Aquatic insect faunas and communities of a mountain stream in Sapa Highland,northern Vietnam

Aquatic insect communities were investigated from the Muonghoa Stream in the Sapa Highland (highest peak 3,143 m), a subtropical mountain stream in northern Vietnam. Field investigations for quantitative (Surber net 50 cm × 50 cm, mesh size 0.2 mm, riffle and pool/run) and qualitative (hand net, mesh size 1 mm) sampling were conducted at nine sites along the watercourse between 27 November and 2 December 2005. As a result, a total of 216 species (the majority of them undescribed) belonging to 139 genera, 61 families, and nine orders were recognized: 53 Ephemeroptera species (24.5%), nine Odonata species (4.2%), 15 Plecoptera species (6.9%), seven Hemiptera species (3.2%), 35 Coleoptera species (16.2%), one Megaloptera species (0.5%), 29 Diptera species (13.4%), 66 Trichoptera species (30.6%), and one Lepidoptera species (0.5%). Trichoptera, Ephemeroptera, and Coleoptera represented the major aquatic insect groups with regard to taxonomic and individual richness, whereas Hemiptera and Odonata were relatively less diverse and abundant than in studies of other tropical Southeast Asian streams. The dominance, richness, and diversity indices (H′) fell within the following ranges [mean ± standard deviation (SD)]: 0.18–0.76 (0.42 ± 0.19), 4.13–9.19 (7.06 ± 1.45), and 1.61–3.22 (2.67 ± 0.55), respectively. Riffle habitats generally yielded numbers of aquatic insect species and individuals approximately twice that sampled in pool/run habitats. Shredders were relatively larger in proportion within the headwater reach, whereas scrapers and collector-gatherers were more abundant in the middle and lower stream reaches. This functional feeding group composition is characteristic of temperate streams in East Asia. The results of detrended correspondence analysis and Bray–Curtis cluster analysis indicated that aquatic insect compositions at the sampling sites were very reflective of the reach characteristics, which evidence gradual changes with altitude and stream order along the stream watercourse. This is the first comprehensive investigation of aquatic insects in highland Southeast Asian regions.     

Effects of omnivorous shrimp in a montane tropical stream: sediment removal,disturbance of sessile invertebrates and enhancement of understory algal biomass

Freshwater shrimp dominate the faunal biomass of many headwater tropical streams: however, their role in community organization is unclear. Enclosure/exclosure experiments in a montane Puerto Rican stream examined direct and indirect effects of two dominant taxa of atyid (Atyidae) shrimp, Atya lanipes Holthuis and Xiphocaris elongata Guerin-Meneville. Both shrimp taxa caused significant reductions in sediment cover on rock substrata, reducing sedimentation and enhancing algal biovolume on clay tiles in cages. When tiles incubated in shrimp exclosures for 2 wks were placed outside of cages, atyid shrimp removed 100% of the sediment cover within a 30 min observation period. Atyid shrimp appear to play an important role in stream recovery after high discharge events by rapidly removing sediments and detritus deposited on benthic substrata in pools. We evaluated the mechanism by which A. lanipes influences algae and benthic insects by comparing patterns of algal biomass, taxonomic composition, and insect abundance between shrimp-exclusion and shrimp-presence treatments both with and without manual sediment removal. The shrimp exclusion treatment without manual sediment removal bad significantly lower algal biomass and greater sedimentation than all other treatments. The treatment in which shrimp were excluded but sediment was manually removed, however, accrued almost the same algal biovolume as the shrimp enclosure treatment, supporting the hypothesis that sediment removal enhances the biovolume of understory algal taxa. Algal community composition was similar between stream bottom bedrock exposed to natural densities of shrimp and all experimental treatments for both Atya and Xiphocaris: a diatom community strongly dominated (78–95%) by the adnate taxon, Achnanthes lanceolata Breb ex. Kutz. Atyid shrimp are important in determining the distribution and abundance of benthic insects through both direct and indirect effects. Sessile, retreat-building chironomid larvae (Chironomidae: Diptera) are negatively affected by both A. lanipes and X. elongata, through direct removal by foraging activities and/or indirectly through depression of sediment resources available to larvae for the construction of retreats. In constrast, the mobile grazer, Cloeodes maculipes (Baetidae: Ephemeroptera) was not adversely affected and atyid shrimp have the potential to exert positive indirect effects on this taxon by facilitating its exploitation of algal resources and/or through enhancement of understory algal food resources through sediment removal.     

