A climate change context for the decline of a foundation tree species in south-western Australia: insights from phylogeography and species distribution modelling

Background and Aims A worldwide increase in tree decline and mortality has been linked to climate change and, where these represent foundation species, this can have important implications for ecosystem functions. This study tests a combined approach of phylogeographic analysis and species distribution modelling to provide a climate change context for an observed decline in crown health and an increase in mortality in Eucalyptus wandoo, an endemic tree of south-western Australia.Methods Phylogeographic analyses were undertaken using restriction fragment length polymorphism analysis of chloroplast DNA in 26 populations across the species distribution. Parsimony analysis of haplotype relationships was conducted, a haplotype network was prepared, and haplotype and nucleotide diversity were calculated. Species distribution modelling was undertaken using Maxent models based on extant species occurrences and projected to climate models of the last glacial maximum (LGM).Key Results A structured pattern of diversity was identified, with the presence of two groups that followed a climatic gradient from mesic to semi-arid regions. Most populations were represented by a single haplotype, but many haplotypes were shared among populations, with some having widespread distributions. A putative refugial area with high haplotype diversity was identified at the centre of the species distribution. Species distribution modelling showed high climatic suitability at the LGM and high climatic stability in the central region where higher genetic diversity was found, and low suitability elsewhere, consistent with a pattern of range contraction.Conclusions Combination of phylogeography and paleo-distribution modelling can provide an evolutionary context for climate-driven tree decline, as both can be used to cross-validate evidence for refugia and contraction under harsh climatic conditions. This approach identified a central refugial area in the test species E. wandoo, with more recent expansion into peripheral areas from where it had contracted at the LGM. This signature of contraction from lower rainfall areas is consistent with current observations of decline on the semi-arid margin of the range, and indicates low capacity to tolerate forecast climatic change. Identification of a paleo-historical context for current tree decline enables conservation interventions to focus on maintaining genetic diversity, which provides the evolutionary potential for adaptation to climate change.     

Contemporary perspectives on the niche that can improve models of species range shifts under climate change

Pioneering efforts to predict shifts in species distribution under climate change used simple models based on the correlation between contemporary environmental factors and distributions. These models make predictions at coarse spatial scales and assume the constancy of present correlations between environment and distribution. Adaptive management of climate change impacts requires models that can make more robust predictions at finer spatio-temporal scales by accounting for processes that actually affect species distribution on heterogeneous landscapes. Mechanistic models of the distribution of both species and vegetation types have begun to emerge to meet these needs. We review these developments and highlight how recent advances in our understanding of relationships among the niche concept, species diversity and community assembly point the way towards more effective models for the impacts of global change on species distribution and community diversity.     

复杂性-稳定性研究: 数学模型的进展

对自然生态系统的观察给人们以复杂的群落更稳定的直观印象, 但数学模型却得出了截然相反的结论。这一“悖论”使得复杂性-稳定性研究自20世纪70年代以来成为长期的热点。本文对这一领域的数学模型研究进行简要综述。首先对这一论题进行概念剖析, 然后将各类模型分为线性和非线性两大类, 前者即群落矩阵法, 后者包括相互作用矩阵法、复杂网络数值模拟法和食物网构件动力学法。它们分别基于不同的群落构建方法和稳定性判断标准, 探求各物种是如何相互作用并实现共存的。总体而言, 在随机构建的群落模型中, 多样性和连接度的增长不利于系统稳定; 而在更接近真实自然群落的模型中, 相互作用方式、网络拓扑结构、相互作用强度分布等方面的机制提供了稳定效应, 按此组织的生态网络可达到很高的复杂度。然而, 复杂性-稳定性的研究还远未结束, 当前的模型仍不足以反映自然群落中的复杂相互作用, 稳定性的概念也有待拓展。对这一议题的深入研究在生态学理论和生态系统管理实践方面都具有重大价值。     

Continental shelf as potential retreat areas for Austral‐Asian estrildid finches (Passeriformes: Estrildidae) during the Pleistocene

