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Late Season (late + season)
Selected AbstractsSeasonal trophic dynamics affect zooplankton community variabilityFRESHWATER BIOLOGY, Issue 11 2009BEATRIX E. BEISNER Summary 1. The degree to which communities are variable may be affected by the ecological conditions to which they are exposed and can affect their propensity to form alternative states. We examined the influence of two common ecological factors, predation and seasonal successional stage, on the variability in community composition of herbivorous pond plankton. In a highly replicated, two factor, mesocosm experiment we determined whether beta diversity was affected by seasonal successional stage of the community (two levels), by fish predation (presence/absence) or by their interaction. 2. Several significant changes were found in the composition of the rotifer, cladoceran and copepod assemblages. Most cladoceran abundances showed sharp declines in the presence of fish, while some rotifers, as well as their assemblage species richness, responded favourably to fish. The copepod assemblage was composed of omnivorous and carnivorous species, which added invertebrate predation to the experiment and which intensified as the season progressed. Copepods showed responses to fish predation that depended on seasonal successional stage of the initial community, because of changes in their stage structure and edibility as they grew from nauplii to adults. 3. Community variability was consistently high at the end of each month-long experimental period for both cladoceran and rotifer assemblages, except under two conditions. In the early season treatments, the rotifer assemblages were more consistent (lower beta diversity) in the presence of fish. This was attributed to high population growth rates for rotifers under these ecological conditions because of reduced copepod predation on them through a trophic cascade from fish. Low community variability was also observed in the late season for rotifers when fish were excluded and, as a result, they were exposed to high invertebrate predation from cyclopoid copepods. 4. Results from the early season support theoretical predictions that when community size increases, variability in composition should decline because of an increase in competitive processes over stochastic ones. Late season results suggest that a second mechanism, specialist predation, can also reduce prey community variability. Our study demonstrates that plankton communities may be more predictable under certain trophic web configurations and challenges ecologists to find ways to incorporate such inherent variability into experiments and community theory. [source] Partitioning sources of soil respiration in boreal black spruce forest using radiocarbonGLOBAL CHANGE BIOLOGY, Issue 2 2006Edward A.G. Schuur Abstract Separating ecosystem and soil respiration into autotrophic and heterotrophic component sources is necessary for understanding how the net ecosystem exchange of carbon (C) will respond to current and future changes in climate and vegetation. Here, we use an isotope mass balance method based on radiocarbon to partition respiration sources in three mature black spruce forest stands in Alaska. Radiocarbon (,14C) signatures of respired C reflect the age of substrate C and can be used to differentiate source pools within ecosystems. Recently-fixed C that fuels plant or microbial metabolism has ,14C values close to that of current atmospheric CO2, while C respired from litter and soil organic matter decomposition will reflect the longer residence time of C in plant and soil C pools. Contrary to our expectations, the ,14C of C respired by recently excised black spruce roots averaged 14, greater than expected for recently fixed photosynthetic products, indicating that some portion of the C fueling root metabolism was derived from C storage pools with turnover times of at least several years. The ,14C values of C respired by heterotrophs in laboratory incubations of soil organic matter averaged 60, higher than the contemporary atmosphere ,14CO2, indicating that the major contributors to decomposition are derived from a combination of sources consistent with a mean residence time of up to a decade. Comparing autotrophic and heterotrophic ,14C end members with measurements of the ,14C of total soil respiration, we calculated that 47,63% of soil CO2 emissions were derived from heterotrophic respiration across all three sites. Our limited temporal sampling also observed no significant differences in the partitioning of soil respiration in the early season compared with the late season. Future work is needed to address the reasons for high ,14C values in root respiration and issues of whether this method fully captures the contribution of rhizosphere respiration. [source] Diet selection of dry and lactating beef cows grazing extensive pastures in late autumnGRASS & FORAGE SCIENCE, Issue 4 2006A. Farruggia Abstract The diet selection, made by twelve dry and twelve lactating spring-calving Salers beef cows at the end of the grazing season on an extensively grazed natural mountain pasture in