Recent and rapid population growth and range expansion of the Lyme disease tick vector,Ixodes scapularis,in North America

Migration is a primary force of biological evolution that alters allele frequencies and introduces novel genetic variants into populations. Recent migration has been proposed as the cause of the emergence of many infectious diseases, including those carried by blacklegged ticks in North America. Populations of blacklegged ticks have established and flourished in areas of North America previously thought to be devoid of this species. The recent discovery of these populations of blacklegged ticks may have resulted from either in situ growth of long‐established populations that were maintained at very low densities or by migration and colonization from established populations. These alternative evolutionary hypotheses were investigated using Bayesian phylogeographic approaches to infer the origin and migratory history of recently detected blacklegged tick populations in the Northeastern United States. The data and results indicate that newly detected tick populations are not the product of in situ population growth from a previously established population but from recent colonization resulting in a geographic range expansion. This expansion in the geographic range proceeded primarily through progressive and local migration events from southern populations to proximate northern locations although long‐distance migration events were also detected.     

Projection matrices in population biology

Projection matrix models are widely used in population biology to project the present state of a population into the future, either as an attempt to forecast population dynamics, or as a way to evaluate life history hypotheses. These models are flexible and mathematically relatively easy. They have been applied to a broad range of plants and animals. The asymptotic properties of projection matrices have clearly defined biological interpretations, and the analysis of the effects of perturbations on these asymptotic properties offers new possibilities for comparative life history analysis. The connection between projection matrix models and the secondary theorem of natural selection opens life cycle phenomena to evolutionary interpretation.     

Craniometric variation,genetic theory,and modern human origins

Recent controversies surrounding models of modern human origins have focused on among-group variation, particularly the reconstruction of phylogenetic trees from mitochondrial DNA (mtDNA) and, the dating of population divergence. Problems in tree estimation have been seen as weakening the case for a replacement model and favoring a multiregional evolution model. There has been less discussion of patterns of within-group variation, although the mtDNA evidence has consistently shown the greatest diversity within African populations. Problems of interpretation abound given the numerous factors that can influence within-group variation, including the possibility of earlier divergence, differences in population size, patterns of population expansion, and variation in migration rates. We present a model of within-group phenotypic variation and apply it to a large set of craniometric data representing major Old World geographic regions (57 measurements for 1,159 cases in four regions: Europe, Sub-Saharan Africa, Australasia, and the Far East). The model predicts a linear relationship between variation within populations (the average within-group variance) and variation between populations (the genetic distance of populations to pooled phenotypic means). On a global level this relationship should hold if the long-term effective population sizes of each region are correctly specified. Other potential effects on withingroup variation are accounted for by the model. Comparison of observed and expected variances under the assumption of equal effective sizes for four regions indicates significantly greater within-group variation in Africa and significantly less within-group variation in Europe. These results suggest that the long-term effective population size was greatest in Africa. Closer examination of the model suggests that the long-term African effective size was roughly three times that of any other geographic region. Using these estimates of relative population size, we present a method for analyzing ancient population structure, which provides estimates of ancient migration. This method allows us to reconstruct migration history between geographic regions after adjustment for the effect of genetic drift on interpopulational distances. Our results show a clear isolation of Africa from other regions. We then present a method that allows direct estimation of the ancient migration matrix, thus providing us with information on the actual extent of interregional migration. These methods also provide estimates of time frames necessary to reach genetic equilibrium. The ultimate goal is extracting as much information from present-day patterns of human variation relevannt to issues of human origins. Our results are in agreement with mismatch distribution analysis of mtDNA, and they support a “weak Garden o Eden” model. In this model, modern-day variation can be explained by divergence from an initial source (perhaps Africa) into a number o small isolated populations, followed by later population expansion throughout our species. The major populationn expansions of Homo sapiens during and after the late Pleistocene have had the effect of “freezing” ancient patterns of population structure. While this is not the only possible scenario, we do note the close agreement with ecent analyses of mtDNA mismatch distibutions. © 1994 Wiley-Liss, Inc.     

