Factors Influencing Site Abandonment and Site Selection in a Sit-and-Wait Predator: A Review of Pit-Building Antlion Larvae

There is a large body of evidence indicating that predator behavior may strongly influence patterns and processes at the population and community level. Site selection is a major component of fitness in sit-and-wait predators, especially when relocation is rare. Although several review articles dealt with these issues in web-building spiders, this is the first attempt to summarize the effects of biotic and abiotic factors on site selection and relocation in another group of sit-and-wait predators, the pit-building antlions (Neuroptera: Myrmeleontidae). Our synthesis shows that prey abundance may have relatively little effect on pit relocation and that physical properties of the habitat or competition often override its effect. We suggest that owing to a variety of constraints such as physiological constraints or difficulties in assessing site quality, site selection and relocation are not necessarily optimal and thus food intake rate is not maximized. We call for a multi-factorial study on a single species in order to pinpoint the dominant factors and to assess to what extent they influence site selection and relocation. We conclude by proposing new research directions, such as studying whether pit relocation is an adaptive response, when controlling for possible phylogenetic effects.     

冀中农林复合环境瓢虫资源及优势种种群动态

瓢虫科(Coccinellidae)昆虫大多为捕食性种类,其中一些种类是农区重要的天敌昆虫.针对华北冀中农林复合环境瓢虫种群在作物生长期的分布动态与空间格局、以及瓢虫优势种群对栖息地的选择趋向进行了研究,结果表明:(1)林带在作物生长早期是瓢虫赖以生存的主要生境,是后继作物环境瓢虫种群建立的\"种库\";(2)冀中农区瓢虫的优势种为龟纹瓢虫(Propylea japonica);(3)瓢虫种群随季节变化在各生境斑块间有明显的移动现象;(4)龟纹瓢虫种群在作物生长早期呈均匀或随机分布,在作物生长中后期呈密度依赖型聚集分布;(5)间作田成为作物生长后期瓢虫主要的聚集地显示在生境趋向不利时复杂的环境是理想的栖息场所.     

Why are antlion larvae rare under the leaf litter? Testing the hypothesis of improper trap maintenance¿Por qué las larvas del león de las hormigas son tan raras bajo la hojarasca? Probando la hipótesis del mantenimiento inadecuado de las trampas

1. Understanding why animals avoid some locations is needed to improve the theory of habitat selection. This is key in semi-sedentary organisms, such as antlion larvae, because once established they rarely move, and their performance largely depends on local environmental conditions.
2. Antlion larvae are sit-and-wait predators that build conical pitfall traps in sandy soils to capture passing prey. They clean constantly their traps, expelling soil, prey carcasses and debris out of the pit to maintain their trapping success. Therefore, we propose that they avoid soils with leaf litter because leaves hinder the maintenance of their pits; a hypothesis that has not yet been tested.
3. We first demonstrated that antlion larvae (Myrmeleon inmaculatus) are rare from soils with leaf litter in a tropical semi-deciduous forest in Mexico. We then experimentally tested the effect of leaf litter on pit maintenance by adding debris in 90 antlion traps, 45 of which were covered with a leaf, and 45 remained uncovered. Two hours after adding the debris, we recorded its location and quantified the variation in depth and diameter of the pits.
4. Larvae in uncovered traps were twice as effective at cleaning up the debris than larvae in covered traps. Furthermore, in just 2 h, covered traps were on average 21% shallower than control traps, probably because unsuccessful attempts to clean debris caused sand slides to fill the pit partially.
5. Leaf litter seems to hinder the proper maintenance of antlion traps, explaining at least partially, why these animals are rare under leaf litter.

