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.     

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.     

Implications of temporal and spatial variability in Paracentrotus lividus populations to the associated commercial coastal fishery

Analysis of population structure and behaviour of a semi-enclosed and theoretically non-fished population of the echinoid Paracentrotus lividus at Lough Hyne marine nature reserve, Co. Cork, Ireland, showed distinct variability. Aspects of the behavioural variability in this species have significant consequences for the natural fishery harvest potential of this species. Whether or not, when and where individuals migrate to the upper surfaces of rocks varies on a local and regional scale as well as seasonally. The effect of this is apparent changes in (a) the population structure, (b) the population size and (c) the population centres of abundance. The population structure and size of the Lough Hyne population has changed substantially, as have those on a larger spatial scale, although the causative agents are debatable. Such changes are the result of large-scale mortality of adults and failure of cohort recruitment. Despite the undeniable pressures of overfishing at many localities, it seems likely there is a strong `natural' and possibly predictable element to the variability in P. lividus population size and structure. For the restoration and sustainable harvest of Irish P. lividus aspects of its behavioural ecology need to be taken more closely into consideration.     

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...     

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.     

A mathematical approach to spatial distribution and temporal succession in plant communities

The Volterra equations which represent competitions between two species are utilized to examine the phenomenon of boundary formation between two species of plants. The set of stable stationary points for these equations is determined and is illustrated in a product space of parameters and dynamical variables. The stages of boundary appearance and succession are visualized by considering slow changes of the parameters as functions of time and space.     

Dietary variability in fishes: the roles of taxonomic, spatial, temporal and ontogenetic factors

In spite of the general use of diet data in ecological research, still very little is known about the relative roles of spatial, temporal and biotic (e.g. taxonomic identity, size, sex) factors in dietary variability of fishes. Here, we applied canonical correspondence analysis and variation partitioning to examine the roles of taxonomic, annual, seasonal, lake basin, habitat and ontogenetic (standard length, L _S) factors in the dietary variation of fishes in large and shallow Lake Balaton, Hungary. The analyses were performed at the assemblage (15 fish species) and the individual species levels, and based on high (24 fine resource categories) and low resolution (nine broad resource categories) diet data. As hypothesised, most of the explained variation related to interspecific differences, while the roles of sampling year, season, lake area, habitat and L _S proved to be unexpectedly low at the assemblage level. In addition, no regularity was found in how the relative roles of these factors change between fish species. The high ratio of the unexplained variation suggests that individual variations in foraging strategies and resource use of fishes and unascertained stochastic processes had a strong influence on dietary variability both at the assemblage and the individual species levels.     

Isolation of an eclosion hormone gene from the cotton bollworm, Helicoverpa armigera: temporal and spatial distribution of transcripts

The cDNA encoding eclosion hormone (EH), which plays an integral role in triggering ecdysis behavior at the end of each molt, was cloned from the cotton bollworm, Helicoverpa armigera (Har) (Lepidoptera: Noctuidae). The EH polyprotein precursor contains a 26-amino acid signal peptide and a single 62-amino acid mature EH. Compared the mature Har-EH with other known EHs, it shows 94%, 84%, and 59% identities to Manduca sexta, Bombyx mori, and Drosophila melanogaster, respectively. Har-EH mRNA is expressed only in the brain by Northern blot and RT-PCR, but not in other tissues. By in situ hybridization and immunocytochemistry, both Har-EH mRNA and protein are localized in two pairs of neurosecretory cells of the brain. Prior to a molt, expression level of Har-EH gene reaches the highest point, and then drops after molt. EH release is detected both centrally, within the ganglia, and peripherally, into the hemolymph. A peak of the EH titer in hemolymph measured by ELISA presents at ecdysis. These results are consistent with the biological function of Har-EH associated with ecdysis. Furthermore, Har-EH gene is expressed throughout all of the developmental stages examined, implicating that the EH gene may possess other biological functions in post-embryonic development other than triggering ecdysis behavior.     

