Regionalized phosphorus fate factors for freshwater eutrophication in Bahia,Brazil: an analysis of spatial and temporal variability

The International Journal of Life Cycle Assessment - Fate factors, for freshwater eutrophication, represent the route of a limiting-nutrient, phosphorus or nitrogen, and their degradation in the...     

Small-scale temporal variability in assemblages of larval fishes: implications for sampling

Short-term changes in the assemblages of larval fishes in watersover the inner continental shelf off Sydney (Australia) wereexamined.This was done to highlight the potential sampling problemof confounding short-term variability with longer-term and spatialvariability in plankton communities. Assemblages at the surfaceand at 30 m depth were sampled twice a day over consecutivedays at two locations 5 km apart. The assemblages and the densitiesof individual taxa varied greatly between sampling times anddays. The small-scale temporal changes in densities of larvaewere not the same at both locations or between depths. Largeand consistent depth-related differences in assemblages andabundances of most taxa were evident. The consequences of small-scaletemporal variations are discussed relative to the design ofsampling programs for ecological and environmental purposes.Studies that include the double sampling of some stations arerecommended. Greater emphasis needs to be placed on fine-scaleoceanography and larval behaviour to determine causative mechanismsof short-term changes in assemblages of larval fishes.     

Multiple driving factors explain spatial and temporal variability in coral calcification rates on the Bermuda platform

Experimental studies have shown that coral calcification rates are dependent on light, nutrients, food availability, temperature, and seawater aragonite saturation (Ω _arag), but the relative importance of each parameter in natural settings remains uncertain. In this study, we applied Calcein fluorescent dyes as time indicators within the skeleton of coral colonies (n = 3) of Porites astreoides and Diploria strigosa at three study sites distributed across the northern Bermuda coral reef platform. We evaluated the correlation between seasonal average growth rates based on coral density and extension rates with average temperature, light, and seawater Ω _arag in an effort to decipher the relative importance of each parameter. The results show significant seasonal differences among coral calcification rates ranging from summer maximums of 243 ± 58 and 274 ± 57 mmol CaCO₃ m^?2 d^?1 to winter minimums of 135 ± 39 and 101 ± 34 mmol CaCO₃ m^?2 d^?1 for P. astreoides and D. strigosa, respectively. We also placed small coral colonies (n = 10) in transparent chambers and measured the instantaneous rate of calcification under light and dark treatments at the same study sites. The results showed that the skeletal growth of D. strigosa and P. astreoides, whether hourly or seasonal, was highly sensitive to Ω _arag. We believe this high sensitivity, however, is misleading, due to covariance between light and Ω _arag, with the former being the strongest driver of calcification variability. For the seasonal data, we assessed the impact that the observed seasonal differences in temperature (4.0 °C), light (5.1 mol photons m^?2 d^?1), and Ω _arag (0.16 units) would have on coral growth rates based on established relationships derived from laboratory studies and found that they could account for approximately 44, 52, and 5 %, respectively, of the observed seasonal change of 81 ± 14 mmol CaCO₃ m^?2 d^?1. Using short-term light and dark incubations, we show how the covariance of light and Ω _arag can lead to the false conclusion that calcification is more sensitive to Ω _arag than it really is.     

Modelling the spatial and temporal variability of diatoms in the River Murray

We have developed a simple mechanistic model, which simulates the temporaland spatial variability of concentrations of the diatomAulacoseira granulata in the River Murray, NSWAustralia, over large distances under different flow conditions. The modelincorporates a simple growth function determined by the availabilities ofsilica and light, and by temperature. It also includes losses due tosinking and downstream advection. The model is tested against weeklymeasurements for the period 1981-1990, at three sites separated by 1100 km.The seasonal cycle of Aulacoseira concentrations alongthe river is well represented by the model. During times of high flow, theconcentrations of Aulacoseira remain fairly uniformalong the river as the diatoms have insufficient time to grow before beingadvected downstream.     

Partial migration in fishes: definitions, methodologies and taxonomic distribution

Partial migration, where populations are composed of both migratory and resident individuals, is extremely widespread across the animal kingdom. Researchers studying fish movements have long recognized that many fishes are partial migrants, however, no detailed taxonomic review has ever been published. In addition, previous work and synthesis has been hampered by a varied lexicon associated with this phenomenon in fishes. In this review, definitions and important concepts in partial migration research are discussed, and a classification system of the different forms of partial migration in fishes introduced. Next, a detailed taxonomic overview of partial migration in this group is considered. Finally, methodological approaches that ichthyologists can use to study this fascinating phenomenon are reviewed. Partial migration is more widespread amongst fishes than previously thought, and given the array of techniques available to fish biologists to study migratory variation the future of the field looks promising.     

