RELATIONSHIP OF GENETIC DIVERSITY AND NICHE CENTRALITY: A SURVEY AND ANALYSIS

The distribution of genetic diversity within and among populations in relation to species’ geographic ranges is important to understanding processes of evolution, speciation, and biogeography. One hypothesis predicts that natural populations at geographic range margins will have lower genetic diversity relative to those located centrally in species’ distributions owing to a link between geographic and environmental marginality; alternatively, genetic variation may be unrelated with geographic marginality via decoupling of geographic and environmental marginality. We investigate the predictivity of geographic patterns of genetic variation based on geographic and environmental marginality using published genetic diversity data for 40 species (insects, plants, birds, mammals, worms). Only about half of species showed positive relationships between geographic and environmental marginality. Three analyses (sign test, multiple linear regression, and meta‐analysis of correlation effect sizes) showed a negative relationship between genetic diversity and distance to environmental niche centroid, but no consistent relationship of genetic diversity with distance to geographic range center.     

Species richness and evolutionary niche dynamics: a spatial pattern-oriented simulation experiment

Evolutionary processes underlying spatial patterns in species richness remain largely unexplored, and correlative studies lack the theoretical basis to explain these patterns in evolutionary terms. In this study, we develop a spatially explicit simulation model to evaluate, under a pattern-oriented modeling approach, whether evolutionary niche dynamics (the balance between niche conservatism and niche evolution processes) can provide a parsimonious explanation for patterns in species richness. We model the size, shape, and location of species' geographical ranges in a multivariate heterogeneous environmental landscape by simulating an evolutionary process in which environmental fluctuations create geographic range fragmentation, which, in turn, regulates speciation and extinction. We applied the model to the South American domain, adjusting parameters to maximize the correspondence between observed and predicted patterns in richness of about 3,000 bird species. Predicted spatial patterns, which closely resemble observed ones (r2=0.795), proved sensitive to niche dynamics processes. Our simulations allow evaluation of the roles of both evolutionary and ecological processes in explaining spatial patterns in species richness, revealing the enormous potential of the link between ecology and historical biogeography under integrated theoretical and methodological frameworks.     

Assessing concurrent patterns of environmental niche and morphological evolution among species of horned lizards (Phrynosoma)

The prediction that variation in species morphology is related to environmental features has long been of interest to ecologists and evolutionary biologists. Many studies have demonstrated strong associations between morphological traits and local habitat characteristics, but few have considered the extent to which morphological traits may be associated with environmental features across broad geographic areas. Here, we use morphological, environmental and phylogenetic data compiled from Phrynosoma species to examine morphological and climatic variation across the geographic ranges of these species in an evolutionary context. We find significant phylogenetic signal in species’ environmental niches, but not in morphological traits. Furthermore, we demonstrate a significant correlation between species’ environmental niches and morphological traits when phylogenetic history is accounted for in the analysis. Our results suggest the importance of climatic variables in influencing morphological variation among species, and have implications for understanding how species distributions are constrained by environmental variation.     

Postglacial recolonization of North America by spadefoot toads: integrating niche and corridor modeling to study species’ range dynamics over geologic time

Understanding the factors that shape species’ distributions is a key topic in biogeography. As climates change, species can either cope with these changes through evolution, plasticity or by shifting their ranges to track the optimal climatic conditions. Ecological niche modeling (ENM) is a widespread technique in biogeography that estimates the niche of the organism by using occurrences and environmental data to estimate species’ potential distributions. ENMs are often criticized for failing to take species’ dispersal abilities into consideration. Here, we attempt to fill this gap by combining ENMs with dispersal and corridor modeling to study the range dynamics of North American spadefoot toads (Scaphiopodidae) over the Holocene. We first estimated the current and past distributions of spadefoot toads and then estimated their past distributions from the Last Glacial Maximum (LGM) to the present day. Then, we estimated how each taxon recolonized North American by using dispersal and corridor modeling. By combining these two modeling approaches we were able to 1) estimate the LGM refugia used by the North American spadefoot toads, 2) further refine these projections by estimating which of the putative LGM refugia contributed to the recolonization of North America via dispersal, and 3) estimate the relative influence of each LGM refugium to the current species’ distributions. The models were tested using previously published phylogeographic data, revealing a high degree of congruence between our models and the genetic data. These results suggest that combining ENMs and dispersal modeling over time is a promising approach to investigate both historical and future species’ range dynamics.     

