Population Densities Of Different Species Research Articles

Population dynamics of thrips (Insecta: Thysanoptera) in cut chrysanthemum cultivated under photoselective screens

The chrysanthemum is one of the main ornamental species in the world, having high relevance in the market of cut flowers and potted plants. Thrips are among the main pests of the chrysanthemum crop, causing direct and indirect damage to plants. The objective of this work was to evaluate the influence of photoselective screens and climatic factors on the population density of different species of thrips chrysanthemum. The study was carried out in the experimental area of the Instituto Federal do Espírito Santo – Campus Itapina, in a randomized complete block design, with split plots in time. The experiment was established in 3 blocks of 12 m in length, with plots of 3 m in length containing the different photoselective screens (red, silver, and black) and the control treatment (open field), which consisted of the primary factor. Repeated evaluations in time (0, 15, 30, 45, and 60 d) consisted of the secondary factor. Data were submitted to Tukey's test (p < 0.05) and the multivariate technique of principal component analysis (PCA). The mean of the thrips population at 60 days was statistically higher. The climatic variables rain and average humidity showed a highly significant negative correlation with the population fluctuation of the pest. Black, red, and silver photoselective screens promote significant reductions in thrips populations in chrysanthemums of the Zembla variety in the environmental conditions of southeastern Brazil.

Distribution Patterns of Vector Snails and Trematode Cercaria in their Vectors in Some Selected Areas of Mymensingh

Different species of vector snails carry larval stages of different trematodes. Studies were performed to investigate different snail species and parthinate of trematodes carried by them, in some selected areas of Mymensingh Sadar, Mymensingh. Snails were collected by hand picking method and examined after crushing. Among 864 tested snails, it revealed the presence of six species of snails like Lymnaea auricularia 145 (16.8%), Lymnaea luteola 205 (23.7%), Indoplanorbis exustus 273 (31.6%), Vivipara spp. 164 (18.9%), Brotia spp. 35 (4.1%) and Pila spp. 42 (4.8%) in the study areas. Among them 5.8% L. luteola and 6.2% L. auricularia were infected with gymnacephalus cercariae. Again, 1.4% L. auricularia and 1.8% I. exustus were infected with echinostome cercaria. In this study, 1.8% Vivipara spp. and 2.6% I. exustus were positive for furcocercus cercaria. On the other hand, 1.8% Vivipara spp. was positive for xiphidocercus cercariae and 1.8% I. exustus was also positive for amphistome cercariae. One or more species of snails were found to harbor single or mixed types of cercariae such as gymnacepahlus, echinostome and furcocercous. Population densities of different species of snails were determined in per unit time which were statistically significant (p&lt;0.01). More studies are needed to focus on the determination of different vector snails and cercariae carried by them throughout the Bangladesh especially from plain lands, hilly areas, alluvial lands and coastal areas during four conventional seasons.DOI: http://dx.doi.org/10.3329/jesnr.v5i2.14599 J. Environ. Sci. &amp; Natural Resources, 5(2): 37-46 2012

MOISTURE IN DIFFERENT SOIL LAYERS DEPENDING ON WEED DENSITY IN COTTON

The main competitors of cotton during the crop production are annual late-spring weeds with some perennial species representing the second most important group. During the 1999-2001 period the effect of 3 main weed species – namely Solanum nigrum L., Amaranthus retroflexus L. and Convolvulus arvensis L. on the soil moisture in 3 layers (0-10, 20-20 and 20-30 cm) was studied at the Cotton and Durum Wheat Research Institute in Chirpan. Seven variants of increasing population density of different species were evaluated and the moisture content of the soil was calculated by weighing samples in the phases of square formation, flowering and maturity of the crop. Two-factor dispersion analysis (ANOVA) was used to determine the significance of the differences between treatments. Soil moisture content was found to be affected at two stages (flowering and maturity) by both weed density and soil layer. In the phase of square formation no differences were observed between moisture content of the three studied soil layers (0-10, 10-20 and 20-30 cm).

