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271.
272.
273.
A trophic cascade triggers collapse of a salt-marsh ecosystem with intensive recreational fishing 总被引:1,自引:0,他引:1
Overexploitation of predators has been linked to the collapse of a growing number of shallow-water marine ecosystems. However, salt-marsh ecosystems are often viewed and managed as systems controlled by physical processes, despite recent evidence for herbivore-driven die-off of marsh vegetation. Here we use field observations, experiments, and historical records at 14 sites to examine whether the recently reported die-off of northwestern Atlantic salt marshes is associated with the cascading effects of predator dynamics and intensive recreational fishing activity. We found that the localized depletion of top predators at sites accessible to recreational anglers has triggered the proliferation of herbivorous crabs, which in turn results in runaway consumption of marsh vegetation. This suggests that overfishing may be a general mechanism underlying the consumer-driven die-off of salt marshes spreading throughout the western Atlantic. Our findings support the emerging realization that consumers play a dominant role in regulating marine plant communities and can lead to ecosystem collapse when their impacts are amplified by human activities, including recreational fishing. 相似文献
274.
Isabelle Amat Emmanuel Desouhant Carlos Bernstein 《Behavioral ecology and sociobiology》2009,63(4):563-572
When foraging partially depleted patches (i.e., a fraction of hosts are already parasitized), female parasitoids must decide:
1—whether to superparasitize, and 2—whether to stay in their current patch (thus missing the opportunity of finding a better
patch elsewhere). To make these decisions, parasitoids may rely on different cues, produced both by the environment and by
conspecifics. Animals thriving in different environments may differ in cues they use. In the solitary parasitoid Venturia canescens, thelytokous (asexual) and arrhenotokous (sexual) individuals are found in two contrasting environments. Thelytokous females,
from anthropogenic conditions, are known to cope with superparasitism in an adaptive way. On the other hand, little is known
about superparasitism by arrhenotokous females. We compared the host exploitation strategies of thelytokous and arrhenotokous
females in partially depleted patches. Hosts parasitized by thelytokous females were more frequently avoided than those parasitized
by arrhenotokous females, suggesting a stronger chemical marking of the former. Only thelytokous females used information
from conspecifics for patch-leaving decisions. The conformity of the differences in the behavior of thelytokous and arrhenotokous
females with the environmental conditions they experience in their habitat is discussed. 相似文献
275.
Mohamed Batal Isabelle Boudry Cécile Cléry-Barraud Stéphane Mouret Thierry Douki 《毒物与环境化学》2013,95(2):260-276
Sulphur mustard (SM) is known as an efficient vesicating agent as well as a carcinogenic chemical. This warfare agent remains a threat for both civilians and militaries. DNA alkylation is one of the critical molecular pathways at the origin of the symptoms associated with SM exposure. SM forms monoadducts with guanine and adenine as well as a biadduct between two guanine bases. The aim of the present work is to determine the relative yields of these three lesions in DNA samples after SM exposure without using radiolabeled SM as in earlier works. For this purpose, we have developed a high performance liquid chromatography/tandem mass spectrometric method to simultaneously quantify the SM monoadducts and biadduct in the same DNA sample. We observed in isolated and cellular DNA that the guanine monoadduct was the predominant lesion, while the biadduct was present in twofold lower yield. The adenine monoadduct was generated in lowest amounts. The analytical approach was extended to 2?chloroethyl ethyl sulphide, a widely used SM analog. Again, the adenine adduct was much less frequent than the guanine derivative. The developed assay will allow performing studies involving large numbers of samples. 相似文献
276.
S. Hummel B. Herrmann J. Rameckers D. Müller K. Sperling H. Neitzel H. Tönnies 《Die Naturwissenschaften》1999,86(10):500-503
In PCR-supported amplification of ancient, degraded DNA, contamination with contemporary DNA can lead to false-positive results,
which frequently give rise to discussions in which the mere existence of ancient DNA is doubted. Our confirmation of ancient
DNA using comparative genome hybridization (CGH) eliminates these doubts. Unlike PCR methods, CGH requires no amplification
of the DNA to be analyzed if adequate amounts of specimen DNA is used. Thus, false results traceable to contaminations are
practically ruled out. The examples provided here prove the authenticity of ancient DNA for a 250-year-old and a 3000-year-old
sample. At the same time, the CGH of ancient DNA offers the chance to gain insight into the pattern of DNA degradation and
to monitor the preservation of certain chromosomal segments.
Received: 10 May 1999 / Accepted in revised form: 29 July 1999 相似文献
277.
S. Herrmann 《Die Naturwissenschaften》1958,45(8):195-195
278.
Lutts S Lefèvre I Delpérée C Kivits S Dechamps C Robledo A Correal E 《Journal of environmental quality》2004,33(4):1271-1279
To identify Cd- and Zn-accumulating plants exhibiting a high growth rate, seeds from the halophyte species Mediterranean saltbush (Atriplex halimus L.) were collected on a heavy-metal-contaminated site in southeastern Spain (Llano del Beal, Cartagena). Seedlings from this ecotype were exposed for 3 wk to 0.1 mM Cd or Zn in a nutrient solution in a fully controlled environment. All plants remained alive and no significant growth inhibition was recorded until the end of the experiment. Mean Cd and Zn accumulation in aerial parts was 830 and 440 mg kg(-1), respectively, and the rate of metal translocation even increased with the duration of stress exposure. Resistance to heavy metals in this species may be partly linked to precipitation of Cd in oxalate crystals in the stems. A Cd-induced decrease in glutathione concentration also suggests that phytochelatins overproduction may occur in these conditions. We conclude that Mediterranean saltbush, which is able to produce up to 5 Mg dry matter ha(-1) yr(-1), may be an effective species for phytoextraction and should be tested for this purpose in field conditions. 相似文献
279.
Landscape changes over a period of 25 years were assessed for a catchment basin in Normandy, France. Landscape attributes, i.e. land use, land cover and natural habitat, were obtained from aerial photographs (1964, 1989) and soil maps, to define a landscape typology. Data were aggregated on a 500 m×500 m grid system and treated by multivariate analysis. Results of these analysis show that this rural landscape has undergone changes in landcover (mainly grassland receding to crop) as well as changes in spatial structure (mainly increase of plot size and uniformisation). These changes were related to a typology of farms (realised by multivariate analysis of a field survey on the 38 registered farms of the site). Results suggest that (i) farms with a narrow range of production, i.e. specialised farms, are located on a narrow range of environmental conditions and are associated with stable landscapes, while (ii) farms with a broader range of production (i.e. polyculture) are distributed more widely throughout the landscape, and are mostly associated with the landscape changes. 相似文献
280.