Dry-season spawning in a cyprinid fish of southern India

Synopsis A population of the S. Indian cyprinid fishBarbus melanampyx was sampled monthly through 24 months. Seasonal cycles of the gonado-somatic index (GSI), ovarian stages, male breeding tubercles, spawning behaviour and population structure were assessed. These fish breed strictly seasonally during the main dry period: December/January through April. Comparison with other Barbus species of the same general region led to the conclusion that the patterns of reproductive investment ofB. melanampyx are similar to those of perennial species, and different from those of wet-season spawners. The reasons for this rather unexpected result were found in the more constant conditions prevailing during a dry season as compared to the monsoon. It was argued thatB. melanampyx and the species spawning perennially are in effect small-brood spawners, rather than partial spawners.     

Seasonal growth activity of local and foreign gracilarioid strains in Israel

Six gracilarioid strains originating from different climatical environments were cultured in two cultivation systems: a short-term indoor one with a cross gradiant table, and a long-term outdoor one. Seasonal growth performances of the different strains were determined. The growth results in the two culture systems showed similar trends. The tropical species.Gracilaria cornea andG. cornea mutant, showed highest growth rates during summer and no growth at all during winter. The temperate species,Gracilaria verrucosa andGracilariopsis lemaneiformis, showed best growth performances during winter with small fluctuations between seasons. The subtropical speciesGracilaria conferta (local) showed seasonal growth fluctuations all over the year. The foreign species definitely did not acclimate under local conditions, but successfully preserved their original response to temperature. Regression equations confirmed that temperature was the dominant environmental variable in most of the gracilarioid strains. The growth rate results obtained showed encouraging prospects for high algal productivity as compared to other cultivation systems. Seasonal cultivation strategy ofGracilaria spp. in Israel is discussed.     

热带胶茶人工群落中土壤动物季节变化的研究

热带胶茶人工群落中土壤动物季节变化的研究邓晓保（中国科学院昆明生态研究所,６５０２２３）ＳｅａｓｏｎａｌＶａｒｉａｔｉｏｎｏｆＳｏｉｌＡｎｉｍａｌｓｉｎＭａｎ－ＭａｄｅＲｕｂｂｅｒ－ＴｅａＣｏｍｍｕｎｉｔｙｉｎＴｒｏｐｉｃｓ．￥ＤｅｎｇＸｉ－ａｏｂａ...     

Estimating regional carbon stocks and spatially covarying edaphic factors using soil maps at three scales

Most estimates of regional and global soil carbon stocks are based on extrapolations of mean soil C contents for broad categories of soil or vegetation types. Uncertainties exist in both the estimates of mean soil C contents and the area over which each mean should be extrapolated. Geographic information systems now permit spatially referenced estimates of soil C at finer scales of resolution than were previously practical. We compared estimates of total soil C stocks of the state of Maine using three methods: (1) multiplying the area of the state by published means of soil C for temperate forests and for Spodosols; (2) calculating areas of inclusions of soil taxa in the 1:5,000,000 FAO/UNESCO Soils Map of the World and multiplying those areas by selected mean carbon contents; and (3) calculating soil C for each soil series and map unit in the 1:250,000 State Soil Geographic Data Base (STATSGO) and summing these estimates for the entire state. The STATSGO estimate of total soil C was between 23% and 49% higher than the common coarse scale extrapolations, primarily because STATSGO included data on Histosols, which cover less than 5% of the area of the state, but which constitute over one-third of the soil C. Spodosols cover about 65% of the state, but contribute less than 39% of the soil C. Estimates of total soil C in Maine based on the FAO map agreed within 8% of the STATSGO estimate for one possible matching of FAO soil taxa with data on soil C, but another plausible matching overestimated soil C stocks. We also compared estimates from the 1:250,000 STATSGO database and from the 1:20,000 Soil Survey Geographic Data Base (SSURGO) for a 7.5 minute quadrangle within the state. SSURGO indicated 13% less total soil C than did STATSGO, largely because the attribute data on depths of soil horizons in SSURGO are more specific for this locality. Despite localized differences, the STATSGO database offers promise of scaling up county soil survey data to regional scales because it includes attribute data and estimates of areal coverage of C-rich inclusions within map units. The spatially referenced data also permit examination of covariation of soil C stocks with soil properties thought to affect stabilization of soil C. Clay content was a poor predictor of soil C in Maine, but drainage class covaried significantly with soil C across the state.     

