How do biodiversity patterns of river animals emerge from the distributions of common and rare species?

We studied the patterns of commonness and rarity for one vertebrate (fish) and four freshwater insect taxa (Ephemeroptera, Plecoptera, Trichoptera and Coleoptera) in southwestern France (57,000 km²), and we analysed the relationships between the location of sites and the contribution of commonness and rarity to species richness within a large stream system. Richness patterns in fish and aquatic insects were related to the location of sites within the stream system. The number of common and rare fish species increased from up- to downstream areas as a result of downstream additions of species. The number of common insect species peaked in the intermediate section of the river continuum, whereas rarity increased with decreasing elevation. In all taxa, common species gave a closer approximation to overall patterns of species richness than did rare ones. The biodiversity patterns of river animals emerged from convergence in the distributions of common and rare species (fish), or mostly from the distribution of common species (insects). However, in fish, Ephemeroptera and Plecoptera, the rarer species became almost equally, or more strongly correlated with overall species richness when increasing information along the common-to-rare and rare-to-common sequences. These patterns suggested that rarer species show a similar or stronger affinity, on a species-for-species basis, for high richness areas than do the commoner species. These schemes have implications for biodiversity assessments, as studies using common species richness to target important areas for monitoring or conservation efforts within stream systems will not necessarily identify areas important for rare species, and vice versa.     

How many soil samples are neccessary to obtain a reliable estimate of mean nitrate concentrations in an agricultural field?

In Germany, field‐average soil NO₃^‐ measurements are used to identify agricultural risks of groundwater pollution and to evaluate the compliance of land users with environmental regulations. In the present study, it was tested at three typical agricultural sites if common practices of soil NO₃^‐ sampling were appropriate to obtain reliable estimates of the mean field NO₃^‐ content in fall. Three sites of 1 ha area were extensively sampled for NO₃^‐. Ordinary statisticial analyses were conducted on the NO₃^‐ data in order to calculate how many samples per ha were required to predict the mean field NO₃^‐ with a given accuracy. Variograms were derived to assess applicability and relevance of ordinary statistical methods for heterogeneous fields. Results from statistical analysis suggest that at two sites common practices of soil NO₃^‐ sampling would have been adequate to obtain estimates of the actual mean field NO₃^‐ content with a sampling error less than 10 kg NO₃^‐‐N ha^—1 at a 95% probability level. At the other site, common practices obviously would have failed because NO₃^‐ contents varied much more spatially. It remains a problem of soil sampling for NO₃^‐ analysis that information on field heterogeneity is frequently not available a priori.     

How long does the Atlantic Rain Forest take to recover after a disturbance? Changes in species composition and ecological features during secondary succession

We evaluated floristic and ecological changes in plant communities after disturbance in Southern Atlantic Rain Forests, in the Brazilian states of Rio de Janeiro, São Paulo, Paraná and Santa Catarina. We compiled data for 410 tree species from 18 forests ranging from 4 to 120 years after disturbance, and classified them by dispersal mode (animal vs. non-animal), successional group (pioneer vs. non-pioneer), vertical position (understorey vs. non-understorey) and geographic distribution (Atlantic Forest vs. widespread). We found that both geographical location and time since disturbance affect species distribution and β-diversity. Regression analyses showed significant, positive and strong relations (0.26 ? r² ? 0.63; P < 0.05) between fragment age and species richness, proportion of animal dispersed species, of non-pioneer species, of understorey species and with restricted distribution. Applying our data to values found in literature we predict that a forest needs about one to three hundred years to reach the proportion of animal-dispersed species (80% of the species), the proportion of non-pioneer species (90%) and of understorey species (50%) found in mature forests. On the other hand much more time is necessary (between one and four thousand years) to reach the endemism levels (40% of the species) that exist in mature forests. Our findings indicate that disturbance results in significant changes in species composition (decrease in endemic species) and ecological guilds (decrease in zoochory and in non-pioneer and understorey species), but forests can gradually recover over time spans of hundreds of years.     

Does the influence of earthworms on water infiltration, nitrogen leaching and soil respiration depend on the initial soil bulk density? A mesocosm experiment with the endogeic species Metaphire posthuma

Soil compaction has a negative impact on both earthworm abundance and diversity. Recent studies, however, suggest that earthworm cast properties are not influenced by the initial soil bulk density. With time, earthworms could therefore transform soils with different bulk densities into a soil with the same physical state and thus with a similar ecological functioning. This study aimed to test this hypothesis in two laboratory incubation experiments. First, we measured the influence of soil bulk density (1.1 or 1.4?g?cm^?3) on the production of cast by the endogeic earthworm species Metaphire posthuma. In a second experiment, we investigated the effect of M. posthuma on water infiltration, NH ₄ ⁺ , and NO ₃ ^? leaching and soil respiration at the same two soil bulk densities. Although initially higher, earthworm casting activity in soil at 1.4?g?cm^?3 decreased until it reached the same level of activity as earthworms in soil at 1.1?g?cm^?3. This behavioral plasticity led to a transformation of compacted and loose soils, with their own functioning, to a third and similar state with similar hydraulic conductivity, nitrogen leaching, and soil respiration. The consequences for soil organization and soil functioning are discussed.