不同农业景观结构对麦蚜种群动态的影响

研究表明农业景观结构的复杂性与害虫种群发生强度关系密切,然而在不同农业景观结构下研究麦蚜的发生、种群及寄生蜂的变化还不多。设计了不同的麦田景观结构,调查研究了不同麦田景观结构对麦蚜种群的影响。在简单与复杂两种农业景观结构下,分析了不同种类麦蚜的入田时间、入田量、种群增长率、种群密度及寄生性天敌的多样性与寄生率。结果表明:景观结构对不同种类麦蚜影响不同,但复杂农业景观下麦蚜迁飞入田时间都要晚于简单农业景观(连片种植)下的入田时间,复杂农业景观下有翅蚜的迁入量显著低于简单景观下有翅蚜的迁入量,并且复杂农业景观下麦蚜种群增长速率高于简单农业景观下的增长速率。不同种类麦蚜对景观结构的不同反应可能与形态学与生活史特征有关,两种不同农业景观结构下寄生性天敌的多样性与寄生率无显著差异。复杂景观结构下的麦蚜有翅蚜低的迁入量、高的增长速率可能与生境高度破碎化有关,其中与温室大棚塑料白色反光有的很大的影响。生境破碎化影响了麦蚜对寄主植物寻找以及天敌对猎物的寻找效应。     

农业景观格局与麦蚜密度对其初寄生蜂与重寄生蜂种群及寄生率的影响

农业景观格局与过程能够强烈影响寄生蜂对寄主的寻找及寄生作用,寄主密度亦是影响寄生蜂分布的重要因素,然而农业景观的格局和寄主密度对寄生蜂寄生率的相互影响是一项值得研究的工作.在简单与复杂2种麦田农业景观结构下,调查了麦蚜的分布格局与2种寄主密度下麦蚜的初寄生率与重寄生率,分析了景观结构对麦蚜密度的影响、景观格局与麦蚜密度对寄生蜂寄生率与重寄生率的影响及交互作用.结果表明:景观结构的复杂性对麦蚜分布和寄生蜂初寄生率与重寄生率的影响均不明显,但寄主密度与景观结构的复杂性对寄生蜂的影响存在着明显的交互作用,寄主密度与寄生率呈正相关,寄主密度较低时烟蚜茧蜂为优势种,寄主密度较高时燕麦蚜茧蜂为优势种.麦蚜初寄生蜂与重寄生蜂对寄主密度的反应与其形态学、体型大小以及生活史特征相关,初寄生蜂与重寄生蜂的群落组成显著影响其对麦蚜的寄生率,而与景观结构的复杂性关系不大.     

麦蚜寄生蜂和捕食性天敌种群对景观复杂性的响应

农业景观结构影响昆虫的物种组成与多样性,本文选择复杂景观和简单景观的麦田景观为研究对象,研究了不同麦田景观结构对麦蚜天敌种群的影响。在简单与复杂两种景观下,分析了麦蚜寄生蜂和捕食性天敌的迁入时间、迁入量、种群增长率及种群密度之间的差异。结果表明:复杂景观中麦蚜寄生蜂和捕食性天敌的物种多样性较高,复杂景观下寄生蜂的迁入量高于简单景观下寄生蜂的迁入量。景观复杂性同样影响捕食性天敌的迁入时间,且捕食性天敌在复杂景观下迁入量均高于简单景观,而且存在显著性差异。两种景观中寄生蜂和捕食性天敌种群增长速率与最大种群密度均存在显著性差异。     

