Variation In Annual Production Research Articles

Ecological and anthropogenic drivers of waterfowl productivity are synchronous across species, space, and time.

Knowledge of interspecific and spatiotemporal variation in demography-environment relationships is key for understanding the population dynamics of sympatric species and developing multispecies conservation strategies. We used hierarchical random-effects models to examine interspecific and spatial variation in annual productivity in six migratory ducks (i.e., American wigeon [Mareca americana], blue-winged teal [Spatula discors], gadwall [Mareca strepera], green-winged teal [Anas crecca], mallard [Anas platyrhynchos] and northern pintail [Anas acuta]) across six distinct ecostrata in the Prairie Pothole Region of North America. We tested whether breeding habitat conditions (seasonal pond counts, agricultural intensification, and grassland acreage) or cross-seasonal effects (indexed by flooded rice acreage in primary wintering areas) better explained variation in the proportion of juveniles captured during late summer banding. The proportion of juveniles (i.e., productivity) was highly variable within species and ecostrata throughout 1961-2019 and generally declined through time in blue-winged teal, gadwall, mallard, pintail, and wigeon, but there was no support for a trend in green-winged teal. Productivity in Canadian ecostrata declined with increasing agricultural intensification and increased with increasing pond counts. We also found a strong cross-seasonal effect, whereby more flooded rice hectares during winter resulted in higher subsequent productivity. Our results suggest highly consistent environmental and anthropogenic effects on waterfowl productivity across species and space. Our study advances our understanding of current year and cross-seasonal effects on duck productivity across a suite of species and at finer spatial scales, which could help managers better target working-lands conservation programs on both breeding and wintering areas. We encourage other researchers to evaluate environmental drivers of population dynamics among species in a single modeling framework for a deeper understanding of whether conservation plans should be generalized or customized given limited financial resources.

Seasonal Variations And Forecasting In Wholesale Prices Of Okra In Surat Market Of Gujarat, India

The analysis of prices and market arrivals over time is important for formulating a sound agricultural price policy. Fluctuations in market arrivals largely contribute to price instability. In order to devise the appropriate ways and means for reducing the price fluctuations of agricultural commodities, there is a need to have a thorough understanding of the price behavior over time.Forecasting the price of agricultural commodities, presents some unique challenges such as data quality issues, weather aberrations, high fluctuations, price variations across neighboring marketplaces, etc. On the demand side, the instability in the prices of agricultural commodities is influenced by a number of factors such as annual variation in production, low price elasticity of demand and seasonality of agricultural production.The study relied upon the secondary time series data on monthly market prices and arrivals of Okra collected from the Agricultural Produce Market Committee, Surat. Analysis was performed on the monthly and annual time series data on wholesale price to develop reliable forecast for 2022. Month wise Seasonal indices of Okra in the Surat market showed that the seasonal price indices were above average from November to March while below average from May to October when market arrivals are more. The seasonal pattern showed that prices declined from April to October and reached the lowest point in May and reached peak in December. Seasonal fluctuations were observed both in market arrivals as well as prices of Okra. In the present investigation, various Seasonal, Non-seasonal, and Seasonal ARIMA (Box-Jenkins) models were developed to measure the forecast accuracy. The best model was chosen on the basis of the least values of Schwarz Bayesian criteria (SBC) and Mean absolute percentage error (MAPE). After performing a series of diagnostic tests, it was observed that N-BIC (12.417) and MAPE (22.88) were the least for SARIMA (0,0,2) (0,1,1)12 model. It came out to be the most representative model for the price of Okra in the Surat market. The model can be used for reaching dependable price forecasts. The quantification of these aspects in the vegetables is an immediate need to formulate effective policies to make prices stable thereby safeguard the interest of the farmers as well as the consumer.

