Dolphin sympatric ecology

Interspecific associations between two or more species of the family Delphinidae have been reported by many scientists, but the sympatric ecology of such dolphin associations has not been studied in great detail. A few field investigations have been conducted on this subject in different parts of the world on species such as bottlenose dolphins (Tursiops spp.), short-beaked common dolphins (Delphinus delphis), and killer whales (Orcinus orca). Sympatric dolphins seem to use different strategies to co-exist when resources appear to be limited, including dietary divergence (different prey preference, slightly diverse diet, different feeding time) and/or different habitat use (shallow versus deep waters, flat areas versus submarine canyons and escarpments, different travel routes). This paper presents a review of some well-studied dolphin species found in sympatry and discusses the nature of habitat and resource partitioning as well as studies on aggressive behaviour displayed by species living in the same habitat.     

The dietary basis for temporal partitioning: food habits of coexisting Acomys species

Two rodent species of the genus Acomys coexist on rocky terrain in the southern deserts of Israel. The common spiny mouse (A. cahirinus) is nocturnally active whereas the golden spiny mouse (A. russatus) is diurnally active. An early removal study suggested that competition accounts for this pattern of temporal partitioning: the golden spiny mouse is forced into diurnal activity by its congener. Theoretically, temporal segregation should facilitate coexistence if the shared limiting resources differ at different times (primarily among predators whose prey populations have activity rhythms), or if they are renewed within the period of the temporal segregation. We studied food preferences of the two Acomys species in a controlled cafeteria experiment in order to assess resource overlap and the potential for competition for food between the two species. We found no significant difference in food preferences between species. The dietary items preferred by both were arthropods. We also carried out a seasonal study of the percentage and identity of arthropods taken in the field by individuals of the two species. Individuals of both species took on annual average a high percentage of arthropods in their diets. Seasonal diet shifts reflect seasonal abundance of arthropods at Ein Gedi during day and night. Diurnal activity may also reduce interspecific interference competition between A. russatus and A. cahirinus. However, the strong interspecific dietary overlap in food preference, the heavy reliance on arthropods in spiny mouse diets, and the seasonal and circadian differences in arthropod consumption suggest that prey partitioning may be a viable mechanism of coexistence in this system. Received: 6 July 1998 / Accepted: 10 May 1999     

Effects of intermittent exposure to high atmospheric CO2 on vegetative growth in soybean

Short-term exposure to high CO₂ increases rates of photosynthesis and growth in soybeans, but with prolonged high CO₂ exposure, these high rates are sometimes not maintained. Growth of soybean (Glycine max (L.) Merrill cv. Fiskeby V) seedlings kept for 25 days at atmospheres of 350 or 1000 μ/l CO₂ was compared with growth of plants given 2, 4 or 6 day alternating exposure to high and low CO₂ levels (13 days of total exposure to each level). Final dry weight of plants increased with number of days in high CO₂ but leaf areas were not greatly affected. Thus dry weight gains per unit leaf area (net assimilation rates) were higher in high CO₂ than in low CO₂ throughout the entire period of the experiment and the pattern of exposure to high CO₂ did not affect the rate of dry weight gain in high CO₂.     

Translocation of photoassimilate from leaves of two popyploid genotypes of tall fescue differing in photosynthetic rates

The photosynthetic rate of a decaploid genotype (1-16-2) of tall fescue ( Festuca arundinacea Schreb.) is about twice that of a common hexaploid genotype (V6-802) (Plant Physiol. 72: 16–21, 1983). Translocation of photosynthate out of the leaves is a possible means of regulating carbon assimilation. To evaluate this possibility, we have examined a) translocation velocity, b) time course of translocation from leaves, c) photoassimilate partitioning pattern into whole plants in pulse and chase experiments, and d) interveinal distances between two ploidy genotypes. Most of the ¹⁴C accumulated in sucrose, and the labelled carbon moved down the leaf blades at similar velocities (6 to 10 cm h⁻¹) in both genotypes. Recent ¹⁴C assimilate was rapidly translocated from the fed area of the leaf blade. For example, the decaploid and the common hexaploid had translocated 40 and 26% of the ¹⁴C, respectively, at 6 h, and 79 and 49% of the ¹⁴C, respectively, at 24 h. Partitioning of ¹⁴C among plant organs was considerably different between the genotypes after a 24 h chase. For example, out of the total ¹⁴C recovered from the whole plant, the decaploid had retained 40% in the labelled leaf with 10, 33 and 29% in other leaves, stem bases and roots, respectively; whereas the hexaploid had retained 91% in the labelled leaf with 4, 3 and 2% in other leaves, stem bases and roots, respectively. However, the higher rate of translocation was correlated with greater interveinal distances in the decaploid genotype. These results suggested that the higher translocation percentage in the decaploid than the hexaploid genotype was due to greater sink activity.     

