Effects of hydropower-induced flow perturbations on mayfly (Ephemeroptera) richness and abundance in north Swedish river rapids

Mayfly species richness and abundance were investigated at 52 Swedish river rapids. These were either unregulated, or regulated with or without reduced discharge. Sites impacted by regulation had lower mayfly richness and abundances than unregulated reference sites. The relative importance of reduced discharge, daily fluctuations in flow, flow constancy, and the distance to nearest rapid (as a measure of isolation) was evaluated in multiple regression analyses. These indicated negative effects of diel fluctuations on both abundance and richness, whereas flow constancy was favourable for richness. Neither the distance to nearest rapid nor reduced flow were significantly related to mayfly richness and abundance. In total, 26 mayfly species were recorded. Only Baetis rhodani was found at all sites, but another five species were present at more than 40 sites. The strongest effects were found for species within the Heptageniidae. Nineteen of 20 mayfly species present in both the regulated (with unreduced flow) and unregulated reference rapids were on average more common in the unregulated ones. Mayfly assemblage structure was primarily influenced by regional factors and nutrient status, although daily fluctuations in flow together with rapids dimensions also had a significant influence. No rare species appears to be threatened by hydropower regulation though it is conceivable that depressed abundances in regulated rivers indirectly influence predators and periphyton.     

New species of Nanomis Lugo-Ortiz and McCafferty, 1999 (Ephemeroptera: Baetidae) from Venezuela

As the first taxonomic and faunistic report of Nanomis Lugo-Ortiz and McCafferty, 1999 for Venezuela, we describe a new species, N. rasmusseni sp. n., based on material from Andean streams. Comparisons of the nymphal and imaginal stages of N. rasmusseni with those of N. galera Lugo-Ortiz and McCafferty, 1999 – the only species currently known for this genus – are done in detail. Further, additional morphological characters are discussed to delineate the genus from the other baetid genera. Likewise, ecological data and distribution of N. rasmusseni in the Andean highlands of Venezuela are provided, which improves knowledge of the richness and distribution of the genus in South America.

http://www.zoobank.org/urn:lsid:zoobank.org:pub:C9DF3936-101F-4240-B067-AC5DF394C805     

Life History,Growth and Secondary Production of Caenis luctuosa and Cloeon simile (Ephemeroptera) in a Small Pond,S.W. France

In the present paper, based on material from Brazil, we present a contribution to the taxonomy of the Neotropical two-winged Leptophlebiidae. The male imago of Perissophlebiodes Savage is described, in addition to a new species of Askola Peters from Amazonas. Askola emmerichi Domínguez, Molineri and Mariano, so far recorded from Venezuela, is reported from Brazil and compared to the new species herein described. Askola yanoman, sp. nov. can be separated from other species of the genus by the following combination of characters: (1) general colouration yellowish brown with areas washed with greyish brown; (2) dorsal portion of eyes brown, eyes meet on meson of head; (3) penis yellowish brown with darker margin, extending beyond the posterior margin of the styliger plate.     

Physical and Chemical Limnology of 34 Lentic Waterbodies along a Tropical‐to‐Alpine Altitudinal Gradient in Nepal

Physical and chemical factors were studied in 34 lentic waterbodies distributed along a steep altitudinal gradient ranging from tropical (77 m) to high alpine (up to 4,980 m) environments in Nepal. Bicarbonate and calcium were dominant among anions and cations, respectively, reflecting a strong influence of carbonate weathering and watershed area, rather than altitudinal climate. The relative patterns of dominant ions were similar among lakes in all altitudinal regions, although total concentrations increased with decreasing altitude. Total suspended solids were relatively high in the study lakes, as is also typical of rivers in the Ganges watershed. Suspended solids had a greater influence on water transparency than did algal biomass in the study lakes. In general, high‐altitude waterbodies were oligotrophic, while those at low altitude were eutrophic. The productivity of high‐altitude study lakes appeared to be limited by both available phosphorus and nitrogen, while lowland ones were nitrogen‐limited. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of large South American rivers of the Plata Basin on distributional patterns of tropical snakes: a panbiogeographical analysis

Aim The main drainages of the Plata Basin – the Paraná, Paraguay and Uruguay rivers – begin in tropical latitudes and run in a north–south direction into subtropical–temperate latitudes. Consequently, the biota of these rivers has tropical elements that contrast with temperate biomes through which the rivers run. We apply a panbiogeographical approach, to test whether the large rivers of the Plata Basin have a differential influence on distributional patterns of tropical snakes in subtropical and temperate latitudes of South America. Location Subtropical and temperate sections of the major Plata Basin rivers, South America. Methods We compared the individual tracks of 94 snake taxa. The track analysis consisted of: (1) plotting the localities of each taxon on maps, (2) connecting the localities of each taxon using a minimal geographical proximity determinant of the ‘individual tracks’, and (3) superimposing the individual tracks to determine generalized tracks. To detect tropical snakes that reach higher latitudes through the rivers we used the preferential direction of distribution concept. For each taxon we measured the angular deviations between the line of its individual track and the course of the rivers in a 100 × 100 km scaled grid. Average angular values < 45° indicated a positive association with the rivers. Results Thirty‐five of 94 taxa showed distributions associated with the major rivers of the Plata Basin, including fauna from distinct biogeographical lineages, supported by the occurrence of five generalized tracks as follows: (1) the Paraguay–Middle Paraná, (2) the Paraguay–Paraná fluvial axis, Upper Paraná and Middle Paraná to Upper Delta, (3) the Lower Paraguay, Paraná and Uruguay rivers, excluding the sectors High Paraná and High Uruguay, (4) the Uruguay River and Upper Paraná, and (5) the High Paraná. The Atlantic species occurred with significantly higher frequency in the Uruguay River and High Paraná river sections, the Amazon species were found with significantly higher frequency in the Paraguay and Middle Paraná sections, and the species with a Pantanal distribution were found in all sections. Main conclusions The observed distributional patterns may be explained by the interaction of ecological, geographical and historical factors. Previous authors have developed ecological (hydrological or environmental similarity) or dispersalist (effect of rivers as migration routes) explanations. The coincidence between generalized tracks and past geomorphological events that caused displacements and changed relationships between the Paraguay, Paraná and Uruguay river sections supports hypotheses involving the strong influence of historical factors in the present configuration of tropical snake distribution in temperate latitudes.     