Net anthropogenic phosphorus inputs: spatial and temporal variability in the Chesapeake Bay region

We estimated net anthropogenic phosphorus inputs (NAPI) in the Chesapeake Bay region. NAPI is an index of phosphorus pollution potential. NAPI was estimated by quantifying all phosphorus inputs and outputs for each county. Inputs include fertilizer applications and non-food phosphorus uses, while trade of food and feed can be an input or an output. The average of 1987, 1992, 1997, and 2002 NAPI for individual counties ranged from 0.02 to 78.46 kg P ha⁻¹ year⁻¹. The overall area-weighted average NAPI for 266 counties in the region was 4.52 kg P ha⁻¹ year⁻¹, indicating a positive net phosphorus input that can accumulate in the landscape or can pollute the water. Large positive NAPI values were associated with agricultural and developed land cover. County area-weighted NAPI increased from 4.43 to 4.94 kg P ha⁻¹ year⁻¹ between 1987 and 1997 but decreased slightly to 4.86 kg P ha⁻¹ year⁻¹ by 2002. Human population density, livestock unit density, and percent row crop land combined to explain 83% of the variability in NAPI among counties. Around 10% of total NAPI entering the Chesapeake Bay watershed is discharged into Chesapeake Bay. The developed land component of NAPI had a strong direct correlation with measured phosphorus discharges from major rivers draining to the Bay (R ² = 0.81), however, the correlation with the simple percentage of developed land was equally strong. Our results help identify the sources of P in the landscape and evaluate the utility of NAPI as a predictor of water quality.     

Dissecting apple tree architecture into genetic, ontogenetic and environmental effects: mixed linear modelling of repeated spatial and temporal measures

The present study aimed to dissect tree architectural plasticity into genetic, ontogenetic and environmental effects over the first 4 yr of growth of an apple (Malus x domestica) F1 progeny by means of mixed linear modelling of repeated data. Traits related to both growth and branching processes were annually assessed on different axes of the trees planted in a staggered-start design. Both spatial repetitions, (i.e. different axis types) and temporal repetitions (i.e. successive ages of trees) were considered in a mixed linear model of repeated data. A significant genotype effect was found for most studied traits and interactions between genotype and year and/or age were also detected. The analysis of repeated temporal measures highlighted that the magnitude of the decrease in primary growth is mainly determined by the first year of growth, and the decrease in bottom diameter increment is concomitant with the first fruiting occurrence. This approach allowed us to distinguish among the traits that were under genetic control, those for which this control is exerted differentially throughout tree life or depending on climatic conditions or an axis type. Mapping quantitative trait loci (QTL) that are specific to these different effects will constitute the next step in the research.     

Polychaetes associated with the sciaphilic alga community in the northern Aegean Sea: spatial and temporal variability

Polychaete biodiversity has received little attention despite its importance in biomonitoring. This study describes polychaete diversity, and its spatial and temporal variability in infralittoral, hard substrate assemblages. Seven stations were chosen in the central area of the northern Aegean Sea. At each station, one to three depth levels were set (15, 30 and 40 m). Five replicates were collected by scuba diving with a quadrat sampler (400 cm²) from each station and depth level during summer for the spatial analysis, and seasonally for the study of temporal changes. Common biocoenotic methods were employed (estimation of numerical abundance, mean dominance, frequency, Margalefs richness, Shannon-Weaver index and Pielous evenness). A total of 5,494 individuals, belonging to 79 species, were counted and classified. Diversity indices were always high. Clustering and multidimensional scaling techniques indicated a high heterogeneity of the stations, although these were all characterized by the sciaphilic alga community. A clear seasonal pattern was not detectable. Summer and autumn samples discriminate, while winter and spring form an even group. The abundance/biomass comparison indicated a dominance of k-strategy patterns, characteristic of stable communities.Communicated by H.-D. Franke     

The emergence of automated high-frequency flow cytometry: revealing temporal and spatial phytoplankton variability