Ancient DNA: Using molecular biology to explore the past

Ancient DNA has been discovered in many types of preserved biological material, including bones, mummies, museum skins, insects in amber and plant fossils, and has become an important research tool in disciplines as diverse as archaeology, conservation biology and forensic science. In archaeology, ancient DNA can contribute both to the interpretation of individual sites and to the development of hypotheses about past populations. Site interpretation is aided by DNA-based sex typing of fragmentary human bones, and by the use of genetic techniques to assess the degree of kinship between the remains of different individuals. On a broader scale, population migrations can be traced by studying genetic markers in ancient DNA, as in recent studies of the colonisation of the Pacific islands, while ancient DNA in preserved plant remains can provide information on the development of agriculture.     

mtDNA variation in East Africa unravels the history of afro‐asiatic groups

East Africa (EA) has witnessed pivotal steps in the history of human evolution. Due to its high environmental and cultural variability, and to the long‐term human presence there, the genetic structure of modern EA populations is one of the most complicated puzzles in human diversity worldwide. Similarly, the widespread Afro‐Asiatic (AA) linguistic phylum reaches its highest levels of internal differentiation in EA. To disentangle this complex ethno‐linguistic pattern, we studied mtDNA variability in 1,671 individuals (452 of which were newly typed) from 30 EA populations and compared our data with those from 40 populations (2970 individuals) from Central and Northern Africa and the Levant, affiliated to the AA phylum. The genetic structure of the studied populations—explored using spatial Principal Component Analysis and Model‐based clustering—turned out to be composed of four clusters, each with different geographic distribution and/or linguistic affiliation, and signaling different population events in the history of the region. One cluster is widespread in Ethiopia, where it is associated with different AA‐speaking populations, and shows shared ancestry with Semitic‐speaking groups from Yemen and Egypt and AA‐Chadic‐speaking groups from Central Africa. Two clusters included populations from Southern Ethiopia, Kenya and Tanzania. Despite high and recent gene‐flow (Bantu, Nilo‐Saharan pastoralists), one of them is associated with a more ancient AA‐Cushitic stratum. Most North‐African and Levantine populations (AA‐Berber, AA‐Semitic) were grouped in a fourth and more differentiated cluster. We therefore conclude that EA genetic variability, although heavily influenced by migration processes, conserves traces of more ancient strata. Am J Phys Anthropol, 2013. © 2013 Wiley Periodicals, Inc.     

Pre‐Columbian population dynamics in coastal southern Peru: A diachronic investigation of mtDNA patterns in the Palpa region by ancient DNA analysis

Alternative models have been proposed to explain the formation and decline of the south Peruvian Nasca culture, ranging from migration or invasion to autochthonous development and ecological crisis. To reveal to what extent population dynamic processes accounted for cultural development in the Nasca mainland, or were influenced by them, we analyzed ancient mitochondrial DNA of 218 individuals, originating from chronologically successive archaeological sites in the Palpa region, the Paracas Peninsula, and the Andean highlands in southern Peru. The sampling strategy allowed a diachronic analysis in a time frame from approximately 800 BC to 800 AD. Mitochondrial coding region polymorphisms were successfully analyzed and replicated for 130 individuals and control region sequences (np 16021–16408) for 104 individuals to determine Native American mitochondrial DNA haplogroups and haplotypes. The results were compared with ancient and contemporary Peruvian populations to reveal genetic relations of the archaeological samples. Frequency data and statistics show clear proximity of the Nasca populations to the populations of the preceding Paracas culture from Palpa and the Peninsula, and suggest, along with archaeological data, that the Nasca culture developed autochthonously in the Rio Grande drainage. Furthermore, the influence of changes in socioeconomic complexity in the Palpa area on the genetic diversity of the local population could be observed. In all, a strong genetic affinity between pre‐Columbian coastal populations from southern Peru could be determined, together with a significant differentiation from ancient highland and all present‐day Peruvian reference populations, best shown in the differential distribution of mitochondrial haplogroups. Am J Phys Anthropol 2010. © 2009 Wiley‐Liss, Inc.     

