of some other origin; (2) they are attracted to other queens, and are more likely to cofound as contact with the
potential cofoundress becomes more frequent and (3) they choose whether or not to cofound partly on the basis of their own
reproductive characteristics.
Received: 20 November 1997 / Accepted after revision: 14 March 1998 相似文献
826.
The effects of ultraviolet radiation (UVR 280–400 nm) on the germination of Porphyra
haitanensis conchospores and on the growth and morphogenesis of the subsequent sporelings were investigated by culturing the released
conchospores under natural sunlight from 29 September to 6 October 2005. Germination increased with time and was faster when
UV-B was excluded using cut-off filters. There were significant negative effects of UV-B radiation on growth and cell division
of sporelings, with decreases up to 18% for thallus length, between 6 and 18% for thallus width, up to 29% for thallus area,
and between 6 and 14% for cell size as compared to PAR-controls. UV-A had a significant positive effect on morphogenesis,
enhancing the formation of sporelings with cells dividing transversely; on the other hand, UV-B delayed the formation of such
sporelings. We also tested the effects of solar UVR on the growth of P.
haitanensis juveniles and found no significant effects. Our results indicate that UV-A has an important role in the germination and morphogenesis
of the species, but on the other hand, sporelings of P.
haitanensis are more sensitive to UV-B radiation than juveniles. 相似文献
827.
828.
829.
Walter Wheaton Dimmick †‡ Michael J. Ghedotti † Michael J. Grose † Anne M. Maglia † Daniel J. Meinhardt † and David S. Pennock 《Conservation biology》1999,13(3):653-660
Abstract: Conservation biology is linked inextricably with systematic biology. The principles of systematic biology, however, have not been integrated completely into the practice and principles of conservation biology. Systematists have recognized for some time that a number of evolutionary processes lead to the diversification of lineages. Yet some present units of conservation, such as the evolutionarily significant unit ( Waples 1991), primarily emphasize only one of these processes, adaptation. Allopatric speciation produces biodiversity without requiring any adaptive shift (and consequent adaptive differences between daughter species), so definitions of conservation units that emphasize adaptation may underestimate biodiversity. We estimated the frequency of different modes of speciation for three groups of vertebrates. The frequency of allopatric speciation varies among these groups, but is an important type of speciation in two of the three groups studied. Our results, and the results of other published studies of the frequency of modes of speciation, demonstrate that any unit of conservation defined solely in terms of adaptation is likely to underestimate biological diversity. 相似文献
830.
Incorporating covariates into fisheries stock assessment models with application to Pacific herring.
We present a framework for evaluating the cause of fishery declines by integrating covariates into a fisheries stock assessment model. This allows the evaluation of fisheries' effects vs. natural and other human impacts. The analyses presented are based on integrating ecological science and statistics and form the basis for environmental decision-making advice. Hypothesis tests are described to rank hypotheses and determine the size of a multiple covariate model. We extend recent developments in integrated analysis and use novel methods to produce effect size estimates that are relevant to policy makers and include estimates of uncertainty. Results can be directly applied to evaluate trade-offs among alternative management decisions. The methods and results are also broadly applicable outside fisheries stock assessment. We show that multiple factors influence populations and that analysis of factors in isolation can be misleading. We illustrate the framework by applying it to Pacific herring of Prince William Sound, Alaska (USA). The Pacific herring stock that spawns in Prince William Sound is a stock that has collapsed, but there are several competing or alternative hypotheses to account for the initial collapse and subsequent lack of recovery. Factors failing the initial screening tests for statistical significance included indicators of the 1989 Exxon Valdez oil spill, coho salmon predation, sea lion predation, Pacific Decadal Oscillation, Northern Oscillation Index, and effects of containment in the herring egg-on-kelp pound fishery. The overall results indicate that the most statistically significant factors related to the lack of recovery of the herring stock involve competition or predation by juvenile hatchery pink salmon on herring juveniles. Secondary factors identified in the analysis were poor nutrition in the winter, ocean (Gulf of Alaska) temperature in the winter, the viral hemorrhagic septicemia virus, and the pathogen Ichthyophonus hoferi. The implication of this result to fisheries management in Prince William Sound is that it may well be difficult to simultaneously increase the production of pink salmon and maintain a viable Pacific herring fishery. The impact can be extended to other commercially important fisheries, and a whole ecosystem approach may be needed to evaluate the costs and benefits of salmon hatcheries. 相似文献