Towards the top: niche expansion of Taraxacum officinale and Ulex europaeus in mountain regions of South America

In the current context of ongoing global change, the understanding of how the niches of invasive species may change between different geographical areas or time periods is extremely important for the early detection and control of future invasions. We evaluated the effect of climate and non‐climate variables and the sensitivity to various spatial resolutions (i.e. 1 and 20 km) on niche changes during the invasion of Taraxacum officinale and Ulex europaeus in South America. We estimated niche changes using a combination of principal components analyses (PCA) and reciprocal Ecological Niche Modelling (rENM). We further investigated future invasion dynamics under a severe warming scenario for 2050 to unravel the role of niche shifts in the future potential distribution of the species. We observed a clear niche expansion for both species in South America towards higher temperature, precipitation and radiation relative to their native ranges. In contrast, the set of environmental conditions only occupied in the native ranges (i.e. niche unfilling) were less relevant. The magnitude of the niche shifts did not depend on the resolution of the variables. Models calibrated with occurrences from native range predicted large suitable areas in South America (outside of the Andes range) where T. officinale and U. europaeus are currently absent. Additionally, both species could increase their potential distributions by 2050, mostly in the southern part of the continent. In addition, the niche unfilling suggests high potential to invade additional regions in the future, which is extremely relevant considering the current impact of these species in the Southern Hemisphere. These findings confirm that invasive species can occupy new niches that are not predictable from knowledge based only on climate variables or information from the native range.     

Dispersal and neutral sampling mediate contingent effects of disturbance on plant beta‐diversity: a meta‐analysis

A major challenge in ecology, conservation and global‐change biology is to understand why biodiversity responds differently to similar environmental changes. Contingent biodiversity responses may depend on how disturbance and dispersal interact to alter variation in community composition (β‐diversity) and assembly mechanisms. However, quantitative syntheses of these patterns and processes across studies are lacking. Using null‐models and meta‐analyses of 22 factorial experiments in herbaceous plant communities across Europe and North America, we show that disturbance diversifies communities when dispersal is limited, but homogenises communities when combined with increased immigration from the species pool. In contrast to the hypothesis that disturbance and dispersal mediate the strength of niche assembly, both processes altered β‐diversity through neutral‐sampling effects on numbers of individuals and species in communities. Our synthesis suggests that stochastic effects of disturbance and dispersal on community assembly play an important, but underappreciated, role in mediating biotic homogenisation and biodiversity responses to environmental change.     

Revisiting the Holy Grail: using plant functional traits to understand ecological processes

One of ecology's grand challenges is developing general rules to explain and predict highly complex systems. Understanding and predicting ecological processes from species' traits has been considered a ‘Holy Grail’ in ecology. Plant functional traits are increasingly being used to develop mechanistic models that can predict how ecological communities will respond to abiotic and biotic perturbations and how species will affect ecosystem function and services in a rapidly changing world; however, significant challenges remain. In this review, we highlight recent work and outstanding questions in three areas: (i) selecting relevant traits; (ii) describing intraspecific trait variation and incorporating this variation into models; and (iii) scaling trait data to community‐ and ecosystem‐level processes. Over the past decade, there have been significant advances in the characterization of plant strategies based on traits and trait relationships, and the integration of traits into multivariate indices and models of community and ecosystem function. However, the utility of trait‐based approaches in ecology will benefit from efforts that demonstrate how these traits and indices influence organismal, community, and ecosystem processes across vegetation types, which may be achieved through meta‐analysis and enhancement of trait databases. Additionally, intraspecific trait variation and species interactions need to be incorporated into predictive models using tools such as Bayesian hierarchical modelling. Finally, existing models linking traits to community and ecosystem processes need to be empirically tested for their applicability to be realized.     

微生物降解芘过程中的关键细菌

【目的】探究在渤海沉积物中参与降解芘的关键细菌及他们之间潜在的相互关系。【方法】构建以芘为唯一碳源的微宇宙培养体系驯化来自渤海的表层沉积物,借助Illumina Hiseq 2500获取驯化过程中的细菌群落组成,基于CCLasso算法及相对丰度数据预测细菌之间的相互作用关系以构建微生物生态网络。【结果】30 d后芘的降解率为(67.07±2.37)%,细菌群落结构也发生了明显改变:Alphaproteobacteria、Flavobacteriia、Planctomycetia等的相对丰度明显增加,而Deltaproteobacteria、Anaerolineae及Spirochaetes等则明显减少。本研究获得一个由29个点143条边构成的微生物生态网络。分类已知的属中,Erythrobacter及Planctomyces等拥有较高的点度中心度。较强的互作关系发生在Erythrobacter与Flavobacteriaceae、Alphaproteobacteria中的未知属之间。【结论】在芘的微生物降解过程中,关键细菌之间存在紧密互作。Erythrobacter为关键细菌的代表属。     

Experimental assemblage of novel plant–herbivore interactions: ecological host shifts after 40 million years of isolation

