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91.
Decline of Native Freshwater Fishes in a Mediterranean Watershed on the Iberian Peninsula: A Quantitative Assessment 总被引:2,自引:0,他引:2
Enric Aparicio Maria Josep Vargas Josep Maria Olmo Adolfo de Sostoa 《Environmental Biology of Fishes》2000,59(1):11-19
We examined changes in the distribution of 9 native and 18 introduced freshwater fishes in the south-eastern Pyrenees watershed, Iberian Peninsula, using data from 1996, 1984–1988 and historical information. This region suffers many modifications to its freshwater ecosystems that are linked to human activity in the Mediterranean regions. Fish communities, stream physical habitat and environmental degradation were assessed at 168 sites from 11 basins in 1996. Seven native species (78%) showed decline from previous data, one of which became extirpated in the first half of the 20th century. On the other hand, introduced species are expanding. As a consequence, intact native communities are increasingly rare, declining from presence in 22% of river courses in 1984–1988 to 15% in 1996. The most typical community type is a mixture of native and introduced species occupying 30% of river courses. Stream degradation seems to be the main cause of this process because fish communities differed between degraded streams and streams suffering less impact. A principal component analysis showed that water pollution and modifications to the habitat were the two anthropogenic factors that accounted for most changes in the fish community integrity. Habitat alteration, primarily through construction of dams and water diversions, has fragmented habitats and isolated native fish communities in headwater streams. Current protection measures do not offer effective conservation of threatened species and communities. A global conservation and restoration programme from an ecosystem-based approach is essential to reverse the trend affecting native freshwater fishes in this Mediterranean region. 相似文献
92.
Experiments were carried out to investigate the effects of different degrees of water stress on cowpea in the presence and
absence of Bradyrhizobium spp. inoculation and to evaluate physiological responses to stress. The soil used was Yellow Latosol, pH 6.3 and the crop
used was cowpea (Vigna unguiculata (L.) Walp.) cv. ‘IPA 204’. Stress was applied continuously by the control of matric potential (ψ
m
) through a porous cup. The lowered soil ψ
m
had a direct effect on the N2 fixation, but the strains Bradyrhizobium introduced by inoculation in the cowpea plants were superior to the indigenous strain demonstrating the importance of inoculation
in the stressed plants. At the more negative ψ
m
plants inoculated with the strains EI 6 formed associations of greater symbiotic efficiency which helped the cowpea plants
to withstand drought stress better than the strain BR 2001 and the uninoculated control. The leghaemoglobin concentration
was not inhibited in the drought-stressed plants at ψ
m
-70 kPa when inoculated with the strain EI 6, which confered a differential degree of drought resistance in plants. The ψ
w
declined in the stressed plants reaching values of -1.0 MPa which was sufficient to cause disturbance in nodulation and biomass
production.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
93.
94.
Shahrzad Shirazi Fard Julianna Kele Mar?al Vilar Gustavo Paratcha Fernanda Ledda 《PloS one》2010,5(3)
Nerve Growth Factor (NGF)-induced neuronal differentiation requires the activation of members of the Rho family of small GTPases. However, the molecular mechanisms through which NGF regulates cytoskeletal changes and neurite outgrowth are not totally understood. In this work, we identify the Rac1-specific guanine exchange factor (GEF) Tiam1 as a novel mediator of NGF/TrkA-dependent neurite elongation. In particular, we report that knockdown of Tiam1 causes a significant reduction in Rac1 activity and neurite outgrowth induced by NGF. Physical interaction between Tiam1 and active Ras (Ras-GTP), but not tyrosine phosphorylation of Tiam1, plays a central role in Rac1 activation by NGF. In addition, our findings indicate that Ras is required to associate Tiam1 with Rac1 and promote Rac1 activation upon NGF stimulation. Taken together, these findings define a novel molecular mechanism through which Tiam1 mediates TrkA signaling and neurite outgrowth induced by NGF. 相似文献
95.
Several experiments have been performed on three congenericspecies of the calanoid copepod Acartia to determine the effectsof small-scale turbulence on metabolic rates. Both inorganicnitrogen and phosphorus excretion rates significantly increased 相似文献
96.
97.
