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161.
Sandra?BrucetEmail author Dani?Boix Rocìo?López-Flores Anna?Badosa Xavier?D.?Quintana 《Marine Biology》2005,148(1):131-139
Changes in amino acid composition (AAC) during ontogeny of some planktonic crustacean species commonly found in fresh and brackish coastal waters were compared. For these comparisons two calanoid copepods (Eurytemora velox and Calanipeda aquae-dulcis), two cyclopoid copepods (Diacyclops bicuspidatus odessanus and Acanthocyclops robustus) and two Daphnia (Daphnia pulicaria and Daphnia magna) species were selected. A discriminant analysis was performed to determine whether there were significant differences between the AAC of the different stages of each species. Results show gradual changes in AAC during ontogeny of the copepod species. Calanoids showed the greatest differences in AAC between stages, followed by cyclopoids. Gradual changes in AAC were due to the increase in some amino acids such as alanine, valine, glutamic acid, glycine, arginine, proline and tyrosine from nauplii to adults. The latter showed a remarkable increase in all copepod species. In contrast, Daphnia species showed a relatively constant AAC during development, with only minor changes being detected, and not related with ontogeny. Differences in the physico-chemical variables of the lagoons do not seem to be the cause of copepod ontogenic changes in AAC. Data suggest that AAC differences found between stages of copepod species could indicate a gradual change in diet during the life cycle of these copepods. 相似文献
162.
163.
Leonardo?Alberto?Rios?OsorioEmail author Manuel?Ortiz?Lobato Xavier?álvarez?Del?Castillo 《Environment, Development and Sustainability》2005,7(4):501-518
The paper analyzes the concept of sustainable development in the light of the different interpretations existing on the issue
since its appearance and establishment as an ideal to lead humanity’s line of progress. Within these interpretations, a characteristic
generation of diverse debates can be appreciated, arising from different perspectives, academic as well as ideological, aiming
at describing, clarifying and determining their conceptual reach.
Based on these facts a model of categorization for these debates has developed, a model in which interpretations generated
on the concept of sustainable development were catalogued into four realms: conceptual, contextual, academic and geopolitical.
The configuration of these four areas of debate, as well as the recognition of the diversity of interpretations existing on
sustainable development, is a reflection of the intrinsic complexity of the phenomena, which affect the natural and social
world, both at the local and global level. The analysis of this complexity is based on the subjectivity, which is inherent
to the interpretation of these phenomena, with permanent reference to the cultural context from which the diverse discourses
were structured.
This global perspective on the state-of-the-art controversy concerning the idea of sustainable development as an articulatory
axis reveals the necessity of building epistemological models, which can give a new direction to scientific research. From
these new models, based on the analysis of the holistic character of reality, the subjective and the objective must be integrated
in the generation of knowledge, which contributes usefully to the unceasing reconstruction of our world-(view).
Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue. 相似文献
164.
Harvester ants have traditionally been considered as seed predators that negatively affect plants. In some cases, however, they can also act as positive seed dispersers. During field observations, we noted that a portion of Psoralea bituminosa seeds that were collected and carried to the nest by the granivorous harvester ant Messor barbarus were discarded intact in refuse piles outside the nest. We analyzed and compared the physical characteristics of size, mass and toughness in P. bituminosa seeds from two different origins: intact seeds found in the ant's refuse piles and seeds collected directly from the plants. Seeds from refuse piles were similar in width but lighter and tougher than seeds from the plant. Our results point to a mechanical defence based on seed toughness to avoid predation by M. barbarus and suggest that an elevated proportion (~69%) of the seeds produced by P. bituminosa could be too tough to be consumed by this ant. These transported but uneaten seeds could benefit by being moved far from the mother plant and this could act as a selective evolutionary pressure towards tough seeds. 相似文献
165.
Susanna López-Legentil Nataly Bontemps-Subielos Xavier Turon Bernard Banaigs 《Marine Biology》2007,151(1):293-299
Temporal variation is one of the least known components of defence production in marine organisms. Here we examined whether
there is a predictable temporal pattern in the production of chemical and structural defences by a marine invertebrate. To
assess the seasonal variation in chemical defence, we measured ascididemin, the main pyridoacridine alkaloid in the blue Mediterranean
morph of the ascidian Cystodytes sp. Structural defence variability was assessed on the basis of colony ash content, as it contains mainly spicules. Ascididemin
concentration and the colony ash content displayed an annual cycle, reaching a minimum in spring and peaking in summer. Cross-correlation
analyses with existing data on growth and reproduction suggested a significant trade-off between investment in reproduction
and the other biological parameters considered (growth, inorganic content and ascididemin concentration). Our results suggest
that optimization of resource allocation, probably influenced by biotic interactions and physical factors, shaped the temporal
trends observed in secondary metabolite concentration and inorganic content. 相似文献
166.
