Ecology of diapausing copepodids of Cyclops kolensis Lill. in reservoirs of the Upper Volga

Cyclops kolensis Lill. forms dense populations in different water-bodies of the Upper Volga basin. In spring, when the other planktonic crustaceans have not yet appeared, C. kolensis is an important food object for fishes. Its active reproduction occurs from April to the beginning of June. A rapid accumulation of stage IV copepodids in the plankton occurs in June and at 12–14° they sink into the pelogene in a diapause stage. During the summer stagnation period the diapausing copepodids are distributed evenly over the bottom; their abundance here is 0.7–0.8 million ind. m^-2 (Rybinsk reservoir). During storms and autumn active water mixing the copepodids together with detritus are disturbed and brought to the deepest, silt rich, part of the water-bodies. After the ice formation and at the beginning of bottom heating the diapausing copepodids are transported by near bottom currents and are concentrated in depressions; their biomass here reaches 60 g m^-3. After the thermo-oxy-cline formation they revive and begin to live actively. Copepodids feed, accumulate adipose matter and in February–March they begin to moult.     

Tropical ant communities are in long-term equilibrium

Communities change with time. Studying long-term change in community structure permits deeper understanding of community dynamics, and allows us to forecast community responses to perturbations at local (e.g. fire, secondary succession) and global (e.g. desertification, global warming) spatial scales. Monitoring efforts exploring the temporal dynamics of indicator taxa are therefore a critical part of conservation agendas. Here, the temporal dynamics of the Otongachi leaf litter ant community, occurring in a cloud forest in coastal Ecuador, were explored. By sampling this community six times over eleven years, I assessed how the ant fauna caught by Winkler traps (more diverse and cryptic fauna) and caught by pitfall traps (larger, more mobile fauna) changed over time. The Otongachi leaf litter ant community was dynamic. Although species richness in the community remained constant, temporal turnover of species was high: on average, 51% of the ant species in Winkler traps, and 56% of those in pitfall traps, were replaced with other ant species from one year to the other. Shifts in the rank abundance of species in the community were also large across the eleven years and, on average, shifts in the rank abundance of species collected by Winkler traps doubled those occurring in pitfall traps from one census to the other. In spite of these trends, the Otongachi ant fauna showed no (Winkler) or weak (pitfall) evidence of directional change (towards a new community). Thus, this tropical ant community can be divided in two community compartments. The Winkler compartment composed by a more diverse and cryptic ant fauna appears to be resilient and stable in time. The pitfall compartment composed by larger and more mobile ants may be prone to respond to disturbance. This study suggests that 1) species appearing/disappearing from a site may be rather the rule, difficult to separate from responses to ecological stress. 2) Conclusions made in short-term studies, or studies comparing two (e.g. before and after) snapshots of a community, should thus be revisited. Finally, 3) the ant fauna caught by pitfall traps (a rather simple and cheap survey method) is the most likely community compartment to indicate ecological perturbation. This study adds to the growing evidence that using ants as ecological indicators should incorporate long-term temporal dynamics.     

Cedrela nebulosa: A novel species for dendroclimatological studies in the montane tropics of South America

Up to now, the development of dendrochronological records from tropical regions in South America has been limited to the lowlands with emphasis in the Amazon basin. In this contribution, we present the first chronology of Cedrela nebulosa, a species that develops in the tropical mountainous regions of South America. We collected samples from trees in Monobamba district in Peru, analysed the anatomical features that determine the growth rings, and processed following the methods commonly used in dendrochronology. The 133-years chronology covering the 1883–2015 period, showed large correlation between series. In order to determine the climatic variables that control tree growth, we performed correlation analyses between tree-growth and local and regional precipitation and temperature records. We found that precipitation triggers tree growth at the beginning of the spring season but temperature seems to be the main control in annual growth. Also, C. nebulosa chronology present coherent variations with Multivariate Enso Index (MEI) and Pacific Ocean sea surface temperatures during summer months. This climate-sensitive tree-ring record indicates good potential for dendroclimatic studies and provides an opportunity to reconstruct climatic variations in montane forests of the tropical Andes.     

