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991.
Diane Webb Marthe Monique Gagnon 《Journal of Aquatic Ecosystem Stress and Recovery (Formerly Journal of Aquatic Ecosystem Health)》2002,9(4):259-269
The estuarine portion of the Swan–Canning riversystem runs through the centre of Perth,Western Australia's capital city, with apopulation of approximately 1.4 million people. Little is known about impact of chemicalsentering the estuary via road runoff andstormwater drains on biota inhabiting thesystem. Black bream (Acanthopagrusbutcheri) were collected from seven sites inthe Swan–Canning estuary during August andSeptember 2000, at the end of the winter (wet)season. Serum sorbitol dehydrogenase (s-SDH)was unaffected by the sex of the fish and nosignificant differences were observed betweenthe sites indicating that the measuredethoxyresorufin-O-deethylase (EROD)activity was not hindered by hepatic tissuedamage. The black bream were in an advancedstage of gonad maturation, which affected ERODhepatic activity with lower EROD activity infemale compared to male fish. EROD activityand bile metabolite levels were significantlyhigher at the site closest to the Perth CentralBusiness District, while most downstream sitewas the least impacted, which may be due totidal flushing of the lower estuary by marinewaters. The ratio of naphthalene-type tobenzo(a) pyrene (B(a)P)-typemetabolites suggests that the source ofpetroleum hydrocarbons within the river systemis a mixture polycyclic aromatic hydrocarbons(PAHs) from pyrolytic origin and from unburntfuels. Biomarker levels in the black breamindicate that major roads and drains aresignificant contributors of mixed functionoxygenase (MFO) inducing chemicals includingpolycyclic aromatic hydrocarbons (PAH) into theSwan–Canning estuary and that there is noupstream or downstream gradient in biomarkerresponse. 相似文献
992.
This paper examines the functional relationships among species in an Australian rangeland community with mixed life forms.
It follows a previous study (Walker and others 1999) that explored the role of dominant and minor species in maintaining functional
diversity and resilience in a rangeland ecosystem. Unlike our previous results, which were based on estimates of five plant
functional attributes, the dominant species in this second community apparently are functionally no more dissimilar to each
other than to all other species. We suggest that the lack of clear results in mixed life form communities represents a confounding
of the relationships between the “hard” attributes that actually govern how a plant performs in an ecosystem and the “soft”
attributes that we use as surrogates. There are very few data on the hard functional attributes of plant species and consequently
little information on precisely how the (soft) measurable traits are related to their imputed functions. What evidence there
is shows that although the relationships are strong within life forms, they differ between life forms. This poses a problem
for the development of research relating plant biodiversity to ecosystem function. Until such a database is developed, it
will be very difficult to advance our understanding and measurement of functional diversity in mixed life form communities.
Received 30 April 2001; Accepted 23 January 2002. 相似文献
993.
Stoichiometry of nutrient recycling by vertebrates in a tropical stream: linking species identity and ecosystem processes 总被引:5,自引:0,他引:5
Michael J. Vanni Alexander S. Flecker James M. Hood & Jenifer L. Headworth 《Ecology letters》2002,5(2):285-293
Ecological stoichiometry offers a framework for predicting how animal species vary in recycling nutrients, thus providing a mechanism for how animal species identity mediates ecosystem processes. Here we show that variation in the rates and ratios at which 28 vertebrate species (fish, amphibians) recycled nitrogen (N) and phosphorus (P) in a tropical stream supports stoichiometry theory. Mass-specific P excretion rate varied 10-fold among taxa and was negatively related to animal body P content. In addition, the N : P ratio excreted was negatively related to body N : P. Body mass (negatively related to excretion rates) explained additional variance in these excretion parameters. Body P content and P excretion varied much more among taxonomic families than among species within families, suggesting that familial composition may strongly influence ecosystem-wide nutrient cycling. Interspecific variation in nutrient recycling, mediated by phylogenetic constraints on stoichiometry and allometry, illustrates a strong linkage between species identity and ecosystem function. 相似文献
994.