central France, was compared. Sward structure, selection bites, daily grazing time and digestibility of the diet were measured in mid-October (P1) and mid-November (P2). Live weights were measured twice monthly throughout the experiment. Daily milk production was assessed in the week before the grazing behaviour measurements. Lactating cows grazed more selectively than dry cows: they took more bites on green patches (0·20 vs. 0·13 of total bites, P < 0·01; Jacob's selectivity index: 0·13 vs. ,0·25, P < 0·001), which is consistent with the higher overall nitrogen concentration in faeces (18·1 vs. 17·3 g kg,1 DM, P < 0·05). Lactating cows tended to slightly increase their daily grazing time compared with dry cows (on average 9·9 vs. 9·5 h, P = 0·07) and grazed faster in mid-November (74 vs. 69 bites min,1, P < 0·05). The lactating cows lost more live weight (,24 vs. ,12 kg cow,1, P < 0·05) between P1 and P2. A positive correlation was found between consumption of green patches by lactating cows and their daily milk production in P2 (r = 0·574, P = 0·05), whereas no correlation occurred between individual milk production and liveweight loss. Dry cows were less selective, which supports management practices that promote the use of cows with low requirements on extensively grazed pastures in late season. [source] Seasonal patterns of growth, expenditure and assimilation in juvenile Atlantic salmonJOURNAL OF ANIMAL ECOLOGY, Issue 6 2002Wayne Jones Summary 1We report a modelling study of a data-set describing the growth of individual Atlantic salmon (Salmo salar L.) parr in the Girnock Burn (Scotland). A development of the compensatory growth model due to Broekhusien et al. (1994) was fitted to these data by numerical optimization. 2The model uses carbon mass as a surrogate for an energy currency. This mass is divided into structure and reserve components, so as to describe decoupled changes in length and wet-weight. 3Using the same parameters for all fish, our model explained 83% of the variability in length and weight at age. Adding a single additional parameter for each individual enabled the model to explain over 96% of length and weight variability. 4Weak negative correlation between size at first capture and within-study growth argues against genetic causality of observed growth variability. 5The energetic basis of our model enables us to infer time-series of net assimilation and basal maintenance rates for the observed individuals. Maximal growth occurs early in the season when high assimilation is accompanied by low temperatures and maintenance rates. In late season, continuing high assimilation is balanced by high maintenance rates consequent on summer temperatures. [source] Insect pests and natural enemies in two varieties of quinua (Chenopodium quinoa) at Cusco, PeruJOURNAL OF APPLIED ENTOMOLOGY, Issue 6 2002E. Yábar The quinua varieties differ, among other traits, in their content of saponins (secondary metabolites associated to plant resistance) late in the season. Whereas Agromyzidae and Cicadellidae were abundant only in the early season, both Chrysomelidae and Aphididae populations showed fluctuations. Likewise, Araneae and Braconidae showed fluctuating numbers during the season. The abundance of Coccinellidae peaked at mid-season whereas that of Syrphidae was high only in the late season. Although the overall abundance of insects was very similar in both varieties of quinua, there were different patterns depending on the season. In the early season there was a tendency towards greater insect numbers on Blanca, but in contrast, in the late season Amarilla (the high-saponin variety) had a higher load of insect pests. This suggests that saponins do not play a major role in quinua resistance against insects. In the early season, no significant relationship between pests and natural enemies held across quinua varieties. In the late season, Aphididae and Coccinellidae were negatively and significantly correlated in both varieties. The temporal population dynamics of Aphididae and both Coccinellidae and Braconidae resembled the traditional predator,prey dynamics. [source] Developmental change in RNA: DNA ratios of fed and starved laboratory-reared Japanese flounder larvae and juveniles, and its application to assessment of nutritional condition for wild fishJOURNAL OF FISH BIOLOGY, Issue 4 2001W. S. Gwak Starved Japanese flounder Paralichthys olivaceus larvae were characterized by relatively lower levels of RNA content throughout their early life stages. Significant differences in the RNA: DNA ratios were found between fed and starved fish, and appeared to increase as starvation proceeded. Ontogenetic changes in RNA: DNA ratios were clearly observed during metamorphosis, especially decreasing during the period from the late-metamorphic to postmetamorphic stages. The criteria established from these laboratory experiments, were applied to the nutritional condition of wild larvae and juveniles collected in Wakasa Bay, Sea of Japan in 1994 and 1995 by measuring RNA and DNA content. Starved fish were mainly found in stage I (settling stage) fish during the late season of settlement in 1995. This