Responses to Predation Cues and Food in Two Species of Sympatric, Tropical Sea Urchins

Abstract. We examined the responses of two tropical sea urchins, Lytechinus variegatus and Tripneustes ventricosus, to cues from predators, simulated predation events and food. Cues released from damaged conspecifics, heterospecifics and heteroclassics (holothurian) were used to simulate predation events in field experiments. Responses to the presence of seagrass, spiny lobster or both were tested in tanks. Findings were supplemented by natural history observations of dispersion patterns off Bermuda. In field experiments, neither species formed groupings in the presence of conspecific, heterospecific or heteroclassic cues. Flight responses were greatest in conspecific treatments; responses to heterospecific cues were intermediate to control and conspecific cues. Urchins in pre‐assembled associations remained in groups in control trials but dispersed when exposed to predation cues. Lytechinus exhibited greater sensitivity to predation cues than Tripneustes. Cues from a damaged sea cucumber invoked a response from Lytechinus but not Tripneustes. Both species employed a two phased response to cues from damaged conspecifics: initially a rapid, but ephemeral (2 min), alarm response followed by a slower (≈ 35 % lower) sustained flight phase for 6+ min, which in nature would disperse urchins downstream and away from a predator. In tank experiments, Lytechinus formed groupings only around food or food + predators. The presence of a predator reduced the aggregation response to food, suggesting that Lytechinus employed a risk aversion strategy. Tripneustes exhibited escape or refractory behavior in both control and experimental treatments in laboratory tanks.     

Crustal structure of seismic velocity in southern Tibet and east-westward escape of the crustal material——An example by wide-angle seismic profile from Peigu Tso to Pumoyong Tso

The Tibetan plateau, which results from continu- ous collision between India continent and southern Eurasia continent, is cross-cut by no less than three major east-west sutures[1—6]. Yarlung Zangbo suture, marked by one 1500km long ophiolite belt appearing at the southernmost Tibet, separates the Tethyan Hi- malaya to the south from the Lhasa block to the north. In order to understand the deep structure of Tibetan crust and the uplifting process of Tibetan Plateau, one wide-angle seismic…     

Orbital Distribution Arbitrarily Close to the Homothetic Equilateral Triple Collision in the Free‐Fall Three‐Body Problem with Equal Masses

The existence of escape and nonescape orbits arbitrarily close to the homothetic equilateral triplecollision orbit is considered analytically in the threebody problem with zero initial velocities and equal masses. It is proved that escape orbits in the initial condition space are distributed around three kinds of isosceles orbits. It is also proved that nonescape orbits are distributed in between the escape orbits where different particles escape. In order to show this, it is proved that the homotheticequilateral orbit is isolated from other triplecollision orbits as far as the collision at the first triple encounter is concerned. Moreover, the escape criterion is formulated in the planarisosceles problem and translated into the words of regularizing variables. The result obtained by us explains the orbital structure numerically.     

Distribution of minima of the current size of the triple systems and their disruption

The dynamical evolution of triple systems has been studied by computer simulations. A function (t) has been defined, where p is the maximum distance of the components from their centre of inertia, and t is the time. The value of is used to indicate the current size of the triple system. The minima of have been followed during the course of evolution of the triples. A distribution of f(_min) has been obtained, which is described by the following statistical parameters: the mode is equal to 0.65d, the mean value _min= 0.750d, r.m.s. is 0.477d, the asymmetry is 0.218, the excess is 2.04 where d is the mean harmonic distance between the bodies in the equilibrium state of the triple system. As a rule, escapes from triples occur only after close three-body approaches.     

辽宁抚顺盆地始新世古气候定量研究

利用德国科学家 Mosbrugger 和 Utescher 在 1997 年提出的共存分析法对辽宁抚顺盆地始新世古气候进行定量重建。通过共存分析获得的抚顺盆地始新世古气候参数为：年均温度为 14.3～19.8℃（中值为 17.05℃）,最热月均温为 24.1～27.7℃,最冷月均温为 2.5～10.9 ℃,年较差为 17.7～22.7℃,年降雨量为 803.6～1 113.3 mm (中值为 958.45 mm),最大月降雨量为 179.4～268.1 mm,最小月降雨量为 10.2～12.7 mm。与现代气候对比发现：始新世时气温较现在（7.8℃）高9.25℃,年降雨量较现在（734.5 mm）多约224 mm,始新世时属于亚热带季风气候,现今为温带季风气候。     

Raman Micro-Imaging of the Coexistence of sI and sII Hydrates Formed from a Mixed Methane-Propane Gas in a Confined Space

Natural gas hydrate contains a specific amount of heavy hydrocarbons, such as ethane, propane, etc., aside from the primary guest gas of methane. Although the coexistence of two or even three hydrate structures has been discovered at several hydrate sites, the requisite formation mechanism is still not well understood. In-situ observation of the formation process of mixed methane-propane hydrate in a confined space was conducted using confocal Raman imaging microscopy. The Raman imaging results reveal that sI methane hydrate and sII mixed methane-propane hydrate are formed and coexist in the reaction system. In the confined space, the sI hydrate originates from the dissolved gas in water, while the sII hydrate is formed from free gas. The results obtained can help explain the coexistence of sI and sII hydrates found in natural hydrate samples, as well as providing insights into a possible dynamic scenario of hydrate reservoirs in geological history.     