设施农业景观下破碎化麦田麦蚜及寄生蜂种群的最小适生面积

最小适生面积(MASH)指在一定的时空范围内物种能稳定存在的最小生境面积,它是种群生存力分析(PVA)的重要方法之一.本文采用基于种群数量-面积关系原理的MASH模型模拟了银川平原设施农业景观下破碎化麦田麦蚜、初寄生蜂与重寄生蜂种群发生的MASH.研究表明：密度 面积、增长速度-面积关系模型间存在反比例函数关系,不同物种存在的函数关系明显不同,尤其在不同营养级别的物种间,其函数关系差异更为明显.根据密度-面积关系,利用多项式回归模型计算了麦二叉蚜、麦长管蚜、燕麦蚜茧蜂、烟蚜茧蜂与蚜虫宽缘金小蜂的MASH,其营养级间的MASH差异显著.不同物种的MASH与营养级高低、体型大小、生境质量等有关.初寄生蜂最高的寄生率出现在800～1000 m²,可作为利用初寄生蜂自然控制麦蚜的依据,而不同营养级物种MASH差异可用于害虫的种群控制.     

农业景观结构对麦蚜寄生蜂群落组成的影响

麦蚜是中国北方小麦上最重要的害虫之一,既能直接刺吸危害也可传播多种病毒,但麦蚜通常的危害期只有2～3个月。随着现代农业与设施农业的发展,农业景观结构发生了巨大的改变,整个麦蚜寄生蜂群落也随之发生了显著的变化。经典假说认为复杂的农业景观能够维持局部的物种多样性及种间关系,也能够维持更大的天敌资源。作者在4种不同的麦田景观类型下研究了麦蚜及寄生蜂的群落结构,发现简单农业景观与复杂农业景观中寄生蜂寄生率与多样性差异不显著,但初寄生蜂在800m2左右的生境面积中寄生率与多样性最高,重寄生蜂却并没有表现出这种分布,而在更大的生境中重寄生率与多样性更高。研究结果表明:1)生境面积是影响麦蚜及寄生蜂群落的重要因子,2)简单农业景观与复杂农业景观下麦蚜及寄生蜂群落多样性差异不显著,3)一定程度的生境破碎化能够促进初寄生蜂的种群而抑制重寄生蜂的种群,但高度的生境破碎化会同时抑制2种寄生蜂的种群。     

区域性农田景观格局对麦蚜及其天敌种群的生态学效应

明确农田景观格局对害虫及其天敌种群的生态学效应,是开展区域性害虫生态调控的基础.以前的研究大多集中于小空间尺度下、单个景观因子对昆虫种群的作用,而从省级范围的大空间尺度、多个景观因子的分析很少.本文以山东省区域性小麦种植区为研究对象,基于遥感影像和土地覆盖分类数据以及田间调查的昆虫种群数据,分析了景观组成类型(component type)、构成比例(component proportions)和形状结构(shape structure)多因子对麦蚜及其天敌寄生蜂和瓢虫种群的综合作用.结果发现,农田景观组成类型中斑块类型(patch type)越多,越利于麦蚜和天敌瓢虫种群数量的增长;且斑块密度(patch density)越大,越利于麦蚜寄生蜂和天敌瓢虫数量的增加;景观形状结构中边界密度(edge density)越高,也越利于麦蚜寄生蜂和天敌瓢虫种群数量的增加.进一步定量评估了农田景观组成类型、构成比例和形状结构对麦蚜及其天敌种群影响的作用大小.结果表明,三类景观格局因子对麦蚜影响较小,权重为9.81%;而对麦蚜寄生蜂的影响权重为25.87%;对天敌瓢虫种群高达47.86%.本研究清楚地表明,通过优化农田景观中作物与非作物生境布局,可直接调节和增加天敌昆虫种类与数量,有效控制和减少小麦蚜虫的种群数量,从而提高区域性农田景观中天敌昆虫的生物控害服务功能.     

