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991.
992.
- 1.
- An organism's thermal tolerance to the environment may indicate a thermal limit to its geographical distribution. 相似文献
993.
Summary . In environmental risk analysis, it is common to assume the stochastic independence (or separability) between the marks associated with the random events of a spatial-temporal point process. Schoenberg (2004, Biometrics 60, 471–481) proposed several test statistics for this hypothesis and used simulated data to evaluate their performance. He found that a Cramér-von Mises-type test is powerful to detect gradual departures from separability although it is not uniformly powerful over a large class of alternative models. We present a semiparametric approach to model alternative hypotheses to separability and derive a score test statistic. We show that there is a relationship between this score test and some of the test statistics proposed by Schoenberg. Specifically, all are different versions of weighted Cramér-von Mises-type statistics. This gives some insight into the reasons for the similarities and differences between the test statistics' performance. We also point out some difficulties in controlling the type I error probability in Schoenberg's residual test. 相似文献
994.
The purpose of this study was to examine the relationship between species composition of tropical seagrasses and various physical
environmental factors: depth, sediment thickness and silt–clay content in the sediments. We investigated species composition
and abundance of seagrasses as well as the physical environmental factors for six transects around Ishigaki Island, southwest
Japan. Eight species occurred in the quadrat census. The occurrence frequencies ranged from 66.8% (Thalassia hemprichii) to 4.5% (Enhalus acoroides). Both canonical correspondence analysis (CCA) and cluster analysis elucidated that depth was mainly responsible for the
distributions of species and assemblage type. Monte Carlo permutation for partial CCA revealed that 37.5% of the variance
was explained by depth, 10.3% by sediment thickness and 4.6% by silt–clay content in the sediment. Twenty-six sites were categorized
into four assemblage types by a cluster analysis using the leaf area index (LAI; the ratio of total leaf area to bottom area)
as a measure of species abundance. Type I was dominated by T. hemprichii and Cymodocea rotundata, Type II by C. serrulata, Type III by E. acoroides, and Type IV by Halodule pinifolia and Halophila ovalis. Type I occurred mostly in the intertidal zone (91.3±30.5 cm below MSL, mean sea level), Type II in the subtidal zone (179.1±75.0 cm
below MSL) and Type IV in both shallow sites (between 47.8 and 75.6 cm below MSL) and in those with low silt–clay contents
(between 2.0 and 3.8%). 相似文献
995.
The distribution and relative biomass of cephalopods from pelagic waters off eastern Australia was examined between 1997 and
2004 from stomach contents of swordfish, yellowfin tuna and dolphinfish taken in the domestic longline fishery. A total of
38 taxa from 19 families were identified. Comparison of the species composition of the three predators indicated pronounced
differences in cephalopod species composition. In swordfish, species of the family Ommastrephidae, particularly Ommastrephes bartramii (Lesueur 1821) and Nototodarus gouldi (McCoy 1888) dominated, whereas a more diverse mix of species was identified from yellowfin-sampled cephalopods. Todaropsis eblanae (Ball 1841) was the main cephalopod sampled from the surface-dwelling dolphinfish. For swordfish-sampled cephalopods, significant
relationships were found between biomass and season, fluorescence and year. In yellowfin tuna, cephalopod biomass was significantly
correlated with season, area and sea surface temperature. Significant factors differed between predator-sampler, possibly
reflecting the limits of the predator, but could also give insights into individual cephalopod species distributions. However,
the increase in cephalopod biomass over summer in both swordfish and yellowfin tuna suggested cephalopod biomass was higher
over summer in the region. 相似文献
996.
997.
C. Sérgio C. A. Garcia M. Sim-Sim C. Vieira H. Hespanhol S. Stow 《Journal of bryology》2017,39(1):1-7
Previous molecular studies have done much to shed some light on the taxonomy and phytogeographic position of Homalothecium sericeum and H. meridionale and the present study clarifies the taxonomy and distribution of the two species across Iberia. By conducting a revision of Homalothecium specimens available in Spanish and Portuguese herbaria, we concluded that sporophytic differences are the most appropriate characters for the delimitation of each species. Scanning electron microscope examination of the peristomes of the two taxa helped distinguish between them.
We also noted that H. meridionale is a frequently distributed taxon throughout the Iberian territory, but occurs mostly in Portuguese areas with a Mediterranean influence, becoming less frequent in the Atlantic as well as in continental parts of the Peninsula. As a result of this study, based on numerous new localities in Portugal and Spain, we provide an updated map of the distribution of H. meridionale, and an account of its ecology and habitat affinities. 相似文献
998.
999.
四合木(Tetraena mongolica)分布区景观结构时空变化分析 总被引:5,自引:0,他引:5
利用3S技术,1972年航空黑白像片,1988年TM CCT磁带数据以及1995年1:10万TM影像等信息源,以斑块为最小景观结构单元,对西鄂尔多斯特有种四合木(Tetraena mongolica)的分布及其分布区的景观结构进行了研究,结果表明:(1)四合木的分布区面积约为2 754km2;(2)分布区面积及斑块平均面积都在减少,1988年实际占有1456km2,1995年为15.38km2,减少了18.1%;(3)四合木分布面积的减少在不同时空尺度上并不相同,1988-1995年间的年变化率比1972-1988年间的年变化率高5倍,空间尺度上城市工业区的年变化率比放牧分布区高。 相似文献
1000.
In a first synoptic evaluation, the temporal and spatial distribution of bacterioplankton and chlorophyll-a were determined
in the German Wadden Sea. Three surveys were undertaken in winter, spring, and summer of 1994 using up to eight ships simultaneously
between the river Ems and Sylt island. Despite intensive hydrodynamic mixing of the Wadden Sea water, spatial gradients were
obvious. The abundance of bacterioplankton ranged from 0.4 to 26×105 ml–1 and chlorophyll-a varied between <0.1 and 79 μg l–1. In winter, relatively homogeneous distribution patterns of both parameters with small gradients were found. Highest chlorophyll-a
values connected with a highly patchy structure were observed in spring, while in summer both total chlorophyll-a values and
the complexity of the distribution pattern had decreased. In contrast, bacterial numbers increased steadily from January to
July with the highest bacterial densities and greatest patchiness observed in summer. Moreover, in some regions of the Wadden
Sea, a trophic succession of algae as carbon producers and bacteria as consumers was evident. Correlation analysis verified
the relationship between bacteria and chlorophyll a, indicating bottom-up control of bacterial abundance in the northern part
of the German Wadden Sea. Since the observed regression slope is remarkably low (0.12–0.46) compared to literature values
(0.5–0.8), we suggest that the link between phytoplankton and bacteria found here is a special characteristic of the Wadden
Sea as a transition zone between the coastal region and the outer North Sea.
Received: 26 May 1998 / Accepted:12 November 1998 相似文献