Land-Use Planning in the Chaco Plain (Burruyacú, Argentina). Part 1: Evaluating Land-Use Options to Support Crop Diversification in an Agricultural Frontier Area Using Physical Land Evaluation

The Burruyacú district (Tucumán province, Argentina) is a farming frontier in the western Chaco plain, at the foothills of the sub-Andean mountain ranges, where agricultural land-uses are in conflict with the conservation and management of the Chaco forest. Over the last decades, large-scale farming rapidly expanded due to population pressure, attractive market prices, easy accessibility, favourable annual rainfall, fertile soils, and flexible land tenure. Cropland extension, mainly for heavily mechanized soybean production, has resulted in important reduction of the Chaco forest and also caused physical soil degradation, especially soil compaction, and soil erosion. Land suitability was assessed using the Food and Agriculture Organization (FAO) framework for a set of crops ecologically adapted to the area, including soybean, maize, wheat, sugarcane, citrus, and safflower. Only 16% of the study area has high suitability for most of the selected crops. Major limitations for cropping are low annual rainfall and flooding in the east of the study area, and topography (slope) and flooding in the west. As climate varies over relatively short periods of time, with recurrent cycles of dry and rainy years, land suitability for the selected crops was also assessed under extreme but realistic climatic conditions. Under rainy-year conditions, almost all the study area is unsuitable or marginally suitable for most of the crops. Under dry-year conditions, the study area is unsuitable for all crops, except safflower, which is more drought-resistant. This article proposes alternatives to the mono-cropping of soybean with the aim to help farmers make adequate decisions on land-use and management under deteriorating environmental conditions and for addressing the issue of competitive land uses in the context of land-use planning.     

不同温度下铜绿微囊藻和斜生栅藻的最佳生长率及竞争作用

以温度为主要控制因子,研究了单独培养和按不同接种密度比混合培养下铜绿微囊藻(Microcystis aerugino-sa)和斜生栅藻(Scenedesmus obliquus)的生长状况。结果表明,在温度为7～35℃条件下,微囊藻比增长率随着温度的升高而增大,而栅藻增长率随着温度的升高先增大后减小。竞争体系对2种藻的比增长率均有影响,微囊藻在微囊藻与栅藻接种比例为10∶1的混合培养体系中增长最慢,栅藻则在微囊藻与栅藻接种密度比为1∶10的混合培养体系中增长最慢。不同温度条件下在2种藻不同接种密度比的混合培养体系中,微囊藻对栅藻的竞争抑制能力均大于栅藻对微囊藻的竞争抑制能力。藻种间的竞争抑制能力因温度的变化而得到不同程度的强化或减弱,铜绿微囊藻具有更强的竞争能力。     

赤潮异湾藻与三角褐指藻的竞争及其化感作用初探

文章通过对赤潮异湾藻和三角褐指藻间竞争及其化感作用的论述,定性分析了两种微藻单独培养和共培养的最大环境容量(K)和生长速率(r)等生长参数,同时利用逻辑斯谛方程和Lotka-Volterra的竞争模型进一步定量比较了微藻间的竞争力参数(α和β),并采用对比微藻在f/2培养基中和其他微藻滤液中生长情况的方法,初步探讨了赤潮异湾藻和三角褐指藻间竞争产生的原因。结果表明,赤潮异湾藻对三角褐指藻有强烈抑制作用(α=6.38),而三角褐指藻对赤潮异湾藻抑制非常轻微(β=0.23),赤潮异湾藻的竞争能力大大强于三角褐指藻,推测这种竞争作用与这两种微藻间存在的化感作用相关外,还可能与其他因素如接触性信息传递等相关。此研究对调控藻类生物的生长和数量变化、鱼虾蟹等水产养殖水体中藻害的防治以及海洋生态环境的改善都具有相当的理论意义。     