Altitudinal distribution of chytrid (Batrachochytrium dendrobatidis) infection in subtropical Australian frogs

The disappearance of amphibian populations from seemingly pristine upland areas worldwide has become a major focus of conservation efforts in the last two decades, and a parasitic chytrid fungus, Batrachochytrium dendrobatidis, is thought to be the causative agent of the population declines. We examined the altitudinal distribution of chytrid infections in three stream‐dwelling frog species (Litoria wilcoxii, L. pearsoniana and L. chloris) in southeast Queensland, Australia, and hypothesized that if B. dendrobatidis were responsible for the disappearance of high‐altitude frog populations, infection prevalence and intensity would be greatest at higher altitudes. Overall, 37.7% of the 798 adult frogs we sampled were infected with B. dendrobatidis, and infections were found in all the populations we examined. Contrary to our initial hypothesis, we found no consistent evidence that high‐altitude frogs were more likely to be infected than were lowland frogs. Further, the intensity of fungal infections (number of zoospores) on high‐altitude frogs did not differ significantly from that of lowland frogs. Batrachochytrium dendrobatidis appears to be capable of infecting frogs at all altitudes in the subtropics, suggesting that all populations are at risk of decline when conditions favour disease outbreaks. We did find evidence, however, that chytrid infections persist longer into summer in upland as compared with lowland areas, suggesting that montane amphibian populations remain susceptible to disease outbreaks for longer periods than do lowland populations. Further, we found that at high altitudes, temperatures optimal for chytrid growth and reproduction coincide with frog metamorphosis, the life‐stage at which frogs are most susceptible to chytrid infections. While these altitudinal differences may account for the differential population‐level responses to the presence of B. dendrobatidis, the reason why many of southeast Queensland's montane frog populations declined precipitously while lowland populations remained stable has yet to be resolved.     

A panbiogeographical model to prioritize areas for conservation along large rivers

Aim The large rivers of the Neotropics are considered areas of high diversity and endemism, which play an important role in the distribution patterns and evolution of Neotropical biota. Several methods have been proposed for prioritizing terrestrial conservation areas, but there has been little effort to develop models for river systems. We propose a panbiogeographical approach to identify priority areas for conservation along rivers. Location The Plata Basin rivers. Methods We compared the individual tracks (IT) of 96 snake taxa and identified the species associated with rivers using the concept of preferential direction of distribution. For each taxon, we measured the angular deviations between the line of its IT and the course of the rivers on a 100 × 100 km scaled grid. Average angular values < 45° indicated a positive association with rivers. We detected 35 taxa associated with rivers, and their IT were used to determine the generalized tracks (GT) and nodes. We applied a complementarity algorithm to identify the minimum set of nodes required to represent all species. Results Six nodes were found. The region where the High and Upper Paraná Rivers converge (Node 1) is of first priority, with 60 of 96 species. The second priority is the Lower Paraguay River and northern section of Middle Paraná River (Node 2). The third is the High Paraná, which together with Nodes 1 and 2, comprises 94% of the total species. The fourth and fifth are the High and Middle Uruguay, and the western section of the Upper Paraná and Iberá Marsh system, respectively. These five nodes include all species. Main conclusions Our results highlight the areas of particular interest for the conservation of rivers and provide a biogeographical algorithm for detecting priority conservation areas. The nodes are a biogeographical approach that allows evolutionary and ecological traits to be included in conservation assessment.     

Altitudinal distribution of tropical planktonic Cladocera

The altitudinal distributions of planktonic Cladocera in Africa in three latitudinal bands: 0–10 °, 10–20 ° and 28–31 ° are described. Some species have altitudinal ranges of 2000 m within a latitudinal band of 10 °. It is possible to distinguish tropical species which do not extend up to high altitudes, particularly at higher latitudes. At the lowest latitudes, some species are found only at high altitudes, but occur at progressively lower altitudes with increasing latitude: Daphnia pulex and D. obtusa are good examples. A study in South America, with a smaller database, gives similar results.     

Factors affecting the distribution and abundance of Cloeon and Caenis (Ephemeroptera) larvae in a tropical impounded river, Nigeria

Impoundment of rivers affects the mayfly (Ephemeroptera) fauna inhabiting such water bodies, especially with respect to their distribution and abundance. A two‐year study of the mayfly fauna and some of the physicochemical parameters of the Opa stream–reservoir revealed that there are two mayfly genera inhabiting it, Cloeon and Caenis. The number of Cloeon larvae collected was 10,930 while the number of Caenis larvae was 450. It was observed that although both genera occurred at all the sampling stations, their numbers were reduced in the stream below the dam due to increased water current velocity. There were significant differences in the abundance of Cloeon among the stations, but none for Caenis. Submerged aquatic plants and water current velocity were found to be the major factors responsible for the significant differences. There were significant correlations between the number of Cloeon larvae and pH as well as between dissolved oxygen concentration and Caenis. These findings are discussed with reference to inter‐specific differences in patterns of response to environmental parameters. A species‐specific approach is suggested for studies on the strategies that enable mayfly species maintain their populations in stressed and unstable aquatic ecosystems.