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排序方式: 共有205条查询结果,搜索用时 46 毫秒
111.
Davison AW Neufeld HS Chappelka AH Wolff K Finkelstein PL 《Environmental pollution (Barking, Essex : 1987)》2003,125(1):61-70
Visible injury caused by ozone is recorded every year in native plant species growing in Great Smoky Mountains National Park (USA). One of the most sensitive species, cutleaf coneflower (Rudbeckia laciniata L.), shows great variation in symptoms between and within populations but the causes of this variation and its ecological significance are currently unknown. This paper presents data relating to genetic variation, ozone concentrations, stomatal conductance and light (PAR) within populations. The data show that populations differ in genetic diversity, one consisting of only three genets while another was very diverse. In the former population, symptoms varied greatly within a single genet, pointing to a large micro-environmental influence. Measurements of ozone, stomatal conductance and PAR within plant canopies suggest that variation in symptom expression is unlikely to be due to differences in ozone flux and more likely to be due to variation in light. The variation in visible symptoms raises the question of what bioindicators actually indicate, and it suggests that symptoms should be interpreted with great caution until the underlying causes of that variation are fully understood. 相似文献
112.
D. Martin Fleming Wilfried F. Wolff Donald L. DeAngelis 《Environmental management》1994,18(5):743-757
Declines in populations of and reproductive success of wood storks and other wading birds have occurred in the Florida Everglades
over the past several decades. These declines have been concurrent with major changes in the Everglades’ landscape characteristics.
Among the plausible hypotheses that relate to landscape change are the following: (1) general loss of habitat; (2) heavy loss
of specific habitat, namely, short-hydroperiod wetlands that provide high prey availability early in the breeding season;
and (3) an increase in frequency of major drying out of the central slough areas, which can affect prey availability late
in the breeding season.
These three hypotheses were compared using an individual-based model of wood stork (Mycteria americana) reproduction. This model simulated the behavior and energetics of each individual wood stork in a breeding colony on 15-min
time intervals. Changes in water depth and prey availability occurred on daily time steps. Simulation results showed a threshold
response in reproductive success to reduction of wetland heterogeneity. Model comparisons in which (1) only short-hydroperiod
wetlands were removed and (2) wetlands of both long and short hydroperiods were removed showed that, for the same loss of
total area, the specific habitat removal caused a much greater reduction in wood stork reproduction, indicating hypothesis
2 may be a more likely explanation than hypothesis 1. Reduction of initial prey availability in the central slough areas (simulating
frequent drying; hypothesis 3) reduced fledging success by an average of more than 90% in the model. 相似文献
113.
Carsten Niemitz 《Die Naturwissenschaften》2010,97(3):241-263
During the last century, approximately 30 hypotheses have been constructed to explain the evolution of the human upright posture
and locomotion. The most important and recent ones are discussed here. Meanwhile, it has been established that all main hypotheses
published until the last decade of the past century are outdated, at least with respect to some of their main ideas: Firstly,
they were focused on only one cause for the evolution of bipedality, whereas the evolutionary process was much more complex.
Secondly, they were all placed into a savannah scenario. During the 1990s, the fossil record allowed the reconstruction of
emerging bipedalism more precisely in a forested habitat (e.g., as reported by Clarke and Tobias (Science 269:521–524, 1995) and WoldeGabriel et al. (Nature 412:175–178, 2001)). Moreover, the fossil remains revealed increasing evidence that this part of human evolution took place in a more humid
environment than previously assumed. The Amphibian Generalist Theory, presented first in the year 2000, suggests that bipedalism
began in a wooded habitat. The forests were not far from a shore, where our early ancestor, along with its arboreal habits,
walked and waded in shallow water finding rich food with little investment. In contrast to all other theories, wading behaviour
not only triggers an upright posture, but also forces the individual to maintain this position and to walk bipedally. So far,
this is the only scenario suitable to overcome the considerable anatomical and functional threshold from quadrupedalism to
bipedalism. This is consistent with paleoanthropological findings and with functional anatomy as well as with energetic calculations,
and not least, with evolutionary psychology. The new synthesis presented here is able to harmonise many of the hitherto competing
theories. 相似文献
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119.
Etienne Paul Delmira Beatriz Wolff Juan Carlos Ochoa Rejane Helena Ribeiro da Costa 《Water environment research》2007,79(7):765-774
The reduction of organic and nitrogen pollution of wastewater was investigated in two hybrid reactors and compared with the reduction obtained by using a conventional activated sludge reactor (ASR) run as a control. Both HR-1 and HR-2 were activated sludge systems where a low-density carrier, P1 (polyethylene) for HR-1 and P2 (recycled plastics) for HR-2, was added. Firstly, the three reactors were operated at 10 days Suspended Solid Retention Time (SRT(SS)), leading to a complete nitrification. Secondly, the SRT(SS) for each reactor was lowered to 3 days. Nitrification was lost for the ASR but remained complete for HR's. Respirometric techniques were used to measure fixed or suspended biomass activities for heterotrophic and autotrophic biomass. More than 90% of the autotrophic activity was found on the supports whatever the SRT(SS) used. The results may underline the role of the carrier geometry or surface characteristics on the autotrophic/heterotrophic microorganism distribution. 相似文献
120.
In order to investigate the oxygen tolerance capacity of upflow anaerobic solid-state(UASS)with anaerobic filter(AF) system, the effect of microaeration on thermophilic anaerobic digestion of maize straw was investigated under batch conditions and in the UASS with AF system. Aeration intensities of 0–431 m L O2/gvswere conducted as pretreatment under batch conditions. Aeration pretreatment obviously enhanced anaerobic digestion and an aeration intensity of 431 m L O2/gvsincreased the methane yield by 82.2%. Aeration intensities of 0–355 m L O2/gvswere conducted in the process liquor circulation of the UASS with AF system. Dissolved oxygen(DO) of UASS and AF reactors kept around 1.39 ±0.27 and 0.99 ± 0.38 mg/L, respectively. p H was relatively stable around 7.11 ± 0.04. Volatile fatty acids and soluble chemical oxygen demand concentration in UASS reactor were higher than those in AF reactor. Methane yield of the whole system was almost stable at 85 ± 7 m L/gvs as aeration intensity increased step by step. The UASS with AF system showed good oxygen tolerance capacity. 相似文献