Establishing Causality between Exposure to Metals and Effects on Fish

This study evaluates causal relationships between chronic exposure of fish to metals and effects at different levels of biological organization based on a weight-of-evidence approach. Criteria for evaluation of causality were strength, consistency, and specificity of the association, as well as biological gradient and plausibility. Field sampling was conducted three times between 1998 and 2000, in Furnas Stream, impacted by an abandoned lead mine, and in three other locations, including two reference and one impacted sites. Levels of Pb, Zn, Cd, and Ag in sediments from the Furnas Stream exceeded background levels, and their concentrations were above sediment quality guidelines. Residual levels of metals in fish tissue were high enough to indicate reduced growth, reproduction and/or survival according to toxicological benchmarks. Lead-induced biochemical changes (ALA-D activity depletion) were observed in two species of siluriform catfish. The condition factor of a predatory catfish was reduced, and the percentage of prey generalists was higher in Furnas than at the noncontaminated sites. Reduction in fish community diversity and density was observed. Integration of data provided supporting evidence that observed effects on fish from the Furnas Stream resulted from long-term exposure to metals, however influences from other stressors cannot be ruled out.     

Environment versus dispersal in the assembly of western Amazonian palm communities

Aim It is a central issue in ecology and biogeography to understand what governs community assembly and the maintenance of biodiversity in tropical rain forest ecosystems. A key question is the relative importance of environmental species sorting (niche assembly) and dispersal limitation (dispersal assembly), which we investigate using a large dataset from diverse palm communities. Location Lowland rain forest, western Amazon River Basin, Peru. Methods We inventoried palm communities, registering all palm individuals and recording environmental conditions in 149 transects of 5 m × 500 m. We used ordination, Mantel tests and indicator species analysis (ISA) to assess compositional patterns, species responses to geographical location and environmental factors. Mantel tests were used to assess the relative importance of geographical distance (as a proxy for dispersal limitation) and environmental differences as possible drivers of dissimilarity in palm species composition. We repeated the Mantel tests for subsets of species that differ in traits of likely importance for habitat specialization and dispersal (height and range size). Results We found a strong relationship between compositional dissimilarity and environmental distance and a weaker but also significant relationship between compositional dissimilarity and geographical distance. Consistent with expectations, relationships with environmental and geographical distance were stronger for understorey species than for canopy species. Geographical distance had a higher correlation with compositional dissimilarity for small‐ranged species compared with large‐ranged species, whereas the opposite was true for environmental distance. The main environmental correlates were inundation and soil nutrient levels. Main conclusions The assembly of palm communities in the western Amazon appears to be driven primarily by species sorting according to hydrology and soil, but with dispersal limitation also playing an important role. The importance of environmental characteristics and geographical distance varies depending on plant height and geographical range size in agreement with functional predictions, increasing our confidence in the inferred assembly mechanisms.     

Streamflow-induced variations in nitrate flux in tributaries to the Atlantic Coastal Zone

Streamflow-related variability in nutrient flux represents an important source of uncertainty in managing nutrient inputs to coastal ecosystems. Quantification of flux variability is of particular interest to coastal resource managers in adopting effective nutrient-reduction goals and monitoring progress towards these goals. We used historical records of streamflow and water-quality measurements for 104 river monitoring stations in an analysis of variability in annual and seasonal flux of nitrate to the Atlantic coastal zone. We present two measures of temporal flux variability: the coefficient of variation (CV) and the exceedence probability (EP) of 1.5 times the median flux. The magnitude of flux variations spans a very wide range and depends importantly upon the season of year and the climatic and land-use characteristics of the tributary watersheds. Year-to-year variations (CV) in annual mean flux range over two orders of magnitude, from 3–200% of the long-term mean flux, although variations more typically range from 20–40% of the long-term mean. The annual probability of exceeding the long-term median flux by more than 50% (EP) is less than 0.10 in most rivers, but is between 0.10 and 0.35 in 40% of the rivers. Year-to-year variability in seasonal mean flux commonly exceeds that in annual flux by a factor of 1.5 to 4. In western Gulf of Mexico coastal rivers, the year-to-year variablity in the seasonal mean flux is larger than in other regions, and is of a similar magnitude in all seasons. By contrast, in Atlantic coastal rivers, the winter and spring seasons, which account for about 70% of the annual flux, display the smallest relative variability in seasonal mean flux. We quantify the elasticity of nutrient flux to hypothetical changes in Streamflow (i.e., the percent increase in flux per percentage increase in mean discharge) to allow the approximation of flux variability from streamflow records and the estimation of the effects of future climatically-induced changes in Streamflow on nutrient flux. Flux elasticities are less than unity (median = 0.93%) at most stations, but vary widely from 0.05% to 1.59%. Elasticities above unity occur most frequently in the largest rivers and in rivers draining the arid portions of the western Gulf of Mexico Basin. Historical flux variability and elasticity generally increase with the extent of arid conditions and the quantity of nonurban land use in the watershed. We extend the analysis of flux variability to examine several case studies of highly unusual meteorological events capable of significantly elevating nitrate flux and degrading estuarine ecology.