Intraspecific,size-dependent variation in the movement behaviour of a brackish-water isopod: a resource-free laboratory experiment

Intraspecific variability represents an important, yet inadequately investigated factor affecting the movement behaviour and ecology of mobile organisms. Here, the influence of sex, seasonality and body size on the movement behaviour of the brackish isopod Lekanesphaera hookeri were examined under resource-free laboratory conditions. The mean step length, total path length and average speed were determined twice during the year for adult and juvenile isopods encompassing a 10-fold range in body length. The scale-independent fractal dimension D was used to quantify the tortuosity of the movement paths. No relationships were observed between sex or season and all the movement metrics. In contrast, isopods' body size scaled negatively with the fractal dimension D of movement paths with a breakpoint at 2.6 mm, roughly corresponding to the size of morphometric maturation. No other relationships were observed between the body length of isopods and mean step length, total path length and average speed. The results indicate a sex- and season-independent ontogenetic shift in movement behaviour in L. hookeri. This suggests that in sphaeromatid isopods post-embryonic development determines not only continuous variations in size and proportions, but also a discontinuous change in the movement strategy adopted to interact with the surrounding space. Overall, these findings underscore the need to account explicitly for such changes in models predicting the spatial distribution of organisms characterised by wide intra-population size variation.     

陆生植物稳定碳同位素组成与全球变化

分析了大气CO₂浓度、温度、降水和海拔高度等环境因素对陆生植物稳定性碳同位素组分的影响及其作用机理,综述了国内外碳稳定同位素技术在全球变化研究中的进展和应用,如重建大气CO₂浓度变化,揭示温度、降水对树木生长的“滞后效应”和“幼龄效应”,确定不同光合型植物随海拔高度的分布变化,以及通过碳稳定同位素技术揭示不同时间尺度上和不同气候条件下的植物水分利用效率变化及不同生活型植物的水分利用效率差异,并探讨研究中存在的问题及其研究前景.     

Neottia cordata (Orchidaceae) at its southernmost distribution border in Europe: Threat status and effectiveness of Natura 2000 Network for its conservation

Neottia cordata is an orchid species that exclusively occurs in Picea abies subsp. abies and Pinus sylvestris stands and forms its southernmost distribution limits in Greece. Over the last decade, it has been recorded in numerous sites, in which it forms small colonies, both in terms of population and area. This research re-evaluates the threat status of Neottia cordata based on updated chorological and population data; it also checks the effectiveness of the Natura 2000 Network as far as its conservation is concerned by applying the MaxEnt model. The recently collected data justify the classification of N. cordata as "Vulnerable". The most significant variables that affect its distribution were found to be the vegetation type and the precipitation of the warmest quarter. The results of the MaxEnt model suggest that: (i) the Natura 2000 Network is characterised by areas of higher habitat suitability values when compared to the areas that fall outside this network; and, (ii) Picea abies subsp. abies forests are more suitable for its conservation than those of Pinus sylvestris. It is concluded that the most appropriate management measure for the species conservation is the maintenance of the tree layer canopy closed.     

The role of controlled propagation on an endangered species: demographic effects of habitat heterogeneity among captive and native populations of the socorro isopod (Crustacea: Flabellifera)

The Socorro isopod, Thermosphaeroma thermophilum, became the focus of a novel conservation strategy when apparent extirpation of the species from the wild prompted construction of the Socorro Isopod Propagation Facility (SIPF) near the native spring in Socorro, New Mexico, USA. We subjected captive populations to 4 habitat treatments over 2 consecutive 50-month experimental trials. Native populations of T. thermophilum remained significantly more abundant than captive subpopulations during the 100-month study. Population trends among artificial habitats differed slightly between the trials, but the magnitude of this difference was independent of linear flow within either pool series, suggesting that captive isopods responded to habitat quality. Isopod age structure was most heterogeneous in pools with plants suggesting that vertical structural diversity is necessary to maintain long-term viability of T. thermophilum in captivity. Observations of `breeding huddles' in the SIPF pools implied that controlled propagation may affect the social basis of the species' mating system. This could be a behavioral response to selection on body size that may reduce predation risks from larger male cannibals, or to increase fitness of both sexes under spatially altered sex ratios of artificial environments. Our results accentuate the need for continued research on species-specific management practices for geographically restricted invertebrate taxa such as the endangered Socorro isopod.     

Surprisingly high orchid diversity in travertine and forest areas in the Huanglong valley, China, and implications for conservation

The presence of such a large number of terrestrial orchid species in a small area (ca. 1 km²) of the Huanglong valley in southwestern China is uncommon for this country. Studying the relationship between the distribution patterns of these orchid species and their microenvironments may help us understand this uncommon phenomenon. We established 662 1 m × 1 m plots, measured the cover of each species and found that there were 33 orchid species distributed mainly in two different habitats, i.e. travertine areas and forest. In the travertine areas, 30 orchid species were found; the six most common ones being Cypripedium bardolphianum, Cypripedium flavum, Cypripedium tibeticum, Galearis diantha, Ponerorchis chusua and Phaius delavayi. However in the forested habitat, we found 21 orchid species; the most common ones being Tipularia szechuanica and Goodyera repens. Travertine areas had a higher number of orchid species as well as higher numbers of orchid species per plot as compared to forest. Light availability seems critical to the performance and distribution of orchid species. Stream flow through the travertine area during the orchids growing season appears to be an important factor in shaping and maintaining stable microenvironments favorable to the growth and reproduction of orchids. The results presented in this study suggest that some orchid species in the travertine area might be threatened if the travertine stream flows were to change or be disrupted.     

