Temporal Variation In Density Research Articles

Temporal variation in density and diversity of cyanobacteria and cyanotoxins in lakes at Nagpur (Maharashtra State), India

Toxic cyanobacteria (TCB) are known worldwide for the adverse impacts on humans and animals. Species composition and the seasonal variation of TCB in water bodies depend on interactions between physical and chemical factors. The present investigation delineates temporal variations in physico-chemical water quality parameters, viz. nutrients and density, diversity, and distribution of toxic cyanobacteria and cyanotoxins in Lake Ambazari (21 degrees 7'52''N, 79 degrees 2'22''E) and Lake Phutala (21 degrees 9'18''N, 79 degrees 2'37''E) at Nagpur (Maharashtra State), India. These lakes are important sources of recreational activities and fisheries. Toxic cyanobacterial diversity comprised Anabaena, Oscillatoria, Lyngbya, Phormidium, and Microcystis, a well-known toxic cyanobacterial genus, as dominant. Chlorophyll-a concentrations in the lakes ranged from 1.44 to 71.74 mg/m(3). A positive correlation of Microcystis biomass existed with orthophosphate-P (p < 0.05) and nitrate-N (p > 0.05). Identification and quantification of microcystin variants were carried out by high performance liquid chromatography equipped with photodiode array detector. Among all the tested toxin variants, microcystin-RR (arginine-arginine) was consistently recorded and exhibited a positive correlation (p < 0.05) with Microcystis in both the water bodies. Microcystis bloom formation was remarkable between post-monsoon and summer. Besides nutrient concentrations governing bloom formation, the allelopathic role of microcystins needs to be established.

Modeling utilization distributions in space and time

W. Van Winkle defined the utilization distribution (UD) as a probability density that gives an animal's relative frequency of occurrence in a two-dimensional (x, y) plane. We extend Van Winkle's work by redefining the UD as the relative frequency distribution of an animal's occurrence in all four dimensions of space and time. We then describe a product kernel model estimation method, devising a novel kernel from the wrapped Cauchy distribution to handle circularly distributed temporal covariates, such as day of year. Using Monte Carlo simulations of animal movements in space and time, we assess estimator performance. Although not unbiased, the product kernel method yields models highly correlated (Pearson's r = 0.975) with true probabilities of occurrence and successfully captures temporal variations in density of occurrence. In an empirical example, we estimate the expected UD in three dimensions (x, y, and t) for animals belonging to each of two distinct bighorn sheep (Ovis canadensis) social groups in Glacier National Park, Montana, USA. Results show the method can yield ecologically informative models that successfully depict temporal variations in density of occurrence for a seasonally migratory species. Some implications of this new approach to UD modeling are discussed.

Dinâmica sazonal da comunidade fitoplanctônica de um canal lateral (Canal Cortado) do Alto Rio Paraná (PR, Brasil)

The seasonal variability of the phytoplanktonic community was studied in one lateral channel of the Upper Parana River. The extensive samplings (monthly) were taken in three stations in the Cortado Channel (22o47‘30”S, 53o24‘37”W) from March of 1993 to February of 1994. Temporal changes in taxonomic composition, density, biomass, diversity and dominance were analyzed in relation to regional climate and hydrology, and to the physical and chemical factors of the water column. The phytoplanktonic community was composed of 95 taxa. The classes Cyanophyceae ( Anabaena circinalis ) and Bacillariophyceae ( Aulacoseira granulata ) were the most abundant, being responsible for the biomass peaks that occurred. The temporal variation in density and biomass did not show a clear seasonality, however, the highest biomass occurred in the late low waters (limnophase), with dominance of microplankton. Nanoplanktonic species, C-strategists common in Parana River, mainly Cryptomonas brasiliensis , were abundant throughout the study period

Ephemeroptera, Plecoptera and Trichoptera assemblages in two Atlantic Rainforest streams, Southeastern Brazil

Assemblages of Ephemeroptera, Plecoptera and Trichoptera (EPT) of rocky substrates were studied in two streams of the Intervales State Park. Monthly collections with a Surber sampler (10 random sampling units, 1m²) were carried out from September 1999 to September 2000 and quarterly from December 2000 to September 2001 in the Bocaina and Água Comprida Streams. The EPT fauna in the Bocaina Stream was more diversified and more abundant than in the Água Comprida Stream. The EPT fauna was quite different in the two streams both in composition as in functional aspects. The results of this study indicate that there was not a clear seasonal pattern in the temporal variation of density.