Geographic isolation is the first step in insect herbivore diet specialization. Such specialization is postulated to increase insect fitness, but may simultaneously reduce insect ability to colonize novel hosts. During the Paleocene‐Eocene, plants from the order Zingiberales became isolated either in the Paleotropics or in the Neotropics. During the Cretaceous, rolled‐leaf beetles diversified in the Neotropics concurrently with Neotropical Zingiberales. Using a community of Costa Rican rolled‐leaf beetles and their Zingiberales host plants as study system, we explored if previous geographic isolation precludes insects to expand their diets to exotic hosts. We recorded interactions between rolled‐leaf beetles and native Zingiberales by combining DNA barcodes and field records for 7450 beetles feeding on 3202 host plants. To determine phylogenetic patterns of diet expansions, we established 20 experimental plots in the field, in which we planted plots five exotic Zingiberales, recording beetles feeding on these exotic hosts. In the laboratory, using both native and exotic host plants, we reared a subset of insect species that had expanded their diets to the exotic plants. The original plant–herbivore community comprised 24 beetle species feeding on 35 native hosts, representing 103 plant–herbivore interactions. After exotic host plant introduction, 20 percent of the beetle species expanded their diets to exotic Zingiberales. Insects only established on exotic hosts that belong to the same plant family as their native hosts. Laboratory experiments show that beetles are able to complete development on these novel hosts. In conclusion, rolled‐leaf beetles are preadapted to expand their diets to novel host plants even after millions of years of geographic isolation.     

Density dependence and temporal plasticity of competitive interactions during utilisation of resources by a community of lepidopteran stemborer species

Interactions within and between species sharing the same resources are characterised by competition or facilitation, and can be influenced by factors such as larval numbers and phenotypic plasticity of the interactions. The effect of larval density on the survival and relative growth rate of the stemborers Busseola fusca (Fuller) and Sesamia calamistis Hampson (both Lepidoptera: Noctuidae), and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) were studied, as well as the temporal plasticity of their competitive interactions. These stemborers attack maize crops (Zea mays L.) (Poaceae) in sub‐Saharan Africa. Experiments were conducted in the laboratory under controlled conditions at the optimum development temperature (25 °C) for the three species. Surrogate stems filled with artificial diet were intra‐ and interspecifically infested with larvae of each species. The effect of larval density on competition was studied at low (six larvae) and high (12 larvae) levels of infestation, whereas the temporal plasticity of competition was evaluated at 7, 14, 21, or 28 days after infestation. The two experiments involved single‐ and multi‐species infestation treatments. Larval numbers and wet mass in each artificial stem were recorded in each experiment. Survival and relative growth rate of the three species were significantly higher at low‐infestation levels when facing either intra‐ or interspecific competition. The intensity of competition was also temporally plastic among the species and increased as the duration of competition increased. These results are discussed in terms of general infestations of cereal crops by borers.     

Host‐associated differentiation in a pecan and water hickory Aphidomorpha community

Host‐associated differentiation (HAD) is the formation of genetically distinct, host‐associated populations created and maintained by ecologically mediated reproductive isolation. HAD potentially accounts for species origins in parasites, including herbivorous insects. Although case studies testing the occurrence of HAD are accumulating, it is still unclear how common HAD is and which specific ecological traits explain its occurrence. To address these issues, studies are needed that include negative results (i.e., instances in which parasite populations do not exhibit HAD) and test for HAD across communities (i.e., several parasite species on the same set of host species). In this study, HAD was tested in a community of six species of Aphidomorpha (Hemiptera) that share a host‐plant pair: pecan [Carya illinoinensis (Wangenh.) K.Koch] and water hickory [Carya aquatica (F.Michx) Nutt., both Juglandaceae] trees. All six species are parthenogenetic and three species are endophagous, traits that can exacerbate host‐specific selection. AFLP markers were employed to detect the presence of genetically distinct, host‐associated populations for each insect species. Strict HAD (i.e., the occurrence of genetically distinct pecan‐associated and water hickory‐associated genotypes) was found in Phylloxera notabilis Pergande (Phylloxeridae), Phylloxera devastatrix Pergande, and Monelliopsis pecanis Bissel (Aphididae). Monellia caryella Fitch (Aphididae) displayed a pattern of partial HAD (i.e., the occurrence of only a genetically distinct pecan‐associated genotype). No HAD was found in Melanocallis caryaefoliae Davis (Aphididae) or Phylloxera texana Stoetzel. The pattern of HAD occurrence in the pecan and water hickory Aphidomorpha community indicated that neither parthenogenesis nor endophagy sufficiently explain the occurrence of HAD in this system.     

农地整理中路沟渠生态化设计研究进展

农地整理是人类对农田生态系统的强烈干扰.传统农地整理中路沟渠设计的主要技术经济指标是方便生产通行和调配水资源以及提高水的利用率,尚缺少系统化、生态化考量,已经影响了农田物种扩散,导致生物栖息地环境的退化,并对农田生态系统的生物竞争机制、缓冲和补偿能力、抵御虫害能力产生了显著的负效应.本文系统总结了路沟渠生态化的功能,着重介绍了近年来生态化路沟渠的形式与结构设计、路沟渠生态工法参数的试验以及路沟渠生态材料选择的技术和方法.未来的相关研究应根据各级道路、灌排沟渠的不同功能要求和规格,按照田间不同生物的习性和栖息要求,精确设计能够满足大多数生物需求的农田路沟渠形态、结构和控制性尺寸,切实解决农地整理带来的上述问题.