Chorion patterns on eggs of Lutzomyia sandflies from the Peruvian Andes

Abstract. Scanning electron microscopy (SEM) was used to depict and describe the eggs of five species of phlebotomine sandfly from the Andean region of Peru: Lutzomyia caballeroi, Lu.noguchii, Lu.peruensis, Lu.tejadai and Lu.verrucarum. Two new types of chorionic sculpturing of sandfly eggs are reported: these were named disperse (Lu.tejadai) and verrucose (Lu.noguchii). The aeropylar area of the eggs is also described for the first time for neotropical sandflies. These character states appear to vary for ecological rather than phylogenetic reasons and could be used for species identification.     

The distribution,abundance and trends in the establishment of the family schilbeidae (osteichthyes: siluriformes) in Lake Kainji,Nigeria

The distribution and abundance of the five species of Schilbeidae in Lake Kainji were studied. The gill net samples showed that Eutropius niloticus was the most abundant and very common species in the lake. Physailia pellucida although greatly under-estimated by the gill nets was the next abundant and fairly common species. Schilbe mystus was not as abundant as the two previous species but was found to be common. Schilbe uranoscopus and Siluranodon auritus were very rare in the Lake. The spatial distribution showed that E. niloticus and P. pellucida occurred in high numbers in the open lake and the shorelines, while S. mystus had its highest number in the riverine areas of the Lake. An upward trend in the abundance of E. niloticus and P. pellucida was indicated while a decrease in the abundance of S. mystus within the lake was noted.     

The effect of habitat stability on benthic invertebrate communities: the utility of species abundance distributions

Spatial and temporal patterns in the species abundance distribution of benthic invertebrate communities of 11 freshwater habitats (10 streams and a wind-swept lake shore) were examined with respect to habitat stability. Abundance patterns varied markedly between seasons at most sites. However, mean abundance distributions at 4 of the 5 unstable sites and the 2 most stable sites were dominated by one or two taxa with a large number of rare species, whereas sites of intermediate stability had more equitable distributions. Both the log series and log normal distributions were statistically indistinguishable, at the 5% level, from all the observed mean abundance patterns. In contrast, graphical comparisons of the observed and fitted distributions suggested the log series may be the better fit at most of the unstable sites and the two most stable sites, whereas the more equitable distribution at sites of intermediate stability suggested the log normal distribution was the better fit. If conditions at a site favoured one or two species, either through severe physical conditions, or through competitive superiority in the absence of disturbance then the log series distribution may result. However, if no species in the community was strongly advantaged over others, a log normal distribution should result. Given the discriminating power of the appropriate statistical test it may not, however, be possible to pick up these differences without graphical comparisons as well.     

The relationship between CDC light-trap and human-bait catches of endophagic sandflies (Diptera: Psychodidae) in the Peruvian Andes

Abstract. A study was carried out in the Peruvian Andes to test the suitability of CDC light traps for monitoring changes in the human-landing rate of endophagic phlebotomine sandflies, following house-spraying with pyrethroid insecticide. On four pairs of consecutive nights, sandflies were caught inside eight sprayed and eight unsprayed houses, either by human bait or by CDC light traps. The sandflies collected were Lutzomyia verrucarum (97%) and Lu. peruensis (3%), both probable vectors of Leishmania peruviana , and the species composition was unaffected by house-spraying. A non-linear relationship was detected between light-trap and human-bait catches, but the relationship did not diverge significantly from linearity within the range of sandfly abundance found in most houses in the endemic area (i.e. between 3 and 200 sandflies/house-night), and did not differ significantly between sprayed and unsprayed houses. However, light trap catches had a significantly lower proportion of blood-fed females in sprayed than in unsprayed houses, probably due to an insecticidal effect on post-blood-feeding behaviour. The proportion of Lu. verrucarum was significantly higher in light trap than in human bait catches, indicating that Lu. peruensis is either more anthropophilic or less phototropic than Lu. verrucarum.     

Factors influencing the abundance of Japanese encephalitis vectors in ricefields in India--II. Biotic

The relationship of insect predators and phytoplankton with the abundance of Culex tritaeniorhynchus Giles, Cx. vishnui Theobald and Cx. pseudovishnui Colless mosquito larvae and pupae (Diptera: Culicidae) in ricefields was investigated during three rice growing seasons. Notonectids were the most abundant insect predators, whereas diatoms dominated among phytoplankton. Multiple regression analysis showed that the occurrence of notonectids (both nymphs and adults) was negatively associated with larval abundance. Phytoplankton, especially diatoms and blue green algae (BGA), were found to favour abundance of culicine immatures during Navarai and Kuruvai crops, respectively. Larval gut analysis showed that the intake of algae by late instars was high, with 93%, 58% and 24% of diatoms, BGA and green algae, respectively. Filamentous algae may not necessarily be of nutritive value, but they are observed to form mats, which provide protection to the mosquito immatures from the predators.     