Understanding the Population, Coordination, and Orientation of Water Species Contributing to the Nonlinear Optical Spectroscopy of the Vapor−Water Interface through Molecular Dynamics Simulations

Molecular dynamics simulations are used to deconvolve the vibrational spectral features of the vapor-water interface based on molecular environment. A simple geometric description of hydrogen bonding is deployed to identify the OH stretch modes that comprise the vibrational sum-frequency spectrum of the vapor-water interface with direct comparison to our experimental results. The population densities of different species of water molecules are presented as functions of interfacial depth and orientation. It is found that surface water molecules that possess one proton donor bond and one proton acceptor bond make the dominant contribution to both the SSP- and SPS-polarized spectral responses and are located within an angstrom of the Gibbs dividing surface.

Habitat diversity and ostracod distribution patterns in Belarus

Ostracod diversity and abundance was studied in 10 different types of water bodies of Belarus (bogs, brooks, canals, oxbows, ponds, reservoirs, rivers, springs, shoal of lake and temporary pools). Hydrochemical variables, sediment, and vegetation were analyzed. In total 156 different localities were investigated. Habitat diversity was based mainly upon the closely correlated hydrochemical variables of mineralization (hardness total and carbonate, conductivity, total value of dissolved substances), although bottom, vegetation characteristics and other factors (pH, dissolved oxygen, nutrients) were also significant. The ostracods found included 62 species in 27 genera comprising 8 cosmopolitan, 17 Holarctic, 13 Palearctic species; 21 of these species are known from central and southern Europe and adjacent areas, while 3 are characteristic for eastern Europe. The distribution of freshwater ostracod assemblages reflected the habitat and depended on water body type. Heterogeneous oxbows and temporary pools supported 37 species, while other types of pool maintained only 27–14 species. The population density of different species varied from 0.5 to more than 10 000 ind./m2. Indices of local alpha diversity were significantly correlated with the number of species and temperature and were maximal in heterogeneous habitats. The variation of population density was not connected with habitat patterns but appeared to be regulated by the biotic interactions in the community. Habitat diversity, verified by the beta-diversity indices, enabled us to find localities with a similar heterogeneity level and species richness. Beta-diversity values were independent of species number as well as abundance but a significant positive correlation (p < 0.05) was found with temperature, pH and dissolved oxygen. This index probably reflected the general patterns of different localities.

Farming and the Fate of Wild Nature

World food demand is expected to more than double by 2050. Decisions about how to meet this challenge will have profound effects on wild species and habitats. We show that farming is already the greatest extinction threat to birds (the best known taxon), and its adverse impacts look set to increase, especially in developing countries. Two competing solutions have been proposed: wildlife-friendly farming (which boosts densities of wild populations on farmland but may decrease agricultural yields) and land sparing (which minimizes demand for farmland by increasing yield). We present a model that identifies how to resolve the trade-off between these approaches. This shows that the best type of farming for species persistence depends on the demand for agricultural products and on how the population densities of different species on farmland change with agricultural yield. Empirical data on such density-yield functions are sparse, but evidence from a range of taxa in developing countries suggests that high-yield farming may allow more species to persist.

INFLUENCE OF LANDSCAPE ELEMENTS ON POPULATION DENSITIES AND HABITAT USE OF THREE SMALL-MAMMAL SPECIES

Corridor effects on population densities and habitat use of 3 small-mammal species were assessed during 1998-2000 in an experimentally fragmented landscape. Corridor presence did not have a statistically significant effect on population densities of cotton rats (Sigmodon hispidus) or cotton mice (Peromyscus gossypinus); however, a significant effect was observed for old-field mice (Peromyscus polionotus) during 2000. Cotton rats were captured more frequently than expected in corridors, while old-field mice were captured more frequently than expected in habitat-patch interior; and cotton mice exhibited a more uniform distribution across habitat types. These results suggest that landscape fragmentation and habitat structure may have varying effects on population densities of different species.

