Soil nematode biodiversity in terrestrial ecosystems

A review of the literature on nematode diversity (=number of species identified) of soil inhabiting nematodes was undertaken and analysed with regard to distance from the equator, vegetation type and sampling effort. After applying a correction factor for sampling effort the results indicated that species richness was greatest in temperate broadleaf forest (61.7 species per sample) followed by cultivated soil, grassland, tropical rainforest, temperate coniferous forests and polar vegetation. The maintenance of high biodiversity in cultivated soils is unexpected but may reflect the impact of dominance in calculating many indices. Species richness was greatest between latitudes 30–40° (93.9 species per sample) and least above 70°, the mean richness near the equator (i.e. 0–10°) was 80.6 species per sample. While these data would suggest that nematode diversity is not necessarily greatest at the equator, and evidence to support a 'humped back' theory of species richness is not conclusive, they contradict the suggestion that nematode diversity increases with increased latitude.     

Fishes of floodplain habitats of the Fly River system, Papua New Guinea, and changes associated with El Niño droughts and algal blooms

Biological monitoring of the Fly River system in Papua New Guinea has shown that floodplain habitats (oxbow lakes, blocked valley lakes and seasonally inundated grassed floodplain) support diverse and abundant populations of freshwater fishes. Since monitoring first commenced in the early 1980's, a total of 66 fish species representing 33 families has been sampled, with gillnets and rotenone, from a range of sites located on the floodplains of the Fly and Strickland rivers. The fish fauna was dominated by catfishes in the families Ariidae (11 species) and Plotosidae (7 species), with aquatic invertivores being the dominant feeding group. Herring species (Nematalosa spp.) were often very abundant in the oxbow lakes, forming 66% of the total catch in all the floodplain habitats. The fish communities in the oxbow lakes and blocked valley lakes were distinctly different, with several of the smaller fish species being more abundant in the blocked valley lakes, while the oxbow lakes supported more of the larger predatory species. Catches in the oxbow lakes were also generally higher and more diverse than the blocked valley lakes or grassed floodplain sites. Since the commencement of monitoring, catches from the floodplain sites have varied considerably, both spatially and temporally. Reduced catches seen at some sites are probably associated with natural climatic factors, particularly El Niño-induced droughts and algal blooms. Introduced species and increased commercial and artisanal fishing may also be affecting stocks of native fish. Fish populations were shown to recover only slowly in lakes affected by severe drought conditions, with extensive mats of floating grasses hindering fish recolonisation. Fish stocks in a lake affected by an algal bloom recovered more quickly than stocks in lakes affected by drought.     

Landscape-scale Variation in Taxonomic Diversity in Four Groups of Aquatic Organisms: The Influence of Physical, Chemical, and Biological Properties

We evaluated several factors influencing the taxonomic richness of macrophytes, benthic invertebrates, snails, and fish in a series of northern Wisconsin lakes. We chose the study lakes to decouple the potential effects of ionic strength of lake water and stream connection, two factors that are usually highly correlated and therefore have been confounded in previous studies. In addition, our study lakes covered a wide range in a variety of characteristics, including residential development, abundance of exotic species, nutrient concentrations, predator abundance, and lake size. Species richness within each of the four taxonomic groups was significantly positively related to ionic strength (as measured by specific conductance); we also found secondary associations with other variables, depending on the specific group of organisms. The relationship between richness and lake area was dependent on the specific conductance of the lake and the vagility of the organisms; less vagile groups of organisms showed stronger and steeper species–area relationships in low-conductivity lakes. Further, after variance owing to specific conductance was removed, the presence of stream connections was positively related to species richness for fish, snails, and macrophytes as well as familial richness in benthic invertebrates. Our results indicate that lakes with relatively more groundwater input have lower extinction rates for all four groups of taxa and that lakes with stream inlets and outlets have enhanced immigration rates for fish, snails, benthic invertebrate families, and macrophytes. These findings link processes of immigration and extinction of four groups of organisms of varying vagility to landscape-level hydrologic characteristics related to the glacial history of the region.     