Pathogeography: leveraging the biogeography of human infectious diseases for global health management

Biogeography is an implicit and fundamental component of almost every dimension of modern biology, from natural selection and speciation to invasive species and biodiversity management. However, biogeography has rarely been integrated into human or veterinary medicine nor routinely leveraged for global health management. Here we review the theory and application of biogeography to the research and management of human infectious diseases, an integration we refer to as ‘pathogeography’. Pathogeography represents a promising framework for understanding and decomposing the spatial distributions, diversity patterns and emergence risks of human infectious diseases into interpretable components of dynamic socio‐ecological systems. Analytical tools from biogeography are already helping to improve our understanding of individual infectious disease distributions and the processes that shape them in space and time. At higher levels of organization, biogeographical studies of diseases are rarer but increasing, improving our ability to describe and explain patterns that emerge at the level of disease communities (e.g. co‐occurrence, diversity patterns, biogeographic regionalisation). Even in a highly globalized world most human infectious diseases remain constrained in their geographic distributions by ecological barriers to the dispersal or establishment of their causal pathogens, reservoir hosts and/or vectors. These same processes underpin the spatial arrangement of other taxa, such as mammalian biodiversity, providing a strong empirical ‘prior’ with which to assess the potential distributions of infectious diseases when data on their occurrence is unavailable or limited. In the absence of quality data, generalized biogeographic patterns could provide the earliest (and in some cases the only) insights into the potential distributions of many poorly known or emerging, or as‐yet‐unknown, infectious disease risks. Encouraging more community ecologists and biogeographers to collaborate with health professionals (and vice versa) has the potential to improve our understanding of infectious disease systems and identify novel management strategies to improve local, global and planetary health.     

Geographic range size and evolutionary age in birds

Together with patterns of speciation and extinction, post-speciation transformations in the range sizes of individual species determine the form of contemporary species range-size distributions. However, the methodological problems associated with tracking the dynamics of a species' range size over evolutionary time have precluded direct study of such range-size transformations, although indirect evidence has led to several models being proposed describing the form that they might take. Here, we use independently derived molecular data to estimate ages of species in six monophyletic groups of birds, and examine the relationship between species age and global geographic range size. We present strong evidence that avian range sizes are not static over evolutionary time. In addition, it seems that, with the regular exception of certain taxa (for example island endemics and some threatened species), range-size transformations are non-random in birds. In general, range sizes appear to expand relatively rapidly post speciation; subsequently; and perhaps more gradually, they then decline as species age. We discuss these results with reference to the various models of range-size dynamics that have been proposed.     

The Impact of West African Trade on the Distribution of Chimpanzee and Elephant Populations (Guinea,Guinea-Bissau,Senegal, 19th–20th Century)

This article elaborates a relational historical geography of human, chimpanzee and elephant populations, working mainly from precolonial and early colonial (nineteenth and twentieth century) narratives by travellers to regions now corresponding to parts of Guinea, Guinea-Bissau and Senegal. It then compares a global ‘West African trade’ model of human and animal population’s spatial distribution with elements of an ‘East African settlement colony’ model drawn from other historical research. This perspective balances mainstream evolutionary approaches to animal biogeography with the human history, ecology and the geopolitics of their habitats. Taking such historical processes into account helps to unravel contrastive spatial and temporal dynamics of large mammal populations and to raise new questions about the anthropogenic causes of present-day population distributions.     