Estructura de la comunidad de cunáxidos (Acarina) edáficos de una selva baja caducifolia en Chamela, México

The structure community of cunaxids mites was studied at a tropical dry forest in the Chamela Biological Station, Jalisco, Mexico. Monthly samples of litter and soil were taken during one year (July 1991-May 1992), in two small watersheds. A total of 43 species was recorded. We studied their abundance, species frequency (F), rareness and relative abundance (Ar), density (ind m(-2)), species richness (S), Shannon's diversity index (H'), and Pielou's evenness index (J'). The species richness was similar in litter and soil (38 species), but species composition was different. The higher density was found in soil, with 5 074 ind m(-2); litter density was 2 199 ind m(-2). The subfamilies with the highest density in both biotopes were Coleoscirinae (H=1127 ind m(-2); S=2235 ind m(-2)) and Cunaxiinae (H=887 ind m(-2); S=1936 ind m(-2)). The genus Pulaeus had the most species, and all were new to science. Mean and variance indicate an aggregate distribution for these cunaxids. By permanency and relative abundance, the dominant species were: Cunaxa potchensis, Coleoscirus simplex, Armascirus harrisoni, Cunaxoides sp. nov. 1, Cunaxoides sp. nov. 2, Pulaeus sp. nov. 15 and Pulaeus sp. nov. 16. An significant effect of the month and the biotope were recorded on the diversity and composition of cunaxid communities. Most of the species presented a significant effect of the month (24 spp.) and biotope (23 spp.), and five species only had a significant effect of the watersheds. The highest similarity was in litter (75 %) and soil (74 %). The highest temporal variation in density, diversity and species richness was from April through June in litter, and from September through November insoil. The evenness was constant in both biotopes. In the dry period the soil presented higher values of density, while in the litter it was in the rainy season. The species with high soil density (February-June: dry season) in both watersheds, were: C. simple, C. potchensis, Cunaxa sp. nov. 1, Cunaxa sp. nov. 2, C. veracruzana, Dactyloscirus sp. nov. 2, A. harrisoni, Cunaxoides sp. nov. 1, Cunaxoides sp. nov. 2, P. pectinatus, Pulaeus sp. nov. 14, Pulaeus sp. nov. 15 and Pulaeus sp. nov. 16. They were the most representative species in the soil and litter of Chamela communities. The most abundant dry season species were C. potchensis in the soil and A. harrisoni in the litter.

Influences on Brown Trout and Brook Trout Population Dynamics in a Michigan River

AbstractUnderstanding the influences of local and regional processes on the dynamics of self‐sustaining trout populations would help fishery biologists better manage trout populations and protect rivers supporting trout. We explored hypotheses behind long‐term temporal variation in density, growth, and survival of brown troutSalmo truttaand brook troutSalvelinus fontinalisusing data collected over several decades on Michigan's Au Sable River. Regression models developed for these species emphasized the influence of year‐class strength on older age‐classes, year‐class strength being positively related to spawner abundance for both species and negatively related to high spring streamflow conditions for brown trout. Age‐class density was also positively associated with high levels of large woody debris (LWD) in streams. Annual growth increments of brown trout and brook trout were often negatively related to increased age‐class density and LWD and positively affected by elevated total phosphorus levels, cool summers, and warm winters. Annual survival of trout from age 0 to age 4 was negatively related to intra‐ and interspecific age‐class density, and in three of seven models, positively associated with levels of LWD. Our findings emphasize the importance of year‐class strength to trout population dynamics as well as the need to include collection of regional‐ and local‐scale habitat data in studies of trout population dynamics.

