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871.
Roughly 40 years after its introduction, the metapopulation concept is central to population ecology. The notion that local populations and their dynamics may be coupled by dispersal is without any doubt of great importance for our understanding of population-level processes. A metapopulation describes a set of subpopulations linked by (rare) dispersal events in a dynamic equilibrium of extinctions and recolonizations. In the large body of literature that has accumulated, the term "metapopulation" is often used in a very broad sense; most of the time it simply implies spatial heterogeneity. A number of reviews have recently addressed this problem and have pointed out that, despite the large and still growing popularity of the metapopulation concept, there are only very few empirical examples that conform with the strict classical metapopulation (CM) definition. In order to understand this discrepancy between theory and observation, we use an individual-based modeling approach that allows us to pinpoint the environmental conditions and the life-history attributes required for the emergence of a CM structure. We find that CM dynamics are restricted to a specific parameter range at the border between spatially structured but completely occupied and globally extinct populations. Considering general life-history attributes, our simulations suggest that CMs are more likely to occur in arthropod species than in (large) vertebrates. Since the specific type of spatial population structure determines conservation concepts, our findings have important implications for conservation biology. Our model suggests that most spatially structured populations are panmictic, patchy, or of mainland-island type, which makes efforts spent on increasing connectivity (e.g., corridors) questionable. If one does observe a true CM structure, this means that the focal metapopulation is on the brink of extinction and that drastic conservation measures are needed. 相似文献
872.
Pilar Santidrián Tomillo Jack S. Suss Bryan P. Wallace Kimberly D. Magrini Gabriela Blanco Frank V. Paladino James R. Spotila 《Marine Biology》2009,156(10):2021-2031
Reproductive output of leatherback turtles (Dermochelys coriacea) is affected by the stochastic nature of emergence success. Average emergence success of nests at Playa Grande, Costa Rica
was 0.38 ± 0.27. Incubation temperature affected development of leatherback turtle eggs and emergence of hatchlings from the
nest. We found that high temperatures reduced hatching success and emergence rate and increased embryonic mortality both early
and late during incubation at Playa Grande. There was a temporal effect on emergence success that resulted in more hatchlings
being produced at the beginning of the season, because of higher emergence success, than toward the end. Likewise, production
of hatchlings varied from year to year. The average annual reproductive output was 252 ± 141 hatchlings per female. The 2005–2006
nesting season had the highest emergence success and produced the greatest number of hatchlings per female compared to the
2004–2005 (+120%) and 2006–2007 (+41%) seasons. However, average clutch size (62 ± 10) and clutch frequency (9.45 ± 1.63),
were not different among years. Turtles that had nested a high number of years exhibited greater clutch frequency and arrived
earlier to nest than turtles that had nested in fewer numbers of years. Nesting when environmental conditions favor high developmental
success and emergence rate may constitute an advantageous reproductive strategy. 相似文献
873.
Frank David Matthew S Klee 《环境化学》2014,(3):532-534
采用毛细管GC结合安捷伦7000A三重串联四极杆GC/MS(G7010AA)系统的多反应监测(MRM)模式分析了大气颗粒物中的硝基多环芳烃(nitro-PAHs).传统硝基多环芳烃的分析方法是在样品前处理之后,使用单四极杆GC/MS的选择离子监测SIM模式或者多维GC/MS,但基于MS/MS检测模式超强的选择性,可直接分析大气颗粒物的粗提物.实际样品中的硝基多环芳烃可以检测到pg·μL-1的级别,相对应于大气样品中pg·m-3级的含量. 相似文献
874.
The effect of the spin-trap α-phenyl-N-t-butylnitrone (PBN) on the formation of fatty acid dimers induced by the anoxic microsomal metabolism of tetrachloromethane was investigated in vitro, in particular, with respect to cross-linking of arachidonic acid with a second one (C20–C20) and of arachidonic acid with docosahexaenoic acid (C20–C22). PBN exerted no effect on anaerobic tetrachloromethane metabolism but inhibited dimer formation, half-maximally at a concentration of 0.1 mmol L?1. Trichloromethyl octadecenoic acid was also found, but at levels 10-fold lower than the fatty acid dimers. The data suggest that the hepato-protective effect of PBN against tetrachloromethane-toxicity may be due to its ability to scavenge fatty acid radicals, resulting in stable, non-reactive entities, which do not undergo secondary reactions such as cross-linking. The data confirm and extend previous findings that crosslinking plays an important role in tetrachloromethane toxicity and similar cases of metabolic radical-induced toxicity. 相似文献
875.
Pinot noir, bastardo, rkaziteli and semillon grapes on vines grown in the Barossa Valley of South Australia were treated with a commercial dithianon formulation. The grapes were harvested by hand eight days later, and made into wine. Grab samples of berries, grape juice and the young wine were analysed for fungicide residues. No dithianon was detected in control grape samples, grape juices or wines. Significant dithianon levels were detected on the skins of treated grape samples. Dithianon is stable on the surface of grapes under the ambient conditions prevalent under the grape canopy for at least two weeks. No dithianon was detected in grape juice, on grape skins after berry crushing, in the lees, or in the young wine. Dithianon is unstable in grape juice and wine. Dithianon half‐life (initial concentration = 1 μg/mL) in semillon grape juice = 2.8 h, semillon wine = 0.58 h, pinot noir grape juice = 4.6 h, and pinot‐noir wine = 0.29 h. Treatment with fining agents or heat does not significantly reduce the rate of degradation. These results suggest that spraying table grapes with dithianon two weeks before harvest would result in exposure to essentially the full dose of active ingredient sprayed, and increase the risk to human health through ingestion of this compound. However, any threat to human health from ingestion through grape juice or wine is limited since any contact with grape juice or wine leads to rapid decomposition of dithianon by some as yet undetermined process. 相似文献
876.