Range edges in heterogeneous landscapes: Integrating geographic scale and climate complexity into range dynamics

The impacts of climate change have re‐energized interest in understanding the role of climate in setting species geographic range edges. Despite the strong focus on species' distributions in ecology and evolution, defining a species range edge is theoretically and empirically difficult. The challenge of determining a range edge and its relationship to climate is in part driven by the nested nature of geography and the multidimensionality of climate, which together generate complex patterns of both climate and biotic distributions across landscapes. Because range‐limiting processes occur in both geographic and climate space, the relationship between these two spaces plays a critical role in setting range limits. With both conceptual and empirical support, we argue that three factors—climate heterogeneity, collinearity among climate variables, and spatial scale—interact to shape the spatial structure of range edges along climate gradients, and we discuss several ways that these factors influence the stability of species range edges with a changing climate. We demonstrate that geographic and climate edges are often not concordant across species ranges. Furthermore, high climate heterogeneity and low climate collinearity across landscapes increase the spectrum of possible relationships between geographic and climatic space, suggesting that geographic range edges and climatic niche limits correspond less frequently than we may expect. More empirical explorations of how the complexity of real landscapes shapes the ecological and evolutionary processes that determine species range edges will advance the development of range limit theory and its applications to biodiversity conservation in the context of changing climate.     

Where am I and why? Synthesizing range biology and the eco‐evolutionary dynamics of dispersal

Although generations of researchers have studied the factors that limit the distributions of species, we still do not seem to understand this phenomenon comprehensively. Traditionally, species’ ranges have been seen as the consequence of abiotic conditions and local adaptation to the environment. However, during the last years it has become more and more evident that biotic factors – such as intra‐ and interspecific interactions or the dispersal capacity of species – and even rapidly occurring evolutionary processes can strongly influence the range of a species and its potential to spread to new habitats. Relevant eco‐evolutionary forces can be found at all hierarchical levels: from landscapes to communities via populations, individuals and genes. We here use the metapopulation concept to develop a framework that allows us to synthesize this broad spectrum of different factors. Since species’ ranges are the result of a dynamic equilibrium of colonization and local extinction events, the importance of dispersal is immediately clear. We highlight the complex interrelations and feedbacks between ecological and evolutionary forces that shape dispersal and result in non‐trivial and partially counter‐intuitive range dynamics. Our concept synthesizes current knowledge on range biology and the eco‐evolutionary dynamics of dispersal. Synthesis What factors are responsible for the dynamics of species' ranges? Answering this question has never been more important than today, in the light of rapid environmental changes. Surprisingly, the ecological and evolutionary dynamics of dispersal – which represent the driving forces behind range formation – have rarely been considered in this context. We here present a framework that closes this gap. Dispersal evolution may be responsible for highly complex and non‐trivial range dynamics. In order to understand these, and possibly provide projections of future range positions, it is crucial to take the ecological and evolutionary dynamics of dispersal into account.     

Strong genetic differentiation but not local adaptation toward the range limit of a coastal dune plant

All species have limited geographic distributions; but the ecological and evolutionary mechanisms causing range limits are largely unknown. That many species’ geographic range limits are coincident with niche limits suggests limited evolutionary potential of marginal populations to adapt to conditions experienced beyond the range. We provide a test of range limit theory by combining population genetic analysis of microsatellite polymorphisms with a transplant experiment within, at the edge of, and 60 km beyond the northern range of a coastal dune plant. Contrary to expectations, lifetime fitness increased toward the range limit with highest fitness achieved by most populations at and beyond the range edge. Genetic differentiation among populations was strong, with very low, nondirectional gene flow suggesting range limitation via constraints to dispersal. In contrast, however, local adaptation was negligible, and a distance‐dependent decline in fitness only occurred for those populations furthest from home when planted beyond the range limit. These results challenge a commonly held assumption that stable range limits match niche limits, but also raise questions about the unique value of peripheral populations in expanding species’ geographical ranges.     