Varying effects of anadromous sockeye salmon on the trophic ecology of two species of resident salmonids in southwest Alaska

1. Anadromous salmon transport marine‐derived nutrients and carbon to freshwater and riparian ecosystems upon their return to natal spawning systems. The ecological implications of these subsidies on the trophic ecology of resident fish remain poorly understood despite broad recognition of their potential importance. 2. We studied the within‐year changes in the ration size, composition and stable isotope signature of the diets of two resident salmonids (rainbow trout, Oncorhynchus mykiss; Arctic grayling, Thymallus arcticus) before and after the arrival of sockeye salmon (Oncorhynchus nerka) to their spawning grounds in the Bristol Bay region of southwest Alaska. 3. Ration size and energy intake increased by 480–620% for both species after salmon arrived. However, the cause of the increases differed between species such that rainbow trout switched to consuming salmon eggs, salmon flesh and blowflies that colonized salmon carcasses, whereas grayling primarily ate more benthic invertebrates that were presumably made available because of physical disturbances by spawning salmon. 4. We also observed an increase in the δ¹⁵N of rainbow trout diets post‐salmon, but not for grayling. This presumably led to the observed increase in the δ¹⁵N of rainbow trout with increasing body mass, but not for grayling. 5. Using a bioenergetics model, we predicted that salmon‐derived resources contributed a large majority of the energy necessary for growth in this resident fish community. Furthermore, the bioenergetics model also showed how seasonal changes in diet affected the stable isotope ratios of both species. These results expand upon a growing body of literature that highlights the different pathways whereby anadromous salmon influence coastal ecosystems, particularly resident fish.     

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.     

Factors influencing the abundance of Japanese encephalitis vectors in ricefields in India – I. Abiotic

Mosquitoes of the Culex vishnui subgroup (Diptera: Culicidae) are the most important vectors of Japanese encephalitis (JE) and ricefields are their most productive breeding sites in south India, where predominant species of this subgroup are Culex tritaeniorhynchus Giles, Cx. pseudovishnui Colless and Cx. vishnui Theobald sensu stricto. The relationship of 13 abiotic variables with the abundance of Cx. vishnui subgroup immatures was investigated in transplanted rice fields for 3 years (1991-94) covering three different crop seasons. The results from the multiple regression model suggested paddy height (- ve), water temperature (+ ve), dissolved oxygen (- ve), ammonia nitrogen (- ve) and nitrate nitrogen (+ ve) to be the best predictor variables associated with the immature abundance, nearly always consistent in their effects within and between seasons. Application of synthetic nitrogenous fertilizers to the rice fields was followed by a rise in concentration of ammonia nitrogen and a subsequent increase in nitrate nitrogen level in the rice field water, during which an increase in the density of larval instars was observed.     

Factors influencing the distribution and abundance of diaptomid copepods in high-elevation lakes in the Pacific Northwest, USA

We investigated the impact of abiotic factors and trout density on distribution and abundance of diaptomid copepods in high-elevation lakes in North Cascades National Park Service Complex (NOCA), Washington, USA. The most common large diaptomid, D. kenai (mean length = 1.88 mm), was able to persist over a wide range of abiotic factors, but the small herbivorous diaptomid, D. tyrrelli (mean length = 1.18 mm), was restricted to shallow lakes (maximum depth < ≈ 10 m) with relatively high concentrations of total Kjeldahl nitrogen and total phosphorous. There was a significant negative relationship between the density of D. tyrrelli and the density of large diaptomids ( D. kenai and D. arcticus), which could imply interaction between large and small diaptomids. The abundance of large diaptomids was significantly lower in shallow lakes with high densities of reproducing trout (> 250 fish ha-1) than in fishless lakes, in deep lakes with reproducing trout, or in lakes where trout do not reproduce and are 0periodically stocked with fry at low densities (average 179 fry a-1). In lakes where chemical conditions were suitable for D. tyrrelli, the small diaptomid was often abundant when trout density was high and large diaptomids were either absent or in low abundance. Our research suggests that trout density, nutrient concentration, and lake depth influence the abundance of diaptomid copepods in high lakes in NOCA. This revised version was published online in July 2006 with corrections to the Cover Date.     