Biomass structure and dry matter dynamics of subtropical alluvial and exotic Ligustrum forests at the Río de la Plata,Argentina

Biomass, litterfall, litter standing crop, and decomposition was studied in a native subtropical alluvial forest locally known as Selva Marginal (SM) and an exotic Ligustrum lucidum forest (LF) at the Reserva Integral de Punta Lara, Buenos Aires Province, 34°47S and 58°1W. The alluvial forest site was at the southern limit of distribution of subtropical forests in South America. The Ligustrum forest was invading disturbed areas. Total biomass was 147.7 Mg/ha (86% aboveground and 14% belowground) in the SM, and 71.4 Mg/ha (93% and 7%, respectively) in the LF. Litterfall was 10.3 Mg/ha·yr and 13.8 Mg/ha·yr respectively. Annual leaf decomposition rate was greater for Ligustrum (k=4.07) than for SM species (k=1.48). The mean residence time of aboveground biomass was 12 yr for the SM and 5 yr for the LF. The k₁ values (litterfall/standing crop) were 1.9 and 2.0 for SM and LF respectively. The influence of coastal road and wall in the hydroperiod, native forested wetland ecosystem survival and exotic forest invasion is discussed.     

The feeding rates ofPleurobrachia (ctenophora) andSagitta (chaetognatha), with notes on the potential seasonal role of planktonic predators in the dynamics of north sea zooplankton communities

The zooplankton off the north-east coast of England has been the subject of a number of studies focusing on its productivity. It has also been shown to be representative of the zooplankton of much of the western North Sea. The community contains a number of predatory species, three of which are widely described as ‘voracious’, the ctenophorePleurobrachia pileus, the chaetognathSagitta elegans and the hyperiid amphipodThemisto compressa (≡ Parathemisto gaudichaudi). This study investigates the role of these planktonic predators in this community, with special reference to the seasonal changes in predation pressure. The functional response ofPleurobrachia pileus feeding onAcartia was determined from laboratory experiments. It was found to be linear at prey densities typical of UK coastal waters, although the linear relationship appeared to break down at low and high prey densities. Feeding rate data forSagitta elegans were obtained from gut content analysis and published laboratory derived estimates of digestion time. Of the 1,789 individuals examined 198 (11.1%) had food remains in the gut. A linear relationship betweenSagitta length and prey size was established and the daily feeding rate ofSagitta elegans was estimated to be 0.4 prey items d⁻¹ ind⁻¹. For comparative purposes, the proportion of the copepod standing stock removed bySagitta elegans, Pleurobrachia pileus andThemisto gaudichaudi was estimated for each month of the year. From this model it was shown thatThemisto applied the most predation pressure, andSagitta elegans applied the least predation pressure of the three planktonic predators considered. The impact ofPleurobrachia will be to a large extent offset due to its peak of seasonal abundance coinciding with the zooplankton peak in the summer.     

Biology of the bamboo Chusquea culeou (Poaceae: Bambusoideae) in southern Argentina