Colonization and substratum preference of an introduced burrowing crustacean in a temperate estuary

Habitat use in marine invertebrates is often influenced by multiple abiotic and biotic factors. Substratum composition is one factor known to have a dramatic effect on habitat selection. The Australasian burrowing isopod (Sphaeroma quoianum, H. Milne Edwards 1840) is a common introduced species in many estuaries on the Pacific coast of North America. S. quoianum burrows into a variety of firm substrata including marsh banks (composed of peat, clay, and/or mud), wood, friable rock, and Styrofoam floats. In some areas, isopods achieve high densities and may accelerate the rate of shoreline erosion and damage marine structures; thus, understanding the substratum preference of this species may be important for conservation and management efforts. Field experiments were conducted in Coos Bay, Oregon to examine substratum preference, burrowing rates, and the life stage of colonizers. In three experimental trials (Fall 2005, Spring 2006, Fall 2006), replicates of four intertidal substrata (marsh banks, decayed wood, sandstone, Styrofoam) were deployed near intertidal populations of S. quoianum. The numbers of burrows created in each substratum were enumerated weekly or daily (depending on trial). After the trials were completed, the total numbers of isopods inhabiting each substratum were counted. In weeks, S. quoianum extensively burrowed the substrata but exhibited a distinct preference for decayed wood. Significantly more isopods were present in wood than the other substrata at the end of the experiments and rates of burrowing were greatest in wood, although significance varied across time in one trial. Nearly 90% of colonizing isopods were under 5 mm in length suggesting that juvenile isopods primarily colonize intertidal substrata. Differences between burrow densities measured in the field and the results from these preference trials may indicate other factors, such as relative availability of substrata, recruitment and dispersal limitations, and possible gregarious behavior also influence local isopod densities.     

Mechanical model for theoretical determination of maximum running speed in mammals

A mechanical model for the determination of maximum speed in terrestrial tetrapods, designed for application to extinct species, is proposed. Only external bone measures and average body mass estimations are used as input data, and the hypothesis is made that leg bones are strong enough to endure the stress of running at maximum speed at a certain universal safety factor. The model is applied to a broad sample of living mammalian species to test its predictive power, and it is found to provide very good estimates of maximum running speed.     

Assessing extinction risk in the absence of species-level data: quantitative criteria for terrestrial ecosystems

The conservation of individual plant and animal species has been advanced greatly by the World Conservation Union’s (IUCN) development of objective, repeatable, and transparent criteria for assessing extinction risk, which explicitly separate the process of risk assessment from priority-setting. Here we present an analogous procedure for assessing the extinction risk of terrestrial ecosystems, which may complement traditional species-specific risk assessments, or may provide an alternative when only landscape-level data are available. We developed four quantitative risk criteria, derived primarily from remotely sensed spatial data, information on one of which must be available to permit classification. Using a naming system analogous to the present IUCN species-specific system, our four criteria were: (A) reduction of land cover and continuing threat, (B) rapid rate of land cover change, (C) increased fragmentation, and (D) highly restricted geographical distribution. We applied these criteria to five ecosystems covering a range of spatial and temporal scales, regions of the world, and ecosystem types, and found that Indonesian Borneo’s lowland tropical forests and the Brazilian Atlantic rainforest were Critically Endangered, while South Africa’s grasslands and Brazil’s Mato Grosso were Vulnerable. Furthermore, at a finer grain of analysis, one region of Venezuela’s coastal dry forests (Margarita Island) qualified as Vulnerable, while another (the Guasare River watershed) was Critically Endangered. In northern Venezuela, deciduous forests were classified as Endangered, semi-deciduous forests Vulnerable, and evergreen forests of Least Concern. We conclude that adoption of such a standardized system will facilitate globally comparable, repeatable geographic analyses that clearly separate risk assessment (a fundamentally scientific process), from the definition of conservation priorities, which should take into account additional factors, such as ecological distinctiveness, costs, logistics, likelihood of success, and societal preferences. Jon Paul Rodríguez and Jennifer K. Balch are contributed equally to this work     

基于地基激光雷达点云的植被表型特征测量

植物表型是基因型与外界环境共同作用的结果。精确测量植物表型对于植物生理特征与功能性状研究具有重要意义。本研究以加拿大一枝黄花(Solidago canadensis)为对象,对20株植株进行3个月室内培养,各月利用地基激光雷达扫描(terrestrial Li DAR scanning,TLS)系统对实验植株进行多站扫描和点云融合,实现对植株生长过程的连续观测。对于扫描获取的离散点云,利用多端点三维坐标重构法获取植株高度,并基于叶片点云的Delaunay三角网重构叶片表面,获得植株的真实高度、叶面积、叶倾角和方位角等结构参量。对比手动测量结果,发现基于点云重构获得的植株高度与真实植株高度对比,二者间相似性的决定系数(R2)为0.991,叶面积、叶倾角、方位角相似性R2分别为0.989、0.949和0.871;基于TLS点云重构法实现了非破坏性的植物表型测量,能够获得高精度的植物表型特征;多时相扫描能精确监测植物生长过程的表型特征变化。