Trophic relationships in a tropical stream food web assessed by stable isotope analysis

1. Stable isotope analysis, coupled with dietary data from the literature, was used to investigate trophic patterns of freshwater fauna in a tropical stream food web (Guadeloupe, French West Indies).
2. Primary producers (biofilm, algae and plant detritus of terrestrial origin) showed distinct δ¹³C signatures, which allowed for a powerful discrimination of carbon sources. Both autochthonous (¹³C-enriched signatures) and allochthonous (¹³C-depleted signatures) resources enter the food web. The migrating behaviour of fishes and shrimps between marine and freshwater during their life cycles can be followed by carbon isotopes. Here, shrimp δ¹³C signatures were shown to shift from −16‰ (for juveniles under marine influence) to −24.7‰ (for adults in freshwater habitats). For resident species, δ¹³C values partly reflected the species' habitat preferences along the river continuum : species living in river mouths were ¹³C-enriched in comparison with those collected upstream.
3. Nitrogen isotopic ratios were also discriminating and defined three main trophic guilds among consumers. The δ¹⁵N values of herbivores/detritivores were 5.0–8.4‰, omnivores 8.8–10.2‰ and carnivores 11–12.7‰.
4. Mixing model equations were employed to calculate the possible range of contribution made by respective food sources to the diet of each species. The results revealed the importance of omnivorous species and the dependence of riverine biota on terrestrial subsidies, such as leaf detritus and fruits. Finally, the abundance of shrimps and their feeding habits placed in relief their key role in tropical freshwater food webs. Isotopic analysis provides a useful tool for assessing animal feeding patterns.     

Indirect effect of aquatic insect emergence on a terrestrial insect population through by birds predation

A manipulative field experiment was performed to determine the effect of birds, subsidized by aquatic insect emergence, on the insect herbivores in a riparian deciduous forest. Insectivorous birds were observed more frequently in the riparian forest than in upland forest away from the stream, utilizing both herbivorous insects feeding on the riparian vegetation and aquatic insects emerging from the stream as their prey. Field experiments revealed that the insect herbivore population in the riparian forest was more depressed by bird predation than that in the upland forest. This suggests that allochthonous prey input to the in situ prey population was responsible for a modification in the interaction between birds and herbivorous insects, resulting in a heterogeneous food web structure in the forest.     

Effects of different management regimes on aquatic macroinvertebrate diversity in Australian rice fields

The maintenance of invertebrate diversity within agricultural environments can enhance a number of agronomically important processes, such as nutrient cycling and biological pest control. However, few Australian studies have been undertaken which specifically address the effects of commercial management regimes on rice field biodiversity. In this study, we compared aquatic macroinvertebrate communities within Australian rice fields cultivated under three commercial management regimes: conventional-aerial (agrochemicals applied, aerially sown), conventional-drill (agrochemicals applied, directly drill-sown) and organic-drill (agrochemical-free, directly drill-sown). These comparisons were undertaken using a combination of community assessment approaches, including morphospecies richness, abundance, diversity and community composition. In general, greater biodiversity existed within macroinvertebrate communities that developed under organic management regimes than under conventional regimes (i.e., higher morphospecies richness and Shannon diversity). Although there were significant differences in several parameters across management regimes early in the rice-growing season, as the growing season progressed the invertebrate communities that developed in the different management regimes became more similar. Only community composition analyses showed significant differences late in the growing season, with functional differences across aquatic faunal assemblages suggested by increased predator abundance in communities sampled from the organic management regime. In order to improve biodiversity within these aquatic environments, management techniques need to be examined individually and the most disruptive processes identified. Alternative management procedures can then be developed that minimise biodiversity loss whilst still delivering required agronomic outcomes.     

Relationships between spatial configuration of tropical forest patches and woody plant diversity in northeastern Puerto Rico