共培养体系中石莼和江蓠对赤潮异弯藻生长的影响

研究共培养体系中2种大型海藻石莼(Ulva pertusa)和江蓠(Gracilaria lemaneiformis)的鲜组织和培养液滤液对赤潮异弯藻(Heterosigma akashiwo)生长的影响.结果发现:①石莼和江蓠均能明显影响赤潮异弯藻生长,鲜组织的作用更明显,能在短时间内完全灭杀共培养的赤潮异弯藻;石莼对微藻的影响强于江蓠的作用.②除菌作用和补充充足的碳酸盐不能消除或缓解石莼和江蓠对赤潮异弯藻生长的影响,说明细菌和碳限制不是导致大藻对微藻作用的原因.③对共培养体系中硝酸盐和磷酸盐的跟踪测定结果显示,营养盐限制不是造成石莼对赤潮异弯藻影响的原因,但却在江蓠的作用中起重要作用.当向江蓠体系中补充f/2营养盐后发现,充足的营养盐能够减轻但不能完全消除江蓠对赤潮异弯藻生长的影响.另一方面,石莼的起始浓度与其对赤潮异弯藻的生长影响之间存在明显的相关性,石莼的起始浓度越高,对赤潮异弯藻的影响越明显.④实验初步说明,石莼可能通过相生相克作用影响共培养体系中赤潮异弯藻的生长,而相生相克和营养竞争的共同作用是导致江蓠作用的根本原因.     

鹤山针阔叶混交林的种群竞争初步研究

通过对鹤山针阔叶混交林种群竞争的研究发现,10年生同龄大叶相思—马尾松群落中,大叶相思生长良好,马尾松种群生长不良和死亡率高达72％;异龄大叶相思—湿地松群落内两种群均生长良好;马尾松、湿地松和大叶相思等纯 林内个体高度和胸径的分化差异小,而混交林内各种群个体高度和胸径分化差异大,尤其是大叶相思比针叶树种更明显;在考虑种群竞争指标时,个体枝叶的生物量或单位面积的生物量比植株数和构件更好;大叶相思—湿地松混交林总的生物量为69.091/hm~2,大叶相思—马尾松混交林为55.282/hm~2,这两个群落的生物量均低于7年生大叶相思纯林;营造针阔叶混交林时应以异龄块状混交方式为主。     

Male genital traits and mating interval affect male fertilization success in the water strider Gerris lacustris

Parker's seminal work brought attention to the possibility of postmating sexual selection by non-random fertilization success. Mechanisms for these processes are still only partly understood and there is clearly a need for more studies of intraspecific variation in sperm precedence. Here, we report results from an experimental study of the variation in fertilization success between males of the water strider Gerris lacustris. Genital morphology, male body size, and copulation duration were examined as possible correlates of paternity. The significance of guarding duration was also analysed. Only male genital morphology was correlated to fertilization success. This is one of the first studies showing a relationship between male genital traits and fertilization success, supporting the view that sexual selection may be responsible for the rapid and divergent evolution of genital structures in animals with internal fertilization. The fertilization success of last males varied considerably after double matings with a short mating interval (10 min). Last-male priority ranged from 0 to 100% and usually one of the males involved fertilized almost all the eggs. After double matings with a short mating interval, the proportion of eggs fertilized by the last male averaged 0.68 and was greater than 0.5. In contrast, the average fertilization success was biased towards the first male when the matings were more spread out over time (24 h). These results do not support earlier suggestions of a widespread last-male sperm priority in water striders. Received: 28 July 1998 / Received in revised form: 15 March 1999 / Accepted: 28 March 1999     

Exaggerated male eye span influences contest outcome in stalk-eyed flies (Diopsidae)

Evolution of male weapons or status signals has been hypothesized to precede evolution of female mating preferences for those traits. We used staged male fights among three species of Malaysian stalk-eyed flies (Diptera: Diopsidae) to determine if elongated eye span, which is preferred by females in two sexually dimorphic species, influences contest outcome. Extreme sexual dimorphism, with large males possessing longer eye span than females, is shared by Cyrtodiopsis whitei and C. dalmanni. In contrast, C. quinqueguttata exhibits a more ancestral condition – short, sexually monomorphic eye stalks. Videotape analysis of 20-min paired contests revealed that males with larger eye span and body size won more fights in the dimorphic, but not monomorphic, species. To determine if males from the dimorphic species use eye span directly to resolve contests, we competed male C. dalmanni from lines that had undergone artificial selection for 30 generations to increase or decrease eye span. We found that eye span, independently of body size, determines contest outcome in selected-line males. Furthermore, in both dimorphic species, the average encounter duration declined as the eye span difference between contestants increased, as expected if males use eye span to assess opponent size. The number of encounters also increased with age in dimorphic, but not monomorphic, species. Selected-line males did not differ from outbred males in either fight duration or number of encounters. We conclude that exaggerated male eye stalks evolved to influence both competitive interactions and female mating preferences in these spectacular flies. Received: 20 July 1998 / Received in revised form: 2 February 1999 / Accepted: 12 March 1999     