The use of the Bel W3 tobacco variety revealed the existence of an intrapopulation variation of sensitivity to the ozone effect leading to the isolation of two categories of plants: sensitive and resistant. The use of sensitive plants revealed the existence of a biological ozone efficiency threshold at a level close to 34.5 ppb. Under the threshold, the biological effects observed were weak or very weak. They can be attributed to the occurrence of secondary phenomena (chemical, physiological, pathological, etc.), inducing or inhibiting necrosis, which become perceptible here. 相似文献
167.
Process-based modeling of species' distributions: what limits temperate tree species' range boundaries? 总被引:1,自引:0,他引:1
Niche-based models are widely used to understand what environmental factors determine species' distributions, but they do not provide a clear framework to study the processes involved in defining species' ranges. Here we used a process-based model to identify these processes and to assess the potential distribution of 17 North American boreal/temperate tree species. Using input of only climate and soil properties, the model reproduced the 17 species' distributions accurately. Our results allowed us to identify the climatic factors as well as the biological processes involved in limiting species' ranges. The model showed that climatic constraints limit species' distributions mainly through their impact on phenological processes, and secondarily through their impact on drought and frost mortality. The northern limit of species' ranges appears to be caused mainly by the inability to undergo full fruit ripening and/or flowering, while the southern limit is caused by the inability to flower or by frost injury to flowers. These findings about the ecological processes shaping tree species' distribution represent a crucial step toward obtaining a more complete picture of the potential impact of climate on species' ranges. 相似文献
168.
Speciation and sources of atmospheric aerosols in a highly industrialised emerging mega-city in central China 总被引:1,自引:0,他引:1
Querol X Zhuang X Alastuey A Viana M Lv W Wang Y López A Zhu Z Wei H Xu S 《Journal of environmental monitoring : JEM》2006,8(10):1049-1059
Monitoring air quality in large urban agglomerations is the key to the prevention of air pollution-related problems in emerging mega-cities. The city of Wuhan is a highly industrialised city with >9 million inhabitants in Central China. Simultaneous PM10 sampling was performed during 1 year at one urban and one industrial site. Mean PM10 daily levels (156 microg m(-3) at the urban site and 197 microg m(-3) at the industrial hotspot) exceed the US-EPA or EU annual limit values by 3-4 times. A detailed study of daily speciation showed that the mean chemical composition of PM10 presents minimal differences between peak and low PM episodes. This implies that PM10 aerosols in the study area result from local emissions, and air quality management and abatement strategies in Wuhan should thus focus on local anthropogenic sources. The levels of some elements of environmental concern are relatively high (409-615 ngPb m(-3), 66-70 ngAs m(-3), 116-227 ngMn m(-3), 10-12 ngCd m(-3)) due to industrial, but also urban emissions. Principal component analysis identified a mineral source (probably cement and steel manufacture) and smelting as the main contributors to PM10 levels at the industrial site (34%), followed by a coal fired power plant (20%) and the anthropogenic regional background (16%). At the urban site the major PM10 source is a mixed coal combustion source (31%), followed by the anthropogenic regional background (28%) and traffic (16%). 相似文献
169.
Replacement of peat as a growing medium by a renewable material, such as an organic waste, is an issue of concern since harvesting of peat has a considerable environmental impact and, actually, it is a non-renewable resource. Cattle manure is a readily available organic waste, which means that once it goes through the composting process, it can be used as an alternative to peat, specifically, the solid fraction obtained from mechanical liquid-solid separation of cattle slurry (SF). Studies have shown it to be suitable for such uses. The purpose of this study was to detect possible changes in the physicochemical and chemical properties of SF when it is composted using different aeration strategies, with an emphasis on the changes that would make it feasible for use as a substrate. With this aim in mind, an experiment was designed with three aeration strategies that would be used during composting. The first consisted of applying air through a static method (forced ventilation). The second involved improving aeration by adding a bulking agent and a dynamic turning method. In the third strategy, aeration was carried out by turning (control). The results show that the different aeration strategies had a clear effect on the evolution of pH, electrical conductivity (EC), nitrate-N, ammonia-N and bicarbonate content. Nitrification was favored under good aeration conditions using the static composting method, probably due to the greater availability of ammonia-N that was transformed into nitrate-N. In general, the low buffering capacity allowed for a reduction of the pH during the curing stage of composting (in conjunction with low temperatures during this period), a characteristic that favors the use of this compost as a growing medium. We also conclude that measuring bicarbonate levels during composting could be used as an indicator of the possible acidification of the material and as a way of evaluating the level of material aeration. 相似文献
170.