The destruction and fragmentation of tropical forests are major sources of global biodiversity loss. A better understanding of anthropogenically altered landscapes and their relationships with species diversity and composition is needed in order to protect biodiversity in these environments. The spatial patterns of a landscape may control the ecological processes that shape species diversity and composition. However, there is little information about how plant diversity varies with the spatial configuration of forest patches especially in fragmented tropical habitats. The northeastern part of Puerto Rico provides the opportunity to study the relationships between species richness and composition of woody plants (shrubs and trees) and spatial variables [i.e., patch area and shape, patch isolation, connectivity, and distance to the Luquillo Experimental Forest (LEF)] in tropical forest patches that have regenerated from pasturelands. The spatial data were obtained from aerial color photographs from year 2000. Each photo interpretation was digitized into a GIS package, and 12 forest patches (24–34 years old) were selected within a study area of 28 km². The woody plant species composition of the patches was determined by a systematic floristic survey. The species diversity (Shannon index) and species richness of woody plants correlated positively with the area and the shape of the forest patch. Larger patches, and patches with more habitat edge or convolution, provided conditions for a higher diversity of woody plants. Moreover, the distance of the forest patches to the LEF, which is a source of propagules, correlated negatively with species richness. Plant species composition was also related to patch size and shape and distance to the LEF. These results indicate that there is a link between landscape structure and species diversity and composition and that patches that have similar area, shape, and distance to the LEF provide similar conditions for the existence of a particular plant community. In addition, forest patches that were closer together had more similarity in woody plant species composition than patches that were farther apart, suggesting that seed dispersal for some species is limited at the scale of 10 km.     

Aquatic plants diversity in arid zones of Northwest China: patterns, threats and conservation

We investigated aquatic plant diversity by conducting the field investigation and collecting the published data in the arid regions of Northwest China. Two hundred and twenty four taxa of vascular aquatic plants representing 64 genera and 34 families occur in this area, 8.48% of which are endemic. Among these, 1 genus and 6 species were new state records and 1 family, 9 genera and 29 species were new area records. Typhaceae, Potamogetonaceae, Juncaginaceae and Haloragaceae were the most frequent families (considering relative frequency of occurrence), whereas Cyperaceae, Potamogetonaceae and Ranuncnlaceae are the most species-rich. The most frequent genera were Typha, Potamogeton, and Triglochin, and the most species-rich were Potamogeton, Eleocharis and Scirpus. The most frequent species are Triglochin palustre, Myriophyllum spicatum, Potamogeton pectinatus and Typha angustifolia. Aquatic plants diversity is distributed unevenly in the region. The maximum species occurs in Dzungarian basin while the least species in Hexi corridor. The aquatic flora in arid zone of China is not distinctive although some endemic species are found, most species are widely distributed. Local aquatic plants diversity can be influenced by many factors such as hydrological alteration, habitat loss, over-grazing, high human population pressure, global climate change, an inappropriate economic development policy. Among them, the largest threat to aquatic plants biodiversity may be habitat loss due to hydrological alteration. In order to conserve the aquatic plants biological resources and biodiversity in this region, some strategies and measures must be suggested including strengthening scientific research and biodiversity education in the local people, balancing economic development and ecological conservation, and enhancing governmental assistance and subsidy to the local residents.     

Seasonal diversity in aquatic insect communities in an all-year stream system

Summary The general pattern of the data in this study shows that a riffle zone carries more species and, usually, more organisms/m² than a slower current zone. The slower current zone, however, is still apparently able to support a larger number of organisms and species than a pool of standing water. In the West Fork of the Oak Creek system the dominant insects controlling diversity are the Trichoptera, particularly one species of Helicopsyche. Diversity in the fast current zone is high in the summer, and low during other seasons. Diversity in the slow current zone is highest in spring, but is also fairly high in summer. This reflects to a large extent the seasonal fluctuations in abundance of the dominant Trichopterans in the two habitats.     

河南鸡公山国家级自然保护区昆虫多样性研究

2018年5-10月在河南鸡公山国家级自然保护区内开展了昆虫多样性调查工作,共采集到昆虫2110头,分别隶属于15目106科880种.其中以鳞翅目Lepidoptera(274种)、鞘翅目Coleoptera(206种)、半翅目Hemiptera(185种)和膜翅目Hymenoptera(89种)为主,种数占比分别为3...     

Contrasting effects of insect and molluscan herbivores on plant diversity in a long-term field experiment

The importance of invertebrate herbivores in regulating plant communities remains unclear, due to the absence of long-term exclusion experiments. An experiment in an English grassland involving long-term exclusions of insect and mollusc herbivores, along with rabbit fencing, showed strong, but opposing, effects of the invertebrate herbivores. Plant species richness declined and biomass increased following insect exclusion, due to increased dominance by a grass species, whereas mollusc exclusion led to increased herbs abundance. The two herbivores had a compensatory interaction: molluscs had no effects in the absence of insects and large insect effects depended on the absence of molluscs. The effects of invertebrate exclusion became apparent only after 8 years, and would have been seriously underestimated in shorter studies. Our results suggest that theorists and conservation managers need to shift from their historic focus on vertebrate herbivory, to a recognition that invertebrates can be equally important drivers of plant community structure.     