Altitudinal migration: ecological drivers,knowledge gaps,and conservation implications

Animal migration has been the subject of intensive research for more than a century, but most research has focused on long‐distance rather than short‐distance migration. Altitudinal migration is a form of short‐distance migration in which individuals perform seasonal elevational movements. Despite its geographic and taxonomic ubiquity, there is relatively little information about the intrinsic and extrinsic factors that influence altitudinal migratory behaviour. Without this information, it is difficult to predict how rapid environmental changes will affect population viability of altitudinal migrants. To synthesize current knowledge, we compiled literature on altitudinal migration for all studied taxa, and identified the leading hypotheses explaining this behaviour. Studies of animal altitudinal migration cover many taxonomic lineages, with birds being the most commonly studied group. Altitudinal migration occurs in all continents except for Antarctica, but about a third of the literature focused on altitudinal migration in North America. Most research suggests that food and weather are the primary extrinsic drivers of altitudinal migration. In addition, substantial individual‐level variation in migratory propensity exists. Individual characteristics that are associated with sex, dominance rank, and body size explain much of the variation in migratory propensity in partially migratory populations, but individual‐level correlates are poorly known for most taxa. More research is needed to quantify the effects of habitat loss, habitat fragmentation, and climate change on altitudinal migrants. Demographic studies of individually marked populations would be particularly valuable for advancing knowledge of the cascading effects of environmental change on migratory propensity, movement patterns, and population viability. We conclude our review with recommendations for study designs and modelling approaches that could be used to narrow existing knowledge gaps, which currently hinder effective conservation of altitudinal migratory species.     

新疆哈密拉甫却克墓地人的颅面部测量学特征

新疆地处欧亚大陆东西方交汇处,公元前200年以后的人群迁徙、融合历程能够反映丝绸之路沿线地区不同族群的形成历史和多元文化的互动模式。拉甫却克墓地是东疆哈密地区首次发掘的历史时期墓葬群。本文基于该墓地10例成年人颅面部测量数据,采用多元统计及生物距离的方法来评估拉甫却克墓地的人群结构,并对哈密绿洲地带青铜时代晚期到历史时期的人群变迁进行初步探索。结果显示：1）拉甫却克人群呈现出明显的异质性,既有与欧亚大陆东部人群颅面部特征相近的个体,也有表现出东西方混合特征的个体;2）青铜时代晚期至早期铁器时代（公元前2000年至公元前1000年）,哈密人群在体质特征上存在连续性;而早期铁器时代到历史时期（公元前1000年以后）,随着欧亚大陆东部人群遗传贡献的增加,哈密人群体质特征发生明显变化。结合考古证据和历史记录,新的人骨标本让我们对哈密历史时期的人群迁徙和融合有了初步认识,也使后续可以针对这一问题展开更详细的多学科研究。     

When new human‐modified habitats favour the expansion of an amphibian pioneer species: Evolutionary history of the natterjack toad (Bufo calamita) in a coal basin

Human activities affect microevolutionary dynamics by inducing environmental changes. In particular, land cover conversion and loss of native habitats decrease genetic diversity and jeopardize the adaptive ability of populations. Nonetheless, new anthropogenic habitats can also promote the successful establishment of emblematic pioneer species. We investigated this issue by examining the population genetic features and evolutionary history of the natterjack toad (Bufo [Epidalea] calamita) in northern France, where populations can be found in native coastal habitats and coalfield habitats shaped by European industrial history, along with an additional set of European populations located outside this focal area. We predicted contrasting patterns of genetic structure, with newly settled coalfield populations departing from migration–drift equilibrium. As expected, coalfield populations showed a mosaic of genetically divergent populations with short‐range patterns of gene flow, and native coastal populations indicated an equilibrium state with an isolation‐by‐distance pattern suggestive of postglacial range expansion. However, coalfield populations exhibited (i) high levels of genetic diversity, (ii) no evidence of local inbreeding or reduced effective population size and (iii) multiple maternal mitochondrial lineages, a genetic footprint depicting independent colonization events. Furthermore, approximate Bayesian computations suggested several evolutionary trajectories from ancient isolation in glacial refugia during the Pleistocene, with biogeographical signatures of recent expansion probably confounded by human‐mediated mixing of different lineages. From an evolutionary and conservation perspective, this study highlights the ecological value of industrial areas, provided that ongoing regional gene flow is ensured within the existing lineage boundaries.     