Francisco Ciruela Carles Saura Enric I. Canela Josefa Mallol Carmen Lluis Rafael Franco 《FEBS letters》1996,380(3):219-223
Adenosine deaminase (ADA) is not only a cytosolic enzyme but can be found as an ecto-enzyme. At the plasma membrane, an adenosine deaminase binding protein (CD26, also known as dipeptidylpeptidase IV) has been identified but the functional role of this ADA/CD26 complex is unclear. Here by confocal microscopy, affinity chromatography and coprecipitation experiments we show that A1 adenosine receptor (A1R) is a second ecto-ADA binding protein. Binding of ADA to A1R increased its affinity for the ligand thus suggesting that ADA was needed for an effective coupling between A1R and heterotrimeric G proteins. This was confirmed by the fact that ASA, independently of its catalytic behaviour, enhanced the ligand-induced second messenger production via A1R. These findings demonstrate that, apart from the cleavage of adenosine, a further role of ecto-adenosine deaminase on the cell surface is to facilitate the signal transduction via A1R. 相似文献
98.
Llorenç Sabate Rafael Franco Enric I. Canela Josep J. Centelles Marta Cascante 《Molecular and cellular biochemistry》1995,142(1):9-17
A mathematical model based on kinetic data taken from the literature is presented for the pentose phosphate pathway in fasted rat liver steady-state. Since the oxidative and non oxidative pentose phosphate pathway can act independently, the complete (oxidative + non oxidative) and the non oxidative pentose pathway were simulated.Sensitivity analyses are reported which show that the fluxes are mainly regulated by D-glucose-6-phosphate dehydrogenase (for the oxidative pathway) and by transketolase (for the non oxidative pathway). The most influent metabolites were the group ATP, ADP, P1 and the group NADPH, NADP+ (for the non oxidative pathway).Abbreviations GK
Glucokinase, (E.C. 2.7.1.2.)
- G6PDH
D-glucose-6-phosphate dehydrogenase, (E.C. 1.1.1.49)
- PLase
6-Phosphogluconelactonase, (E.C. 3.1.1.31.)
- PGIcDH
6-Phosphogluconate dehydrogenase, (E.C. 1.1.1.44)
- RPI
D-ribose-5-phosphate keto-isomerase, (E.C. 5.3.1.6)
- TK
D-sedoheptulose-7-phosphate: D-glyceraldehyde-3-phosphate glycol-aldehyde transferase, (E.C. 2.2.1.1.)
- TA
D-sedoheptulose-7-phosphate: D-glyceraldehyde-3-phosphate dihydroxyacetone transferase, (E.C. 2.2.1.2)
- EP
D-ribulose-5-phosphate-3-epimerase, (E.C. 5.1.3.1)
- PGI
D-glucose-6-phosphate keto-isomerase, (E.C. 5.3.1.9)
- TPI
D-glyceraldehyde-3-phosphate keto-isomerase, (E.C.5.3.1.1) 相似文献
99.
Food availability as a potential source of bias in the egg production method for copepods 总被引:1,自引:0,他引:1
Enric Saiz; Calbet Albert; Trepat Isabel; Irigoien Xabier; Alcaraz Miquel 《Journal of plankton research》1997,19(1):1-14
The measurement of copepod adult female fecundity as an estimateof adult growth (production) rates has been an approach widelyused in both laboratory and field studies. Here we demonstratethat the basic assumption of this approach, i.e. that estimatedegg production during the incubation reflects the insitu conditions, is not always legitimate and that itis temperature dependent. The enhancement of metabolic ratesinduced by high temperatures induces a more accented bias ofthe method. We also provide guidelines on how to conduct theincubations in order to obtain more reliable estimates. 相似文献
100.
Stefanie Keller Valerio Bartolino Manuel Hidalgo Isabella Bitetto Loredana Casciaro Danila Cuccu Antonio Esteban Cristina Garcia Germana Garofalo Marios Josephides Angelique Jadaud Evgenia Lefkaditou Porzia Maiorano Chiara Manfredi Bojan Marceta Enric Massutí Reno Micallef Panagiota Peristeraki Giulio Relini Paolo Sartor Maria Teresa Spedicato George Tserpes Antoni Quetglas 《PloS one》2016,11(1)