梵争山和张家界地区蜘蛛群落结构及多样性研究

1990年8月对梵净山和张家界两个自然保护区内蜘蛛群落进行调查,结果表明:自然保护区内蜘蛛资源极为丰富,经初步鉴定,计有蜘蛛27科85属180种,其中主要成分依次为肖蛸、园蛛、狼蛛、球蛛和皿蛛等。蜘蛛发生量折合每亩为17,585—54,000头。八个不同生境类型蜘蛛群落的种类数和密度存在明显差异;各种蜘蛛分布群在群落内的比例随栖息地结构变化而改变,因而也导致蜘蛛群落的Shannon-Wiener多样性指数,Simpson优势度和均等度等参数的变化。     

Community response to experimental soil disturbance in a midsuccessional,abandoned pasture

To determine whether soil disturbance by digging and burrowing mammals altered community structure and the rate of succession in a midsuccessional abandoned pasture, species richness, composition and relative abundance were monitored over a two year period both on and off artificially created earth mounds (100, 900, 8100 cm²). Mean species richness increased by up to two species per small mound (100 cm²) and by up to four species per large mound (8100 cm²). However, increased species richness was evident for less than two years. Initially, up to sixteen of the twenty species present occurred more often on earth mounds than off mounds, with two of these species found only on large mounds (8100 cm²). After two years, there was little or no significant difference in species composition and relative frequency on and off earth mounds. Experimental soil disturbance temporarily altered community structure simply by increasing space available for colonization since light, nutrient and water supply did not increase significantly on mounds. Soil disturbance can increase species richness and change species' relative frequency in disturbances as small as 100 cm² but such changes were likely too small and short lived to alter permanently the structure and rate of succession in the abandoned pasture studied here.     

Structural properties of two types of mangrove stands on the northwestern coast of Sri Lanka

Mangrove stands in Puttalam lagoon and Dutch bay, two interconnected lagoons situated on the northwestern coast of Sri Lanka have been classified broadly into two groups, i.e., estuarine and island/mainland-fringing stands. Structural diversity of six mangrove stands, representing the two types was studied in terms of floristic composition, density, basal area, mean stand diameter, tree height, standing above-ground biomass and leaf-area index.Rhizophora mucronata andAvicennia marina were the dominant species. Higher mean stand diameters for the mangrove stands in Puttalam lagoon indicated greater maturity than the estuarine mangrove stands in Dutch bay. Nevertheless, estuarine stands in Dutch bay were structurally more complex (complexity indices 8.11–22.7) than the island/mainland-fringing mangrove stands (complexity indices 1.38–6.78). Higher number of species present in the estuarine mangrove stands is the major element that contributes to the higher values for the complexity indices for those stands. This appears to mask the contribution of stand-age to the complexity of a mangrove stand. Therefore complexity indices alone may not be used to explain adequately the structural diversity among mangrove stands.     

Scale‐dependent biases in species counts in a grassland

Abstract. Numbers of plant species were recorded in species‐rich meadows in the Bílé Karpaty Mts., SE Czech Republic, with the aim to evaluate the sampling error made by well‐trained observers. Five observers recorded vascular plants in seven plots ranging from 9.8 cm² to 4 m² independently and were not time‐limited. In larger plots a discrepancy of 10–20% was found between individual estimates, in smaller plots discrepancy increased to 33%, on average. The gain in observed species richness by combining records of individual observers (in comparison with the mean numbers estimated by single observers) decreased from the smallest plot (27–82% for two to five observers) to the largest one (13–25%). However, after misidentified and suspicious records were eliminated, the gain was much lower and became scale‐independent; two observers added 12% species, on average, and the increase by combining species lists made by three or more observers was negligible (3% more on average). It is concluded that most discrepancies between individual observers were caused by misidentification of rare seedlings and young plants. We suggest that in species‐rich meadows plants should be recorded by at least three observers together and that they should consult all problematic plant specimens together in the field, to minimize errors.     

The influence of local elevation on the effects of secondary salinity in remnant eucalypt woodlands: Changes in understorey communities

Increasing land salinization in Australia is predicted to lead to severe declines in species diversity in affected areas, and perhaps significant numbers of species extinctions. Much of the diversity that will be lost consists of understorey and mid-storey species, yet the overwhelming majority of research has focussed on salinity tolerance in tree species. We investigated how the presence of a shallow, saline water table affected the understorey species composition, species richness and species diversity in two remnant Eucalyptus wandoo Blakely woodlands in the Western Australian wheatbelt. Species richness and species diversity were significantly lower in areas with a shallow water table at elevations < 0.5 m above the lowest local elevation, compared with both higher elevations and with areas of low elevation without a shallow water table. Species composition (Bray-Curtis similarities) was also significantly different in low elevation, saline areas. At one site, saline areas were colonized by native and alien species that were not present in the surrounding vegetation, yet the community that has developed does not contain either the species or structural diversity of the surrounding system. At the other site, no colonisation of saline areas by new species occurred. Even though small differences in elevation (< 0.5 m) at our study sites were important in moderating the impacts of salinity in areas with a shallow water table, the loss of species diversity, species richness and structural complexity in low-lying elevations indicated that the ecological risk from secondary salinity to species associated only with drainage lines, seasonally wet flats and other low-lying areas is severe. The priority is to identify those vegetation communities that are restricted to only low relative elevations within the landscape and that only occur in remnants predicted to be at a high risk of developing a shallow and saline water table.     

Investigating the evolution of floras: problems and progress — An introduction

The Cape flora of southern Africa is a remarkable hotspot for plant species diversity and endemism. At a meeting in Zurich in 2004 progress in understanding the evolution of this diversity was reviewed. In this symposium, four papers presenting several of the methods used in this investigation were reported. These papers deal with molecular dating methods, the reconstruction of ancestral habitats, with possible speciation scenarios for the Cape flora, and the importance of the correct sampling strategies.