Density of Monoporeia affinis and biogeochemistry in Baltic Sea sediments

Abstract This study focused on effects from Monoporeia affinis reworking and ventilation activities on benthic fluxes and mineralization processes during a simulated bloom event. The importance of M. affinis density for benthic solute (O2, ΣNO2− + NO3−, NH4+ and HPO42−) fluxes and sediment reactivity (mobilization of NH4+ and HPO42−) following additions of organic material to the sediment surface was experimentally investigated using sediment–water and closed sediment (jar) incubations. Three different densities of M. affinis were used to resemble a low, medium and high density situation (1300, 2500 and 6400 ind. m− 2, respectively) of a natural amphipod community. The degradation of phytodetritus (Tetraselmis sp., 5 g C m− 2) added to the sediment surface was followed over a period of 20 days. Benthic solute fluxes of O2, ΣNO2− + NO3− and NH4+ were generally progressively stimulated with increasing number of M. affinis, while no such correlation was found for HPO42−. Solute fluxes were initially enhanced 1 to 2 days after the addition of phytodetritius, caused by mineralization of the most labile organic material and a food-stimulated irrigation by the amphipods. There was no effect from the activity of M. affinis on total denitrification (Dtot = Dn + Dw) or denitrification utilizing nitrate from coupled nitrification/denitrification (Dn) for any of the densities examined. Denitrification utilizing overlying water nitrate (Dw) was only about 10% of Dtot. Dw was significantly enhanced for the highest M. affinis density investigated. The reactivity of the sediment decreased progressively with increasing density of M. affinis and with time of the experiment. However, enhanced ammonium production at least 6 days after the organic addition indicated excretion of N-containing organic compounds by M. affinis. In conclusion, large spatial and temporal variations in density of M. affinis may be of significant importance for benthic solute fluxes and overall mineralization of organic material in Baltic Sea sediments.

Larval settlement and recruitment of a brackish water clam, Corbicula japonica, in the Kiso estuaries, central Japan

Population dynamics of the brackish water clam Corbicula japonica were examined in the Kiso estuaries (the Ibi-Nagara Estuary and the Kiso Estuary), central Japan, during the process of larval recruitment. Based on temporal variation in densities (sampling every 2 weeks for planktonic larvae, new settlers, and small individuals, sampling every month for large and commercially important individuals) from May 2001 to April 2004, we conclude that densities of large and of commercially important individuals were determined not by larval supply but by benthic processes. Density-dependent processes were detected between densities of new settlers and recruits. These processes, however, were detected for spring-summer cohorts, but not for autumn-winter cohorts. Spatial distributions of each cohort were almost the same within the Ibi-Nagara Estuary and within the Kiso Estuary, although cohorts were collected mainly in the middle to upper regions of the Ibi-Nagara Estuary but were collected in the upper region of t...

Tidal associated temperature disturbances observed at the middle atmosphere (30–65 km) by a Rayleigh lidar at 23°S

A lidar has been operated in São José dos Campos, Brazil (23.2°S, 45.8°W) since 1972, mainly dedicated to the study of mesospheric sodium at the 589 nm resonant line. The molecular Rayleigh scattering can also be used provided we limit the height to ∼75 km where the sodium scattering begins. Nevertheless, the weak signal obtained only permits the determination of density and temperature profiles by accumulating a large number of shots giving only nocturnal average profiles. Temporal variations in density and temperature on the scale of hours can however, be obtained by performing a superposed epoch analysis for a given time interval and covering a period of several days. In this way we obtained hourly mean profiles grouped by months, seasons and overall, with data acquired from 1993 to 2004. The difference between the hourly temperatures and the nocturnal means shows for some months, with enough data coverage, downward propagating structures that apparently have tidal origin. The seasonal averages show a recurrent feature with high temperatures before and low temperatures after midnight above 50 km. Some similarity is found with the GSWM model, but the observed temperature amplitudes are twice of that for the model.