     

山西五鹿山褐马鸡不同季节的空间分布与栖息地选择研究

1997～1998年在山西省五鹿山自然保护区内对世界珍禽褐马鸡(Crossoptilon mantchuricum)越冬期与繁殖期的空间分布模式及其变化规律进行了研究,同时探讨了种群空间分布模式与栖息地结构特征之间的关系。经Pois—son函数和χ^2检验,发现褐马鸡在越冬期和繁殖期均为聚集分布,但越冬期的聚集程度更为明显。通过对栖息地可利用率与实际利用率的比较,发现褐马鸡在越冬期与繁殖期对栖息地的利用存在显著性差异：越冬期褐马鸡对阔叶林具有明显的负选择性;进入繁殖期后,褐马鸡对落叶阔叶林和灌丛的利用率显著增加,而对针叶林和针阔混交林的利用率有所减少。对两个时期的栖息地样方进行判别分析,发现草本植物数量、草本植物平均高度、乔木胸径、乔木高度是影响褐马鸡越冬期与繁殖期栖息地选择的主要因子。研究结果表明,褐马鸡种群的空间分布模式及其变化,与栖息地结构以及空间资源分布的季节性变化有关。在越冬期,由于温度、降雪等气候因素的影响,草本植物都已枯萎,落叶阔叶林的郁闭度较低,隐蔽条件较差,褐马鸡活动的区域范围受到一定的限制,此时褐马鸡常常在郁闭度较高的针叶林或针阔混交林中,并聚集形成较大的群体,共同取食,聚集分布的程度较高;进入繁殖期后,随着落叶阔叶林郁闭度增大以及林下、灌草丛中草本植物种类和数量的增多,褐马鸡群体逐渐变小,多以配偶对的形式活动,空间聚集程度降低。但由于褐马鸡对栖息地具有严格的选择性,许多配偶对主要集中在质量较好的区域内占区和营巢,因此在大尺度上褐马鸡种群的空间分布仍为聚集型分布。     

秦岭皇冠优势灌木苦糖果的空间分布格局及种内种间关联

以秦岭皇冠暖温性落叶阔叶林25 hm²森林样地中的优势灌木苦糖果为对象,研究了苦糖果不同径级个体的空间分布格局以及种内种间关系。结果表明: 苦糖果径级结构呈现出下宽上窄的金字塔型,小径级植株数量最多,更新状态较好,处于稳定增长阶段,有利于群落更新和演替。以Ripley's K函数为基础,采用单变量和双变量成对相关函数,在3个零模型(完全空间随机模型、异质泊松模型和先决条件模型)的处理下,树种整体和不同径级以聚集分布为主,且聚集程度随研究尺度的加大而逐渐减小,逐渐趋向随机分布。受到生境异质性、扩散限制、负密度制约等影响,种内不同径级个体之间以正关联为主,但也有一定程度的无关联,未出现负关联的情况。种间关系较为复杂,既有无关联,也有正关联和负关联,但以负关联和无关联为主。     