区域性农田景观格局对棉蚜种群数量的生态学效应

农田景观格局的变化显著影响害虫的发生和危害,不同景观格局会对害虫的种群数量产生不同程度的影响,因而明确农田景观格局对害虫的生态学效应是控制害虫的重要前提之一。以山东省的棉花种植区为研究区域,选取14个典型的尽量临近不同土地覆盖类型的棉花生产县,通过卫星遥感影像和土地覆盖分类数据综合分析获得取样县/区的景观因子指数,并系统调查对应县/区的棉蚜种群数量。省级范围的大空间尺度下分析景观组成、景观构成和景观结构等多因子分别与棉田中苗蚜和伏蚜种群的相关性。研究结果表明棉蚜的种群数量与景观格局有密切的关系,且棉蚜发生的两个时期苗蚜和伏蚜对景观因子的响应特征并不完全一致。苗蚜的种群数量与景观总面积、耕地的分形指数、县域范围的蔓延度和县域范围的回旋半径等呈显著正相关,与Simpson多样性指标呈显著负相关;伏蚜的种群数量与斑块丰富密度、居住工业交通的蔓延度等呈显著正相关。总之,苗蚜和伏蚜对景观的蔓延度(形)响应基本上是一致的,景观的破碎化程度越小,伏蚜和苗蚜发生越重。而苗蚜和伏蚜对景观多样性(质)的响应不一致,景观多样性高的农田景观不利于苗蚜的发生,对伏蚜的影响不显著;而丰富度密度有助于伏蚜的发生,却对苗蚜没有显著影响。这一结果显示了农业害虫的不同发生时期对农田景观格局响应的复杂性。     

区域农田景观格局对麦蚜种群数量的影响

明确农田景观格局对麦田蚜虫种群的影响,是开展区域性害虫生态调控的重要理论依据之一。以区域性小麦种植区为研究对象,基于遥感影像与土地覆盖分类数据以及田间调查的蚜虫种群数据,计算景观格局指数,使用负二项分布的广义线性模型从农田景观、非作物生境景观和区域景观3个方面分析了区域农田景观格局对麦田蚜虫种群的影响。结果表明,蚜虫种群的数量与草地的平均斑块面积和最大斑块指数显著正相关,与县域的平均几何最邻近距离和面积加权平均斑块面积显著负相关,与耕地的面积加权平均斑块面积显著负相关,与耕地的斑块密度显著正相关。草地斑块面积的增大、区域景观与耕地的破碎化、区域景观的聚集会促进蚜虫种群数量的增加。使用草地的斑块面积和最大斑块指数、区域景观的平均几何最邻近距离可以预测蚜虫种群的发生量。非作物生境草地的斑块面积、耕地的破碎化、区域景观的空间分布及破碎化是影响麦田蚜虫种群发生的重要景观因素。     

农田景观格局对华北地区麦田早期瓢虫种群发生的影响

【目的】评价在华北地区农田景观格局对早期麦田瓢虫种群数量的影响。【方法】本文通过黄板诱集法调查4月中下旬麦田瓢虫成虫数量,对不同空间尺度下的景观格局进行调查与主成分分析,并结合"校正后赤池信息准则(AICc)"对构建的线性模型进行筛选,评估了景观因子对瓢虫种群数量的影响。【结果】在半径0.5、1.0、1.5、2.0 km 4个景观尺度下以林地为主的非作物生境均有利于麦田瓢虫成虫种群数量的增加,在较大的尺度范围内村落和休耕地与麦田瓢虫的发生数量正相关。其中,0.5 km尺度下的景观因子最能预测麦田瓢虫种群数量,其中林地面积和瓢虫种群数量呈正相关,而麦田瓢虫却随着景观多样性指数的增加而降低。此外,龟纹瓢虫作为麦田早期瓢虫的优势种类对景观多样性的响应与瓢虫复合种群一致。【结论】在华北地区,农田景观系统中非作物生境有利于麦田早期瓢虫种群的发生。     