美洲森林群落beta多样性的纬度梯度性

Beta多样性度量不同时空尺度物种组成的变化,是生物多样性的重要组成部分;理解其地理格局和形成机制已成为当前生物多样性研究的热点问题。基于Alwyn H. Gentry在美洲收集的131个森林样方数据,采用倍性和加性分配方法度量群落beta多样性,检验beta多样性随纬度的变化趋势,并分析其形成机制。研究表明:(1) 美洲森林群落beta多样性随纬度增加显著下降,热带和亚热带地区beta多样性高于温带地区;此格局可由物种分布范围的纬度梯度性和不同粒度(grain)下物种丰富度与纬度回归斜率的差异推论得出;(2) 加性分配方法表明beta多样性对各个温度带森林群落gamma多样性的相对贡献率平均为78.2%,并且随纬度升高而降低;(3) 美洲南半球森林群落beta多样性高于其北半球,这可能反映了区域间物种进化和环境变迁历史的差异。此外,还探讨了不同beta多样性计算方法的适用情景,首次证实了森林生态系统群落水平beta多样性的纬度梯度性,这对研究生物多样性的形成机制和生物多样性保护都具有重要的意义。     

Trophic ecology of Pacific salmon (<Emphasis Type="Italic">Oncorhynchus</Emphasis> spp.) in the ocean: a synthesis of stable isotope research

Increasing interest in the marine trophic dynamics of Pacific salmon has been motivated by the recognition of their sensitivity to changing climate and to the competitive effects of hatchery fish on wild stocks. It has become more common to use stable isotopes to supplement traditional diet studies of salmon in the ocean; however, there have been no integrated syntheses of these data to determine whether stable isotope analyses support the existing conventional wisdom of feeding strategies of the Pacific salmon. We performed a meta-analysis of stable isotope data to examine the extent of trophic partitioning among five species of Pacific salmon during their marine lives. Pink, sockeye, and chum salmon showed very high overlap in resource use and there was no consistent evidence for chum relying on alternative food webs dominated by gelatinous zooplankton. δ¹⁵N showed that Chinook and coho salmon fed at trophic levels higher than the other three species. In addition, these two species were distinctly enriched in ¹³C, suggesting more extensive use of coastal food webs compared to the more depleted (pelagic) signatures of pink, sockeye, and chum salmon. This paper presents the first synthesis of stable isotope work on Pacific salmon and provides δ¹⁵N and δ¹³C values applicable to research on the fate of the marine derived nutrients these organisms transport to freshwater and riparian ecosystems.     

高等植物光合同化物的运输与分配

高等植物光合同化物的运输受维管束发育状况影响较大,有时会限制产量。而同化物在各库器官间的分配主要决定于库本身的特性,它常用库强度和优先权来描述。库强度是库容量和库活力的乘积,库容量用细胞数目来度量,而库活力常用相对生长速度来度量。近年来人们也用酶少戌一来度量库活力或库强度。而库的优先权描述的是各库器官需求同化物的优先次序,种子被认为是优等权最高的库。同化物的运输分配不仅决定于植物本身源、流、库的特     

油菜地上部干物质分配与产量形成模拟模型

利用油菜器官生长与发育进程及环境因子之间的定量关系,构建了基于分配指数的油菜地上部器官干物质分配动态模拟模型.各器官干物质分配指数随着生理发育时间而变化,基因型、播期、氮素及水分水平影响各器官干物质在地上部分配的大小.其中,氮素营养水平对绿色叶片干物质分配影响最大,氮素营养水平越高,绿色叶片分配指数越大;播期影响角果分配指数,晚播的角果分配指数高于早播.模型引入氮素营养指数、水分及播期影响因子来定量油菜各器官在实际生产条件下的分配强度,同时考虑了品种遗传特性的影响.通过不同品种氮肥处理试验建立模型,利用不同品种播期试验资料对模型进行了初步检验,表明模型具有较好的预测性和适用性.     