Effects of male dominance and courtship display on female choice in the ring-necked pheasant

Male traits and behaviours acting in mate choice and intrasexual competition are expected to be congruent. When studying their evolution, this often makes it difficult to differentiate between these two components of sexual selection. Studies are therefore needed on mate choice in conjunction with the role of displays and dominance. We present the results from two experiments conducted to investigate the effects of male dominance and courtship displays on female choice in the ring-necked pheasant, Phasianus colchicus, controlling for differences in morphological male traits. We found: (1) different courtship behaviours had different effects on female choice: females were mainly attracted by the feeding courtship behaviour, while another courtship display (the lateral display) was effective in producing the copulation-acceptance response by the females; (2) subordinate males performed the courtship behaviour before females less frequently than dominant males, and females reinforced intrasexual selection by choosing dominant males, and (3) subordinate males in visual contact with a dominant became less attractive to females. The results support the idea (armament-ornament model) that female pheasants may benefit from using traits selected in male-male competition as clues for mate choice. Received: 23 October 1997 / Accepted after revision: 7 October 1998     

Interspecific interactions of amphipods <Emphasis Type="Italic">Gammarus lacustris</Emphasis> and <Emphasis Type="Italic">Gmelinoides fasciatus</Emphasis>

Experimental studies of interactions between two amphipod species (Gmelinoides fasciatus and Gammarus lacustris) showed that predation is the basic mechanism accounting for their mutual exclusion in nature. Mortality from predation among similar-sized specimens of both species at an equal abundance ratio was similar (24–25% in G. lacustris and 27–30% in G. fasciatus). The displacement of G. lacustris by G. fasciatus was observed when the latter was dominant. Adult G. fasciatus and G. lacustris successfully preyed on juveniles of their competitors and did not differ significantly in daily food consumption as a percentage of body weight: 6–24% at a fresh body weight of 18–24 mg in both species. The potential for rapid population growth under new conditions contributed to the success of the invasive Baikal species G. fasciatus in displacing G. lacustris from many water bodies of Russia.     

地方政府竞争与环境规制:基于区域开放的异质性研究

随着全球化推进,各国开始不断消减贸易壁垒,环境规制程度跟着提升,各级地方政府作为环境规制相关政策执行者,国家的环境治理直接受到其环境规制策略影响。论文围绕地方政府恶性竞争导致的环境规制失灵问题,采用变截距GLS方法和Hansen提出的"门槛回归"模型,并利用我国29个省级单位2000-2013年面板数据,将地方政府竞争作为门槛变量,分析在不同门槛值下地方政府竞争、区域开放对工业环境规制的影响,并进一步研究财政收支分权和贸易政策对这种影响是否存在积极或恶化作用,力求从根本上解决地方政府恶性竞争,实现环境有效规制。研究表明:在样本期间内,财政收入分权度较低、财政支出分权度较高、贸易开放度高、金融开放度高和制度环境不完善的地区,地方政府竞争对工业环境规制的促进作用更加凸显。全国和东部地区地方政府竞争对工业环境规制呈边际递减的促进作用,中部地区表现出地方政府竞争对工业环境规制非单调性,西部地区存在对工业环境规制呈边际递减的抑制作用。总之,样本期间内地方政府竞争程度有助于全国和东部地区环境进行有效规制,中部地区跨越门槛值后环境规制失灵,西部地区则存在较严重环境规制失灵问题。为了规避环境规制失灵,我们应提高外商投资的进入环境门槛,地方政府在治理环境时,应削减对自己地区的行政垄断,推动各级地方政府跨区域环境保护合作,并由较高层级的政府来承担环境规制的财政支出责任,不断降低地方政府恶性竞争导致的环境规制失灵。