This paper introduces the effects of species diversity on ecosystem functioning: the mechanisms and hypotheses, including the redundant species hypothesis, rivet hypothesis, idiosyncratic hypothesis, null hypothesis, compensatory/keystone species hypothesis, non-linear hypothesis, and monotonic/unimodal hypothesis. To date, no single hypothesis is accepted as truly reflecting the real relations, if they do exist, between species diversity and ecosystem function. According to our analysis, there is an intrinsic relationship among these hypotheses. They either include or complement each other and may all be considered as related to the redundant species hypothesis.

This review is divided into three parts. First, several problems in studying mechanisms of species coexistence in ecological communities are generalized. Second, some concepts explaining plant and animal species coexistence are reviewed. Within plant communities, these concepts include environmental factors, seed re-immigration, niche differentiation, balanced competition, species-pool, regeneration niche, coexistence of ecologically similar species and the null community. In animal communities, the effects of patch, edge, congregation, dispersion, interference and response to environmental heterogeneity are discussed. Finally, coexistence of specialists and generalists are discussed.

Microorganisms are an important group of organism mainly performing catabolic metabolism, which display extreme abundance in biodiversity. However, due to their microscopic sizes, especially prokaryotes with simple unicellular structure, their asexual propagation, their rapid replication and the lack of base line inventory of their groups and quantity, the biodiversity of microorganisms has so far not been studied thoroughly and has been paid little attention compared with macro organisms. In the present paper, the biodiversity of microorganisms is reviewed briefly, with consideration of the following aspects: species diversity, diversity of phylogenetic lines, physiological diversity and genetic diversity. The aim is to improve awareness of investigation of microorganism resources, not only in the scientific community but also in society as a whole.

The propagules of plants are exposed to high risk of attack by natural predators, such as insects, vertebrates and fungi. Seed mortality due to predation by animals may affect plant fitness, population dynamics, community structure and maintenance of species diversity. The time and intensity of seed predation can be a major selective force in the evolution of life history traits in plants, such as germination rates and production of a soil seed bank. Seed size and the type and patchiness of habitat affect seed predation by animals. Predator satiation is a highly coevolved behavior interaction of plant with seed predator, and has been proposed as a selective factor limiting the destructive abilities of animals and promoting the survival of dispersed seeds. Several hypotheses have been proposed to explain the spatial relationship between plant regeneration and seed dispersal. Seed dispersal can be regarded as a key process in the survival and distribution of plant species. Seeds are dispersed through a variety of ways. Seed dispersal affects the fitness of parent and offspring plants through its effects on seed density, the distance seeds are moved from the parent tree, and the habitat where seeds arrive. Difference in dispersal may influence early seed and seedling survival by affecting incidence of predation or attack by pathogens, the habitat into which seeds are dispersed, and the types of plants with which the developing plant will compete. Seed distribution generally exhibits a negative exponential function, most seeds are not disperse very far from the parent plant. Predation risk, habitat type and vegetation cover are factors which affect animal dispersal of seeds. The fruiting season and fruit loss process of plants reflects adaptation to dispersal opportunities. A large number of animals hoard plant seeds. This behavior not only adjusts spatio temporal distribution of food and enhances animal survival in times of food shortage, but also promotes plant dispersal. So, there is coevolutionary relationship between plant and animal which cache or hoard seeds. Seed dispersal by animals is one of the most important of mutualistic systems. Many factors affect the survival and establishment of seedling, such as microhabitat, humidity, slope, gradient, cover of the cache. Frugivorous animals usually consume the pulp and regurgitate or defecate the seeds intact. Seed treatment within the guts of seed dispersers is contributive to seed emergence.

To date, bacterial,algal and other microbial symbionts have been found in more than 100 species of ciliates. The study of the host-symbiont system in ciliates shows that: (1) The inheritance of kappa particles in the cytoplasm of Paramecium aurelia is a classic example of the cytoplasmic inheritance theory. (2)Bacterial symbionts in some anerobic ciliates that lack mitochondria play the major role in the host's metabolism. (3) In the P. caudatum Holospora obtusa system, 39-and 15-kDa periplasmic proteins of the infectious H. obtusa reacted with IF-3-1 and IF-3-2 monoclonal antibodies respectively. The amounts of both antigens were reduced during the early infection process. The reproductive H. obtusa selectively synthesized a 63-kDa protein, which may function as a key molecules in the various symbiotic systems. (4) In the P. bursaria Chlorella system, the precondition of the symbiosis may be the gluosamine composition that exists in the rigid wall of the algae. The symbiotic algae takes part in the host's metabolism, and the specific association between the symbiont and host is mutually beneficial. Some genomic structures in P. bursaria may be influenced by the function of the Chlorella,so that the host's gene expression may change.A general trend in the research of symbiosis in ciliates is further exploration of the influence of the symbiont on the gene structure and gene expression of the host. The expected results will contribute to a better understanding of the regulatory mechanisms controlling the interaction,the exchange of substances between the host and symbiont at a molecular level, and the pattern of life processes surrounding the relationship between cellular structures and functions in eukaryocytes.