Detection of barbiturate-induced surface changes in cerebrocortical synaptosomes by phase partitioning in an aqueous two-phase system

The barbiturates tested in this work (barbital, phenobarbital, thiopental and pentobartial) modify the partition of synaptosomes in a Dextran T500-poly(ethylene glycol) 4000 two-phase system. Under adequate experimental conditions, the drugs increase the partition into the upper phase and this effect appears to be due to an action on the biological material and not on the interface potential of the system. This conclusion can be drawn from the fact that synaptosomes preincubated with low concentrations (0.1 mM) of barbital and pentobarbital maintained an increased partition into the upper phase. The extent of the effect observed appeared to be inversely proportional to the hydrophobicity of the drugs since phenobarbital and barbital showed a higher effect than thiopental and pentobarbital. Dithionite-induced anoxia, rotenone and ouabain also induced a similar increase of partition of synaptosomes into the upper phase, suggesting that the surface changes detected by phase partitioning modification of synaptosomes could be somehow related to the bioenergetic maintenance of the membrane ATPase.     

Carbon and nitrogen partitioning in the biennial monocarp Arctium tomentosum Mill

Summary Growth and nitrogen partitioning were investigated in the biennial monocarp Arctium tomentosum in the field, in plants growing at natural light conditions, in plants in which approximately half the leaf area was removed and in plants growing under 20% of incident irradiation. Growth quantities were derived from splined cubic polynomial exponential functions fitted to dry matter, leaf area and nitrogen data.Main emphasis was made to understanding of the significance of carbohydrate and nitrogen storage of a large tuber during a 2-years' life cycle, especially the effect of storage on biomass and seed yield in the second season. Biomass partitioning favours growth of leaves in the first year rosette stage. Roots store carbohydrates at a constant rate and increase storage of carbohydrates and nitrogen when the leaves decay at the end of the first season. In the second season the reallocation of carbohydrates from storage is relatively small, but reallocation of nitrogen is very large. Carbohydrate storage just primes the growth of the first leaves in the early growing season, nitrogen storage contributes 20% to the total nitrogen requirement during the 2nd season. The efficiency of carbohydrate storage for conversion into new biomass is about 40%. Nitrogen is reallocated 3 times in the second year, namely from the tuber to rosette leaves and further to flower stem leaves and eventually into seeds. The harvest index for nitrogen is 0.73, whereas for biomass it is only 0.19.     

Size,sex and seasonal patterns in the assemblage of Carcharhiniformes in a sub‐tropical bay

Size, sex and seasonal patterns among Carcharhiniformes were examined in shallow regions of Moreton Bay, Queensland, Australia. A total of 1259 sharks were caught, comprising 13 species. The Australian sharpnose shark Rhizoprionodon taylori and the blacktip complex Carcharhinus limbatus–Carcharhinus tilstoni comprised 55% of all shark individuals. Neonates were observed for five species including the dusky shark Carcharhinus obscurus, which contrary to previous reports was relatively abundant in shallow, predominantly estuarine waters. Three contrasting patterns of occurrence were observed: smaller species were abundant and present throughout much of their ontogeny, larger species were mainly caught as neonates or juveniles and vagrant species were only caught during the warmer months. The shark assemblage differed significantly among seasons. While many species were observed during the warmer months, species diversity was lower in winter when C. obscurus comprised 43% of the catch. Overall, the results indicated that spatial and temporal distribution patterns were not synchronous for all species. The capture of small numbers of neonate C. obscurus in late autumn and winter demonstrates that parturition among Carcharhiniformes is not confined to spring and summer in sub‐tropical waters.     

