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401.
Juan Camilo Marín Loaiza Carlos L. Céspedes Till Beuerle Claudine Theuring Thomas Hartmann 《Chemoecology》2007,17(2):109-115
Summary. The occurrence of pyrrolizidine alkaloids (PAs) in Pittocaulon (ex Senecio) praecox (Asteraceae) a species endemic to Mexico was established. The aboveground plant organs contain the 1,2-saturated monoester
7-angeloyl-dihydroxyheliotridane together with a small proportion of its 9-angeloyl isomer as major alkaloid. The monoesters
are accompanied by the macrocyclic otonecine derivative senkirkine. Roots contain only related macrocyclic PAs with senecionine,
senkirkine and platyphylline as major components; monoesters are absent. The broom-like succulent stems of P. praecox are infested by the scale insect Ceroplastes albolineatus conspicuously visible by its huge wax cover. All life-history stages, i.e. females, eggs, first instar nymphs (crawlers)
and the wax cover were found associated with PAs. The measured PA concentrations clearly indicate sequestration. The highest
PA concentrations (mg / g dry weight) reached are: mature females, 0.44; eggs, 0.58; crawlers, 0.37; wax cover, 0.08. The
host plant as well as in the infesting scale insect contain the PAs exclusively as free bases. As a phloem-feeder C. albolineatus must acquire the PAs with the ingested phloem sap. This appears plausible since in Senecio species PA are transmitted and circulated through the phloem path. It is suggested that PAs may protect particularly the
crawlers as the most endangered stage in the life-cycle of the scale insect. 相似文献
402.
This paper describes the environmental characteristics and situation of aquatic habitats and communities in southern continental and maritime areas of southeastern South America (Patagonian Shelf GIWA Subregion), resulting from an overall assessment carried out within the framework of a GIWA project, mostly on the basis of publicly available data. The main focus of the analysis was on the current situation of transboundary water resources and anthropogenic impacts. In the inland waters, habitat and community modifications result, principally, from dams and reservoirs built in the main watercourses for hydroelectric power generation and other uses. The transformation of lotic environments into lentic ones have affected habitats and altered biotic communities. In the La Plata River basin, invasive exotic species have displaced native ones. Habitats in the ocean have been degraded, as their biodiversity becomes affected by overfishing and pollution. This article includes a discussion on the causal chain and the policy options elaborated for the Coastal Ecosystem of Buenos Aires province and the Argentinean-Uruguayan Common Fishing Zone, where fishing resources are shared by both countries. 相似文献
403.
Catalina T. Pastor-de-Ward Tamara Rubilar María E. Díaz-de-Vivar Ximena Gonzalez-Pisani Erica Zarate Marina Kroeck Enrique Morsan 《Marine Biology》2007,151(1):205-217
The starfish Cosmasterias lurida was sampled from the pier piles of Almirante Storni in the Golfo Nuevo, northern Patagonia, from November 2001 to November
2003. In this anthropogenically modified site there is an unusually abundant food supply of mussels and large aggregations
of starfishes. The reproductive cycle was studied by organ indices and histological examination of gonads. The highest gonad
index (GI) values were found in the summer (February–March), followed by a drop in GI values, indicating spawning. Histological
analyses indicated that gametogenesis takes place from June to January, sexual maturity occurred during the summer and spawning
occurred in April. The GI and pyloric caeca index (PCI) tended to have an inverse relationship, but this was only statistically
significant in males. However, biochemical analyses of the starfish indicated no transfer of nutrients between pyloric caeca
and gonads in either sex. In fact, simultaneous accumulation of carbohydrates was found in the pyloric caeca and gonads of
both sexes. 相似文献
404.
María J. Darias Harry M. Murray Jeffrey W. Gallant Susan E. Douglas Manuel Yúfera Gonzalo Martínez-Rodríguez 《Marine Biology》2007,152(1):109-118
A restoration programme was introduced in the Mondego Estuary (Portugal) to recover seagrass beds of Zostera noltii endangered by eutrophication. A long-term survey of 10 years was used to assess the development of the processes involved,
focusing one of the key species (Cyathura carinata, Isopoda). The mitigation measures implemented since 1998 (nutrient loading reduction, freshwater circulation improvement
and seagrass bed protection) enhanced water quality and seagrass recovery, thus preventing the development of macroalgal blooms.
C. carinata was resilient to the occurrence of floods and macroalgal blooms, although both events caused dispersion of individuals. This
isopod was not much influenced by the changes occurring in the estuary, showing an unalterable population structure during
the entire study period. After 1998, its density and biomass became more stable at an inner unvegetated sand flat area, where
this isopod was most abundant; its population slightly increased in a bare mud flat at the middle section of the estuary;
but it could not establish successfully in a downstream Z. noltii bed, contrarily to other common estuarine species. Apart from other unknown reasons, the disrupted balanced between trematodes
and their hosts, caused by the eutrophication processes, may have an important role in the discontinuity of C. carinata at the Z. noltii bed. If the intertidal areas become fully restored to the original seagrass coverage, high prevalence and intensity trematodes
may prevent this isopod and other crustaceans from recovering within the intervened areas, by enhancing host mortality and
recruitment failure. In order to avoid this kind of situation, it may be necessary to survey the levels of parasite infestation
within the target hosts and safeguard areas where crustaceans present healthy populations. 相似文献
405.