Studies dealing with changes of biodiversity in time and space constitute an important part of biogeography, ecology and conservation biology. Areas of long‐term climate stability are particularly interesting as they might have facilitated the survival of species over historical times and thus are crucial for understanding contemporary diversity patterns. In this study, we assessed the potential distribution of 23 estrildid finch species in order to analyse stability in recent and past diversity patterns and diversity centres in the Austral‐Asiatic region. We used Maxent to predict recent distributions of each species and to project them onto the climatic conditions of the Last Glacial Maximum (LGM, 21 000 yr BP) using two different scenarios (CCSM, MIROC). The resulting diversity patterns were tested on presence and possible shifts of distribution centres. Diversity patterns of forest‐ and savannah‐living species were considered combined and separately. During the LGM, potential diversity patterns of forest‐living species corroborated well with postulated rainforest refuges situated on the eastern coast of Cape York Peninsula. Our results indicate a remarkably high stability of existing diversity centres. Although projections into the past show some differences in detail in the extent and exact position of the diversity centres, they reveal largely congruent large scale patterns in both time slices. However, the models suggest a northward shift towards exposed continental shelf areas that where dry during the LGM. Clearly, centres of diversity were situated on this land bridge between Australia and New Guinea, highlighting their importance as areas of retreat for estrildid finches and maybe other savannah species in times of changing climatic conditions and associated sea‐level fluctuations.     

On metapopulations and microrefugia: palaeoecological insights

We highlight the importance of microrefugia in the light of population migration and genetic drift by synthesizing lessons learnt from metapopulation and palaeoecological studies. The concept of microrefugia is considered as a long‐term variant of conventional metapopulations, in which microclimatic stability supersedes gene flow in determining species survival. Not all species can maintain populations in microrefugia. Life history traits such as small body size, the capacity for asexual reproduction, and species with light genetic loads favour survival. Microrefugia will facilitate faster rates of species responses to climate change than envisioned in diffusion models, and potentially provide a means to alleviate the negative effects posed by natural or anthropogenic barriers to migration. Predictive models based on relatively coarse‐grained approaches that ignore microrefugia will lead to overestimates of extinction risk. Microrefugia should be identified and conserved, not for the species they contain, as these are likely to turn over with time, but as an important component of landscape diversity that will provide a safe haven for species not yet identified as at risk.     

不同农业景观背景下传粉昆虫群落的分布差异

农业景观中的自然、半自然生境等非农生境可为传粉昆虫提供丰富的食物来源、栖息地、繁殖地、避难所等,对维持生物多样性的稳定起着不可替代的作用。以巩义典型的山地-丘陵-河川混杂的复杂景观和民权的平原农业简单景观为研究区,分析不同景观背景下传粉昆虫群落的物种组成及其在不同生境中的分布特征。结果表明:(1)巩义研究区内累计捕获传粉昆虫18582头,民权研究区内累计捕获传粉昆虫18518头,优势传粉昆虫功能群为双翅目、膜翅目、鞘翅目和鳞翅目等;(2)景观复杂度更高的巩义研究区的传粉昆虫多样性、丰富度以及均匀度均显著高于民权研究区;存在大面积农田斑块的平原景观中则有更多的优势传粉昆虫个体;(3)农田斑块中具有更高的物种丰富度,但林地物种的多样性和均匀度则相对稍高些。农田斑块在作物花期能有效的提高传粉者种群密度,但林地等自然、半自然生境对于维持传粉者多样性和食物缺乏期种群的稳定具有重要作用。因此在未来为确保农业景观中传粉者的多样性与传粉服务的稳定,一方面要关注自然、半自然生境的作用,同时也要考虑不同景观背景下异质性特征对不同生物类群的影响差异。     

Threshold policies control for predator-prey systems using a control Liapunov function approach

The stability of predator-prey models, in the context of exploitation of renewable resources, subject to threshold policies (TP) is studied in this paper using the idea of backstepping and control Liapunov functions (CLF) well known in control theory, as well as the concept of virtual equilibria. TPs are defined and analysed for different types of one and two species predator-prey models. The models studied are the single species Noy-Meir herbivore-vegetation model, in a grazing management context, as well as the Rosenzweig-MacArthur two species predator-prey model, in a fishery management context. TPs are shown to be versatile and useful in managing renewable resources, being simple to design and implement, and also yielding advantages in situations of overexploitation.     