An exploration of factors influencing lotic insect species richness

An understanding of factors that influence species richness of lotic insects is generally lacking. We present comparative data on aquatic insect species richness from several North American and other streams. Factors such as large sample numbers and drainage area (species area relationships) are not significant predictors of species richness across the streams we examined. We explore several hypotheses regarding the origins and maintenance of species richness using Upper Three Runs Creek (UTR), South Carolina, USA, as a reference stream. UTR has the highest species richness of any stream in the Western Hemisphere. Hypotheses examined included historical, regional and local processes such as: (1) Evolutionary time, (2) disturbance regime/environmental variability, (3) temperature/evolutionary-speed, (4) productivity, and (5) habitat heterogeneity. Of these hypotheses, we suggest that productivity and habitat heterogeneity appear to contribute most to the high species richness found in UTR. We believe that multidisciplinary analysis of other streams is necessary because without this crucial information our knowledge of, and desire to protect biodiversity in streams will be wanting.     

Spatial and Temporal Patterns of Diversity and Distribution of the Upper Juruá River Fish Community (Brazilian Amazon)

We studied spatial and temporal patterns in fish species composition and diversity at the upper Juruá River located in the west Brazilian Amazon. We collected with gillnet 822 fishes belonging to 90 species in the main Juruá River, its tributaries and the floodplain lakes during wet and dry seasons. Fish abundance and species richness were greater in the dry season. During that season, fishes may be concentrated due to the low water level, being caught more easily by gillnets. There has been a trend towards a greater fish biomass caught in lakes. This might be associated with a greater environmental stability as lakes may be less subject to large variations in water level. The fish communities differed between the two seasons and between lakes and the lotic environments (main river and tributaries). Fish species from the family Curimatidae were most abundant in the lakes, while Pimelodus spp. and Hypostomus spp. predominated in the main Juruá River. Seasonal variations in fish communities may be related to differences in the migratory behavior among fish species. Such spatial and temporal patterns influencing fish community structure at the Upper Juruá Extractive Reserve must be accounted for in management and conservation strategies.     

生物多样性与生态系统功能:进展与争论

生物多样性与生态系统功能的关系已成为当前人类社会面临的一个重大科学问题,生物多样性的空前丧失,促使人们开展了大量研究工作来描述物种多样性-生态系统功能关系,并试图揭示多样性与系统功能关系的内在机制,本文将多样性对生态系统功能作用机制的有关假说分为统计学与生物学两大类：前者是从统计学角度来解释观察到的多样性-系统功能模式,包括抽样效应,统计均衡效应等;而后者是基于多样性的生物学效应给出的,包括生态位互补,种间正相互作用,保险效应等,本文较为详细地介绍了该领域内有代表性的实验工作,包括“生态箱”实验,Cedar Creek草地多样性实验,微宇宙实验,欧洲草地实验,以及在这些实验结果解释上的激烈争论。     

Species richness of aquatic macrophyte communites in Central Canada

Aquatic macrophyte species richness (SR) was examined at 430 sites in the central Canadian region in relation to water body type, bottom substrate and 8 water chemistry parameters. SR was highest in rivers and lakes, intermediate in creeks, and lowest in ponds. The highest values occurred where granitic bedrock, highly organic substrates or sand predominated. SR was significantly inversely correlated in the study area as a whole with 7 of the water chemistry parameters; of these, total alkalinity was the most important. However, the relative importance of the respective parameters differed for various water body types. The relationship between SR and phosphorus was positive in ponds, but negative for all other water body types. Stepwise sultiple regression analysis identified phosphorus, total alkalinity and dissolved organic matter as important factors in ponds; sulphate, total alkalinity and chloride in lakes, and sulphate and phosphorus in lotic habitats. Log transformations improved the correlations for some variables. However, the water chemistry parameters examined accounted for less than half of the total variability in SR. Apparently SR depends on many different factors, including surface areaand bottom type, whose relative contributions vary with situation.     

Regional patterns of diversity and estimates of global insect species richness

The total number of insect species in the world is an important if elusive figure. We use a fresh approach to estimate global insect species richness, based on biogeographic patterns of diversity of well or better documented taxa. Estimates generated by various calculations, all variations on a theme, largely serve to substantiate suggestions that insect species are likely to number around 10 million or less.