Network structure and biodiversity loss in food webs: robustness increases with connectance 总被引:11,自引:2,他引:9
Food-web structure mediates dramatic effects of biodiversity loss including secondary and `cascading' extinctions. We studied these effects by simulating primary species loss in 16 food webs from terrestrial and aquatic ecosystems and measuring robustness in terms of the secondary extinctions that followed. As observed in other networks, food webs are more robust to random removal of species than to selective removal of species with the most trophic links to other species. More surprisingly, robustness increases with food-web connectance but appears independent of species richness and omnivory. In particular, food webs experience `rivet-like' thresholds past which they display extreme sensitivity to removal of highly connected species. Higher connectance delays the onset of this threshold. Removing species with few trophic connections generally has little effect though there are several striking exceptions. These findings emphasize how the number of species removed affects ecosystems differently depending on the trophic functions of species removed. 相似文献
995.
转化生长因子β的生物学特性、功能及其临床应用前景 总被引:5,自引:0,他引:5
转化生长因子β是一种高度多效性,多功能性的生长与分化因子,它广泛地调节机体的生长,发育,炎症,修复和免疫等许多生理和病理过程,具有重要的生物学功能和广阔的临床应用前景。 相似文献
996.
997.
Abstract. We investigated the variability in spatial pattern of some structural, dendrochronological and dendroclimatological features of a mixed Larix decidua‐Pinus cembra forest at the timberline in the eastern Italian Alps at fine geographical and temporal scales. Forest structure variables such as stem diameter, tree height, age and tree‐ring related parameters (yearly growth index, mean sensitivity, first order autocorrelation and some dendroclimatic variables) have been compared at various scale levels. We observed that most of the variables show positive autocorrelated structures due to both forest dynamics and fine‐scale driving forces, probably related to microrelief. Spatial structure of yearly indexed radial growth appears sensitive to extreme climatic events. Secondary succession after past disturbances drives the forest towards a structure governed by a gap regeneration dynamics that seems to ensure the different requirements of the two main tree species present. Small spatial scale studies of forest structures, especially if integrated to dendro‐ecological data, seem an efficient tool to assess the disturbance regime and species sensitivity to environmental change. 相似文献
998.
Christina M. Kraemer-Pecore Andrew M. Wollacott John R. Desjarlais 《Current opinion in chemical biology》2001,5(6):690-695
The field of computational protein design is reaching its adolescence. Protein design algorithms have been applied to design or engineer proteins that fold, fold faster, catalyze, catalyze faster, signal, and adopt preferred conformational states. Further developments of scoring functions, sampling strategies, and optimization methods will expand the range of applicability of computational protein design to larger and more varied systems, with greater incidence of success. Developments in this field are beginning to have significant impact on biotechnology and chemical biology. 相似文献
999.
M. Elyaqtine 《Human Evolution》2001,16(3-4):159-168
The morphological variability of the temporal articular tubercle was studied inHomo erectus andHomo sapiens. Five configurations have been defined. There is a high heterogeneity amongHomo erectus. The Neandertal lineage and that leading toHomo sapiens sapiens are more homogenous, each of them exhibits a high frequency of one configuration. This study has also focused on the functional
implications of this variation. A theoretical approach to two different configurations of the articular tubercle is considered
in the same bony, muscular and ligamentary context. This suggests that the configuration which consists of a transverse concavity
is, for the mandible depression, concomitant with a slight functional disadvantage in comparison with the cylindrical configuration.
It appears that a midfacial projection allows for a compensation of this disadvantage. It is concluded that this model can
be proposed for Neandertals which present a very concave articular tubercle and a typical midfacial projection. 相似文献
1000.
短肽蝎毒素的结构分类与功能特征 总被引:8,自引:0,他引:8
大量的资料已证实蝎毒中主要致死成分是一类由60~70个残基组成, 选择性地作用于电压门控Na+通道的长肽毒素.另一类由30~40个残基组成的短肽蝎毒素,由于其具有结构致密,易于合成改造的优点,特别是具有选择性地阻遏K+或Cl-通道的特异药理功效,近年来倍受学术界的关注,并在结构与功能方面取得了很大的研究进展. 相似文献