The ‘Hutchinsonian niche’ as an assemblage of demographic niches: implications for species geographic ranges

Hutchinson defined the ecological niche as a hypervolume shaped by the environmental conditions under which a species can ‘exist indefinitely’. Although several authors further discussed the need to adopt a demographic perspective of the ecological niche theory, very few have investigated the environmental requirements of different components of species’ life cycles (i.e. vital rates) in order to examine their internal niche structures. It therefore remains unclear how species’ demography, niches and distributions are interrelated. Using comprehensive demographic data for two well‐studied, short‐lived plants (Plantago coronopus, Clarkia xantiana), we show that the arrangement of species’ demographic niches reveals key features of their environmental niches and geographic distributions. In Plantago coronopus, opposing geographic trends in some individual vital rates, through different responses to environmental gradients (demographic compensation), stabilize population growth across the range. In Clarkia xantiana, a lack of demographic compensation underlies a gradient in population growth, which could translate in a directional geographic range shift. Overall, our results highlight that occurrence and performance niches cannot be assumed to be the same, and that studying their relationship is essential for a better understanding of species’ ecological niches. Finally, we argue for the value of considering the assemblage of species’ demographic niches when studying ecological systems, and predicting the dynamics of species geographical ranges.     

A long winter for the Red Queen: rethinking the evolution of seasonal migration

This paper advances an hypothesis that the primary adaptive driver of seasonal migration is maintenance of site fidelity to familiar breeding locations. We argue that seasonal migration is therefore principally an adaptation for geographic persistence when confronted with seasonality – analogous to hibernation, freeze tolerance, or other organismal adaptations to cyclically fluctuating environments. These ideas stand in contrast to traditional views that bird migration evolved as an adaptive dispersal strategy for exploiting new breeding areas and avoiding competitors. Our synthesis is supported by a large body of research on avian breeding biology that demonstrates the reproductive benefits of breeding‐site fidelity. Conceptualizing migration as an adaptation for persistence places new emphasis on understanding the evolutionary trade‐offs between migratory behaviour and other adaptations to fluctuating environments both within and across species. Seasonality‐induced departures from breeding areas, coupled with the reproductive benefits of maintaining breeding‐site fidelity, also provide a mechanism for explaining the evolution of migration that is agnostic to the geographic origin of migratory lineages (i.e. temperate or tropical). Thus, our framework reconciles much of the conflict in previous research on the historical biogeography of migratory species. Although migratory behaviour and geographic range change fluidly and rapidly in many populations, we argue that the loss of plasticity for migration via canalization is an overlooked aspect of the evolutionary dynamics of migration and helps explain the idiosyncratic distributions and migratory routes of long‐distance migrants. Our synthesis, which revolves around the insight that migratory organisms travel long distances simply to stay in the same place, provides a necessary evolutionary context for understanding historical biogeographic patterns in migratory lineages as well as the ecological dynamics of migratory connectivity between breeding and non‐breeding locations.     

Using Marine Snails to Teach Biogeography and Macroevolution: The Role of Larvae and Dispersal Ability in the Evolution and Persistence of Species

While some marine animals are capable of traveling great distances, many have limited mobility as adults and spend the majority of their lifetimes in a small geographical area or may even be cemented to a single place. While it might be expected that species with limited mobility would have small geographic distributions, some nevertheless occur over very large areas. This is the case for some marine snails (gastropods). A key factor that impacts the geographic distribution of marine snails is the type of larvae they have during the phase of their life history that follows hatching from an egg. Because adult snails do not typically travel vast distances, the mobility of the larval stage determines the species?? ability to reach new territories. Some larvae are capable of long-distance travel, while others are not. An important component of the process of speciation involves geographic isolation, so the type of larvae a snail species possesses impacts the likelihood that it will become geographically isolated and give rise to a new species. Larval form also affects how long snail species will persist on geological timescales before going extinct, as well as rates of speciation. This paper briefly reviews the evolutionary consequences of different types of larval development in marine gastropods (especially cone snails, which are one of the most diverse groups of marine animals), particularly in determining the dispersal ability and geographic ranges of individual species, the amount of genetic exchange among populations within species, and the duration of species through time. The goal of this short review is to provide context and examples for classroom discussions of the connections between biogeography and macroevolution. Furthermore, a classroom activity is presented that involves students?? using information about snail life history and biogeography to develop research plans (and predicted results) that could be utilized to test (i.e., support or reject) several macroevolutionary hypotheses.     