Tropical bird species richness is strongly associated with patterns of primary productivity captured by the Dynamic Habitat Indices

Biodiversity science and conservation alike require environmental indicators to understand species richness and predict species distribution patterns. The Dynamic Habitat Indices (DHIs) are a set of three indices that summarize annual productivity measures from satellite data for biodiversity applications, and include: a) cumulative annual productivity; b) minimum annual productivity; and c) variation in annual productivity. At global scales and in temperate regions the DHIs predict species diversity patterns well, but the DHIs have not been tested in the tropics, where higher levels of productivity lead to the saturation of many remotely sensed vegetation indices. Our goal was to explain bird species richness patterns based on the DHIs in tropical areas. We related the DHIs to species richness of resident landbirds for five guilds (forest, scrub, grassland, generalist, and all resident birds) based on a) species distribution model (SDM) maps for 217 species, and b) range map for 564 species across Thailand. We also quantified the relative importance of the DHIs in multiple regression models that included two measures of topography, and two climate metrics using multiple regression, best-subsets, and hierarchical partitioning analyses. We found that the three DHIs alone explained forest bird richness best (R2adj 0.61 for both SDM- and rangemap based richness; 0.15–0.54 for the other guilds). When combining the DHIs with topography and climate, the richness of both forest birds and all resident bird species was equally well explained (R2adj 0.85 and 0.67 versus 0.81 and 0.68). Among the three DHIs, cumulative annual productivity had the greatest explanatory power for all guilds based on SDM richness maps (R2adj 0.54–0.61). The strong relationship between the DHIs and bird species richness in Thailand suggests that the DHIs capture energy availability well and are useful in biodiversity assessments and potentially bird conservation in tropical areas.

Variation in annual production of copepods, euphausiids, and juvenile walleye pollock in the southeastern Bering Sea

We synthesize recent research on variation in annual production of copepods (Calanus spp.), euphausiids (Thysanoessa spp.), and juvenile walleye pollock (Gadus chalcogrammus) in the southeastern Bering Sea. We reach five conclusions: 1) the timing of the spring bloom is more important than the amount of annual primary production for the transfer of primary to secondary production (i.e., timing matters); 2) summer and fall, not just spring, matter: organisms must maximize energy intake devoted to somatic growth and storage of lipids and minimize energy expenditures during each season; 3) stored lipids are important for the overwinter survival of both zooplankton and age-0 walleye pollock; 4) variation in ice extent and timing of ice retreat affect the spatial distributions of phytoplankton, zooplankton, and age-0 walleye pollock; when these spatial distributions match in late-ice-retreat years, the annual production of copepods, euphausiids, and juvenile walleye pollock often increases (i.e., location matters); 5) if years with late ice retreat, which favor copepod, euphausiid, and juvenile walleye pollock production, occur in succession, top–down control increases. These conclusions help to explain annual variation in production of copepods, euphausiids and juvenile walleye pollock. Copepods and euphausiids often are more abundant in cold years with late ice retreat than in warm years with early ice retreat due to bloom timing and the availability of ice algae during years with late ice retreat. As a consequence, age-0 walleye pollock consume lipid-enriched prey in cold years, better preparing them for their first winter and their overwinter survival is greater. In addition, there is a spatial match of primary production, zooplankton, and age-0 walleye pollock in cold years and a mismatch in warm years.

Reproductive success and productivity of the Cyprus Wheatear Oenanthe cypriaca, a migratory, island endemic