Temporal Variations in Densities of Y, Ba, and Cu Atoms in Magnetron Sputtering Plasmas with YBaCuO Target

In this study, we used optical emission spectroscopy (OES) for examining the temporal variations in the densities of Y, Ba, and Cu atoms sputtered from a YBaCuO target in a magnetron plasma source. It was found that the densities of Y and Cu changed with the discharge period. In a low-pressure, low-power discharge, the temporal variations in the Y and Cu densities were small, whereas they became significant at a high pressure and a high power. Ten minutes after the initiation of the discharge, Y density decreased to 8% of the initial value at an rf power of 70 W and a gas pressure of 300 mTorr. On the other hand, the optical emission intensities from Ar and Ba were roughly constant during the same discharge period. The roughly constant Ar intensity indicates that electron density and electron temperature were almost constant. The discovery of temporal variations in the Y and Cu densities is important for optimizing the discharge parameters for the deposition of high-quality, high-critical-temperature (high-Tc) superconductor films.

Spatial and temporal variation in density and thallus morphology of Turbinaria ornata in Thailand

Turbinara ornata (Turner) J. Agardh, is a common brown alga, which occurs on tropical shores worldwide. We studied the effects of wave action and seasonal variation on T. ornata populations at Koh Pling, Sirinart Marine National Park, Thailand. Density, length of thallus, length of blade, number of blades, number of reproductive organs, and dry weights were investigated. The algae were collected bimonthly during August 2003–May 2004, at three different areas of wave exposure: sheltered, semi-exposed, and exposed. There were variations in all factors at sites and seasons ( P < 0.05). We found that T. ornata populations were denser on the semi-exposed shore and their biological characteristics reached their peaks during October 2003. The highest density of T. ornata was 27 ± 10 fronds/m 2 (mean ± S.E.). While the average frond length, for example, was 24 ± 1.5 cm, 4 times greater than the minimum; and the number of blades on the thallus were 329 ± 47 blades, 15 times greater than the minimum. Surprisingly, the population disappeared at the beginning of May 2004, and returned in July 2004. In this work, we attempt to explain the differences in various characteristics of T. ornata in relation to the degree of wave exposure, nutrient concentration and other physical factors. We also discuss how our results may provide some insight into the current rapid expansion of T. ornata populations.

Are Point Counts of Boreal Songbirds Reliable Proxies for More Intensive Abundance Estimators?

AbstractPoint counts are often used to provide information on abundance of songbirds. If data from point counts are to be compared in space or time, however, any bias in the estimate should be consistent and linearly related to the true abundance. Several studies have suggested that this assumption may be violated for songbirds. Here, we used double sampling to test whether point counts are linearly related to true abundance, as estimated from spot mapping, for 12 songbird species in the boreal mixed-wood forest of northern Alberta, Canada. We found that total abundance of birds across several point-count stations was positively correlated with the number of territories and confirmed that point counts were linearly related to spot-mapping abundance for the species tested. However, large sampling errors masked this relationship at the scale of a single point-count station (100-m fixed-radius plot). Double-sampling models that accounted for differences in abundance between spot-mapping grids using random effects improved prediction for most species. We found no year effect on detectability. Maximum abundance over point-count rounds was a more sensitive index of abundance than mean abundance and tended to produce better-fitting models. Point-count abundance was more closely related to true abundance in species with relatively small territories, or those with large spatial or temporal variation in density. Our results further suggest that point-count abundance may be proportional to the total length of territorial boundaries in the plot rather than the total fraction of territories in the plot. Our analysis suggests that point counts provide a reasonable index of abundance, even though individual point-count stations are not consistently effective in estimating the density of territorial individuals.Est-ce que les Points D'Écoute de Passereaux Boréaux Constituent une Méthode Fiable pour L'Obtention D'Estimateurs D'Abondance Plus Avancés?