Fifty three strains of organisms were isolated from Hailaer Soda Lake, Inner Mongolia and DNA was extracted followed by amplification of 16S rRNA genes and sequencing. The phenotypic characteristics and the subsequent ARDRA showed that these strains displayed great diversity. Phylogenetic analysis revealed that all of the Gram-negative isolates were confined to the Gamma subdivision of Proteobacteria and that the Gram-positive isolates showed great diversity, but most of them belonged to the Bacillus spectrum.

To research the species diversity change of the regeneration layer in gap gradients, we computed the Margalef index, Simpson diversity index, Shannon-Wiener index, Pielou evenness index and Alatolo index with the data from transects through the regeneration layer in a coniferous-broadleaved forest in Jinyun Mountain. Species diversity of the regeneration layer gradually increased from non-gap to the gap central area, such that: Non-gap Middle phase gap > Late phase gap.

The species diversity of interlayer plants and their distribution in Dinghushan Biosphere Reserve were studied. The results showed that the species diversity of interlayer plants of Dinghushan was rich. The species diversity of lianas decreased with forest succession while epiphyte showed a contrasting trend. This suggests that the diversity indices of lianas might be employed to measure forest succession. The individual number, species number and Shannon Wiener index of lianas in ravine rain forest and riverbank forest were richer than that of other forests. These indices were the lowest in the most closed forest; monsoon evergreen broad leaved forest . This indicates that both humidity and illumination were important factors affecting the growth and distribution of lianas.

Arthopod communities in various layers of pine stands were investigated from January 1997 to December 1998 in two sample plots with similar stands and equivalent area (22 m×22 m) and without any sylvicultural and pest suppressing measures in the Jiulianshan Forest Farm in Southern Anhui Province. In every sample plot the percentages of species number of phytophagous, predatory, and parasitic insects and spiders that accounted for the total species number were about 52%, 14%, 8% and 20%, respectively. The ratio of beneficial to harmful species numbers was around 1:1.2 in each sample plot; the ratio of beneficial to harmful organism individual numbers was 1:5.7 and 1:6.6, respectively . Dominant groups existed in the same layers of the two sampling plots . Species number ranked in the following order: brush and herb layer > tree layer > litter layer > soil layer. Averages of the individual percentage of tree layer, brush and herb layer, litter layer and soil layer in two sample plots were 39.6%, 33.1%, 22.8% and 4.6%, respectively. The species number and index of diversity from March to August were largest, and there were two peaks emerging in May and August, respectively. Principal component analysis indicated that recovery stability of this kinds of community was not strong, and the natural control potential was weak.

Nanjing Botanical Garden Mem. Sun Yat-Sen is located in the southern foot of Zhongshan Mountain. Avian frugivores such as Turdus merula, Pycnonotus sinensis, Garrulax perspicillatus, Cyanopica cyana, Streptopelia orientalis and Turdus naumanni feed mainly on tree fruits in the garden during autumn and winter. One hundred and sixty samples of birds faeces were randomly collected within the garden from October 20, 1999 to January 20, 2000. Totally 874 intact seeds, which were generally enclosed by a hard seed coat or by hard endocarp,three pieces of insect remnants of Coleoptera and one remnant of bird were found in these birds' faeces. Among the seeds, 842 have been identified as belonging to 26 plant species of 20 genera and 16 families. Plant species comprising the highest percentage in frequency in the 160 samples of birds' faeces are Ilex purpurea(22.2%), Sabina chinensis(11.1%), Rhus chinensis(10.6%), Celtis sinensis(9.2%), Parthenocissus tricuspidata (7.7%) and Sabina chinensis cv. kaizuca(7.3%). Plant species with highest percentage of seed number in the samples are Ilex purpurea(23.5%), Rhus chinensis(16.2%), Sabina chinensis(13.5%),Parthenocissus tricuspidata(8.0%), Sabina chinensis cv. kaizuca(8.0%)and Rosa cymosa(5.3%). Avian frugivores may disperse from the parent trees by (i) ingesting fruits around the parent trees, then defecating or regurgitating the seeds away from it, or (ii) picking the fruits up away from the parent trees. Both fecal borne seeds, such as Rhus chinensis and Parthenocissus tricuspidata, and regurgitated seeds, such as Cinnamomum camphora and Melia azedarach, were viable to produce seedlings based on a preliminary germination test. Seedlings of Cinnamomum camphora,Ilex purpurea, Pittosporum tobira, Taxus chinensis and some other trees cultivated in the garden have successfully invaded into a natural Pinus thunbergii Liquidambar formosana community on a hillside at the edge of the garden and into a natural Pterocarya stenoptera-Celtis sinensis community beside a mountain stream through the garden, as a result of seed dispersal by frugivorous birds. Avian seed dispersers have spread the distribution of some cultivated fleshy fruiting species in the botanical garden and have promoted their natural regeneration.