Effects of gap size and associated changes in light and soil moisture on the understorey vegetation of a Hungarian beech forest

In European beech forests windstorms often create canopy gaps and change the level of incident light, soil moisture and nutrient availability on the forest floor. Understanding the interrelations between gap size and environmental change, and the effects these have on regeneration processes is a prerequisite for developing techniques of nature-based forestry. The aims of this study were to investigate the effects of gap size on the resulting spatial distributions of key abiotic environmental variables (light and soil moisture) in gaps, and to study how light and soil moisture affect the abundance and distribution of herb layer species. To do this we used eight artificially created gaps – three large (diameter: 35–40 m) and five small (diameter: 10–15 m) – in a mesotrophic submontane beech forest. Data on species’ importance and substrate types were collected in systematically distributed 1 m×1 m quadrats before gap creation and on four occasions during the next two growing seasons. Hemispherical photographs were taken and analysed to estimate relative light intensity. Soil moisture was measured by frequency domain and capacitance probes. It was found that gap size had a profound effect on the environmental variables measured. While relative light intensity values in small gaps did not reach those in large gaps, soil moisture levels did reach similar maximum values in gap centres regardless of gap size. Richness, composition and total cover of herbaceous vegetation were different in small versus large gaps. Much of this difference was attributed to the presence of specific relative light intensities and also to the increased amount of available soil moisture in gaps. Species were differently affected by the combined effects of light and soil moisture, as well as by differences in available substrates. All this resulted in species-specific distribution patterns within gaps.     

Resource partitioning and competition for shells between intertidal hermit crabs on the outer coast of Washington

Summary Resource partitioning was quantified for 6 species of intertidal hermit crabs in the genus Pagurus, that occur on the outer coast of Washington. This, together with field evidence of shell shortage and with laboratory experiments to quantify the mechanism of interactions for shells, allowed estimation of the relative intensities of inter-and intraspecific competition between these species. The findings were that: (1) the magnitude of intraspecific competition was greater than any single interspecific competitive effect for all of the species; and (2) the relative proportion of intraspecific competition was greater for the middle and upper intertidal species than for the lower intertidal species. Studies at several outer coast sites supported these generalizations. Both of these findings are consistent with the hypothesis that competitive divergence has occurred in the past. The structure of the outer coast hermit crab assemblage is compared with that of the San Juan Archipelago hermit crab assemblage. Differences between the two do not seem to be the result of adaptive responses to the presence of more competing species in the former group.     

Variation in species light acquisition traits under fluctuating light regimes: implications for non‐equilibrium coexistence

Resource distribution heterogeneity offers niche opportunities for species with different functional traits to develop and potentially coexist. Available light (photosynthetically active radiation or PAR) for suspended algae (phytoplankton) may fluctuate greatly over time and space. Species‐specific light acquisition traits capture important aspects of the ecophysiology of phytoplankton and characterize species growth at either limiting or saturating daily PAR supply. Efforts have been made to explain phytoplankton coexistence using species‐specific light acquisition traits under constant light conditions, but not under fluctuating light regimes that should facilitate non‐equilibrium coexistence. In the well‐mixed, hypertrophic Lake TaiHu (China), we incubated the phytoplankton community in bottles placed either at fixed depths or moved vertically through the water column to mimic vertical mixing. Incubations at constant depths received only the diurnal changes in light, while the moving bottles received rapidly fluctuating light. Species‐specific light acquisition traits of dominant cyanobacteria (Anabaena flos‐aquae, Microcystis spp.) and diatom (Aulacoseira granulata, Cyclotella pseudostelligera) species were characterized from their growth–light relationships that could explain relative biomasses along the daily PAR gradient under both constant and fluctuating light. Our study demonstrates the importance of interspecific differences in affinities to limiting and saturating light for the coexistence of phytoplankton species in spatially heterogeneous light conditions. Furthermore, we observed strong intraspecific differences in light acquisition traits between incubation under constant and fluctuating light – leading to the reversal of light utilization strategies of species. This increased the niche space for acclimated species, precluding competitive exclusion. These observations could enhance our understanding of the mechanisms behind the Paradox of the Plankton.     