Phytoplankton observation is the product of a number of trade-offsrelated to sampling processes, required level of diversity andsize spectrum analysis capabilities of the techniques involved.Instruments combining the morphological and high-frequency analysisfor phytoplankton cells are now available. This paper presentsan application of the automated high-resolution flow cytometerCytosub as a tool for analysing phytoplanktonic cells in theirnatural environment. High resolution data from a temporal studyin the Bay of Marseille (analysis every 30 min over 1 month)and a spatial study in the Southern Indian Ocean (analysis every5 min at 10 knots over 5 days) are presented to illustrate thecapabilities and limitations of the instrument. Automated high-frequencyflow cytometry revealed the spatial and temporal variabilityof phytoplankton in the size range 1–50 µm thatcould not be resolved otherwise. Due to some limitations (instrumentalmemory, volume analysed per sample), recorded counts could bestatistically too low. By combining high-frequency consecutivesamples, it is possible to decrease the counting error, followingPoisson’s law, and to retain the main features of phytoplanktonvariability. With this technique, the analysis of phytoplanktonvariability combines adequate sampling frequency and effectivemonitoring of community changes.     

The spatial and temporal variability of the magnetoencephalogram alpha rhythm in the normal human subject

Using one-channel SQUID biomagnetometer alpha rhythm was recorded in five healthy men and eight healthy women. Maps of distribution of maximum values of mean MEG amplitudes were analyzed. Most frequently MEG maxima predominated in the parietal parts of the head. Less frequently they were found in the occipital parts. In single instances they could be found in the posterocentral sections and on the midline. In most cases an amplitude interhemispheric asymmetry of extrema was revealed. In men the mean amplitude of the alpha-rhythm predominated more frequently on the left side and in women--on the right one. The map of distribution of mean amplitudes was stable at least during two weeks. Narrow-band filtration allowed to reveal up to three discrete amplitude modes. At definite frequencies the MEG amplitude was continuously stable during several seconds.     

Patterns of variability in early-life traits of fishes depend on spatial scale of analysis

Estimates of early-life traits of fishes (e.g. pelagic larval duration (PLD) and spawning date) are essential for investigating and assessing patterns of population connectivity. Such estimates are available for a large number of both tropical and temperate fish species, but few studies have assessed their variability in space, especially across multiple scales. The present study, where a Mediterranean fish (i.e. the white seabream Diplodus sargus sargus) was used as a model, shows that spawning date and PLD are spatially more variable at a scale of kilometres than at a scale of tens to hundreds of kilometres. This study indicates the importance of considering spatial variability of early-life traits of fishes in order to properly delineate connectivity patterns at larval stages (e.g. by means of Lagrangian simulations), thus providing strategically useful information on connectivity and relevant management goals (e.g. the creation of networks of marine reserves).     

Metabolic patch dynamics in small headwater streams: exploring spatial and temporal variability in benthic processes

1. To gain a better understanding of the heterotrophic nature of small headwater streams in forested landscapes we explored the spatial and temporal variability of in‐stream organic matter processes. Three methods were used to measure the benthic metabolism of different in‐stream habitats in seven streams throughout a calendar year. This allowed us to analyse the contribution of various metabolic habitats (i.e. sediment, leaf litter, cobbles) to in‐stream metabolism during a natural flow regime. Furthermore, it allowed us to define in‐stream patchiness based on functional rather than structural elements. 2. Bacterial growth, measured using a leucine assay, displayed a quadratic relationship over time with a peak in warmer months and consistently higher bacterial growth in fine depositional (3.00–710.64 mg C m^?2 day^?1) than coarse gravel (38.84–582.85 mg C m^?2 day^?1) sediments. 3. Community metabolism, measured using dissolved oxygen chambers, showed distinct diel patterns and consistently greater net daily metabolism in leaf packs (?261.76 to ?24.50 mg C m^?2 day^?1) than fine depositional sediments (?155.00 to ?15.56 mg C m^?2 day^?1). Coarse gravel sediments (?49.55 to ?16.88 mg C m^?2 day^?1) and cobble habitats (?151.98 to 55.38 mg C m^?2 day^?1) exhibited the lowest metabolic rates. Modelled whole‐stream metabolism was highly variable among streams and temporal patterns appeared driven by temperature and the relative contribution of patch configuration as a function of flow. 4. Cellulose decomposition potential showed higher rates of microbial activity in fine depositional compared to coarse gravel sediments (30.5 and 29.1 kg average cotton tensile strength loss respectively), though there were higher rates of thread loss indicative of macroinvertebrate activity in gravel compared to depositional sediment (21% and 13% average thread loss respectively), with a slight quadratic trend. The high variability among habitats, streams and over time in this integrative measure may be explained by variability in local microbial activity as well as the potential for macroinvertebrates to contribute across patches. 5. There were strong relationships among benthic processes and habitat structure, nutrient status, stream temperature and flow. Different habitats had distinct metabolic characteristics and these characteristics appear to influence stream food webs and biogeochemical cycling depending on the relative abundance of habitats. Generally, within habitat variability was less than among habitat variability and among stream variability was less than temporal variability. Hence, in terms of the spatial and temporal heterogeneity of benthic processes, these small headwater streams showed predictable metabolic patterns. However, there were few correlations between differing measures of benthic metabolism at the same patch and this suggests that caution should be taken when attempting to infer the rates of one level of metabolic activity (e.g. whole community metabolism) based on another (e.g. bacterial productivity).     

