Impact of habitat heterogeneity on plant community pattern in Gurbantunggut Desert

This paper reports a geomorphologic landscape investigation, vegetationsurvey and soil sampling at 14 sites across the Gurbantunggut Desert between87°37′09″-88°24′04″E and 44°14′04″-45°41′52″N. The study encountered 8 species of lowtrees and shrubs, 5 of perennial herbs, 8 of annual plants and 48 of ephemeral and ephemeroidplants. These species of plants represent one-third of the species found in the GurbantunggutDesert, and their communities make up a large proportion of desert vegetation with great landscapesignificance. In the investigation we found that the plant communities are accordingly succeededwith the spatial variation of macro-ecoenvironment. Using Principal Component Analysis (PCA) andCorrelation Analysis (CA) we found that the micro-ecoenvironment heterogeneity of aeolian sandysoil's physical and chemical properties such as soil nutrient, soil moisture, soil salt, pH etc.only impacted the diversity of herb synusia (PIEherb) of the desert, with a negative correlation.Meanwhile, the impact of microhabitat on the plant community pattern with an antagonisticinteraction made vegetation's eco-distribution in a temporary equilibrium.

Community Characteristics of Wild Fruit Forests Along Elevation Gradients and the Relationships Between the Wild Fruit Forests and Environments in the Keguqin Mountain Region ofⅠii

In this paper,the quantitative relationship between the wild fruit communities and direct environmental factors is discussed on the basis of detailed data on landscape scale habitats obtained through field vegetation investigation.The results from TWINSPAN and DCCA showed that:1) In the distribution sections of the wild fruit forest in the Keguqin Mountain region,the basic patterns characteristic of the different habitats are due to topographic factors,nutrients and moisture conditions;2) The elevation affected the most basic differentiation of plant communities in the study area,indicating that the elevation condition was the most important factor restricting the distribution of the wild fruit communities in the study area;3) The close relationship between the moisture content in the upper soil layer and the elevation reflected the influence of moisture conditions on both wild fruit and herb-layer communities;4) Nutrient differences not only indicated that the habitat conditions were different in themselves but also showed that the present nutrient conditions of the habitats were seriously affected by human activities.In summary,under complicated mountainous topographic conditions,the habitat conditions for the communities differed very significantly,and the combination of elevation,soil moisture content,total nitrogen,slope aspect,and pH value influenced and controlled the formation of community distribution patterns in the study area.

The community structure and seasonal dynamics of plankton in Bange Lake, northern Tibet, China

The seasonal variations in biomass, abundance, and species composition of plankton in relation to hydrography were studied in the saline Bange Lake, northern Tibet, China. Sampling was carried out between one to three times per month from May 2001 to July 2002. Salinity ranged from 14 to 146. The air and water temperature exhibited a clear seasonal pattern, and mean annual temperatures were approximately 4.8℃ and 7.3℃, respectively. The lowest water temperature occurred in winter from December to March at-2℃ and the highest in June and July at 17.7℃. Forty-one phytoplankton taxa, 21 zooplankton, and 5 benthic or facultative zooplankton were identifi ed. The predominant phytoplankton species were Gloeothece linearis, Oscillatoria tenuis, Gloeocapsa punctata, Ctenocladus circinnatus, Dunaliella salina, and Spirulina major. The predominant zooplankton species included H olophrya actra, Brachionus plicatilis, Daphniopsis tibetana, Cletocamptus dertersi, and A rctodiaptomus salinus. The mean annual total phytoplankton density and biomass for the entire lake were 4.52×10^7 cells/L and 1.60 mg/L, respectively. The annual mean zooplankton abundance was 52, 162, 322, and 57, 144 ind./L, in the three sublakes. The annual mean total zooplankton biomass in Lakes 1–3 was 1.23, 9.98, and 2.13 mg/L, respectively. The annual mean tychoplankton abundances in Bg1, 2, and 3 were 47, 67, and 654 ind./L. The annual mean tychoplankton biomass was 2.36, 0.16, and 2.03 mg/L, respectively. The zooplankton biomass（including tychoplankton） in the lake was 9.11 mg/L. The total number of plankton species in the salt lake was signifi cantly negatively correlated with salinity.

Species Richness, Spatial Distribution and Abundance of Mbuna in Lake Malawi

Studies were carried out to determine species richness and abundance of rock-dwelling cichlids, Mbuna, in Lake Malawi. A total of 40 heterogeneous sites which yielded 10 genera, 136 species and a species-genus ratio of 13.6, were surveyed by scuba diving in transects laid at six depths on each site. Species diversity and abundance were generally high in the rocky bottom habitats with a general trend of the two variables decreasing with depth, except at Likoma and Chizumulu Islands where they increased with increasing depth. This was due to dominant species inhabiting water depths of 10 to 15 m. Relative abundance was generally low in all the sites where few species had relative abundance of more than 10%. The same was applied to relative site frequency; more than 60% of the species were rare with relative site frequency of less than 10%. These low estimates support the fact that most of the Mbuna species are endemic within localities in the lake. Southern part of the lake has lower abundance and richness of Mbuna with the exception of islands compared to the northern part of the lake. This is explained by high prevalence of sandy and muddy lake bottom in the south as opposed to rocky bottom in the north.