Body‐size distribution and biogeographical patterns in non‐marine ostracods (Crustacea: Ostracoda)

The idea that free‐living minute organisms have ubiquitous distributions has been recently revitalized, causing significant controversy. The ubiquitous model predicts that a threshold where ubiquity leaves room to biogeography might exist somewhere along the animal body‐size range. In the present study, such a prediction is tested by analysing body‐size frequency distribution, species distribution, and local‐to‐global species ratio at the scale of biogeographical realms in cypridoidean non‐marine ostracods, a group with a body‐size range in the ubiquity–biogeography (U‐B) boundary. Data were gathered for all described extant cypridoidean ostracod species (N = 1761), with body‐size recorded for 1134 of them. Although local‐to‐global species ratios show significant over‐dispersal of small‐body ostracods for the Palaearctic and the Australasian regions, there are explanations alternative to the ‘Everything is Everywhere’ model that can account for such a result. Indicators of taxonomic structure do not support the hypothesis of a random distribution of cypridoidean species among realms. Nevertheless, the strong biogeography signal occurring at a large scale vanishes at the local scale (country‐level within the Palaearctic), and suggests wide dispersion within biogeographical realms. Additional factors, including inconsistent taxonomic criteria for species recognition, uneven sampling effort, and an excess of ‘single‐report’ occurrences, have been identified too as potential distorters of the observed patterns. Taxonomic harmonization, open databases of biogeographical data, and better ecological information are suggested as critical goals that need to be achieved for further understanding of ostracod global distribution patterns. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 409–423.     

Mating system shifts a species’ range

Understanding the ecological and evolutionary mechanisms that shape a species’ range is an important goal in evolutionary biology. Evidence indicates that mating system is an effective predictor of the global range of native species or naturalized alien plants, but the mechanisms underlying this predictability are not elaborated. Here, we develop a theoretical model to account for the ranges of plants under different mating systems based on migration‐selection processes (an idea proposed by Haldane). The model includes alternation of gametophyte and sporophyte generations in one life cycle and the dispersal of haploid pollen and diploid seeds as vectors for gene flow. We show that the interaction between selfing rates and gametophytic selection determines the role of mating system in shaping a species’ range. Selfing restricts the species’ range under gametophytic selection in nonrandom mating systems, but expands the species’ range under the absence of gametophytic selection in any mating system. Gametophytic selection slightly restricts the species’ range in random mating. Both logarithmic and logistic models of population demography yield similar conclusions in the case of fixed or evolving genetic variance. The theory also helps to explain a broader relationship between mating system and range size following biological invasion or plant naturalization.     

On the concept of chorotype

Recent reviews of the meaning of the word ‘chorotype’ in biogeography have led to contrasting definitions and a confusion of concepts. This is because ‘chorotype’ has been used by different authors to express two different concepts: (1) groups of species with overlapping ranges (overall distributions) and (2) groups of species with a similar distribution within a certain area. To avoid confusion, I suggest the term ‘global chorotype’ be used to indicate a group into which species with similar ranges can be classified; and ‘regional chorotype’ be used for a group of species with similar distributions within a certain region. Although the global chorotype represents the world‐wide spatial responses of species to historical and environmental pressures, and does not vary with the area under consideration, a particular species might be classified into different regional chorotypes in different study areas.     

宏生态学(Macroecology)及其研究

宏生态学是生态学与其他宏观学科不断交叉和融合后的产物。它以个体、种群和物种的生态特征在大时空尺度上的格局和变化规律为主要研究内容,它比其他生态学更强调归纳和推论,也更依赖数据的积累。近年来,宏生态学在对物种一面积关系进行探讨的基础上,对生物类群间的物种数量的协同变化以及物种和高级分类单元间的关系等进行了新的研究;宏生态学试图将有机论和个体论结合来探讨和总结群落结构中的物种组成规律;并对物种多度和分布格局间的关系从生态位和异质种群角度进行新的解释;个体大小频次分布规律是宏生态学一重要内容,对其深入研究和探讨已与物种多度、能量、分布面积、历史起源等多方面特征相结合,并得到一些普遍性规律;最后,宏生态学还探讨物种在地理区域上的普遍性的分布模式,并对其假说进行检验和探讨。宏生态学在中国还处于刚起步阶段,但中国具有资源的优势,并具有一定的数据积累,将在宏生态学研究中发挥越来越重要的作用。     