Variation in spatial and temporal gradients in zooplankton spring development: the effect of climatic factors

1. We examined the temporal and spatial heterogeneity of zooplankton in lake surface waters during the spring of 3 years in Lake Washington, U.S.A., a large lake with a high production of sockeye salmon fry. 2. We show large within‐season and among‐year variation in the horizontal distribution of temperature, chlorophyll a concentration, and zooplankton in the lake. The main pattern, a delay in zooplankton population increase from the north‐ to the south‐end of the lake, recurred in each year and was persistent within each spring. 3. The delay is primarily caused by the development of a temperature gradient during spring warming, as cold mountain water enters the south end of the lake, while warm water enters the north end via a river draining a nearby lake. Climate factors, such as air temperature and precipitation during winter and spring, appear to influence the extent of the delay of zooplankton increase. 4. If the climate continues to warm, the temporal disconnection in zooplankton development between lake areas immediately influenced by cold river inflow and areas that are influenced by spring warming may increase in magnitude. Thus, the different areas of the lake may not contribute equally to fish production.     

Beta diversity of rock-restricted cichlid fishes in Lake Malawi: importance of environmental and spatial factors

The rock-restricted cichlid fish assemblages of Lake Malawi exhibit high spatial diversity in their species composition and relative abundance. However the extent to which this is due to the effects of local environmental differences, dispersal limitation of constituent taxa, and the assignment of allopatric populations to species is uncertain. We examined the factors associated with diversity within an assemblage from the north-western shores, encompassing a spatial scale of 170 km. For both the whole assemblage, and all constituent species-complexes, spatial variance in community structure was significantly dependent upon both geographic distances between locations and local habitat variables. Pronounced effects of distance indicate limited dispersal, but our results also show that that the spatial variance explained by geographic distance alone was strongly linked to proportion of allopatric populations within a species-complex with species status. Thus, the taxonomic status of allopatric populations underlies, at least partially, the biogeographical structure of this assemblage. Substrate composition and habitat depth were also significant determinants of community structure, although spatial variance attributed to these variables was less than that associated with distance alone. Substantial unexplained variance may be a consequence of the effects of unmeasured habitat variables, high ecological similarity between co-occurring species, stochastic influences on population abundance, and the effects of local adaptation. Despite low spatial variance explained by the assessed environmental variables, significant environmental influence on cichlid assemblage structure across a wide spatial scale indicates that even slight future environmental changes may have the capacity to significantly alter species composition.     

Cranial ontogenetic variability,sex ratio and age structure of the Red fox

Describing the sex ratio, age structure of the population and ontogenetic variability of Red fox, Vulpes vulpes (Canidae, Carnivora) skull parameters, this study is based on 416 male and 289 female skulls collected in the Czech Republic. The skulls analysed came from feral individuals, that were shot by hunters. The male to female ratio was 1:0.69 regarding the whole population. Individuals younger than one year prevailed in the population (54% males, 48% females were in their first year of life). Four growth patterns of skull dimensions were described. The first group included mainly skull length dimensions (e.g. condylobasal length). They grew rapidly until the sixth month of life, becoming stabilised afterwards. The second group comprised parameters that were stable throughout the life (e.g. cheek tooth rows). Measurements representing the third growth pattern showed continual growth (mainly width dimensions, e.g. zygomatic breadth). Conversely, smaller dimensions of postorbital breadth were observed after the sixth month of life. Postorbital breadth represented the fourth growth pattern. It was concluded, that male and female Red foxes had similar ontogenetic skull development, even though there were some differences, e.g. in jugular breadth, which increased after the age of six months in males unlike in females.     