Effects of temporal density variation and convergent geometry on nonlinear bubble evolution in classical Rayleigh-Taylor instability

Effects of temporal density variation and spherical convergence on the nonlinear bubble evolution of single-mode, classical Rayleigh-Taylor instability are studied using an analytical model based on Layzer's theory [Astrophys. J. 122, 1 (1955)]. When the temporal density variation is included, the bubble amplitude in planar geometry is shown to asymptote to integral(t)U(L)(t')rho(t')dt'/rho(t), where U(L) = square root of (g/(C(g)k)) is the Layzer bubble velocity, rho is the fluid density, and C(g) = 3 and C(g) = 1 for the two- and three-dimensional geometries, respectively. The asymptotic bubble amplitude in a converging spherical shell is predicted to evolve as eta approximately etam(-/r0//(lU(L)sp-eta/r0), where r0 is the outer shell radius, eta(t) = integral(t)U(L)sp(t')rho(t') r(0)2(t')dt'/rho(t)r(0)2(t), U(L)(sp) = square root of (-r0(t)r0(t)/l), m(t) = rho(t)r(0)3(t), and l is the mode number.

Population dynamics of Pseudevadne tergestina (Branchiopoda: Onychopoda) in Guanabara Bay, Brazil

Populations of Pseudevadne tergestina were studied in Guanabara Bay, southeastern Brazil, to assess temporal variations in density and population dynamics. Data on temperature, salinity and zooplankton samples were taken from the superficial water of a fixed station, every 3 - 4 days, from February 2 through August 1, 2000. The highest abundance of this species was observed in March, when densities varied widely, from 20 to 600 ind. m-3. Population parameters were calculated, such as birth rate (from 0.25 to 0.90 ind.-1.day-1), growth rate (from -1.30 to 2.09 day-1 ) and death rate ( from -1.6 to 1.9 day-1 ) Start of population could be attributed to the increase of temperature and to the hatching of resting eggs. The population collapsed in fall-winter, as result from the combined effects of different factors: decrease of water temperature (from 27ºC to 21ºC) influencing egg development time (from 2.27 to 3.28 days); predation pressure by chaetognaths (Max. 100 ind. m-3 ) and switch of population from parthenogenic to sexual reproduction. Horizontal transport of water by tidal currents contributed partially to the reduction of population density.

Population parameters of Pleopis polyphemoides (Crustacea, Cladocera) in a tropical bay

Populations of Pleopis polyphemoides were studied in Guanabara Bay, southeastern Brazil, to assess temporal variations in density and population parameters. The abundance of P. polyphemoides varied widely during summer, and collapsed in fall–winter. These variations probably resulted from the combined effects of water temperature and predation pressure. It is assumed that the planktonic population began by hatching from resting eggs, while the collapse of the planktonic population in April seemed to be related to lower temperatures and high densities of predatory chaetognaths.

Spatial and temporal variation in densities of chironomid larvae (Diptera) in two lagoons and two tributaries of the upper Paraná River floodplain, Brazil.

Chironomid larvae were collected and abiotic variables measured at monthly intervals at 21 sampling stations in two lagoons (Guaraná and Patos) and two tributaries (Baía and Ivinheima) of the Upper Paraná River floodplain. The genera Procladius, Chironomus, Goeldichironomus, and Polypedilum were dominant in the lagoons and in the Baía River, while Cryptochironomus and Lopescladius were more dominant in the Ivinheima River. The similarity in the generic composition of the chironomids of the lagoons and the Baía River is probably due to the fact that this river presents hydrodynamic characteristics similar to those of the lagoons. The results obtained suggest that the hydrodynamics of these environments are the main factor determining spatial variation in the chironomid fauna. This is intuitively clear, as this factor itself determines sediment type, quantity of organic matter and presence or absence of aquatic macrophytes. However, on a seasonal scale, the flood pulse seems to be the main controlling factor of the temporal variation in densities and dominance of chironomid larvae. Given that this factor has a large influence on the temporal dynamics of several limnological variables, this is again a logical correlation. Our results suggest a strong relationship between the variations in the chironomid community and fluctuations in limnological characteristics.