Population dynamics of annually breeding bird species depend crucially on productivity, and so this variation can help us understand the causes of declines in migrant birds. We investigated variation in annual productivity 2010–2012 in the Cyprus Wheatear Oenanthe cypriaca, a small endemic migrant passerine at the National Forest Park (NFP) of Troodos. Clutch size for first nests was usually five, although 0.40 eggs lower in 2011. Nest survival did not vary with year, nesting attempt, or clutch initiation date, but was significantly higher in the chick (0.96; 0.88–0.98, 95 % CI) versus the egg stage (0.74; 0.62–0.83, 95 % CI). The number of chicks fledged from a successful nest varied with nest type—with first nests and second nests after failure being similar producing ~3–4.5 chicks dependent on year, and with second nests after success producing ~2 chicks, independent of year. There were only weak positive or negative effects of clutch initiation date dependent on year, controlling for nest type, and no effects of male age on productivity. After fledging, chicks had a >95 % chance of surviving the first month, but with a greater probability of one or rarely two chicks per brood dying if fledged later in the season. Renesting rate was significantly different in all years (26, 48, and 78 % renesting): 2010 had a much lower renesting rate after success with very few second broods (29 versus 76 % and 73 % in 2011 and 2012, respectively). Overall productivity per territory did not vary with year with 3.96 ± 0.09 SE chicks alive 1 month after fledging. Cyprus Wheatears showed several unusual breeding parameters including a highly variable renesting probability, high nestling, and very high fledgling survival, resulting in exceptionally high productivity. This may be because renesting is constrained by high mid-summer temperatures and low abundance of chick predators.

Long-term variations in primary production in a eutrophic sub-estuary: Contribution of short-term events

We determined the role of events in generating short-term variability in production, how they contribute to interannual variability, and their relationship to variability in the determinants of production, primarily biomass and photo-physiological parameters. We examined residuals from the seasonal and spatial mean daily rate in a 20-year time series of primary production in a eutrophic sub-estuary of Chesapeake Bay. The seasonal and spatial means of production and residuals were based on natural log-transformed measurements of daily primary production calculated from measurements of light saturation curves of photosynthesis for 20 years at 6 stations on the Rhode River, Maryland (USA). The variance of the residuals was greater than that explained by the seasonal and spatial statistical model, so that the event scale was the largest single source of variance. Residuals were classified as events if they exceeded ±ln(2), signifying a multiplier or divisor of 2 above or below the seasonal-spatial mean. Spatially, events were most frequent at the most upstream station affected by runoff from the local watershed, and temporally most frequent in spring at all stations. Principal component analysis (PCA) of monthly averaged residuals revealed 3 characteristic temporal modes of residual variance, the first of which was associated with variability in spring due to the occurrence of extremely large spring blooms or their complete absence. Interannual variation in annual production was correlated with the strength of expression of these modes. Production events were analyzed in relation to residuals in the determinants of productivity, i.e. phytoplankton chlorophyll biomass, B, the light-saturated photosynthetic maximum normalized to chlorophyll, PmaxB, the diffuse attenuation coefficient for light, and the depth integral of the dimensionless photosynthesis profile. Negatively correlated changes in B and PmaxB were the most common mode of variation among the determinants, and this mode dampened variations in production and were common in fall months. Positively correlated changes in B and PmaxB constituted the second most common mode of variation amongst determinants, and this mode was positively correlated with variations in production and were most common in spring months. The prevalence of the first mode in fall months modulated the impact of major named storms on primary production in this system.

Using citizen science to investigate the role of productivity in House Sparrow Passer domesticus population trends

Capsule Seasonal variation in garden House Sparrow numbers provides a tool to examine overall annual productivity, measuring the combined success of multiple breeding attempts and post-fledging survival.Aims To develop a metric to use British Trust for Ornithology (BTO) Garden BirdWatch (GBW) data to measure annual productivity in House Sparrows across regions and habitats exhibiting contrasting population trends.Methods We examine variation in annual productivity by quantifying the height of the seasonal peak of garden House Sparrows relative to pre-breeding numbers. We use BTO Nest Record Scheme (NRS) data to explore the demographic drivers of variation in this metric and relate differences to BTO/Joint Nature Conservation Committee/Royal Society for Protection of Birds Breeding Bird Survey regional population trends.Results GBW annual productivity was similar between rural and urban gardens but was lower in the south and the east of Britain (1.32 fledglings per adult), where populations are declining, than in the north and west where populations are stable (1.37 fledglings per adult). Analysis of NRS data showed similar regional variation in clutch and broods sizes.Conclusion The intensity of effort required to measure breeding success directly through nest monitoring has limited the scale of data collection but these results suggest that Garden BirdWatch (GBW) data can provide a measure of annual productivity across multiple sites. Regional variation in annual productivity (primarily driven by reduced clutch sizes) mirrors population trends, suggesting that reduced breeding success may be influencing House Sparrow population recovery.