A strictly species-centric view of human impacts on ecological communities may conceal important trait changes key to ecosystem functioning and stability. Analyses of body size and community composition data for 326 Northwest Atlantic fish species sampled across > 900000 km2 over three decades revealed a rapid and widespread reduction of body sizes driven by declines within species and changes in relative abundances. The changes were unrelated to species richness but of sufficient magnitude to eliminate biogeographic scale gradients of increasing body size with latitude commonly characterized as Bergmann's rule. These changes have persisted despite reduced potential for intraspecific competition and favorable bottom water temperatures, both of which should lead to increased growth rates. The aggregate body sizes in these Northwest Atlantic fish communities may now represent a mismatch between the environmental variability characteristic of the Northwest Atlantic and the historical body size, life history traits, and productivity of species across this region. We discuss how these changes may jeopardize the potential for recovery of these important temperate/subarctic ecosystems. 相似文献
877.
Results are presented from a century-long 1/10° global ocean simulation that included a suite of age-related passive tracers. In particular, an ensemble of five global Boundary Impulse Response functions (BIRs, which are statistically related to the more fundamental Transit Time Distributions, TTDs) was included to quantify the character of the TTD when mesoscale eddies are explicitly simulated rather than parameterized. We also seek to characterize the level of variability in water mass ventilation timescales arising from eddy motions. The statistics of the BIR timeseries are described, and it is shown that the greatest variability occurs at early times, followed by a remarkable conformity between ensemble members at longer timescales. The statistics of the first moment of the BIRs are presented, and the upper-ocean spatial distribution of the standard deviation of the first moment of the BIRs discussed. It is shown that variations in the BIR first moment with respect to the ensemble average are typically only a few percent, and that the variability slightly decreases with increasing ensemble size, implying that only a few ensemble members may be necessary for a reasonable estimate of the TTD. The completeness of the estimated TTD, i.e., the degree to which the century long BIRs capture the range of global ocean ventilation timescales is discussed, and the potential for extrapolation of the BIR to longer times is briefly explored. Several regional BIRs were also simulated in order to quantify the relative abundance of fluid parcels that originate in specific geographical locations. 相似文献
878.
879.
Russell E. Keenan James W. Knight Elizabeth R. Rand Mary M. Sauer Bruce W. Found Frank H. Lawrence 《Chemosphere》1990,20(10-12)
Potential human and wildlife exposures to TCDD in landspread pulp and paper mill sludge in the State of Maine were evaluated by means of a human health and an ecological risk assessment methodology. The highest historical concentrations of TCDD reported for these sludges do not present a risk to American woodcock, selected as an indicator species for this analysis. Concentrations of TCDD as high as 50 ppt in soil are not likely to produce adverse effects in the embryonic/hatchling stage of the woodcock. This soil concentration of TCDD does not present a significant risk to sportsmen and their families that may consume birds which inhabit these sites. 相似文献
880.
Anja Vespermann Frank Riepert und Jochen Pflugmacher 《Umweltwissenschaften und Schadstoff-Forschung》2003,15(3):143-151
Zusammenfassung Ziel der beschriebenen Untersuchungen war die praktische überprüfung eines Methodenentwurfs zur Erfassung der Bioakkumulation
von Umweltchemikalien mitEisenia fetida, der Eignung vonE. fetida als Modellorganismus und des OECD-Kunstbodens als Standardsubstrat. Als Testorganismen wurden aus eigener Zucht der KompostwurmEisenia fetida und nach FeldentnahmeAllolobophora caliginosa, Allolobophora chlorotica, Allolobophora longa undLumbricus rubellus eingesetzt. Testb?den waren der OECD-Kunstboden und ein Boden vom Versuchsfeld der BBA in Berlin-Dahlem. Beiden B?den wurden
die Testsubstanzen Hexachlorbenzol und Pyren in einer Konzentration von 10 mg/kg Bodentrockengewicht zugemischt. Die Expositionszeit
der Regenwürmer betrug 4 Wochen bei w?chentlicher Bestimmung der Konzentrationen der Testsubstanzen in den Würmern und B?den.
Die fürE. fetida sowie die Wildarten errechneten Anreicherungsfaktoren (AF) beliefen sich bei HCB in Abh?ngigkeit des verwendeten Bodens auf
Werte zwischen 10 und 17 und bei Pyren auf Werte zwischen 0,9 und 1,7. Durch Umrechnung der Bodenkonzentrationen auf Gehalte
in der Wasserphase und Ableitung der entsprechenden Anreicherungsfaktoren kann ein Vergleich mit BCF-Werten, die aus QSAR’S
anderer Regenwurmarten und Fischen berechnet wurden, hergestellt werden. Die Ergebnisse lassen den Schluss zu, dass der Regenwurmtest
mitE. fetida (OECD 1984, ISO 1998) für die Untersuchung der Bioakkumulation geeignet ist.
OnlineFirst: 31. 05. 2002 相似文献