Distribution of estuarine benthic diatom species along salinity and nutrient gradients

Changes in relative abundance of estuarine epipelic microalgae along an estuarine gradient were investigated, and population densities of different species along a small-scale nutrient gradient generated by a sewage treatment outfall and in laboratory mesocosms enriched with ammonium were also studied. The relative abundance of certain species of epipelic diatoms was related to location along the estuarine salinity and nutrient gradient: Navicula gregaria and N. phyllepta were abundant at oligo- and mesohaline sites respectively, and Pleurosigma angulatum and Plagiotropis vitrea were abundant at polyhaline sites. On a smaller spatial scale, though there were no significant patterns in microalgal biomass in relation to nutrient enrichment, there were significant differences in the population densities of different epipelic species along a multivariate nutrient gradient (decreasing concentrations of ammonium, nitrite, silicate, organic content, and increasing salinity and pore-water nitrate concentrations) away from a sewage outfall along a saltmarsh creek. The diatoms Nitzschia sigma and Gyrosigma limosum and the cyanobacteria Oscillatoria limosa and O. princeps had significantly higher population densities near the outfall, and Navicula phyllepta, N. pargemina, Nitzschia frustulum, Cylindrotheca signata and Pleurosigma angulatum were significantly more abundant at the seaward end of the gradient. In laboratory tidal mesocosms, sediment cores from along the gradient had their pore-water ammonium concentrations increased to 380–450 μM NH4 +. After 26 days, the population densities of Gyrosigma fasciola, G. littorale, P. angulatum, N. phyllepta, Cylindrotheca signata, C. closterium and Niztschia apiculata were significantly reduced, while those of G. limosum, N. sigma, Scolioneis tumida and O. limosa were unaffected, or were significantly higher compared with control cores. Laboratory manipulations of ammonium concentrations supported the observed field distributions, indicating that epipelic species do have different trophic preferences and ammonium concentration may be a significant factor in determining estuarine species composition of epipelic algae.

The importance of mires as breeding habitat for wetland birds in Sweden

During the last 15 years the bird fauna was censused on 2,250 km2 of mires, which is 10–15% of the estimated total area of larger, treeless mires (&gt;0.5 km2) in Sweden. The total number of bird species breeding on mires increases from 25 in the most southern region (Götaland) to 43 in the most northern region (N. Norrland), but more of the northern species breed at very low densities. Among taxonomic groups, species richness of wildfowl and shorebirds increases with latitude while that of passerines shows no clear trend. One possible explanation for the increased species diversity towards the north may be that northern mires generally have a more complex habitat structure, making more niches available. There was no general geographic pattern in the population density of different species. Wildfowl, birds of prey (including owls) and shorebirds (including the Crane) breed at higher densities in the north while passerines have lower densities. One reason for the higher breeding densities of wildfowl and shorebirds in the north is that mires there to a larger extent consist of fens than do mires in the south. Also, a lower nest predation in the north is a probable reason. Combining all species there was no trend in breeding density. Calculations of population sizes show that 25% of the 44 species recorded have breeding populations of more than 10,000 pairs while 25% have less than 1,000 pairs on mires. Estimates of population sizes in Sweden as a whole for all species breeding on mires show that 11 species have more than 50%, and four have more than 75% of their total Swedish population on mires. These species are especially interesting from a conservation point of view since they may be used as indicators of valuable mires.

Ecological Observations on the Macrobenthos of the Nawran Stream, Mosul, Iraq

Ecological observations on the macrobenthos of the running stream of Nawran have been made for the past several years. The geography, physical and chemical environmental factors, and the seasonal variation in different populations of macrobenthos living there have been studied with respect to seasonal changes in the environment. The regional community comprises of Dugesia sp., Dendrobaena atheca, Allolobophora, .Eropbdella, Potamon magnum, Rivulogammarus syriacus, Caridina fossarum, Chironomoid sp., Melanoides tuberculata, Melanopsis praemorsa carraruta, and nymphs of may fly and caddis fly. In spring and autumn the fauna is rich in number as well as in diversity. The stream consists of two sections. The upper one has hard substratum and more slope gradient. resulting a fast current of water. The lower section has soft and muddy substratum. The current in this section is slow. Owing to such physical differences, these two sections of the stream support different groups of biota. Biota shows neither upward nor downstream movements but shows attitudinal secession. A statistical analysis has been made between the water temperature and different populations. The degree of association between the water temperature and the population density of different species is measured by the correlation coefficient positive and by significant at 0.05 level.