Differential effects of historical migration,glaciations and human impact on the genetic structure and diversity of the mountain pasture weed Veratrum album L.

Aim Today’s genetic population structure and diversity of species can be understood as the result of range expansion from the area of origin, past climatic oscillations and contemporary processes. We examined the relative importance of these factors in Veratrum album L., a toxic weed of mountain grasslands. Location Continental Europe. Methods Forty populations from the Asian border (Urals and Caucasus) to Portugal were studied using amplified fragment length polymorphisms (AFLPs) combined with selected plant and population measures. The data were analysed with phylogenetic, population genetic and regression methods inferring both genetic structure and diversity from geographic and ecological factors. Results Fragment frequency clines together with genetic distance clustering and principal coordinates analysis indicated an east–west direction in the genetic structure of V. album, suggesting ancient migration into Europe from a proposed Asian origin. However, the strong geographic pattern in the genetic structure, pronounced isolation by distance (R² = 0.74) and moderate overall population differentiation (F_ST = 0.13) suggests high historical gene flow, possibly during glacials, and vicariance into mountainous regions during interglacials. Occurrence of V. album during the last glaciation in several areas along the periphery of the Alps and recolonization of this mountain range from both eastern and central–western areas was indicated. Genetic diversity was highest in central Europe, a pattern that did not agree with the expectations from east–west migration into Europe. Furthermore, managed habitats showed higher levels of genetic diversity compared to unmanaged habitats. Stepwise linear regression determined shoot density and soil phosphorus as the main predictors of within‐population genetic diversity (R² = 0.40). Main conclusions Our results showed that V. album retained genetic imprints of historical range expansion into Europe, although this was alleviated by the influence of climatic oscillations and contemporary processes. For example, genetic population structure was strongly affected by post‐glacial vicariance while patterns of genetic diversity seemed mainly to be influenced by human land use. Our findings highlight the importance of applying a synthetic approach, testing the influence of both historical and contemporary processes on genetic structure and diversity in order to understand complex phylogeographic patterns. This may especially apply to widespread species, such as weeds. Implications of our findings for biological control are briefly discussed.     

Relative influences of historical and contemporary forces shaping the distribution of genetic variation in the Atlantic killifish, Fundulus heteroclitus

A major goal of population genetics research is to identify the relative influences of historical and contemporary processes that serve to structure genetic variation. Most population genetic models assume that populations exist in a state of migration-drift equilibrium. However, in the past this assumption has rarely been verified, and is likely rarely achieved in natural populations. We assessed the equilibrium status at both local and regional scales of the Atlantic killifish, Fundulus heteroclitus . This species is a model organism for the study of adaptive clinal variation, but has also experienced a complicated history of range expansion and secondary contact following allopatric divergence, potentially obscuring the influence of contemporary evolutionary processes. Presumptively neutral genetic markers (microsatellites) demonstrated zones of secondary intergradation among coastal populations centred around northern New Jersey and the Chesapeake Bay region. Analysis of genetic variation indicated isolation by distance among some populations and provided supporting evidence that the Delaware Bay, but not the Chesapeake Bay, has acted as a barrier to dispersal among coastal populations. Bayesian estimates indicated large effective population sizes and low migration rates, and were in good agreement with empirically derived estimates of population and neighbourhood size from mark–recapture studies. These data indicate that populations are not in migration-drift equilibrium at a regional scale, and suggest that contributing factors include large population size combined with relatively low migration rates. These conditions should be considered when interpreting the evolutionary significance of the distribution of genetic variation among F. heteroclitus populations.     