406.
In principle, a country cannot endure negative genuine savings for long periods of time without experiencing declining consumption. Nevertheless, theoreticians envisage two alternatives to explain how an exporter of non-renewable natural resources could experience permanent negative genuine savings and still ensure sustainability. The first one alleges that the capital gains arising from the expected improvement in the terms of trade would suffice to compensate for the negative savings of the resource exporter. The second alternative points at technological change as a way to avoid economic collapse. This paper uses the data of Venezuela and Mexico to empirically test the first of these two hypotheses. The results presented here prove that the terms of trade do not suffice to compensate the depletion of oil reserves in these two open economies. 相似文献
407.
Tomer J. Czaczkes Ana María Bastidas-Urrutia Paolo Ghislandi Cristina Tuni 《Die Naturwissenschaften》2018,105(11-12):64
Increased urbanisation is leading to a rise in light pollution. Light pollution can disrupt the behaviour and physiology of animals resulting in increased mortality. However, animals may also benefit from artificial light sources, as these may aggregate prey or signal suitable environments. For example, spiders are commonly seen congregating around artificial light sources. Changes in selective pressures engendered by urban environments are driving changes in urban organisms, driving better adaptation to these environments. Here, we ask whether urban populations of the synanthropic spider Steatoda triangulosa show different responses to light compared to rural populations. Egg-sacs from urban and rural populations were collected and incubated in a common garden setting, and the emerging spiderlings tested for light preference. While rural spiderlings avoided light (37% built webs in the light), urban spiderlings were indifferent to it (49% built webs in the light). Reduced light avoidance may benefit spiders through increased prey capture, increased movement into suitable habitats, or due to a release from selection pressure from visually hunting predators which do not enter buildings. 相似文献
408.
María Elena Méndez-López Isabel Ruíz-Mallén Luciana Porter-Bolland María Consuelo Sánchez-González Victoria Reyes-García 《Journal of Environmental Planning and Management》2019,62(6):1045-1064
Previous studies attempting to explain the factors that determine local participation in conservation initiatives have concluded that socio-political exclusion is the main barrier to being involved in such initiatives. Such studies have not differentiated between different types of conservation initiatives. In this paper, we contribute to the literature analyzing the socio-cultural correlates of participation, by differentiating between participation in three types of conservation schemes: protected areas, payment for environmental services, and community conservation. We use data obtained from six rural communities in Mexico, where different combinations of conservation schemes are found. Through linear regression analysis, we explore the relationship between participation and (1) the community of residence; (2) demographics; and (3) socioeconomic characteristics of individuals. Our results suggest that local participation in conservation strategies depends, to a large extent, on the socio-political context in which they are embedded and that the exclusion of women and young adults is clearly consistent. 相似文献
409.
Molecular topology is an application of graph theory and statistics in fields like chemistry, biology, and pharmacology, in
which the molecular structure matters. Its scope is the topological characterization of molecules by means of numerical invariants,
called topological indices, which are the main ingredients of the molecular topological models. These are statistical models
that are instrumental in the discovery of new applications of naturally occurring molecules, as well as in the design of synthetic
molecules with specific chemical, biological, or pharmacological properties. In this review, we focus on pharmacology, which
is a novel field of application of molecular topology. Besides summarizing some recent developments, we also seek to bring
closer this interesting biomedical application of mathematics to an interdisciplinary readership.
相似文献
Vincent M. VillarEmail: |
410.
Mar′?a Arrib′ere Mar′?a C Di′eguez Sergio Ribeiro Guevar Claudia P Queimali?nos Vesna Fajon Mariana Reissig Milena Horvat 《环境科学学报(英文版)》2010,22(8):1171-1178
The deep, ultraoligotrophic piedmont lakes of Northern Patagonia (Argentina) are located in pristine and barely impacted areas,
along a wide latitudinal range. Several studies have reported moderate to high total mercury (Hg) concentrations and contrasting
methylmercury (CH3Hg+) production in di erent lake compartments. Sources of Hg for western Patagonian terrestrial and aquatic
ecosystems are still not clear; while point sources can be ruled out and atmospheric deposition is a plausible source, along with
contribution from active volcanic areas of the Andes. In this investigation, we reported a noticeably seasonal, spatial (between lake
branches), and vertical (between water column strata) heterogeneity in the total Hg concentrations found in the pelagic zone of Lake
Moreno. Sterile water samples taken in a depth profile of the lake showed moderate to high concentrations of CH3Hg+ in autumn with
a decreasing trend with depth. Our results indicated that Hg is largely allocated in the plankton fraction between 10–53 m; which
dominated within the euphotic (epilimnetic) zone of the lake due to the high densities attained by two species of the dinoflagellate
Gymnodinium. The 53–200 m planktonic size fraction (comprising rotifers, ciliates and immature stages of crustaceans) and the > 200
m fraction (calanoid copepods and cladocerans) were found to bear strikingly lower total Hg concentrations, suggesting that the
magnification of Hg at the planktonic consumer level is negligible. 相似文献