BIODIVERSITY, DENSITY COMPENSATION, AND THE DYNAMICS OF POPULATIONS AND FUNCTIONAL GROUPS

Species richness can affect both the size and stability of populations. Many simple theories predict that complex speciose communities should be less stable than simple ones. In contrast, stability of collective community attributes, such as functional groups, may be greater in more complex communities. We used aquatic microcosms containing microbial food webs to generate an experimental gradient of species richness. Biweekly counts of population samples permitted estimation and comparison of density, persistence time, and temporal variation in density for populations and trophic functional groups embedded in communities of varying richness. Densities of nearly half of the species declined as species richness increased, demonstrating broad community-wide density compensation that resulted from more abundant competitors and predators in species-rich communities. Persistence time, a measure of population stability, also declined with increasing species richness. Another measure of population stability, temporal variation in density, indicated that abundances of most species embedded in diverse communities varied no more than in less diverse communities. In contrast to results for individual species, temporal variation of entire functional groups composed of multiple species decreased as species richness increased. The stability of individual populations was not predicted by that of functional groups. Interspecific interactions and statistical averaging may both contribute to the reduced temporal variability of functional groups created by aggregating multiple species.

Biodiversity, Density Compensation, and the Dynamics of Populations and Functional Groups

Species richness can affect both the size and stability of populations. Many simple theories predict that complex speciose communities should be less stable than simple ones. In contrast, stability of collective community attributes, such as functional groups, may be greater in more complex communities. We used aquatic microcosms containing microbial food webs to generate an experimental gradient of species richness. Biweekly counts of population samples permitted estimation and comparison of density, persistence time, and temporal variation in density for populations and trophic functional groups embedded in communities of varying richness. Densities of nearly half of the species declined as species richness increased, demonstrating broad community-wide density compensation that resulted from more abundant competitors and predators in species-rich communities. Persistence time, a measure of population stability, also declined with increasing species richness. Another measure of population stability, temporal variation in density, indicated that abundances of most species embedded in diverse communities varied no more than in less diverse communities. In contrast to results for individual species, temporal variation of entire functional groups composed of multiple species decreased as species richness increased. The stability of individual populations was not predicted by that of functional groups. Interspecific interactions and statistical averaging may both contribute to the reduced temporal variability of functional groups created by aggregating multiple species.

Contrasting Recolonization Strategies in Multi-Species Seagrass Meadows

This study shows that in a multi-species seagrass meadow in a shallow and clear-water site, all the former seagrass species were able to recolonize in the artificially created gaps of 0.25 m 2 in size within ca. 2 yr. Extrapolation of the recolonization curves of the different species predicted a full recovery within 10 yr post-disturbance. Fitted curves for the dominant species Enhalus acoroides and Thalassia hemprichii showed contrasting strategies, the latter having a comparatively high intrinsic rate, achieving full recovery within ca. 2 yr post-disturbance. E. acoroides was the latest species to establish and the projected full-recovery time was among the longest (ca. 10 yr). The effect of timing of gap creation was generally not significant (except for Syringodium isoetifolium) neither was the temporal variation in density of most species outside the gaps. As recolonization by sexual propagules was found to be low, increasing the gap size would most probably require a much longer recovery period. A crude estimate for E. acoroides would be >10 yr for 1 m 2 of gap. Further, since the densities of most seagrass species vary significantly between sites, and colonization rates depend on adjacent seagrass densities, the recovery curves would also be different across sites.

Spatio‐temporal distribution of young fish in tributaries of natural and flow‐regulated sections of a neotropical river in French Guiana

1. We investigated which environmental parameters control the variation in density, in space and time, of young stages of fish in tributaries of a natural and a flow‐regulated section of the Sinnamary River, French Guiana.2. The density of the progeny in most taxa varied in space and/or time. However, most non‐Perciformes responded differently to space and/or time in the two sections.3. Oxygen, turbidity and habitat structure (i.e. bank length, occurrence of undercut bank, richness in litter, vegetation and substratum) were important, as was the position of the sampling site relatively to the main channel in the downstream tributaries, in explaining the variation of density in space in both sections. Both habitat complexity and distance from the main channel protect young fish against unpredictable flow releases downstream from the Petit Saut dam.4. Hydrological events played an important role in the temporal variation in densities of many fish taxa. The density of most early life and many juvenile stages (mostly Characiformes) was positively related to hydrological events.5. Some fish taxa had reproductive habits which were relatively independent of abiotic factors, such as flow variability, and the density of their progeny did not vary with time.6. The nursery areas of more than 45% of species in the Sinnamary River have been degraded by flow regulation.