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141.
Cross-ecosystem movements of material and energy, particularly reciprocal resource fluxes across the freshwater-land interface, have received major attention. Freshwater ecosystems may receive higher amounts of subsidies (i.e., resources produced outside the focal ecosystem) than terrestrial ecosystems, potentially leading to increased secondary production in freshwaters. Here we used a meta-analytic approach to quantify the magnitude and direction of subsidy inputs across the freshwater-land interface and to determine subsequent responses in recipient animals. Terrestrial and freshwater ecosystems differed in the magnitude of subsidies they received, with aquatic ecosystems generally receiving higher subsidies than terrestrial ecosystems. Surprisingly, and despite the large discrepancy in magnitude, the contribution of these subsidies to animal carbon inferred from stable isotope composition did not differ between freshwater and terrestrial ecosystems, likely due to the differences in subsidy quality. The contribution of allochthonous subsidies was highest to primary consumers and predators, suggesting that bottom-up and top-down effects may be affected considerably by the input of allochthonous resources. Future work on subsidies will profit from a food web dynamic approach including indirect trophic interactions and propagating effects. 相似文献
142.
Insects mediate the effects of propagule supply and resource availability on a plant invasion 总被引:1,自引:0,他引:1
Sanders NJ Weltzin JF Crutsinger GM Fitzpatrick MC Nuñez MA Oswalt CM Lane KE 《Ecology》2007,88(9):2383-2391
Invasive species are a global threat to biodiversity and the functioning of natural ecosystems. Here, we report on a two-year experiment aimed at elucidating the combined and relative effects of three key controls on plant invasions: propagule supply, soil nitrogen (N) availability, and herbivory by native insects. We focus on the exotic species Lespedeza cuneata, a Rank 1 invasive species. Propagule supply and soil N-availability interacted to control the density and foliar cover of L. cuneata. In low N plots, density and foliar cover of L. cuneata were higher in the propagule addition plots than in the plots to which propagules were not added. Surprisingly, this interaction was significant only when the abundance of herbivores was experimentally reduced. This experiment provides evidence that native insect herbivores mediate the interactive effects of propagule supply and resources on invasion by a widespread invasive plant species. 相似文献
143.
Kjell Einar Erikstad Jan Ove Bustnes Svein-Håkon Lorentsen Tone Kristin Reiertsen 《Behavioral ecology and sociobiology》2009,63(6):931-938
In birds, there is ample evidence that the mother can manipulate the sex of the young and produce more of the sex, which gives
the highest fitness return. This has previously been documented in gulls, Laridae. Gulls are sexually size dimorphic with
males larger than females, and there is good evidence that parents in poor body condition switch their investment to the smallest
sex. In the present study, we examined the primary sex ratio and the survival of male and female chicks of lesser black-backed
gull (Larus fuscus fuscus) in relation to their blood levels of organochlorines (OCs), perfluorinated compounds (PFCs) and polybrominated diphenyl
ethers (BDE-47). We show that females with high levels of OCs (but not PFCs and BDE-47) are likely to skew their sex ratio
at hatching towards female offspring. Few females had very high levels of OCs, and the many females with low levels of OCs
overproduced sons resulting in a male skew at hatching (59%). The survival of female offspring was lower than the survival
of male offspring, causing an even stronger male skew in sex ratio (71%). There is evidence to conclude that circulating levels
of OCs in the blood of females may have detrimental effect on the sex allocation strategy and could be of serious threat to
the population.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
144.
Sutter K Jung K Krauss GJ 《Environmental science and pollution research international》2002,9(6):417-421
The assessment of pollution in aquatic systems necessitates an accurate indication of toxicity of heavy metals for organisms and ecosystems. We used the stable nitrogen isotope 15N to estimate the influence of the heavy metals Cd, Pb and Zn on the synthesis of nitrogen-containing fractions in the aquatic moss Fontinalis antipyretica. This method permits conclusions concerning inhibitory effects of these heavy metals on the assimilation of nitrogen and the biosynthesis of amino acids and proteins. The moss was exposed to metal concentrations of 25-500 microM over a period of 5-10 days. 15N abundance of exposed plants was compared with that of control plants. Similar to a loss of vitality determined using a fluorometric assay, a decrease of the 15N abundance in the N fractions of Fontinalis antipyretica was measured in dependence on the metal concentration. Nevertheless, the individual inhibition by the distinct metals was different, so that the following order of toxicity was derived: Cd > Pb > Zn. 相似文献
145.