Characterising the temporal variability of the spatial distribution of animals: an application to seabirds at sea

Understanding the patterns of spatial and temporal variations in animal abundance is a fundamental question in ecology. Here, we propose a method to quantify temporal variations in animal spatial patterns and to determine the spatial scale at which such temporal variability is expressed. The methodology extends from the approach proposed by Taylor (Taylor, L. R. 1961. Aggregation, variance and the mean. Nature 189: 732–735) and relies on models of the relationship between temporal mean and variance in animal abundance. Repeated observations of the spatial distribution of populations are used to construct spatially explicit models of Taylor's power law. The resulting slope parameters of the Taylor power law provide local measures of the temporal variability in animal abundance. We investigate if the value of the slope varies significantly with spatial location and with spatial scale. The method is applied to seabirds distribution in the Bay of Biscay. We study four taxa (northern gannets, large gulls, auks and kittiwakes) that display distinct geographical distribution, spatial structure and foraging strategy. Our results show that the temporal variability associated to the spatial distribution of northern gannets is high and spatially homogeneous. By contrast, kittiwakes present large geographical areas associated with high and low variability. The temporal variability of auk's spatial distribution is strongly scale-dependent: at fine scale high variability is associated to high abundance, but at large scale high variability is associated to the external border of their distribution range. The method provides satisfactory results and useful information on species spatio-temporal distribution.     

Declines in littoral species richness across both spatial and temporal nutrient gradients: a palaeolimnological study of two taxonomic groups

1. Using a palaeolimnological approach in shallow lakes, we quantified the species richness responses of diatoms and Cladocera to phosphorus enrichment. We also examined differences in species richness responses between littoral and pelagic assemblages of our focal communities. To address both spatial and temporal relationships, our study includes an analysis of both surface sediments from 40 lakes and of a lake sediment record spanning c. 120 years. The objective of our study was to determine whether similar species richness patterns occurred across trophic levels, as well as along spatial and temporal gradients. 2. We found that both diatom and Cladocera species richness estimates significantly declined with increasing phosphorus across space and through time. When the assemblages were subdivided according to known habitat preferences, littoral biodiversity maintained a negative trend, whereas pelagic species richness tended to show no relationship with phosphorus. 3. Negative productivity–diversity patterns have been observed across almost all palaeolimnological studies that span large productivity gradients. This congruence in patterns is most likely due to the similarity in data collection methods and in focal communities studied. The contrasting responses between littoral and pelagic assemblages may be explained by the differences in physical habitat and the pool of taxa in each of these environments. Consistent with the literature, we found statistical support for the idea that littoral diversity declines could be explained by an interaction between macrophytes and nutrients along strong trophic gradients. The general lack of a diversity response in our pelagic assemblages could be attributable to the limited pool of subfossil taxa. The response of the pelagic diatom could also be related to their broad range of nutrient tolerances. 4. The observed negative response of species richness to phosphorus enrichment, particularly in the littoral assemblages, has implications for ecosystems functioning because communities with reduced biodiversity often are less resilient to anthropogenic change.     

Patterns of intraspecific variability in carp fishes of the dace subfamily: ecological factors and pathways of phenotypic transformation

The inverstigation of geographical and ecological variations of wide-spread species of daces allows to reveal regular patterns of phenotypic transformations with limited number of their possible ways. The set of characters involved and the directions of their changes are specific for both examined taxa and putative factors of subspeciation. Two basic groups of evolutionary and ecological situations leading to the intensive intraspecific divergence are considered: living or spawning in brackish water and heavy anthropogeneous pollution. Striking morphological similarity was found between populations from zones of hydrochemical anomalies and some remote populations inhabiting non-polluted fresh water bodies. The author discusses possible nature of these isomorphisms and cases of regular phenotype transformation and their implications for microevolutionary and systematic studies in fish. The data obtained suggest key role of water mineralization in evolution of the subfamily of dace fish.