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斑块大小是研究景观要素特征的一个主要参数。物种动态、潜在生境、潜在林产品(木材)、能量、养分和水流以及很多其它参数都受到景观中斑块大小的影响。将研究区域--富阳市富阳镇段滩地划分为6大类81个基本类型,并将其归为低水平斑块(基本类型对应斑块)和高水平斑块(大类对应斑块),采用极大似然估计法进行了研究,Kotliar和Wiens提出的斑块结构的等级框架是对斑块意义的更完整的理解,研究过程中对斑块的确定符合Kotliar和Wiens的等级思想。充分考虑了两个水平上的斑块,及它们对应于斑块类型的两个水平,研究表明:低水平的斑块内部具有较高的同质性,而高水平的斑块内部具有较低的同质性;在两种斑块水平上都显示出斑块大小分布是明显右偏的;只有少数类型斑块大小的分布服从负指数分布,而绝大多数斑块大小的分布服从对数正态分布,这对斑块内的群落和生态系统的稳定性和保护提供了参考。 相似文献
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Charles H. Peterson Melanie J. Bishop Linda M. D'Anna 《Journal of experimental marine biology and ecology》2006,338(2):205-221
Cold-season filling using much coarser sediments than the native caused dramatic suppression of beach macroinvertebrates, demonstrably degrading habitat value for foraging shorebirds. As a dual consequence of persistent steepening of the foreshore, which translated to reduction in habitat area by 14-29%, and disturbance-induced depression of invertebrate densities on filled beaches, abundances of Donax spp. and haustoriid amphipods averaged less than 10% of control levels. Donax spp. is the biomass dominant and a key prey for higher trophic levels. Haustoriids lack pelagic larvae. Recovery on filled beaches was not initiated by either taxon during the March-November sampling. Emerita talpoida, an order of magnitude less abundant than Donax spp. on control beaches, exhibited a pattern of initial depression on filled beaches but recovered by mid summer. Polychaetes, mostly the small Scolelepis squamata, experienced a warm-season bloom of equal magnitude on filled and control beaches. Summertime recruitment of predatory ghost crabs appeared inhibited on filled beaches, perhaps by persistent shell hash. Intertidal shell cover on filled beaches averaged 25-50% in mid summer as compared to 6-8% on control beaches. Largely in response to prey depression, but perhaps also to surface shell armoring and/or coarsening of sediments, shorebird (mostly sanderling) use plummeted by 70-90% on filled beaches until November. Thus, despite likely adaptations to natural sediment dynamics, the high intensity of sediment deposition, cumulative spatial scope (10.8 km), and unnaturally coarse shelly character of the Bogue Banks beach nourishment resulted in a perturbation that exceeded biotic resistance and degraded the trophic transfer function of this highly productive habitat for at least one warm season. 相似文献
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M. D. Rothman R. J. Anderson C. J. T. Boothroyd F. A. Kemp J. J. Bolton 《Journal of applied phycology》2009,21(1):47-53
In South Africa, gracilarioid red algae have been collected as wash-up to be dried and sold for agar extraction for at least
50 years. Despite much research, there is currently no commercial mariculture of the algae locally although this has been
carried out in neighboring Namibia for a number of years. The industry is traditionally confined to Saldanha Bay on the west
coast, although small wash-ups of Gracilariopsis longissima have been collected in nearby St Helena Bay. In Saldanha Bay, wash-ups of Gracilaria. gracilis have been very sporadic over the last few decades, with human alteration of the bay configuration possibly responsible for
an initial major decline in 1974. This unpredictability in the amounts of wash-up has made the industry unstable and increasingly
unprofitable. We compiled the results of previous surveys (some unpublished) of gracilariod populations in St Helena Bay and
the Saldanha-Langebaan sytem, and re-surveyed these populations to examine long-term fluctuations. In Saldanha Bay and Langebaan
Lagoon, standing stock of G. gracilis was estimated at 538 tons fresh weight and 71 tons fresh weight respectively. Less than 4 tons of gracilarioids are estimated
to remain in St Helena Bay. We discuss the fluctuations in biomass and distribution of these South African gracilarioid populations. 相似文献
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Vincent Comor Jérôme Orgeas Philippe Ponel Christiane Rolando Yannick R. Delettre 《Biodiversity and Conservation》2008,17(8):1837-1852
In coastal dunes, influenced by anthropogenic activities such as tourism, it is important to determine the relative influence
of environmental factors at different spatial scales to evaluate the sensitivity of local communities to disturbances. We
analyzed beetle communities of 14 dunes of the French Mediterranean coast: four in the relatively preserved Camargue area,
and ten in the Var department, where tourism is intensive. Beetle communities were studied three times in early spring using
sand sampling. Species-environment relationships were evaluated at the regional, landscape and local scale using redundancy
analysis (RDA) and variability partitioning. About 28 species were identified, of which 15 were sand-specialist species, which
accounted for more than 93% of total abundance. The beetle communities of Camargue were significantly different from those
of the Var department owing to the pullulation of a Tenebrionid species (Trachyscelis aphodioides Latr.) in the Var, except for one restored dune where the community was very similar to those of Camargue. Our results showed
no longitudinal gradient between the two regions. Local factors (dune height, preservation and disturbance index) significantly
explained most of the variation in the dominance of T. aphodioides, while some other local factors were important for other psammophilous species. This study also suggests that dune beetle
communities are strongly affected on beaches intensively managed for tourism, but beetles are still abundant in much disturbed
sites. 相似文献
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Lesions confined to the ventromedial hypothalamus decrease the frequency of coital contacts in female rats 总被引:2,自引:2,他引:0
Ovariectomized female rats received either bilateral radiofrequency lesions of the ventromedial nucleus of the hypothalamus (VMH) or control treatments and were tested for copulatory activity following either estrogen (E) alone, or E plus progesterone (P) administration. In separate experiments the females were tested in two testing apparatuses both of which allowed the test females to control their contacts with sexually active males. One of the testing apparatuses also allowed the females to control their contacts with sexually inactive males and ovariectomized females. Females receiving VMH lesions engaged in fewer coital contacts with sexually active males than sham-operated females in the E plus P condition. Lesioned females also tended to spend less time with sexually active males than did sham operates in both the E and E plus P hormonal conditions. The VMH-lesioned females did not differ from the sham-operated females in the ability to display lordosis during the coital contacts or the frequency and duration of visits to the inactive males or ovariectomized females. The sham-operated females did have some transitory alterations in copulatory behavior in comparison to unoperated control females. 相似文献
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A 19 m thick package of well-sorted lowermost Jurassic (Hettangian-Lower Sinemurian?) sandstones within the Shemshak Formation
of the southeastern Alborz Mountains displays features characteristic of foreshore to upper shoreface environments such as
tabular bedding, low-angle lamination, trough cross-stratification, parting lineation, and oscillation ripples. In contrast
to most other beach successions recorded in the literature the sandstones contain a trace fossil assemblage characterised
by low abundance but comparatively high diversity. The assemblage, comprising 14 ichnotaxa, is dominated by Palaeophycus heberti, Rhizocorallium irregulare, Gyrochorte comosa, and Parahaentzschelinia surlyki. Contrary to predictions, which assume a dominance of suspension-feeders in such high-energy environments, the trace fossil
assemblage represents a variety of ethological groups ranging from suspension-feeders to deposit-feeders, detritus-feeders,
scavengers, and a possible trap constructor (Ctenopholeus), whereby deposit-feeders predominate. This anomaly is explained by a high amount of organic detritus in the sediment, indicated
by abundant plant material, and a position of the beach in the vicinity of a river mouth. 相似文献