Maternal effects and heritability of annual productivity

Within-individual consistency and among-individual heterogeneity in fitness are prerequisites for selection to take place. Within-individual variation in productivity between years, however, can vary considerably, especially when organisms become older and more experienced. We examine individual consistency in annual productivity, the covariation between survival and annual productivity, and the sources of variation in annual productivity, while accounting for advancing age, to test the individual-quality and resource-allocation life-history theory hypotheses. We use long-term data from a pedigreed, wild population of house sparrows. Within-individual annual productivity first increased and later decreased with age, but there were no selective mortality due to individual quality and no correlation between lifespan and productivity. Individuals were consistent in their annual productivity (C = 0.49). Narrow-sense heritability was low (h(2) = 0.09), but maternal effects explained much of the variation (M = 0.33). Such effects can influence evolutionary processes and are of major importance for our understanding of how variation in fitness can be maintained.

Factors driving spatial and temporal variation in production and production / biomass ratio of stream-resident brown trout (Salmo trutta) in Cantabrian streams

Summary 1. The objective was to identify the factors driving spatial and temporal variation in annual production (PA) and turnover (production/biomass) ratio (P/BA) of resident brown trout Salmo trutta in tributaries of the Rio Esva (Cantabrian Mountains, Asturias, north-western Spain). We examined annual production (total production of all age-classes over a year) (PA) and turnover (P/BA) ratios, in relation to year-class production (production over the entire life time of a year-class) (PT) and turnover (P/BT) ratio, over 14 years at a total of 12 sites along the length of four contrasting tributaries. In addition, we explored whether the importance of recruitment and site depth for spatial and temporal variations in year-class production (PT), elucidated in previous studies, extends to annual production. 2. Large spatial (among sites) and temporal (among years) variation in annual production (range 1.9–40.3 g m−2 per year) and P/BA ratio (range 0.76–2.4 per year) typified these populations, values reported here including all the variation reported globally for salmonids streams inhabited by one or several species. 3. Despite substantial differences among streams and sites in all production attributes, when all data were pooled, annual (PA) and year-class production (PT) and annual (P/BA) and year-class P/BT ratios were tightly linked. Annual (PA) and year-class production (PT) were similar but not identical, i.e. PT = 0.94 PA, whereas the P/BT ratios were 4 + P/BA ratios. 4. Recruitment (Rc) and mean annual density (NA) were major density-dependent drivers of production and their relationships were described by simple mathematical models. While year-class production (PT) was determined (R2 = 70.1%) by recruitment (Rc), annual production (PA) was determined (R2 = 60.3%) by mean annual density (NA). In turn, variation in recruitment explained R2 = 55.2% of variation in year-class P/BT ratios, the latter attaining an asymptote at P/BT = 6 at progressively higher levels of recruitment. Similarly, variations in mean annual density (NA) explained R2 = 52.1% of variation in annual P/BA, the latter reaching an asymptote at P/BA = 2.1. This explained why P/BT is equal to P/BA plus the number of year-classes at high but not at low densities. 5. Site depth was a major determinant of spatial (among sites) variation in production attributes. All these attributes described two-phase trajectories with site depth, reaching a maximum at sites of intermediate depth and declining at shallower and deeper sites. As a consequence, at sites where recruitment and mean annual density reached minimum or maximum values, annual (PA) and year-class production (PT) and annual (P/BA) and year-class P/BT ratios also reached minimum and maximum values.