Yeast diversity and killer activity dispersed in fecal pellets from marsupials and rodents in a Brazilian tropical habitat mosaic

Yeasts with counts of above 10⁶ g⁻¹ wet weight and high diversity were found in the fecal pellets of rodents and marsupials from a mosaic of forest fragments, grasslands, cultivated fields and pasture in Rio de Janeiro. The most frequently isolated yeasts were Debaryomyces hamsenii, Pichia membranaefaciens and Issatchenkia orientalis (and its anamorph Candida krusei ), probably reflecting a high fruit content in the diet of these animals. The opportunistic pathogens Candida albicans, Candida glabrata and Candida tropicalis were isolated at lower frequency. Some Pichia anomala and P. membranaefaciens cultures had killer activity affecting many of the other isolates. These animals can be involved in dispersal of yeasts.     

The effects of geothermal water inflow on longitudinal changes in benthic macroinvertebrate community composition of a temperate stream

Studies of macroinvertebrate communities in thermal streams are highly geographically localized and mostly faunistical, making the efforts to understand in situ water thermal regime effects on those biocoenoses barely achievable. We examined the effects of geothermal water inflow on benthic macroinvertebrate community composition in a temperate stream. Environmental data analysis has shown that water temperature is a major factor determining the faunistical composition, especially downstream of the geothermal water inflow situated some 20 m upstream of locality V3. The increase in mean annual water temperature from 11.5±4.1 °C at locality V2 to 22.0±5.0 °C at locality V3 induced an enormous shift in community composition from a diverse one, composed mainly of Gammaridae, Simuliidae, Chironomidae, Trichoptera and Ephemeroptera, and to a lesser extent of Plecoptera, Coleoptera, other Diptera, Hirudinea, Odonata, Mollusca and Oligochaeta, to a uniform one strongly dominated by Chironomidae, Mollusca and Oligochaeta, comprising 98.9±0.5% of collected individuals. While the disappearance of Plecoptera and Ephemeroptera and the increase in representation of Mollusca and Oligochaeta at locality V3 might be solely explained by water temperature increase, in the case of Chironomidae the increase in water discharge and relatively high annual water temperature variation at locality V3 had additional positive effects. However, the latter factor induced disappearance of Gammaridae at locality V3. In addition to the increase in water temperature, increase of water velocity significantly determined the longitudinal dynamics of Coleoptera.     

Studies on Ephemerella ignita (Poda) in a chalk stream in Southern England

The nymphs ofEphemerella ignita occurred in all months except October in the Bere Stream at Bere Heath, a small chalk stream in Southern England. Peak densities of 1,498 m^–2 and 753 m^–2 were recorded in May by two sampling methods used simultaneously. The seasonal patterns of growth and abundance are compared with the findings of other authors. A maximum biomass of 0.82 g m^–2 preserved dry weight is compared with figures for two of the most common invertebrate groups present; the Simuliidae and Oligochaeta.     

Resource partitioning in a tropical stream fish assemblage

An assemblage of freshwater fishes inhabiting a medium-sized stream in tropical central Vietnam was investigated with respect to spatial and trophic distribution. Point-abundance sampling, gut content analysis and relative intestine length yielded interspecific differences in niche expression. Conspecific juvenile and adult habitat and feeding niches were also distinct. Niche differences arose mainly from differences in current velocity, substrata and foraging preferences. Extreme specializations, such as selective feeding on hard incustrations of cyanobacteria by adult Annamia normani , were present. The low niche overlap suggests that this tropical fish assemblage is structured by competitive interactions.     

The consequences of flooding for the dispersal and fate of poeciliid fish in an intermittent tropical stream

Summary We studied the rainy season dispersal of the fish Poecilia gillii (Poeciliidae) from pools in a steepgradient, intermittent stream in Santa Rosa National Park, Costa Rica. The stream consisted of about 20 pools separated by dry streambed except during two floods and subsequent brief periods of flow. Individually recognizable tags permitted mark-recapture estimates of population size and information on individual movements. The first flood was very severe, with pools losing an average of 75% of their populations (range 12–99%). Most of the lost fish died by becoming trapped in desiccating pools. Males and juveniles were more likely to be lost than were females. Population loss was negatively related to pool volume and positively related to streambed slope. In addition, population loss was positively related to preflood population size when the effects of pool volume and slope were removed indicating that pools with higher densities lost more fish. Of the fish recaptured after the flood, the average proportion found in the pool in which they had been tagged varied from 16%–96%, depending on the area of the stream. Of fish that moved, 92% went downstream. The second flood was less severe though stream flow lasted as long, and there was little effect on the pool populations. Involuntary flushing during the flood and voluntary departure apparently interacted to produce the observed patterns.     