suggests that starvation could be associated with settlement in Japanese flounder. [source] Seasonal changes in pollinator activity influence pollen dispersal and seed production of the alpine shrub Rhododendron aureum (Ericaceae)MOLECULAR ECOLOGY, Issue 4 2006A. S. HIRAO Abstract In alpine ecosystems, microscale variation in snowmelt timing often causes different flowering phenology of the same plant species and seasonal changes in pollinator activity. We compared the variations in insect visitation, pollen dispersal, mating patterns, and sexual reproduction of Rhododendron aureum early and late in the flowering season using five microsatellites. Insects visiting the flowers were rare early in the flowering season (mid-June), when major pollinators were bumblebee queens and flies. In contrast, frequent visitations by bumblebee workers were observed late in the season (late July). Two-generation analysis of pollen pool structure demonstrated that quality of pollen-mediated gene flow was more diverse late in the season in parallel with the high pollinator activity. The effective number of pollen donors per fruit (Nep) increased late in the season (Nep = 2.2,2.7 early, 3.4,4.4 late). However, both the outcrossing rate (tm) and seed-set ratio per fruit were smaller late in the season (tm = 0.89 and 0.71, seed-set ratio = 0.52 and 0.18, early and late in the season, respectively). In addition, biparental inbreeding occurred only late in the season. We conclude that R. aureum shows contrasting patterns of pollen movement and seed production between early and late season: in early season, seed production can be high but genetically less diverse and, during late season, be reduced, possibly due to higher inbreeding and inbreeding depression, but have greater genetic diversity. Thus, more pollinator activity does not always mean more pollen movement. [source] Quantification of effects of season and nitrogen supply on tree below-ground carbon transfer to ectomycorrhizal fungi and other soil organisms in a boreal pine forestNEW PHYTOLOGIST, Issue 2 2010Mona N. Högberg Summary ,The flux of carbon from tree photosynthesis through roots to ectomycorrhizal (ECM) fungi and other soil organisms is assumed to vary with season and with edaphic factors such as nitrogen availability, but these effects have not been quantified directly in the field. ,To address this deficiency, we conducted high temporal-resolution tracing of 13C from canopy photosynthesis to different groups of soil organisms in a young boreal Pinus sylvestris forest. ,There was a 500% higher below-ground allocation of plant C in the late (August) season compared with the early season (June). Labelled C was primarily found in fungal fatty acid biomarkers (and rarely in bacterial biomarkers), and in Collembola, but not in Acari and Enchytraeidae. The production of sporocarps of ECM fungi was totally dependent on allocation of recent photosynthate in the late season. There was no short-term (2 wk) effect of additions of N to the soil, but after 1 yr, there was a 60% reduction of below-ground C allocation to soil biota. ,Thus, organisms in forest soils, and their roles in ecosystem functions, appear highly sensitive to plant physiological responses to two major aspects of global change: changes in seasonal weather patterns and N eutrophication. [source] Insect herbivores and their frass affect Quercus rubra leaf quality and initial stages of subsequent litter decompositionOIKOS, Issue 1 2008Christopher J. Frost Defoliation-induced changes in plant foliage are ubiquitous, though factors mediating induction and the extent of their influence on ecosystem processes such as leaf litter decomposition are poorly understood. Soil nitrogen (N) availability, which can be affected by insect herbivore frass (feces), influences phytochemical induction. We conducted experiments to test the hypotheses that insect frass deposition would (1) reduce phytochemical induction following herbivory and (2) increase the decomposition and nutrient release of the subsequent leaf litter. During the 2002 growing season, 80 Quercus rubra saplings were subjected to a factorial experiment with herbivore and frass manipulations. Leaf samples were collected throughout the growing season to measure the effects of frass deposition on phytochemical induction. In live foliage, herbivore damage increased tannin concentrations early, reduced foliar N concentrations throughout the growing season, and lowered lignin concentrations in the late season. Frass deposition apparently reduced leaf lignin concentrations, but otherwise did not influence leaf chemistry. Following natural senescence, litter samples from the treatment groups were decomposed in replicated litterbags for 18 months at the Coweeta Hydrologic Laboratory, NC. In the dead litter samples, initial tannin concentrations were lower in the herbivore damage group and higher in the frass addition group relative to their respective controls. Tannin and N release rates in the first nine months of decomposition were also affected by both damage and frass. However, decomposition rates did not differ among treatment groups. Thus, nutrient