Interannual variability in phytoplankton blooms and plankton productivity over the Nova Scotian Shelf and in the Gulf of Maine

A 1D ecosystem model, driven by surface heat and wind forcing and relaxed toward observed salinity profiles, was applied to simulate the interannual and decadal scale variability of phytoplankton blooms and plankton production from 1984 to 2007 in the Nova Scotian Shelf (NSS) and Gulf of Maine (GoM) region. The model captured the mean observed timing and magnitude of the spring (SPB) and fall phytoplankton bloom (FPB) in both systems, as well as observed interannual variations in SPB peak timing. Model simulations for both the GoM and NSS exhibited marked inter- annual variability in SPB and FPB timing (±2 to 3 wk) and magnitude (up to ~1 mg chlorophyll m -3 ). Earlier SPBs and delayed FPBs are linked to enhanced water column stability generated by less saline surface water or sharper salinity gradients over the top 50 m of the water column. The modeled variation in annual primary productivity, mesozooplankton productivity, and particle export flux was modest (<10% of the mean). Years with high primary production were weakly associated with early SPBs (GoM: r = -0.205; NSS: r = -0.51), but there was no significant relationship with water column stability. This suggests that variation in annual productivity in the GoM and NSS reflects a combina- tion of variation in light limitation (which is alleviated by increased water column stability) and nutri- ent limitation (which is exacerbated by increased water column stability) that offset and are of near equal importance when averaged over the year. Interannual variations in fisheries production due to changes in annual productivity are thus likely secondary to profound shifts in fisheries recruitment and production that have been linked to variations in SPB and FPB timing.

Effects of asynchronous acorn production by co-occurring Quercus trees on resource utilization by acorn-feeding insects

To clarify the effects of asynchronous seed production among tree species on the population of seed predators, we investigated the relationship between the annual variation in production of mature acorns and the insect damage in those acorns of two sympatric oak species, Quercus variabilis Blume and Quercus serrata Thunb. ex Murray, over 4 years at two study sites. The annual variation in acorn production was noticeable, with a coefficient of variation (CV) at the two sites of 1.05 and 0.80 for Q. variabilis and 0.87 and 0.73 for Q. serrata. Annual fluctuation in acorn production by Q. serrata was synchronized between the two sites. Since annual fluctuation in acorn production was not synchronized between the two species, the CVs for the total acorn production by both oak species (0.83 and 0.62 at the two sites) were lower than those for Q. variabilis and Q. serrata alone. The rate of predation by the specialist predators (Curculio weevils) on the acorns of both species was not related to the annual acorn crop size. Prolonged diapause of Curculio weevils might stabilize their populations. The rate of acorn predation by the generalist predators (tortricid moths) was also not related to the annual crop size. Asynchronous acorn production by the two oak species would help to stabilize the population.

Impacts of climate on prey abundance account for fluctuations in a population of a northern wader at the southern edge of its range

AbstractUnderstanding the mechanisms by which climate change will affect animal populations is vital for adaptive management. Many studies have described changes in the timing of biological events, which can produce phenological mismatch. Direct effects on prey abundance might also be important, but have rarely been studied. We examine the likely importance of variation in prey abundance in driving the demographics of a European golden plover (Pluvialis apricaria) population at its southern range margin. Previous studies have correlated plover productivity with the abundance of their adult cranefly (Tipulidae) prey, and modelled the phenology of both plover breeding and cranefly emergence in relation to temperature. Our analyses demonstrate that abundance of adult craneflies is correlated with August temperature in the previous year. Correspondingly, changes in the golden plover population are negatively correlated with August temperature 2 years earlier. Predictions of annual productivity, based on temperature‐mediated reductions in prey abundance, closely match observed trends. Modelled variation in annual productivity for a future scenario of increasing August temperatures predicts a significant risk of extinction of the golden plover population over the next 100 years, depending upon the magnitude of warming. Direct effects of climate warming upon cranefly populations may therefore cause northward range contractions of golden plovers, as predicted by climate envelope modelling. Craneflies are an important food source for many northern and upland birds, and our results are likely to have wide relevance to these other species. Research into the potential for habitat management to improve the resilience of cranefly populations to high temperature should be an urgent priority.