Taxonomic diversity of the terrestrial bird and mammal fauna in temperate and boreal biomes of the northern hemisphere

Abstract. Using comprehensive range information of northern Hemisphere birds and mammals, we assessed the taxonomic diversity of these two groups in four different regions: Europe, east Asia, and western and eastern North America. East Asia is the richest region in the number of bird and mammal species, genera, families and orders, except that mammal species richness is highest in western North America. Eastern North America is taxonomically the poorest region, but when only forest-associated taxa were considered in mammals taxonomic diversity is equally low in Europe and in eastern North America, and in birds, Europe is the least diverse region. Patterns in endemic taxa follow overall taxonomic diversity. The proportion of shared taxa between regions is higher among boreal species and genera than among all taxa. A comparison with tree species diversity underpins the role of east Asia as the most diverse of all northern biota. Largely congruent patterns at different taxonomic levels emphasizes the role of historical processes, such as differential extinction rate in response to paleoenvironmental fluctuations, in producing these patterns, but we stress the need for more research on the coevolution of species diversity and habitat diversity.     

Spatial and temporal patterns in the aquatic insect community of a high altitude Andean stream (Mendoza,Argentina)

Benthic invertebrate communities have been poorly studied in Andean streams apart from the Patagonian region. The primary objective of this work was to analyse the faunal composition at three different altitudes and to observe whether there were differences in aquatic insect community structure at spatial and temporal scales. Physicochemical variables were measured on a monthly basis. Sixteen families were found, the most frequent and abundant taxa being Massartellopsis (Ephemeroptera), Andesiops (Ephemeroptera), Metrichia neotropicalis (Trichoptera), Cailloma lucidula (Trichoptera), Austrelmis (Coleoptera), and the Chironomidae (Diptera). There was a change in benthic composition associated with land use and with the diminution of water quality from the headwaters to the mouth of the system. The middle reach was a transitional area where headwater species coexisted with species characteristic of the lower reach, with Austrelmis and the family Chironomidae being the most abundant elements.     

Behavioral thermoregulatory abilities of tropical coral reef fishes: a comparison with temperate freshwater and marine fishes

Synopsis Eight species in six different families of tropical marine reef fishes from the Indo-West Pacific region (Naso lituratus, Zebrasoma.flavescens, Balistes fuscus, B. vidua, Forcipiger longirostris, Echidna zebra, Cromileptes altivelis, Canthigaster jactator) were tested for ability to thermoregulate behaviorally in electronic shuttleboxes. All of these species preferred mean temperatures between 20 and 30°C, but differed considerably in thermoregulatory precision. All species avoided lethal high or low temperatures (i.e., they did not die during the tests), and some species thermoregulated as precisely as temperate species. Some temperate species prefer higher temperatures (above 30°C) than do these tropical reef species.     

The effect of fine sedimentation on tropical stream macroinvertebrate assemblages: a comparison using flow-through artificial stream channels and recirculating mesocosms

In-situ artificial stream channels and ex-situ laboratory mesocosms were used to measure the responses of macroinvertebrate assemblages, from upland and lowland tropical streams, to high loads of fine clay sediment. Significant responses were observed mainly in the in-situ channels in the upland stream, where densities and the number of taxa were lower in the treatment channels than in controls. There was no evidence of any taxon being particularly sensitive to sedimentation, with a general decrease in densities across several taxa and differences only detectable for abundant taxa. Animals moved downstream in response to the treatment, but only a short distance within the channels. However, further colonization after the treatment was impeded in the treatment channels. In the mesocosm experiments, the upland macroinvertebrate assemblage demonstrated some negative effects; however, the lowland fauna was very tolerant to sedimentation, even when exposure was extended to 15 days. Together, the mesocosm and in-situ experiments indicate that there is a behavioural response to sedimentation because of a change in the habitat, and that the lowland macroinvertebrate assemblage is more tolerant of sedimentation, at least in the short term. Handling editor: D. M. Harper