Functional and compositional comparison of two activated sludge communities remediating coking effluent

The success of engineered microbiological systems is evident in the global application of activated sludge communities to remediate coking effluent. However, there is a lack of understanding of the microbiology underlying treatment efficiency and stability. In this study, two functionally distinct activated sludge pools, treating the same effluent and operating under the same conditions, were examined to establish a relationship between overall diversity and/or functional diversity with respect to process stability. Molecular profiling, sequencing and RNA-based stable isotope probing were used to examine the bacterial diversity, general composition and functional composition of the most abundant members of the two communities. The inferior process stability in one of the pools could not be explained by reduced total bacterial diversity or evenness. RNA-based stable isotope probing revealed that both pools harboured an abundant phenol-degrading Acidovorax species, and that the pool of inferior stability accommodated an additional closely related phenol-degrading Acidovorax species at high abundance. These results are discussed in the context of deterministic and stochastic models of microbial community assembly.     

Analysis of biodiversity across levels of biological organization: a problem of defining traits

Biodiversity is a term that comprises the appearance, structure and function of all levels of biological organization, including genes, species and ecosystems. The vast majority of measures of biodiversity (usually termed ‘diversity indices’) considers only number, proportion and distribution of species which belong to a specified group and exist in a defined area or ecosystem. Genetic diversity as a part of biodiversity within species (or populations) was either not regarded in this respect or was treated (by geneticists) as a separate entity of diversity quantified with separate measures. Little attention has been given to the integration of both types of diversity, within and among species, in a single measurement (termed ‘transspecific’ diversity). In order to attain this integration on a general basis, an operational trait concept is developed which allows the determination of variation in traits observable in members not only of the same species but also of different species. The concept rests on methods of investigation that can be adapted to a broader range of organisms without modification of their characteristics. Once a trait is specified on this basis, any meaningful measure of diversity can be applied to assess biodiversity across levels of biological organization. The utility of the concept is demonstrated by application to the results of an earlier study on associations between species and genetic diversity in a forest tree community. Attributes of isozymes which are visible in electrophoresis are used as a transspecific genetic trait.     

再论生物多样性与生态系统的稳定性

本文在简述生物多样性与生态系统稳定性研究动态的基础上,从生物多样性和稳定性的概念出发,指出忽视多样性和稳定性的生物组织层次可能是造成观点纷争的根源之一。特定生物组织层次的稳定性可能更多地与该层次的多样性特征相关,探讨多样性和稳定性的关系应从不同的生物组织层次上进行,抗动是生态系统多样性与稳定性关系悖论中的重要因子,如果根据扰动的性质,把生态系统（或其他组织层次）区分为受非正常外力干扰和受环境因子时间异质性波动干扰2类系统,稳定性的4个内涵可以理解为：对于受非正常外力干扰的系统而言,抵抗力和恢复力是稳定性适宜的测度指标;对于受环境因子时间异质性波动干扰和系统而言。利用持久性和变异性衡量系统的稳定性则更具实际意义。结合对群落和种群层次多样性与稳定性相关机制的初步讨论,本文认为;在特定的前提下,多样性可以导致稳定性。     

Linking biodiversity to ecosystem function: implications for conservation ecology

We evaluate the empirical and theoretical support for the hypothesis that a large proportion of native species richness is required to maximize ecosystem stability and sustain function. This assessment is important for conservation strategies because sustenance of ecosystem functions has been used as an argument for the conservation of species. If ecosystem functions are sustained at relatively low species richness, then arguing for the conservation of ecosystem function, no matter how important in its own right, does not strongly argue for the conservation of species. Additionally, for this to be a strong conservation argument the link between species diversity and ecosystem functions of value to the human community must be clear. We review the empirical literature to quantify the support for two hypotheses: (1) species richness is positively correlated with ecosystem function, and (2) ecosystem functions do not saturate at low species richness relative to the observed or experimental diversity. Few empirical studies demonstrate improved function at high levels of species richness. Second, we analyze recent theoretical models in order to estimate the level of species richness required to maintain ecosystem function. Again we find that, within a single trophic level, most mathematical models predict saturation of ecosystem function at a low proportion of local species richness. We also analyze a theoretical model linking species number to ecosystem stability. This model predicts that species richness beyond the first few species does not typically increase ecosystem stability. One reason that high species richness may not contribute significantly to function or stability is that most communities are characterized by strong dominance such that a few species provide the vast majority of the community biomass. Rapid turnover of species may rescue the concept that diversity leads to maximum function and stability. The role of turnover in ecosystem function and stability has not been investigated. Despite the recent rush to embrace the linkage between biodiversity and ecosystem function, we find little support for the hypothesis that there is a strong dependence of ecosystem function on the full complement of diversity within sites. Given this observation, the conservation community should take a cautious view of endorsing this linkage as a model to promote conservation goals. Received: 2 September 1999 / Accepted: 26 October 1999     