The vertical distribution of small mammals was investigated in seven important mountain ranges of the Hengduan Mountains in Yunnan Province, such as Mt.Gaoligong and Mt.Yunling. The geographical distribution trends, rules and correlated variables were analyzed, based on the mean diversity indices of small mammals in the vertical zones of these ranges. The results demonstrated that the species diversity index decreased gradually from the south to the north and from the west to the east. The most important variables were latitude and rainfall. In addition, the peak of small mammals'density was analyzed and discussed in those areas.

Field research of macrobenthic fauna at 10 stations in Jiaozhou Bay was carried out seasonally from February of 1998 to November of 1999. There were fewer species and the indices of biodiversity (Shannon-Wiener index) were lower in Stations 2, 3, 7 and 9 than in other stations. Stations 2 and 3 were situated in the inner area near Cangkou, a heavily polluted area. Stations 7 and 9 were situated at the mouth of the bay, where the bottom sediment was coarse sand. The indices in Stations 1 and 6, where the bottom sediment was soft mud, were high. The average Shannon-Wiener index of all the 10 stations was lower in 1999 than in 1998, although the difference was not remarkable. In both of the two years, the average Shannon-Wiener indices were lower in spring and autumn than in winter and summer; Pielou's evenness index was highest in summer and lowest in spring; and the species richness index was slightly higher in winter and slightly lower in autumn. The relationship between biodiversity of the macrobenthos in Jiaozhou Bay and human activities should be studied further.

Selincuo Naked Carp ( Gymnocypris selincuoensis ) is the only fish species distributed in Selincuo Lake. Little had been known before we studied its biological characters since 1997. Based on its age composition , growth rate , feeding , reproduction and stock structure , the present paper int roduced the fishery history of Selincuo Lake and discussed the relationship between fishery catch and minimum catchable age , fishing mortality , mesh size and optimal sustainable yield. To get sustainable economic profits , exploitation of fishery resources of Selincuo Lake must focus on stability of lake ecosystem , and thus maintain a sufficient recruitment population of Selincuo Naked Carp. Because of the ext reme environment condition on the Tibetan Plateau and special biological characters of Selincuo Naked Carp , the model of maximum sustainable fish yield suitable for temperate zones can not be adopted in Selincuo Lake. The total allowed catch should be taken at anoptimal fishing mortality of F_{0. 2} . Finally , we put forward eight strategies for sustainable development of fishery as follows : 1) because of the characteristics of growth and reproduction of Selincuo Naked Carp and the climatic conditions of northerb Tibet Plateau , fishing season in Selincuo Lake should be condensed to winter season ; 2) according to present studies , the annual fishery yield of Selincuo Naked Carp can be increased from 700 ton to 2000 ton in Selincuo Lake ; 3) studies on population dynamics of Selincuo Naked Carp becomes more important when its annual yield rises ; 4) the catchable individuals should be elder than 12 years of age , longer than 290 mm and weightier than 350 g ; 5) the individuals harbouring tapeworms should be sorted out for producing indust rial fishmeal ; 6) promote the consumption of aquatic products of local people so as to maintain a economic profit ; 7) int roduction of exotic fish species should be st rictly limited , and 8) management of fishery production of Selincuo Lake should be improved.

The invasion of alien species is a major factor leading to the biodiversity crisis. Biological invasion is a major cause of biodiversity loss in the United States. The U.S. government is consistently paying more attention to invasive species now. On February 3, 1999, President Clinton signed an executive order(EO)-to coordinate a federal strategy to address the growing environmental and economic threat from invasive plants and animals that are not native to the United States. The President's order directs federal agencies to use their authority to prevent the introduction of invasive species and to restore native species. The EO directs establishment of an Invasive Species Council and prescribes the duties of the Council and federal agencies. The National Strategy for Invasive Plant Management, supported by the U.S. Department of Agriculture and other departments, proposes three national goals: prevention and control of invasive species' and restoration. This National Strategy provides three mechanisms: partnerships, education, and research for different groups and individuals. It requires a high level of cooperation and collaboration among them. Aggressive federal actions are already underway, including measures to prevent entry of invasive species, control and eradication of invasive species, outreach and education for the general public, and an increase in the budget for each fiscal year.