Feeding ecology of two sillaginid fishes and trophic interrelations with other co-existing species in the southern part of South China Sea

Feeding ecology of Sillago sihama and Sillago ingenuua and interrelationship with other 15 fish species, including Stolephorus commersonii, Escualosa thoracata, Lutjanus russelli, Terapon puta, Ambassis kopsii, Ambassis vachellii, Dendrophysa russelli, Gerres filamentosus, Leiognathus decorus, Leiognathus splendens, Leiognathus equulus, Thryssa hamiltonii, Carangoides praeustus, Lethrinus lentjan, and Pomadasys maculatum, utilizing coastal waters off the southern part of the South China Sea were investigated. Dietary contents from 4308 guts of those species collected during July 2003–May 2005 were examined. They were significantly grouped, based on similarity coefficient, into five feeding clusters (P < 0.01). Of these, most of the diets were dominated by calanoid copepods, shrimps, polychaetes and gammarid amphipods. Comparative study on two sillaginid species showed that both Sillago sihama and Sillago ingenuua were carnivores fed mainly on polychaetes and other benthic organisms. Dietary ontogenetic change of Sillago sihama was very distinctive where small sized classes started feeding mainly on calanoid copepods before changing almost completely to polychaetes. The two species applied both sharing and partitioning strategies for food, depending on size classes, to live with each other.     

Factors influencing the species composition,distribution and abundance of benthic invertebrates in the profundal zone of a eutrophic northern lake

Factors influencing the species composition, distribution and abundance of benthic invertebrates were determined in a eutrophic subarctic lake from April 1978 to April 1979. Collections were made at five stations located at depths of 4 to 13 m. The largest populations of up to 5 × 10³ animals m^–2 were found in the deepest part of the lake. of the 24 species recorded in this area, the chironomidsProcladius denticulatus, Dicrotendipes modestus, Chironomus decorus andGlyptotendipes barbipes were most common. The strong development of benthos in the profundal zone was attributed to a consistently large supply of food and warm (4 °C) winter temperatures on bottom. Slightly smaller populations (up to 4 × 10³ animals, m^–2), composed of 19–23 species, occurred in shallower water, a reflection of lower (1.5 °C) winter temperatures. In the anoxic northern part of the lake, only 4–8 species were found in low numbers (400–1 000 animals m^–2). This was likely due to low (<5% saturation) oxygen levels in water and high organic content (18.5%) of the sediments.     

Factors influencing the spatial distribution patterns of the bullhead (<Emphasis Type=Italic>Cottus gobio</Emphasis> L., Teleostei Cottidae): a multi-scale study

We used general linear modelling to assess the influence of environmental variables on the spatial distribution patterns of the bullhead (Cottus gobio) at stream system, site, and microhabitat scales in southwestern France. Bullheads occurred at 67 sites (out of 554 sampling sites), chiefly close to the source, in small and shallow streams. Population density at a site was primarily influenced by thermal conditions. Stream width was negatively related to the probability of presence of bullheads within the stream system, but positively related to local density, showing that bullhead density could increase within a range of stream width, but that wider rivers were unsuitable. Slope was negatively correlated to bullhead’s occurrence and local density, and depth was negatively correlated to local density and microhabitat use, suggesting that bullhead’s shimming performance was weak under greater erosive forces. Therefore, the most significant results suggested that the distribution of populations and individuals was first governed by the suitability of physical and hydraulic habitat, then population dynamics at a site was mainly governed by the thermal regime. Multi-scale studies of factors influencing a species’ distribution thus allow to integrate patterns observed at different scales, and enhance our understanding of interactions between animals and their environment. Such models are essential in the exploratory phase of fundamental and applied investigations, because they help to target further research, and they should influence the measures to be taken in field surveys or conservation plans.     

Factors influencing the distribution of two co-occurring dwarf bamboo species (<Emphasis Type="Italic">Sasa kurilensis </Emphasis>and<Emphasis Type="Italic"> S. senanensis</Emphasis>) in a conifer-broadleaved mixed stand in northern Hokkaido

We have investigated the factors influencing the distribution of co-occurring two dwarf bamboo species, Sasa kurilensis (Ruprecht) Makino et Shibata and S. senanensis (Franchet et Savatier) Rehder, within a conifer-broadleaved mixed stand managed with selection cutting in northern Japan. We first sought the possible determinant factors (physical environment and overstory conditions based on 30 years tree census data) deciding the dominant species in the plots (168 3.14m² area). We then examined the effects of these factors on the culm density and height of the dominant species. Linear discriminant analysis indicated that physical environmental conditions are important in determining the distribution; S. kurilensis tended to dominate plots with steep slope, convex shape and deep snow in early spring. Multiple regression analyses showed that culm density and height decreased significantly on steep slopes for both species. Also, the sum of the basal area (BA) of surrounding conifers (7.5 m radius around the plot), as well as the change in BA over the previous 30 years, had a negative influence on the culm height of both species. A reduction in overstory trees, caused by natural or artificial canopy disturbances, would increase the dwarf bamboo biomass. The effects of physical environment and overstory conditions, working through the dominance of the two dwarf bamboo species, should be taken into account in understanding the dynamics of natural forests in this region.