农业景观动态对林地地表节肢动物多样性的影响

以黄河下游典型农区封丘县为研究区,在林地景观中进行地表节肢动物的观测。用物种丰富度和香农多样性指数代表物种多样性,选择代表景观背景的5个竞争模型:生境特性(H1,2012)、基质特性(H2,2012)、生境变化(H3,1984—2012)、基质变化(H4,1984—2012)和土壤-环境条件(H5,2012)从4个空间尺度上(100,250,350和500 m)进行分析,通过运用基于赤池信息量准则(Akaike information criterion,AIC)的多模型推理(Multi-model Inference,MMI)方法,在R软件里用广义线性模型(Generalized Linear Models,GLM)探究了研究区近30年(1984—2012年)景观背景变化对林地地表节肢动物多样性的影响。研究表明,不同景观背景模型对地表节肢动物多样性的影响具有尺度依赖性。在100 m的尺度下,生境特性(H1)最能够解释香农多样性和物种丰富度,但是随着尺度的增加,生境特性变化(H3)在较大(250、350 m和500 m)的尺度对物种丰富度和香农多样性影响最大,而基质特性和土壤-环境条件(H2和H5)的作用不显著。景观背景对地表节肢动物多样性的解释量达到40%。在研究区域,生境特性是表征香农多样性指数和物种丰富度的指标。     

Combining Niche and Dispersal in a Simple Model (NDM) of Species Distribution

Predicting the distribution of species has become a crucial issue in biodiversity research. Two kinds of model address this question: niche models, which are usually based on static approaches linking species distribution to habitat characteristics, and dispersal models, which are usually dynamic and process-based. We propose a model (NDM: niche and dispersal model) that considers the local presence of a species to result from a dynamic balance between extinction (based on the niche concept) and immigration (based on the dispersal concept), at a given moment in time, in a spatially explicit context. We show that NDM correctly predicts observed bird species and community distributions at different scales. NDM helps to reconcile the contrasting paradigms of metacommunity theory. It shows that sorting and mass effects are the factors determining bird species distribution. One of the most interesting features of NDM is its ability to predict well known properties of communities, such as decreasing species richness with decreasing patch size and increasing distance to the mainland, and the mid-domain effect at the regional scale, contrasting with predictions of much smaller effects at the local scale. NDM shows that habitat destruction in the matrix around patches of forest can affect the forest bird community, principally by decreasing the occurrence of typical matrix birds within the forest. This model could be used as the starting point for applied ecological studies on the management of species and community distributions.     

Ecosystem stability of temperate grasslands in response to variability of hydrological conditions

The relationship between biodiversity and the stability of ecosystem functioning over time has been widely studied. The current global context has refloated this topic for biodiversity's role in buffering the effects of different disturbances. In general, the results of these studies show that ecosystem functioning is more stable over time in more diverse systems. However, these results are derived from empirical research on small-scale studies, where species and disturbances conditions are manipulated. In this work, we used climate and floristic information data obtained from surveys over an extended period on Flooding Pampa grasslands (Argentina) with a remotely sensed indicator of the stability of net primary productivity at a regional scale over a broad temporal range to evaluate the relationship between species diversity and the stability of ecosystem functioning under different water conditions. We found a close correlation between Normalized Difference Vegetation Index responses of natural grasslands and climate variability in the study area. Besides, grasslands with higher species richness and diversity showed greater stability in ecosystem functioning at different water conditions. The results obtained could be relevant in natural resource management for the close relationship between diversity–stability in a local and regional productive context characterized by a simplified landscape of space and time.     

How is diversity related to species turnover through time?