Addressing biofilter limitations: A two-phase partitioning bioreactor process for the treatment of benzene and toluene contaminated gas streams

A two-phase partitioning bioreactor (TPPB) achievedsimultaneous and continuous removal and degradation of benzene and toluene froman air stream. The aqueous-organic system utilized n-hexadecane as the organicphase, and the organism Alcaligenes xylosoxidans Y234 in the aqueous phaseto achieve the degradation of benzene and toluene. The system, which operates asa well-mixed dispersion and is therefore resistant to substrate surges, was firstshown to be capable of utilizing toluene while operating at a loading capacity of 235 g m^-3 h^-1with an elimination capacity of 233 g m^-3 h^-1. It was also determined that to characterize TPPB performance in terms of elimination capacity thedefinition of elimination capacity must be extended to include the cell mass present, a readilycontrollable variable given the nature of the system. Based on this criterion, it wasestimated that for a cell concentration of 1 g l^-1 present in the TPPB, thepotential maximum toluene elimination capacity is 1290 g m^-3 h^-1 whichis substantially higher than any toluene elimination capacity achieved by biofiltersat a high removal efficiency. If no other factor were to limit the system, eliminationcapacities could be many times higher still, and are dependent on maintaining desiredcell concentrations above 1 g l^-1. The TPPB was then operated at nominalloading capacities of 63 g m^-3h^-1 (benzene) and 51 g m^-3 h^-1 (toluene) at a removal efficiency greater than 99% to demonstratedthe applicability of this system in dealing with two chemical species simultaneously. TPPBsystems therefore have been shown to be effective at removing gaseous organiccontaminants at high removal efficiencies while also possessing desirable operatingfeatures, such as providing and maintaining high cell concentrations throughout thereactor, and a capacity to effectively deal with high contaminant loadings.     

Genetic divergence and echolocation call frequency in cryptic species of Hipposideros larvatus s.l. (Chiroptera: Hipposideridae) from the Indo-Malayan region

The intermediate leaf-nosed bat ( Hipposideros larvatus ) is a medium-sized bat distributed throughout the Indo-Malay region. In north-east India, bats identified as H. larvatus captured at a single cave emitted echolocation calls with a bimodal distribution of peak frequencies, around either 85 kHz or 98 kHz. Individuals echolocating at 85 kHz had larger ears and longer forearms than those echolocating at 98 kHz, although no differences were detected in either wing morphology or diet, suggesting limited resource partitioning. A comparison of mitochondrial control region haplotypes of the two phonic types with individuals sampled from across the Indo-Malay range supports the hypothesis that, in India, two cryptic species are present. The Indian 98-kHz phonic bats formed a monophyletic clade with bats from all other regional populations sampled, to the exclusion of the Indian 85-kHz bats. In India, the two forms showed 12–13% sequence divergence and we propose that the name Hipposideros khasiana for bats of the 85-kHz phonic type. Bats of the 98-kHz phonic type formed a monophyletic group with bats from Myanmar, and corresponded to Hipposideros grandis , which is suggested to be a species distinct from Hipposideros larvatus . Differences in echolocation call frequency among populations did not reflect phylogenetic relationships, indicating that call frequency is a poor indicator of evolutionary history. Instead, divergence in call frequency probably occurs in allopatry, possibly augmented by character displacement on secondary contact to facilitate intraspecific communication.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 119–130.     

Water stress leads to a change of partitioning in favour of sucrose in heterotrophic cell suspension cultures of Chenopodium rubrum

Abstract. When heterotrophic cell suspension cultures of Chenopodium rubrum were subjected to water stress by incubation in increasing concentrations of sorbitol there was an immediate shrinking of the protoplast volume. Glucose uptake decreased in parallel. When the external water potential was greater than 0.5 MPa, a change in the partitioning of this incoming carbon was observed, resulting in a doubling of the ratio of sucrose to starch. This was accompanied by an increase in the concentration of the glycolytic intermediates and a particularly pronounced increase in the levels of fructose-2,6-bisphosphate and malate. The extractable activity of sucrose phosphate synthase was determined using a new method which overcomes the problem of uridine-diphosphate loss from the assay medium. It was found that sucrose phosphate synthase activity decreased in the water stressed cells. Therefore, the higher sucrose concentration in these cells is attributed to the increase in metabolite concentrations alone.     

Removal and destruction of high concentrations of gaseous toluene in a two-phase partitioning bioreactor by Alcaligenes xylosoxidans

A two-phase bioreactor consisting of hexadecane dispersed in an aqueous, cell-containing medium (organic fraction = 0.33) was used to trap toluene vapours from an air stream. The affinity for toluene by the solvent resulted in high efficiency of removal and transfer to the aqueous phase based on equilibrium transfer. The system was readily able to handle a loading capacity of 748 mg l^–1 h^–1 at a toluene degradation efficiency of greater than 98%.