云南香格里拉亚高山寒温性针叶林优势种空间分布格局及种内种间关联性

植物种群空间分布格局是散布限制和环境过滤等多种生态过程综合作用的结果。分布在高山树线交错带的植物因其特殊的生境, 对气候变化表现出高度的敏感性。因此, 研究这些植物的空间分布格局及其相互关系, 对理解和预测高山林线森林群落的动态和发展趋势至关重要。该研究基于云南香格里拉亚高山寒温性针叶林20 hm²动态监测样地的调查数据, 以样地内优势种长苞冷杉(Abies georgei)、亚乔木层优势种红棕杜鹃(Rhododendron rubiginosum)和西南花楸(Sorbus rehderiana)、灌木层优势种唐古特忍冬(Lonicera tangutica)和云南双盾木(Dipelta yunnanensis)为研究对象, 采用空间点格局方法分析各优势种的空间分布格局、长苞冷杉不同发育阶段间的种内关联性、长苞冷杉与其他优势种间的种间关联性, 以及其他优势种种间关联性, 并使用Torus-translation方法检验这些植物与地形因子的关联性。结果表明: (1)长苞冷杉的幼树和中树均呈现聚集分布, 这主要由散布限制和生境异质性驱动; 而成树主要呈随机分布, 表明密度依赖性的竞争对大径级个体分布的主导作用。亚乔木层和灌木层的优势种均呈聚集分布, 但剔除环境异质性后部分优势种转变为随机分布, 说明环境过滤驱动了树种空间分布模式。(2)长苞冷杉的幼树与中树呈正关联, 可能是小径级个体通过集群作用来提高抵御外界环境胁迫的能力。幼树和中树与成树呈负关联, 这主要受由密度制约引起的专一性病原菌和植食性昆虫的侵害以及大个体对小个体的不对称竞争的影响。(3)长苞冷杉的幼树与亚乔木层和灌木层的优势种分别呈正关联和负关联; 中树与其他优势种大多表现为负关联, 而成树则多表现为正关联; 乔木层和灌木层优势种之间多表现为正关联。说明亚高山寒温性针叶林优势种之间存在复杂的动态平衡。各优势种通过独特的生存策略和资源利用方式来实现长期共存, 最终形成以长苞冷杉为主导的相对稳定的顶极群落。(4)坡度与长苞冷杉的幼树和中树的密度显著负相关, 与红棕杜鹃和云南双盾木显著正相关, 说明长苞冷杉与其他优势种发生了坡度生态位的分化。此外, 由于冬季积雪时间较长等不利因素, 凹凸度也对优势种的分布具有显著的影响。总体而言, 地形驱动的生境过滤可能是维持亚高山寒温性针叶林群落构建的主要驱动力。     

Spatial variation in colour morph, spotting and allozyme frequencies in the candy-stripe spider, Enoplognatha ovata (Theridiidae) on two Swedish archipelagos

The selective significance, if any, of many invertebrate visible polymorphisms is still not fully understood. Here we examine colour- and black spotting-morph frequencies in the spider Enoplognatha ovata in populations on two Swedish archipelagos with respect to different spatial scales and, in one archipelago, against the background of variation at four putative neutral allozyme marker loci. Every population studied was polymorphic for colour and 28 out of 30 contained all three colour morphs – lineata, redimita and ovata. We found no evidence for a breakdown in the traditional colour morph designation previously suggested for other northern European populations of this species. For colour there is no significant heterogeneity at spatial scales greater than between local populations within islands. Black spotting frequencies show a similar lack of pattern over larger spatial scales except that there are significant differences between the Stockholm and Göteborg archipelagos. Measures of population differentiation (θ) within the Stockholm islands for the two visible systems show them to be significantly more differentiated than the neutral markers, suggesting local selection acting on them in a population-specific manner. On the basis of previous observations and the distribution of spotting phenotypes on a European scale, it is argued that thermal selection might operate on black spotting during the juvenile stages favouring more spots in continental climates. It is not clear what selective forces act on colour.     

生态学中的点格局研究概况及其在国内的应用

点格局分析是研究生态学格局的工具之一,近年来在生态学中的应用越来越多。为深入了解点格局分析方法在国内的研究与应用情况,以所总结的研究进展、一般步骤和基本要点为背景,分析评述了1996—2015年期间以点格局为主题的国内中文核心期刊文献。结果表明,在国内生态学格局研究中,应用研究占据主导地位,研究对象广泛,包括以树木为主的乔、灌、草等不同生活型的植物,甚至包括景观;基础研究,包括概括性统计量、零模型与点过程模型等方面,以及专用软件工具包的开发等研究薄弱。在应用中存在一定问题,主要表现为:概括性统计量使用单一,且以Ripley的K-函数及其变形为主;零模型(或点过程模型)是科学问题的统计表达,但是有一半以上的研究未明确给出零模型。建议在未来应用研究中重视多种统计量的组合使用和原假设的建立,在探讨热带、亚热带森林等具有复杂空间结构系统的多样性格局时,考虑对象的不同世代和系统的不同垂直层次,并加强多变量或三维概括性统计量的开发、点格局分析方法与动态过程模型的结合研究等工作。