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261.
262.
Few studies have assessed the transport of dissolved nutrients at the field scale under natural rainfall conditions. Hysteresis between dissolved nutrients and discharge behavior can complicate such assessments and this effect has only been examined qualitatively. In this study, we investigated factors contributing to short-term variations of dissolved cation (Ca, Mg, Na, and K) and anion (soluble reactive phosphorus [SRP], NO3, and SO4) concentrations in runoff water and developed a quantitative method to study their hysteretic behavior. Within-storm variations of dissolved nutrient concentrations were determined in two agricultural fields during four natural rainfall events along with discharge, sediment, antecedent soil water conditions, and nutrient contents. For each event, nutrient loads were plotted against discharge during the rising and falling limb of the runoff hydrograph. The resulting hysteresis curves were characterized by an index H, which is the ratio between the integrated areas under the rising and falling curves of the hydrograph. Results showed that nutrient concentrations increased with time during each event. Counterclockwise (H < 1) hysteresis, occurring when the falling limb had larger loads, was found when soils were initially dry whereas clockwise hysteresis (H > 1) was associated with prior wet soil conditions. Two hypotheses are suggested to explain these variations. First, suspended sediments could have acted as a sink for dissolved nutrients and the sensitivity of nutrients to hydrological conditions was determined by their preferential sorption on these sediments. Second, movement of nutrients into runoff occurred more readily as soils became wetter during an event. 相似文献
263.
264.
Dental microwear in relation to changes in the direction of mastication during the evolution of Myodonta (Rodentia,Mammalia) 总被引:2,自引:1,他引:1
Observations of dental microwear are used to analyse the correlation between changes in molar tooth crown morphology and the
direction of masticatory movement during the evolution of Myodonta (Rodentia, Mammalia). The studied sample includes 36 specimens
representing both superfamilies of Myodonta (Muroidea and Dipodoidea) spanning 16 dipodoid and 9 muroid species. Microscopic
scratches on occlusal surfaces resulting from contact between opposite teeth during mastication are analysed. Using these
features, we determine the direction of masticatory movements. Microwear patterns display diverse orientations among Dipodoidea:
oblique in Sicistinae, Euchoreutinae and Zapodinae, propalinal in Dipodinae and intermediary in Allactaginae. Similarly, Muroidea
exhibit the following orientations: oblique in Cricetinae and propalinal in Arvicolinae, Cricetomyinae, Gerbillinae and Murinae.
These various chewing types illustrate different evolutionary grades within the superfamilies. Acquisition of the antero-posterior
masticatory movement in Dipodoidea is related to flattening of the molar occlusal surface. However, in some muroid subfamilies,
this direction of mastication is associated with low-crowned and cuspidate molars (Cricetomyinae, Murinae). 相似文献
265.
In holometabolous insects, pupation site selection behaviour has large consequences for survival. Here, we investigated the
combined effects of temperature and parasitism by the parasitoid Asobara tabida on larval pupation behaviour in two of its main Drosophila sp. hosts differing in their climate origin. We found that larvae of Drosophila melanogaster—a species with a (sub)tropical origin—placed at 25°C pupated higher in rearing jars than those placed at 15°C. The opposite
pattern was observed for Drosophila subobscura larvae—a species from temperate regions—which pupated lower, i.e. on or near the substrate at 25°C, than those placed at
15°C. When placed at 25°C, parasitized larvae of both species pupated closer to the substrate than unparasitized ones. Moreover,
the Drosophila larvae that had been exposed and probably stung by A. tabida, but were not parasitized, pupated lower than the control unparasitized larvae. These results provide new insights of host
behaviour manipulation by A. tabida larvae. 相似文献
266.
Firmat C Gomes Rodrigues H Hutterer R Rando JC Alcover JA Michaux J 《Die Naturwissenschaften》2011,98(1):33-37
Malpaisomys insularis is a mouse-like rodent endemic to the eastern Canary Islands. It became extinct during the fourteenth century. It was a remarkable
species living under hyperarid conditions. A dental microwear analysis was performed in order to determine its former diet.
The elevated number of fine scratches found in Malpaisomys molars suggests that it consumed a significant part of Poaceae, grass consumption leaving the most distinctive features on
dental wear facets. A graminivorous diet with a high amount of abrasive items is in agreement with the broad teeth of Malpaisomys, considered as adapted to grass consumption. However, in the absence of potential competitors over its native range, it is
likely that Malpaisomys also foraged on dicots to meet higher nutrient and energetic requirements. The ecology of Malpaisomys is discussed from these results in the context of the desertic climatic conditions of the eastern Canary Islands and with
a special concern on its small body size in contrast to other large-sized island murine species such as the giant rats of
the central Canary Islands. 相似文献
267.
Environmental Modeling & Assessment - This paper investigates whether economic development is impeded by binding national emission standards to control climate change. We develop a simple model... 相似文献
268.
Ahmad Nurul Izzah Mahiyuddin Wan Rozita Wan Azmi Wan Nurul Farah Wan Azlee Ruzanaz Syafira Ruzman Shaharudin Rafiza Sulaiman Lokman Hakim 《Environmental science and pollution research international》2022,29(17):24816-24832
Environmental Science and Pollution Research - The concentration of meHg in freshwater fish and seafood was investigated, as well as the consumption patterns of fish and seafood by different... 相似文献