OBJECTIVE: Although studies have demonstrated that clients in treatment for alcohol abuse are more at risk of driving while impaired (DWI) by alcohol than normal licensed drivers from the general population, no research was found on DWI convictions among those in treatment for abusing cannabis or cocaine. The purpose of this article is to compare DWI convictions among clients in treatment for alcohol, cannabis, cocaine, or various combinations of these substances, compared to a matched population control group. METHOD: A stratified random sample of driver records was drawn from seven client groups who sought treatment in 1994 for alcohol, cannabis, cocaine, or any combination of these substances (n = 445). A random sample of drivers, frequency matched by age and sex (n = 566), served as control subjects. RESULTS: Logistic regression analysis, controlling for sex and age, was conducted to assess whether DWI convictions were elevated for each of the client groups, compared to controls. Two sets of analyses were conducted, before treatment (from 1985 to 1993) and after treatment (from 1995 to 2000). In the time period before treatment, every drug group except the "cannabis only" group had significantly more DWI convictions than controls (p < .05). In the period after treatment, the "alcohol only," "cocaine only," "alcohol and cocaine," and the "cocaine and cannabis" groups still had significantly more DWI convictions than controls (p < .05). CONCLUSION: The results show that DWI convictions are elevated among those who abused cocaine but not among those who abused cannabis. The results suggest that cross-addiction of alcohol and cocaine is common, and problematic drinking among cocaine clients can go undetected when clients are being diagnosed for treatment. 相似文献
146.
Sharks are apex predators, and their evolutionary success is in part due to an impressive array of sensory systems, including
vision. The eyes of sharks are well developed and function over a wide range of light levels. However, whilst close relatives
of the sharks—the rays and chimaeras—are known to have the potential for colour vision, an evolutionary trait thought to provide
distinct survival advantages, evidence for colour vision in sharks remains equivocal. Using single-receptor microspectrophotometry,
we measured the absorbance spectra of visual pigments located in the retinal photoreceptors of 17 species of shark. We show
that, while the spectral tuning of the rod (wavelength of maximum absorbance, λmax 484–518 nm) and cone (λmax 532–561 nm) visual pigments varies between species, each shark has only a single long-wavelength-sensitive cone type. This
suggests that sharks may be cone monochromats and, therefore, potentially colour blind. Whilst cone monochromacy on land is
rare, it may be a common strategy in the marine environment: many aquatic mammals (whales, dolphins and seals) also possess
only a single, green-sensitive cone type. It appears that both sharks and marine mammals may have arrived at the same visual
design by convergent evolution. The spectral tuning of the rod and cone pigments of sharks is also discussed in relation to
their visual ecology. 相似文献
147.
Quantifying climate change mitigation potential in the United States Great Plains wetlands for three greenhouse gas emission scenarios 总被引:1,自引:0,他引:1
148.
Microenvironmental time-activity patterns in Chongqing, China 总被引:1,自引:0,他引:1
Yu Zhao Shuxiao Wang Gangcai Chen Fei Wang Kristin Aunan Jiming Hao 《Frontiers of Environmental Science & Engineering in China》2009,3(2):200-209
An investigation using recall questionnaires was conducted in winter and autumn 2006 to evaluate the time-activity patterns
in Chongqing, China. The average time spent in seven microenvironments (MEs) including outdoors, transit, living room, bedroom,
kitchen, classroom/office, and other indoors were found to be about 3.5, 1.1, 2.5, 9.7, 1.4, 4.2, and 1.7 h per day, respectively.
According to the results of a nonparametric test, the sampling period and day of week were significant for the variation of
the time spent in all MEs except for transit and outdoors. The time budget was analyzed using a general linear model (GLM),
which exhibited significant variability by demographic factors such as gender, age, residence, education, and household income. 相似文献