Demography of the Helmeted Honeyeater (Lichenostomus melanops cassidix)

Understanding the demography of threatened taxa is essential for formulating effective management strategies for their conservation and for making predictions about their long-term prospects. With fewer than 25 breeding pairs in the current wild population, the Helmeted Honeyeater (Lichenostomus melanops cassidix) is one of the most threatened birds in Australia. Demography of the sole wild population of the Helmeted Honeyeater was investigated by monitoring 526 nests between 1984 and 1996 and 324 colour-banded birds between 1984 and 2008. Throughout the study, the population was effectively closed, there being no evidence of immigration or emigration. Mean survivorship of nests from laying to fledging was 0.17, and mean survivorship of juveniles (from 40 days to 1 year of age) was 0.63. Weighted mean annual survivorship of adult females and males was 0.75 and 0.81 respectively. The population showed little between-year variation in annual productivity and survivorship, with sufficient recruitment for positive population growth. In general, the population dynamics of the Helmeted Honeyeater fit the pattern of an ‘old endemic’ Australian passerine, with low survival of eggs and chicks, extended parental care of juveniles and high survivorship of juveniles and adults. Eggs and chicks that would not naturally survive are a resource that may be used to assist recovery of the population.

Mapping the effect of spatial and temporal variation in climate and soils on Eucalyptus plantation production with 3-PG, a process-based growth model

In the wet tropics, near the Atlantic Coast of Brazil, drought may reduce plantation yields by as much one-third over a six-to-seven-year rotation. For land owners, annual variation in production cannot be estimated with empirical models. In this paper, we examine whether the process-based growth model, 3-PG is sufficiently sensitive to climatic variation to provide a virtual record of changes in growing stock across 180,000 ha eucalypt plantation estate. We first mapped variation in climate and soil properties, and then ran simulations for the current planted forest with ages varying from one to seven years. Model predictions of stand volume and mean tree diameter agreed closely with measurements acquired on 60 reference plots monitored over the test period; the prediction of mean annual increment (MAI) was less reliable. Available soil water (ASW) and leaf area index (LAI) were also measured and compared with the model estimations. Vapour pressure deficit (VPD) and ASW accounted for most of the variation in yields. We conclude that this spatial modelling approach offers a reasonable alternative to extensive ground surveys, particularly when climatic variation extends beyond the historical average for a region.

Primary production in the Southern Ocean, 1997–2006

Estimates of primary production in the Southern Ocean are difficult to obtain but are essential if we are to understand its role in the global carbon cycle. Here we present a 9‐year time series of daily primary production calculated from remotely sensed ocean color, sea surface temperature, and sea ice concentration using a primary production algorithm parameterized specifically for use in Southern Ocean waters. Results suggest that total annual production in waters south of 50°S averaged 1949 ± 70.1 Tg C a−1 (where a is years) between 1998 and 2006, approximately half that of previous estimates. The large but relatively unproductive pelagic province accounted for ∼90% of Southern Ocean production, while area normalized rates of production were greatest on the much smaller continental shelf (109 g C m−2 a−1). Surprisingly, production in the marginal ice zone was only slightly higher than in the pelagic province. The Ross Sea was the most productive sector of the Southern Ocean (mean = 503 Tg C a−1), followed closely by the Weddell Sea (mean = 477 Tg C a−1). Unlike the Arctic Ocean, there was no secular trend in either sea ice cover or annual primary production in the Southern Ocean during our 9‐year study. Interannual variability in annual production was most closely tied to changes in sea ice cover, although changes in sea surface temperature also played a role. Only 31% of the variation in annual production was explained by the Southern Annular Mode. Annual primary production could increase in the future as stronger winds increase nutrient upwelling.