dynamics important for some ecosystem processes may be independent from the physical loss of litter mass. Overall, while lingering effects of damage and even frass deposition can therefore carry over and affect ecosystem processes during decomposition, their effects appear short lived relative to abiotic forces that tend to homogenize the decomposition process. [source] Thermal history regulates methylbutenol basal emission rate in Pinus ponderosaPLANT CELL & ENVIRONMENT, Issue 7 2006DENNIS W. GRAY ABSTRACT Methylbutenol (MBO) is a 5-carbon alcohol that is emitted by many pines in western North America, which may have important impacts on the tropospheric chemistry of this region. In this study, we document seasonal changes in basal MBO emission rates and test several models predicting these changes based on thermal history. These models represent extensions of the ISO G93 model that add a correction factor Cbasal, allowing MBO basal emission rates to change as a function of thermal history. These models also allow the calculation of a new emission parameter Estandard30, which represents the inherent capacity of a plant to produce MBO, independent of current or past environmental conditions. Most single-component models exhibited large departures in early and late season, and predicted day-to-day changes in basal emission rate with temporal offsets of up to 3 d relative to measured basal emission rates. Adding a second variable describing thermal history at a longer time scale improved early and late season model performance while retaining the day-to-day performance of the parent single-component model. Out of the models tested, the Tamb,Tmax7 model exhibited the best combination of day-to-day and seasonal predictions of basal MBO emission rates. [source] Seasonal sex role changes in the blenniid Petroscirtes breviceps, a nest brooder with paternal careJOURNAL OF FISH BIOLOGY, Issue 1 2006J. Shibata The plasticity of the sex roles in the blenniid fish Petroscirtes breviceps, a nest brooder with exclusive paternal care, was studied throughout an 8 month breeding season. Males performed most courtships early and late in the breeding season, whereas females performed most in the middle of the season. These results indicated that the sex of individuals initiating courtship changed seasonally, with courtship role reversal in the middle of the season. Intrasexual aggression in both sexes occurred much more frequently in mid-season than in the early and late seasons. Males frequently fought when available nest sites were limited, regardless of the presence of females, suggesting that males competed for nests in order to qualify to mate (resource competition). In contrast, courting females fought only in mid-season, when females' relative success in entering nests decreased, indicating that females competed for limited mating opportunities (mating competition). The reversed courtship roles and female mating competition in mid-season suggested that the sex roles in P. breviceps changed seasonally from the conventional roles to reversed roles and back again during one breeding season. This study provides the first empirical evidence of multiple changes in the sex roles of animals within a breeding season. [source] Glucose, fructose and sucrose content in broccoli, white cabbage and Portuguese cabbage grown in early and late seasonsJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 12 2001Eduardo Rosa Abstract Consumption of Portuguese cabbage and white cabbage is very high in Portugal, but diets including broccoli have been highly recommended owing to recognition of the health-protective effects of secondary plant metabolites. Broccoli production is generally concentrated in the summer/winter season, but the demand for a fresh product throughout the year requires production in other seasons. Sugars might affect flavour and the acceptance of broccoli by consumers. This study reports the free fructose, glucose and sucrose content in primary and secondary inflorescences of 11 cultivars of broccoli, one white cabbage and four Portuguese cabbages grown in early (March,July) and late (August,January) seasons in the northern region of Portugal. On average the results show that the total free sugar content in the broccoli cultivars, except for cv Marathon, is significantly (P,<,0.05) lower than in the other cabbages. Fructose was the major sugar in the three types of Brassica, representing between 48.8 and 56.9% of the total sugar content in broccoli cvs Marathon and Senshi respectively and between 48.7% (cv Mirandela) and 53.8% (cv Murciana) in the other cabbages. Glucose was the second major sugar, while sucrose represented a maximum of 20.5% in broccoli cv Shogun and 11.1% in cv Murciana. The growing season influenced the free sugar content, with generally higher levels in the spring/summer than in the summer/winter season in broccoli, while an opposite tendency was noted in the other Brassica species. In broccoli the sugar levels in the primary inflorescences were generally lower than in the secondary inflorescences, except for sucrose. © 2001 Society of Chemical Industry [source] | ||||||||||||||||||||||