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951.
干旱山地生态系统植物群落不同尺度下物种数的变化特征 总被引:3,自引:0,他引:3
对典型干旱山地生态系统不同生境(土质山坡,石质山坡)的植物群落在不同取样几度下所测定的植物物种数的变化情况进行分析。采用了曲线拟合和分形维数相结合的分析方法进行探讨。从物种数随取样尺度的变化曲线(对数曲线)看(p〈0.01),土质山坡植物群落(草本植物群落)曲线比较平滑,石质山坡(草本和灌丛混合群落)曲线较粗糙。两个样地植物群落物种数在不同取样尺度下变化的趋势不同。分形维数变化趋势表明,两个样地植物物种数随取样尺度(r)变化趋势的差别较大,土质山坡植物群落物种数空间变化异质性不大。可以找到合适的取样面积;石质山坡物种数变化的空间异质性大,物种分布空间格局较复杂。在整个山坡范围内没有合适的取样面积。因此,建议在干旱山地石质山坡上进行植物群落研究时采用设置典型样方方法,同时尽量增加样方数量,使取样尽量代表整个山坡植被。 相似文献
952.
乌兰布和沙漠晚第四纪以来环境演化呈现湖泊与沙漠多次反复的更替模式,湖相层与松散风成砂层迭覆出现.湖泊发育时间段为120-90 ka、60-50 ka、40-20 ka和8-5.5 ka;沙漠扩展时间段为150-130 ka、90-60 ka、50-40 ka、20-10 ka和5.5 ka--近现代时期.由于时空尺度差... 相似文献
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P. E. Roberts 《新西兰海洋与淡水研究杂志》2013,47(1):105-108
Two juvenile slender tuna Allothunnus fallai Serventy, 278 mm and 282 mm fork length, were identified from a catch by a purse seiner 23 km off the Moko Hinau Islands, New Zealand, on 23 January 1974. As the slender tuna were observed to school in association with skipjack tuna Katsuwonus pelamis L., it is probable that adults also school, and could be available as a yet unexploited resource to New Zealand fishermen, especially to the south‐east of New Zealand. 相似文献
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《African Journal of Marine Science》2013,35(3):639-642
The first documented recapture of a South African-tagged juvenile blue shark Prionace glauca off Uruguay lends weight to the hypothesis of a single blue shark population in the South Atlantic. The presence of neonate blue sharks with umbilical scars and females with post-parturition scars, as well as the high frequency of small juveniles in research longline catches, confirm the existence of a parturition and nursery area off South Africa. The final positions of three tagged sharks suggest that large-scale movement patterns in the South Atlantic are a mirror image of movements in the North Atlantic, with sharks using the north-westerly Benguela Drift to migrate into the tropics and ultimately across into South American waters. The confirmed existence of a parturition and nursery area off the south coast of South Africa and the movement of sharks into both adjacent ocean basins suggest that the southern African blue sharks are part of a single stock that straddles the South Atlantic and Indian oceans, and possibly the entire Southern Hemisphere. 相似文献
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《African Journal of Marine Science》2013,35(3):375-392
Shore-based surveys of migrating humpback whales Megaptera novaeangliae were undertaken from Cape Vidal, northern KwaZulu-Natal, South Africa, each year between 1988 and 1991, and in 2002. Daily observations of migrating whale groups were carried out from an approx. 60 m-high platform during all surveys. Whale groups were tracked by position-fixing on surfacing bouts using survey theodolites, to determine swimming speeds and headings and distance offshore, while group size estimation was carried out at each theodolite measurement. Numbers of whales observed or projected (at tracked speeds) to cross the midline of the survey area within the observation period each day were tallied in each of three distance bins. These counts were adjusted to account for daily sighting effort and for proportions that were likely to have been missed on account of their distance offshore or poor sighting conditions to produce daily sighting rates. Such daily tallies were summed over the survey period to estimate the number of whales passing Cape Vidal each year, with counts from days of <2.5 h of observation effort (due to weather or sighting condition restraints) replaced by the mean of the previous and following days. The numbers passing to the north of Cape Vidal during coincident periods of 17 days over the 1988–2002 surveys (6–22 July) and 25 days over the 1990, 1991 and 2002 surveys (6–30 July) provide statistically significant increase rates of 11.5% (SE 2.8) and 9.0% (SE 2.7) per annum respectively. 相似文献
960.
We describe a multi‐stock, length‐based Bayesian assessment model for New Zealand spiny lobster (Jasus edwardsii) fisheries. This model allows simultaneous modelling of two or more stocks with a mixture of common and stock‐specific parameters: recruitment is always stock‐specific, but any other parameter can be specified as either common or stock‐specific. Common parameters are estimated from a wider base than they would be in a single‐stock model. The model's time step is flexible and can be changed during the period being modelled to accommodate better data quality in recent data. Other options include the capacity to estimate movements among stocks, allow density‐dependent growth, and choose among likelihood functions for the various data sets, between finite and instantaneous fishing dynamics and between two forms of selectivity curve. 相似文献