Long-term and large-scale variability in productivity of the tellinid bivalve Macoma balthica on Wadden Sea tidal flats

A series of 27 successive annual estimates of production of soft parts of the bivalve Macoma balthica (L.) populating the tidal flats of Balgzand (western Wadden Sea, The Netherlands) was obtained using multi-station (15 sites) and long-term (27 yr: 1978 to 2004, inclusive) monitoring data on numerical densities and ash-free dry mass (AFDM). Annual production values were esti- mated from seasonal growth increments, which were positive in spring and early summer and (in adults) negative in the remainder of the year, when up to 70% of individual weight gain of the preceding growing season was lost. Annual estimates based on twice-annual sampling were checked and refined on the basis of a detailed 2 yr study. Weight loss proportions increased with age of ani- mals and with water temperature in winter. Net annual somatic production of the entire population varied from 1 to 9 (27 yr mean: 2.9 ± 0.3) g AFDM m -2 yr -1 . Lifetime production per individual averaged 0.007 g AFDM for recruits of ~3 mo old and 0.032 g AFDM for ~10 mo olds. Numerical den- sities of ~10 mo old recruits predicted, within narrow limits, subsequent cohort production by way of a positive linear relationship. However, production of 3 mo old recruits was on average higher at low than at high densities, owing to better juvenile survival at low densities. Local (between-station) variation in mean annual production was primarily related to local variation in recruitment. However, production per recruit was significantly higher at low than at high intertidal levels, in accordance with higher growth and lower mortality rates at lower levels. Strong temporal and local variation was also found in annual production/biomass (P/ - B) ratio values, which reflected the variable age compo- sition of the population: P/ - B ratio values were augmented whenever mean age was low. Consistently higher mean P/ - B ratio values (~0.6 vs. ~0.4 yr -1 ) were found at high near-coast compared with low off-shore tidal flats, in accordance with higher mortality rates on high flats. Environmental factors affecting variation in annual production included between-year variability in recruitment (which was related to winter temperature and shrimp predation pressure) and growth (which was related to diatom abundance).

Variability in annual recruitment success as a determinant of long-term and large-scale variation in annual production of intertidal Wadden Sea mussels (Mytilus edulis)

AbstractTo understand the background of the strong variation and recent decline of stocks and production of mussels (Mytilus edulis) on tidal flats of the Wadden Sea, we analysed long-term (twice-annual for 26 years) and multi-station (15 sites) estimates of numbers, mean individual weights, biomass, and annual production on Balgzand, a 50-km2tidal-flat area in the westernmost part of the Wadden Sea (The Netherlands). Somatic production was estimated from summed growth increments of soft tissues per half-year period and expressed in ash-free dry mass (AFDM). In adults, positive values in spring/summer regularly alternated with negative values in autumn/winter, when up to ∼25% (mean: 14%) of individual weight gains in the preceding season were lost. No weight losses were observed during the first winter of the life of mussels. The 26-year mean of net somatic tissue production P amounted to 5.5 g AFDM m−2 a−1at a mean biomass B of 3.2 g AFDM m−2; the ratioP/Bvaried strongly with age composition of the mussel population and ranged between 0.5 and 3.0 a−1(mean: 1.7). Within the restricted areas of mussel beds, mean biomass and annual production values were two orders of magnitude higher. In the Wadden Sea, mussel beds cover a typical 1% of extensive tidal flat areas. Numerical densities of recruits showed straight-line relationships with subsequent life-time year-class production. Once recruits had reached an age of ∼10 months, their numbers predicted subsequent production within narrow limits. Production per recruit averaged 0.21 g AFDM for 10-mo recruits and was not related to recruit density. Local variation in annual production varied strongly, with maximal values between mid-tide and low-tide level, where recruitment was also maximal. Production per recruit was higher at low than at high intertidal levels. Frequently failing recruitment is indicated as the main cause of declining mussel stocks in the Wadden Sea. As in other bivalve species, a declining frequency of the occurrence of cold winters appears to govern declining recruitment success and consequently declining production.