农业景观生物多样性与害虫生态控制

现代农业的一个重要特征就是人类对农田生态系统的干扰强度及频率不断增加,严重影响农业景观的结构及其生物多样性.农业景观结构的变化及其生物多样性的丧失,必然引起生态系统服务功能的弱化,不利于实施以保护自然天敌为主的害虫生态控制.农业的集约化经营导致自然生境破碎化,减少了农业景观的复杂性,使得作物和非作物变成一种相对离散化的生境类型和镶嵌的景观格局;破碎化的生境不仅会减少某些物种的丰度,还会影响物种之间的相互关系及生物群落的多样性和稳定性.非作物生境类型如林地、灌木篱墙、田块边缘区、休耕地和草地等,是一种比较稳定的异质化环境.非作物生境较少受到干扰,可以为寄生性和捕食性节肢动物提供适宜的越冬或避难场所以及替代猎物、花粉和花蜜等资源,因此,非作物生境有利于自然天敌的栖息和繁衍,也有利于它们迁入邻近的作物生境中对害虫起到调节和控制作用.景观的格局-过程-尺度影响农田生物群落物种丰富度、多度、多样性以及害虫与天敌之间的相互作用.从区域农业景观系统的角度出发,运用景观生态学的理论和方法来研究作物、害虫、天敌等组分在不同斑块之间的转移过程和变化规律,揭示害虫在较大尺度和具有异质性的空间范围内的灾变机理,可为利用农业景观生物多样性来保护农田自然天敌,实施害虫的区域性生态控制提供新的研究思路和手段.     

The effect of semi-natural habitats on aphids and their natural enemies across spatial and temporal scales

Semi-natural habitats in agricultural landscapes are generally assumed to enhance the biological control of insect pests based on native beneficial insects, by providing alternative prey and hosts, resources and refuges for overwintering. We hypothesized that natural enemies of winter wheat aphids should arrive sooner in fields near semi-natural habitats. We compared aphid, hoverfly (larvae and eggs) and parasitized aphid (mummies) abundances in 54 winter wheat fields located in southern France from 2003 to 2007. Six surveys were recorded each spring and were split into the early period (defined as the period before the peak of aphid growth) and the late period (after the peak). The wheat fields differed by their surrounding landscape composition measured as the proportion of semi-natural habitats (woods, hedges and grasslands), at three different spatial scales: 200 m, 500 m, and 1200 m. Despite great variability in abundance data between years, the abundance of hoverflies appeared more sensitive to landscape composition than aphid abundance was. Early abundance for both aphids and hoverflies was positively related to wood cover, but not late abundance in spring. The abundance of hoverflies was positively related to hedge and grassland cover at all spatial scales and both periods considered. Aphid parasitism was higher near hedges at the small spatial scale late in the spring. Our results confirmed that higher proportions of semi-natural habitats in agricultural landscapes enhance the biological control of pests, but this effect depends on the spatial scale, the time period in the spring and the natural enemies considered.     

Temporal variability of aphid biological control in contrasting landscape contexts

Landscape complexity may provide ecosystem services to agriculture through the provision of natural enemies of agricultural pests. Strong positive effect of adjacent semi-natural habitats on natural enemies in croplands has been evidenced, but the resulting impact on biological control remains unclear. Taking into account the temporal dynamics of pest and natural enemies in agricultural landscapes provides better resolution to the studies and better understanding of the biological control service.In this study, the population dynamics of aphids and two groups of predators (coccinellid and carabid beetles) were examined. Insects were sampled in 20 wheat fields, surrounded by structurally simple and complex landscapes in Chilean central valley. Considering the whole sampling period, the diversity of aphids and natural enemies were similar in wheat crops surrounded by both types of landscapes, and the abundance of ladybirds was higher in crops in the complex landscapes. The dynamics of predators was more advanced in complex landscapes than in the simple ones, whereas the dynamics of aphids were similar in both types of landscape. Negative correlation between abundance of predators and aphid population growth rate in both landscape contexts were observed suggesting a control of the pest population by the predators. Different temporal patterns were observed in these correlations in the two landscape contexts, which suggests differences in the biological control related to the landscape composition.The present study shows that colonization of crops by natural enemies occurs sooner in structurally complex landscapes and suggests that this early colonization may facilitate an early and efficient control of aphid populations, nevertheless the biological control efficiency seems to be higher in structurally simple landscapes later in the season.     