Empirical studies across a wide range of taxa show that the slopes of species–time relationships often decline as average species richness increases, indicating that more diverse communities have greater temporal stability in species composition. I explored potential explanations for this observation using two simple model formulations for species temporal dynamics. In the Abiotic model, species turnover is governed by the degree of heterogeneity in the environment and the range of species' tolerances. In this case, more variable conditions lead to lower species richness and higher turnover, but only if the distribution of species' niche widths and the size of the species pool are independent of the degree of environmental variability. The Biotic model represents direct effects of diversity on turnover through positive or negative feedbacks between diversity and species' colonization and extinction rates. Declining turnover with increasing richness occurred when higher diversity either facilitated colonization by new species or reduced extinction rates of extant species. Both models could produce the observed pattern of declining turnover at higher diversity under some circumstances, however the conditions for this outcome in the Abiotic model were restrictive and potentially unrealistic. The models provide a process-based framework for understanding the connection between diversity and species turnover through time.     

物种多样性和系统发育多样性对阔叶红松林生产力的影响

生物多样性与生态系统功能间的关系已成为生态学研究的热点问题之一,其中植物多样性对森林生产力的驱动作用受到广泛关注,而其潜在驱动机制还存在很大争议.本研究依托黑龙江凉水国家级自然保护区典型阔叶红松林9 hm^2森林动态监测样地,利用2005年和2015年的调查数据,采用线性回归和结构方程模型探究不同空间尺度下物种多样性和系统发育多样性对森林生产力的影响.结果表明:物种多样性和系统发育多样性与生产力均呈正相关,随着空间尺度的增大,物种多样性对生产力的作用强度逐渐增强,而系统发育多样性对生产力的作用逐渐减弱;小尺度下系统发育多样性对生产力的影响大于物种多样性.生产力还受到非生物因素影响,在不同尺度下土壤因子与生产力均呈显著正相关,并且随着尺度的增大,土壤因子对生产力的作用逐渐占据主导地位.在今后研究中应将进化信息与生态系统功能相联系,可为其他多样性度量提供额外的解释力,同时还应考虑空间尺度及非生物因素的影响,为深入了解森林生产力的驱动机制提供科学依据.     

Concave trade-off curves between crop production and taxonomic,functional and phylogenetic diversity of birds

In a context of land scarcity, food production and biodiversity conservation objectives compete for land. The shape of the relationship between these two objectives may be helpful to inform decision-making. However, the metrics used to evaluate this relationship have so far been restricted to species abundances and species richness, which give no information on possible consequences on ecosystem functioning or on evolution history. Indeed, the shapes of the relationship between food production and other diversity facets, such as functional diversity and phylogenetic diversity, have rarely been studied. We considered 3 diversity facets: taxonomic diversity, functional diversity and phylogenetic diversity. For each facet, several biodiversity metrics have been proposed. The objective of this work was to investigate whether the shape of the trade-off curve between food production and biodiversity metrics depended on the considered facet of biodiversity. Using data from the national agricultural statistics, we computed edible energy from crops and from livestock on a nation-wide gradient covering French agroecosystems. Using bird observation data provided by the French Breeding Bird Survey (FBBS), we computed 9 (3 for each facet) biodiversity metrics in 516 different sites of the FBBS. The trade-off curves were then computed using additive mixed models. All metrics decreased along a crop production gradient. For functional and taxonomic diversity metrics, the slope was steeper at high levels of production, suggesting that actions aiming at increasing local taxonomic or functional diversity may be more efficient in regions with highest crop production, if restoration follows the same trajectory as biodiversity loss. The decrease was steeper for functional diversity than for taxonomic diversity, suggesting that agriculture can reduce the functional diversity of birds more than their taxonomic diversity.     

A general framework for neutral models of community dynamics

Neutral models of community dynamics are a powerful tool for ecological research, but their applications are currently limited to unrealistically simple types of dynamics and ignore much of the complexity that characterize natural ecosystems. Here, we present a new analytical framework for neutral models that unifies existing models of neutral communities and extends the applicability of existing models to a much wider spectrum of ecological phenomena. The new framework extends the concept of neutrality to fitness equivalence and in spite of its simplicity explains a wide spectrum of empirical patterns of species diversity including positive, negative and unimodal productivity–diversity relationships; gradual and highly delayed declines in species diversity with habitat loss; and positive and negative responses of species diversity to habitat heterogeneity. Surprisingly, the abundance distribution in all of these cases is given by the dispersal limited multinomial (DLM), the abundance distribution in Hubbell's zero-sum model, showing DLM's robustness and demonstrating that it cannot be used to infer the underlying community dynamics. These results support the hypothesis that ecological communities are regulated by a limited set of fundamental mechanisms much simpler than could be expected from their immense complexity.