Over a period of 7 years the biology and phenotypic variability of Chusquea culeou were studied at 5 locations in cool temperate forests of southern Argentina. Excavated rhizomes had an average of 1.1 successful rhizome buds, and an average of 2.1 years elapsed between successive generations of rhizomes. Rhizome buds usually develop within the first four years after a rhizome forms. Height, volume and weight of a culm can be calculated from its diameter 1 m above the ground. Culm size, length of foliage leaf blades, and pattern of secondary branching differed among study sites. Dead culms were numerous and commonly remained erect for more than 7 years after dying. New culm shoots appear in spring and reach full size within a few months. Shoots can grow more than 9 cm/day. Less than half of the shoots survived a year; most were killed by moth larvae. Multiple primary branch buds emerge through the culm leaf sheaths in the second spring. The mean number of branch buds at mid-culm nodes varied between 34.8 and 81.5, and the mean number of primary branches was between 22.8 and 40.8. Number and length of branches, and number and length of foliage leaf blades at each node is related to the position of the node on a culm. Most branches grow about 3 cm and produce 1 to 3 foliage leaves annually. Foliage leaf blades generally live 2 years or more; few survive 6 years. Relative lengths of foliage leaf blades and their spacing along a branch permit recognition of annual cohorts.Both gregarious and sporadic flowering have been reported, and every year a few isolated plants flower and die. Length of the life cycle is unknown. Seedlings require up to 15 years to produce culms of mature size. Foliage branches may live more than 23 years, and culms may survive 33 years. Extensive loss of new shoots to predation suggests that gregarious flowering may be driven by a need to escape parasitism. C. culeou clumps expand slowly. Average annual rate of increase of the number of live culms in a clump was 4.6%. Methods of seed dispersal are undocumented. A dense stand of Chusquea culeou had an estimated phytomass of 179 tons/hectare (dry weight), 28% of which was underground. Net annual production was about 16 t/ha dry weight.     

热带－亚热带森林中猕猴的食性

采用跟踪观察法对热带－亚热带森林中的猕猴种群的食性及其与植被类型的关系进行了调查,结果表明,猕猴主要选择季雨林或次生季雨林为其觅食场所,栖息地植物的地理分布和种类直接影响其食性,猕猴对植物各部位的采食频度随植物生长期而变化．     

Seasonal variations of P compounds and their concentrations in two coastal lagoons (Herault,France)

This article concerns seasonal variations in the phosphate concentrations in two coastal lagoons near Montpellier (Mediterranean coast, France). The o-P concentration in the overlying water is highest during summer. The role of the sediment, particularly that of the different P fractions in the sediment, is discussed. Significant variations, especially in the FeOOH ≈ P fraction, occur. For both Tot-P_sed and the Fe00H≈P fraction a gradient from surface to bottom is observed, as well as a distinct decrease in the FeOOH≈P fraction in the surface sediments during summer and autumn. Variations in the FeOOH≈P fraction appear to be compensated by variations in the CaC0₃≈P fraction. These variations appear to be determined by the ferric hydroxide concentration. This compound represents only a small part (maximally 15%) of the total iron in the sediments and is related to the dissolved oxygen content of the immediately overlying water. Besides the fractions o-P, Fe(OOH)≈P, a large part of the CaC0₃≈P fraction is potentially bioavailable. A large proportion of the Tot-P_sed is therefore bioavailable.[/p]     

Seasonal succession of phytoplankton in a lake of the Paraná river floodplain,Argentina

Phytoplankton biomass, morphological and taxonomic composition, species diversity and productivity were analyzed in a shallow lake of the Middle Paraná River floodplain (El Tigre, 31 ° 41 S and 60° 42 W), between November 1986 and July 1988. Lake inundation (filling and through-flow phases) constituted an intense long-term perturbation in the physical and chemical environment. As the lake filled with river water, K-selected species (netplanktonic filamentous bluegreens, > 37 µm, with low surface area/volume (SA/V) ratios) that had existed prior to filling (late spring 1986) were replaced in summer-fall by r-selected species (nannoplanktonic chlorophytes and cryptophytes, < 37 µm, mainly stout forms with high SA/V ratios). During the through-flow phase, lentic phytoplankton was replaced by lotic flagellate populations due to the direct flushing by river water. During the period of falling water (drainage and isolation phases), nanoplanktonic algae with similar characteristics to those of the filling phase dominated in late winter-spring. Later in the isolation phase, these were succeeded by K-selected species (netplanktonic algae, mainly motile spherical dinoflagellates and filamentous bluegreens with low SA/V ratios). Simultaneously, primary production per unit biomass decreased and total biomass and specific diversity increased. Seasonal changes of phytoplankton in floodplain lakes can be interpreted as the interaction between true successional development (as observed in the drainage and isolation phases) and intermediate disturbance. Using Reynolds' terminology, short-term disturbance (slight inflow of nutrient-rich river water) caused reversion to an earlier stage in the former succession, and long-term disturbance (lake inundation) truncated the successional progression and a new (or shifted) succession was initiated.