Landscape heterogeneity at multiple spatial scales enhances spider species richness in an agricultural landscape

Landscape supplementation, which enhances densities of organisms by combination of different landscape elements, is likely common in heterogeneous landscapes, but its prevalence and effects on species richness have been little explored. Using grassland-dwelling spiders in an agricultural landscape, we postulated that richness and abundances of major constituent species are both highest in intermediate mixtures of forests and paddy fields, and that this effect derives from multi-scale landscape heterogeneity. We collected spiders in 35 grasslands in an agricultural landscape in Japan and determined how species richness and abundances of major species related to local and landscape factors across different spatial scales. We used a generalized linear model to fit data, created all possible combinations of variables at 15 spatial scales, and then explored the best models using Akaike's information criterion. Species richness showed a hump-shaped pattern in relation to surrounding forest cover, and the spatial scale determining this relationship was a 300–500-m radius around the study sites. Local variables were of minor importance for species richness. Abundances of major species also exhibited a hump-shaped pattern when plotted against forest cover. Thus, a combination of paddy fields and forests is important for enhancement of grassland spider species richness and abundance, suggesting habitat supplementation. The effective spatial scales determining abundances varied, ranging from 200 to >1000 m, probably representing different dispersal abilities. Landscape compositional heterogeneity at multiple spatial scales may be thus crucial for the maintenance of species diversity.     

Scaling properties of multivariate landscape structure

Analyses of landscape context is essential for understanding how ecological patterns and processes relate to space. This requires that we quantify variation patterns of different landscape parameters, which may change relative to one another at different spatial scales. Here, we analyzed how statistical relationships of land-use composition parameters changed as a function of extent in 20 real agricultural landscapes. Furthermore, we tested the generality of these scaling relations in numerical simulations using 300 artificial landscapes. We analyzed proportions of artificial habitat types at different extent and compared these patterns with three dominant habitat types in real landscapes (forest, arable land and grassland) at four spatial scales (quadrates of 1–4 km). Both real and simulated landscapes showed that variance of landscape parameters (data differentiation) decreased and their correlations (data consistency) increased as scale increased, thereby suggesting general scaling laws. The potential statistical impact of these scaling relationships is revealed in simultaneous analyses of variation of (local) site parameters of 20 arable fields and their surrounding landscape context. At small and medium extent (quadrates of 1–3 km), variability of local site parameters (e.g. fertilization, pH-value) was high relative to those of landscape parameters. In contrast, at large extent (quadrates of 4 km) variability of landscape parameters was greater than that of site parameters indicating a fundamental shift in the relationship between these sets of parameters at different scales. Hence, it is clear that there is a high risk of artefactual correlations in hierarchical multi-scale landscape analyses when ecological data are related to the landscape context. Accordingly, there is a necessity for multi-scale analyses in landscape ecology to accurately evaluate the relative importance of landscape context at different spatial scales.     

Food web structure and biocontrol in a four-trophic level system across a landscape complexity gradient

Decline in landscape complexity owing to agricultural intensification may affect biodiversity, food web complexity and associated ecological processes such as biological control, but such relationships are poorly understood. Here, we analysed food webs of cereal aphids, their primary parasitoids and hyperparasitoids in 18 agricultural landscapes differing in structural complexity (42-93% arable land). Despite little variation in the richness of each trophic group, we found considerable changes in trophic link properties across the landscape complexity gradient. Unexpectedly, aphid-parasitoid food webs exhibited a lower complexity (lower linkage density, interaction diversity and generality) in structurally complex landscapes, which was related to the dominance of one aphid species in complex landscapes. Nevertheless, primary parasitism, as well as hyperparasitism, was higher in complex landscapes, with primary parasitism reaching levels for potentially successful biological control. In conclusion, landscape complexity appeared to foster higher parasitism rates, but simpler food webs, thereby casting doubt on the general importance of food web complexity for ecosystem functioning.