基于GIS的社区居民避震疏散区划方法及应用研究

在快速城市化和地震灾害频发的背景下,灾前人群紧急疏散区划成为防灾减灾规划研究的重要课题。结合当前城市应急疏散设施布局现状,立足于社区夜间避震疏散需求,综合运用GIS空间分析技术,从应急疏散需求分布、疏散空间可达性、疏散优化归属3方面逐步构建居民避震疏散区划方法,并选择上海市内人群和建筑相对密集的陆家嘴街道为对象开展实证研究。从而为城市防震减灾规划的避难设施优化布局和应急疏散预案编制提供科学适用的技术手段。     

Neotectonics and morphotectonics of the southern Almería region (Betic Cordillera-Spain) kinematic implications

Most previous studies related to the recent tectonic development of southeastern Betic Cordillera, and in particular the south of Almería, agree with the kinematic variety that can be observed in the post-Miocene structures at different scales. This variety is difficult to explain if we consider only the regional stress field related to the convergence of the Eurasian and African plates that remained relatively steady over the last 9 Ma. This work proposes a block tectonics with horizontal and vertical relative movements driven by strike-slip movements of major faults to explain the variety of kinematics observed in the area from Middle Miocene to present. The combined activity of the Alpujarras fault zone (dextral strike-slip) and the Carboneras fault zone (sinistral strike-slip) induces, within the major block bounded by them, the squeezing of minor pre-existing fault bounded crustal blocks. This process generates traction areas inside the escaping block, which are linked with the existence of gradients of westward movement rate. This tectonics can explain some of the structures related with the extensional tectonics predominant in the south of Almería province and the development of the minor and major morphostructures driven by faults with different kinematics. The tectonics of blocks proposed is useful to give a coherent interpretation of apparently incoherent local structural data into a regional and homogeneous compressional stress field.Sadly, Professor José L. Hernández Enrile died in April 2003, and thus this paper represents his last thoughts on the topic. Reviews were addressed by the first author; however, some of the suggested changes were discussed to preserve Professor Hernández Enriless thoughts.     

Fluid escape structures in the north Sicily continental margin

High resolution and multichannel seismic profiles coupled with multibeam echosounder (seafloor relief) data, acquired along the northern Sicily continental margin (southern Tyrrhenian Sea), document the occurrence of mound and pockmark features, revealing fluid escape processes. Along this margin, morphology of the high-gradient continental slope is irregular due to the presence of structural highs, slope failures and canyons, and is interrupted by flat areas at a mean depth of 1500 m.Seismostratigraphic analysis tools and methods were used to identify fluid escape structures and to work out a classification on the basis of their morpho-acoustic characteristics. The detailed 3D bathymetric chart was used to define the top view morphologic features and their areal distribution. With the aim to evaluate the geochemical content of fluids, we collected a 2.3 m long sediment core in correspondence of a pockmark at a depth of 414 m. Pore waters were sampled every 10 cm and analysed in relation to their conductivity (EC) and composition (δ¹⁸O, δD, Li, Na, K, Mg, F, Cl, Br, NO₃, SO₄).The new data show the occurrence of different types of structures with highly contrasting seismic and morphologic signatures, both dome-type and concave-upward structures. The latter have a characteristic circular shape and are known as pockmarks. Morphobathymetric, stratigraphic and structural data suggest that these structures occur along fault planes, mainly associated with diagenetic carbonates and fluid venting activity. Pockmarks could be the result of both fault and landslide structures, as they appear aligned along a straight direction and occur in proximity of the slope, and are associated with slope instabilities. The structural features are possibly associated with the recent tectonics mapped on-land as well as the widespread seismicity of the margin.Geochemical features reveal that pore water is slightly enriched in heavy isotopes with respect to Mediterranean seawater, while the distribution profiles of EC, ion concentration (Cl, SO₄, Na, K, Mg, Ca), ion/Chloride ratios (Na/Cl, K/Cl, Ca/Cl, Mg/Cl and Alk/Cl) seem to indicate the existence of an external source of fluids and the occurrence of sediment-fluids interaction processes. A possible mechanism causing pore water freshening could be the destabilisation of gas hydrates.