Two- or three-layered box-models versus fine 3D models for coastal ecological modelling? A comparative study in the English Channel (Western Europe)

The general trend in ecosystem modelling is to improve the spatial resolution by shifting from rough box-models to fine 3D models. Despite the continuous speeding-up of computing, 3D models involving numerous state variables may remain intractable, especially for parameter calibration, when processes with long half-life periods (i.e, from years to decades) are introduced, such as the behaviour of organic matter in sediment and population dynamics of benthic species. In these cases, a first approach can be provided by fast-running box-models, if they take into account the most crucial hydrodynamic properties of the system. In a macrotidal shelf sea such as the English Channel, the long-term horizontal transport can be summarized by the tidal residual circulation, and the vertical stratification can be sketched by a two- or three-layered integral model. This paper compares the results obtained in the English Channel area by the same biogeochemical equations of pelagic primary production, coupled to 1) a two-layered box-model 2) a three-layered box-model (i.e., with an intermediate cline layer between surface and bottom ones) and 3) a fine-gridded 3D model. Comparison is focused firstly on thermal stratification and summer dinoflagellate blooms in the north-western Channel and secondly on the haline stratification and the sequence of blooms obtained in the eutrophicated Seine river plume. Comparison shows that box-models act as low-pass filters which reproduce correctly the weekly mean time-course, but greatly reduce the variance locally observed in a tide-oscillating plume region. As far as global characteristics are concerned, such as the annual primary production, or the percentage of variation in annual production after reducing the nutrient loadings, the box and 3D models gave very similar results. This conclusion reinforces the usefulness of using box-models as a first approach in long-term processes, for which a long transient phase is expected before reaching the annual periodic solution.

Modeling spatial dynamics of episodic and synchronous reproduction by plant populations: the effect of small‐scale pollen coupling and large‐scale climate

AbstractMany plant species show masting, intermittent and synchronized reproduction at population level. In the present paper, we review the resource‐based model providing a theoretically plausible physiological mechanism underlying masting. In the model, a non‐linear allocation of energy reserves is considered: plants accumulate photosynthate every year, produce flowers when the energy reserve level exceeds a threshold, and set seeds at a rate limited by pollen availability. The model predicted that individual plants alter their reproductive dynamics from annual to intermittent depending on how heavily the plant invests resource in reproduction. When fruit production is limited by the availability of outcross pollen, a plant population showed diverse reproductive behavior such as completely synchronized or desynchronized reproduction. Spatial scale of reproductive synchrony tended to be a few times larger than the range of direct pollen exchange. Impact of climatic fluctuation correlated at a large spatial scale was also investigated as an alternative synchronizing factor. The variation in annual productivity and the reproductive threshold induced from climatic fluctuation was accounted for by incorporating an additional term in the model. When plants show a 2 year reproductive cycle, highly synchronized reproduction at a regional scale was induced due to correlated environmental forcing, but reproductive synchrony with long intermast periods was realized only when pollen coupling and environmental forcing were at work. These results suggest that distance‐dependent processes, such as pollen exchange between nearby trees, induce synchrony at a local scale and external environmental forcing correlated at geographically large scales works to strengthen and maintain such a synchrony.

Estimates of genetic parameters and expected genetic gains with selection in robust coffee

The present paper aimed to study the genetic variation of 15 half-sib progenies of robust coffea ( Coffea canephora Pierre). The trial was conducted at the Instituto Agronomico de Campinas (IAC/APTA) in a randomized complete block design with seven replications and one tree-plot. Annual and joint analyses of variance were obtained to estimate the genetic paramet ers for yield, in order to quantify the genetic gain from selection in eight production years. The genotypic variation coefficient s indicated expressive genetic variability for improvement of the yield. On account of the high variation in annual production, it is recommended that selection should be based on the general mean of the years. In low yield years, larger heritability values, coefficients of genetic variation, index of genotypic determination, and genetic gains were estimated.