Dynamics of antarctic penguin populations in relation to inter-annual variability in sea ice distribution

To investigate the role of sea ice cover on penguin populations we used principal component analysis to compare population variables of Adélie (Pygoscelis adeliae) and chinstrap (Pygoscelis antarctica) penguins breeding on Signy Island, South Orkney Islands with local (from direct observations) and regional (from remote sensing data) sea ice variables. Throughout the study period, the Adélie penguin population size remained stable, whereas that of chinstrap penguins decreased slightly. For neither species were there significant relationships between population size and breeding success, except for an apparent inverse density-dependent relationship between the number of Adélie breeding pairs and the number of eggs hatching. For both species, no general relationship was found between either population size or breeding success and the local sea ice conditions. However, the regional sea ice extent at a particular time prior to the start of the breeding season was related to the number of birds that arrived to breed. For both species, this period occurred before the sea ice reached its maximum extent and was slightly earlier for Adélie than for chinstrap penguins. These results suggest that sea ice conditions outside the breeding season may play an important role in penguin population processes.     

The temporal and spatial distribution of nematodes in percolating filters

The spatial and temporal distribution of nematodes in two low rate percolating filter bed sewage treatment plants at Carnforth and Caton, Lancashire, were investigated. Nematodes were abundant reaching densities up to 900 cm⁻² of media surface. Numbers decreased down the bed and species composition displayed spatial differences with bed depth. Eight orders of nematode were represented, members of the sub-family Diplogasterinae and Rhabditinae were particularly common. A seasonal pattern of abundance was clearly apparent; two peaks occurred, one in May and a second during the winter months. Lowest numbers corresponded with periods of highest temperature. The demise of the nematodes in the spring was related to the sloughing of the surface film on the media.     

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     

Interdependence of plankton spatial distribution and plancton biomass temporal oscillations: mathematical simulation

The dynamics of aquatic biological communities in a patchy environment is of great interest in respect to interrelations between phenomena at various spatial and time scales. To study the complex plankton dynamics in relation to variations of such a biologically essential parameter as the fish predation rate, we use a simple reaction-diffusion model of trophic interactions between phytoplankton, zooplankton, and fish. We suggest that plankton is distributed between two habitats one of which is fish-free due to hydrological inhomogeneity, while the other is fish-populated. We show that temporal variations in the fish predation rate do not violate the strong correspondence between the character of spatial distribution of plankton and changes of plankton biomass in time: regular temporal oscillations of plankton biomass correspond to large-scale plankton patches, while chaotic oscillations correspond to small-scale plankton patterns. As in the case of the constant fish predation rate, the chaotic plankton dynamics is characterized by coexistence of the chaotic attractor and limit cycle.     

Plant traits respond to the competitive neighbourhood at different spatial and temporal scales

Background and Aims Clonal plants can plastically modify their traits in response to competition, but little is known regarding the spatio-temporal scale at which a competitive neighbourhood determines the variability in species traits. This study tests the hypothesis that the local neighbourhood can be expected to influence the processes that are involved in competition tolerance and avoidance, and that this effect depends on organ lifespan.Methods Fragments of the rhizomatous Elytrigia repens (Poaceae) were sampled in 2012 in experimental plant communities that varied in species identity and abundance. These communities had been cultivated since 2009 in mesocosms in a common garden. Fragment performance, shoot and clonal traits were measured, and the effects of past and present local neighbourhoods of five different radius sizes (5–25 cm) were examined. Past and present local neighbourhood compositions were assessed in 2011 and 2012, respectively.Key Results Most of the measured traits of E. repens responded to the local neighbourhood (5–10 cm radius), with an additional effect of the larger neighbourhood (20–25 cm radius) on ramet height, leaf dry matter content, maximal internode length and specific rhizome mass. Contrary to the expectation of the hypothesis, the temporal influence was not due to the organ lifespan. Indeed, five of the eight traits studied responded to both the past and present neighbourhoods. With the exception of specific rhizome mass, all trait responses were explained by the abundance of specific species.Conclusions This study demonstrates that the traits of a single clonal individual can respond to different competitive environments in space and time. The results thus contribute to the understanding of competition mechanisms.