The frequency of fitness peak shifts is increased at expanding range margins due to mutation surfing

Dynamic species' ranges, those that are either invasive or shifting in response to environmental change, are the focus of much recent interest in ecology, evolution, and genetics. Understanding how range expansions can shape evolutionary trajectories requires the consideration of nonneutral variability and genetic architecture, yet the majority of empirical and theoretical work to date has explored patterns of neutral variability. Here we use forward computer simulations of population growth, dispersal, and mutation to explore how range-shifting dynamics can influence evolution on rugged fitness landscapes. We employ a two-locus model, incorporating sign epistasis, and find that there is an increased likelihood of fitness peak shifts during a period of range expansion. Maladapted valley genotypes can accumulate at an expanding range front through a phenomenon called mutation surfing, which increases the likelihood that a mutation leading to a higher peak will occur. Our results indicate that most peak shifts occur close to the expanding front. We also demonstrate that periods of range shifting are especially important for peak shifting in species with narrow geographic distributions. Our results imply that trajectories on rugged fitness landscapes can be modified substantially when ranges are dynamic.     

Broad-scale latitudinal variation in female reproductive success contributes to the maintenance of a geographic range boundary in bagworms (Lepidoptera: Psychidae)

Background

Geographic range limits and the factors structuring them are of great interest to biologists, in part because of concerns about how global change may shift range boundaries. However, scientists lack strong mechanistic understanding of the factors that set geographic range limits in empirical systems, especially in animals.

Methodology/Principal Findings

Across dozens of populations spread over six degrees of latitude in the American Midwest, female mating success of the evergreen bagworm Thyridopteryx ephemeraeformis (Lepidoptera: Psychidae) declines from ∼100% to ∼0% near the edge of the species range. When coupled with additional latitudinal declines in fecundity and in egg and pupal survivorship, a spatial gradient of bagworm reproductive success emerges. This gradient is associated with a progressive decline in local abundance and an increased risk of local population extinction, up to a latitudinal threshold where extremely low female fitness meshes spatially with the species'' geographic range boundary.

Conclusions/Significance

The reduction in fitness of female bagworms near the geographic range limit, which concords with the abundant centre hypothesis from biogeography, provides a concrete, empirical example of how an Allee effect (increased pre-reproductive mortality of females in sparsely populated areas) may interact with other demographic factors to induce a geographic range limit.     

物种分布模型理论研究进展

利用物种分布模型估计物种的真实和潜在分布区,已成为区域生态学与生物地理学中非常活跃的研究领域。然而,到目前为止,这项技术的理论基础仍然存在不足之处,一些关键的生态过程未能被有效纳入到物种分布模型的理论框架中,从而为解释物种分布模型预测的结果带来了诸多困惑。鉴于此,总结了物种分布模型的理论基础;系统探讨了物种分布模型与物种分布区的关系;特别指出了物种分布模型研究中存在的理论问题;重点阐述了物种分布模型未来的发展方向。研究认为,物种分布模型与生态位理论、源-库理论、种群动态理论、集合种群理论、进化理论等具有重要的联系;正确理解物种分布模型的预测结果与物种分布区的关系,有赖于对影响物种分布的3个主要因素(环境条件、物种相互作用与物种迁移能力)做出定量的分离;目前物种分布模型主要存在的问题是未能将物种的相互作用和物种的迁移能力有效纳入到模型的构建过程中;未来物种分布模型的发展应该加强模型背后理论框架的研究,并进一步加强整合物种相互作用过程、种群动态过程、迁移过程和物种进化过程等内容。研究还认为,从更高的理论层次模拟功能群和群落结构将是未来物种分布模型的重要发展方向。