Dispersal-induced desynchronization: from metapopulations to metacommunities

The conceptualization of fragmented populations in terms of metapopulation theory has become standard over the last three decades. It is well known that increases in between‐patch migration rates cause more synchronous population fluctuations and that this coherence increases the risk of global metapopulation extinction. Because species’ migration rates and the probability of individuals surviving migration events depend on the effective distance between patches, the benefit of improving conservation corridors or the matrix between habitat patches has been questioned. As populations occur in the context of larger communities, moving from a metapopulation to a metacommunity model framework is a natural extension to address the generality of these conclusions. We show how considering a metacommunity can modify the conclusion that decreasing the effective distance between habitat patches (via improving matrix quality or other measures) necessarily increases the degree of metapopulation synchrony. We show that decreases in effective between‐patch distance may deter population synchrony because of the simultaneous effect this change has on the migration patterns of other species. These results indicate that species interactions need to be considered when the effect of conservation measures on population synchrony, and ultimately persistence, is addressed.     

When to stay,when to disperse and where to go: survival and dispersal patterns in a spatially structured seabird population

Dispersal is a key process for the population dynamics of spatially structured populations (at local and metapopulation levels), so the understanding of the mechanisms underlying the movement of individuals in space and time is important for evolutionary and ecological studies. Here we analyzed, for the first time, a long‐term (1992–2009) multi‐site capture– recapture database collected at four local populations of a long‐lived seabird, the Audouin’s gull Larus audouinii, covering 90% of its total world population. Those local populations show different ecological and demographic features that allow us to assess the influence of several key factors involved in breeding dispersal patterns at large spatio‐temporal scales. A recently developed analytical tool in mark–recapture modelling, the multi‐event approach, allowed us to obtain separate departure and settlement probabilities and test different biological hypotheses for each step of the dispersal process. Our results revealed that site fidelity was the most common strategy among breeders, and dispersal was only high from the site with the lowest population size and habitat quality. However, departures from the two largest local populations increased over the study period in response to severe ecological perturbations. Dispersers chose different settlement patches depending on their site of origin, with settlement choices determined by the population size of the destination colony rather than by the local reproductive performance, foraging area (a proxy of food availability) or distance to the destination site. Our results indicate that a breeding site is not abandoned by breeders unless a series of cumulative perturbations occur; once dispersing, settlement is directed towards densely populated sites, with dispersers using population size to rapidly assess the quality of the breeding patch.     

Correlates of alternative migratory strategies in western bluebirds

Partial migration occurs when only some animals in a population migrate. While evidence suggests that migratory strategies are partially controlled by genes, individual and environmental conditions which alter the cost‐benefit trade‐off of migration among individuals are also likely to play a role. Three hypotheses have been advanced to explain condition‐dependent partial migration: the arrival time, dominance and body size hypotheses. In this study, we asked whether these hypotheses explained differences in migratory strategy among individuals in a partially migratory population of western bluebirds Sialia mexicana breeding in southern British Columbia, Canada. We used stable hydrogen isotope signatures in claw tissue to determine migratory strategy of individual bluebirds, and examined patterns of migration at both individual and population levels. The proportion of resident bluebirds varied significantly over the three years of the study, and across study sites. Several migrants switched to the resident strategy between years; however, we found no evidence of strategy switching in the opposite direction. Young birds were significantly more likely to be resident than older birds, a pattern which could arise if early arrival is particularly important for birds obtaining a territory for the first time. Furthermore, young females were the most likely of all sex–age classes to be resident, which may reflect a survival advantage of residency for young females. Finally, birds mated assortatively by migratory strategy and isotopic evidence suggests that members of a pair often wintered in the same place. Our results provided no support for the dominance or body size hypotheses, and only limited support for the arrival time hypothesis in bluebirds. However, taken together, we suggest that our findings indicate that social factors may influence migratory strategies in this system.     

Phylogeography of Ophiorrhiza japonica (Rubiaceae) in continental islands,the Ryukyu Archipelago,Japan

Aim Phylogeographical patterns in the Ryukyu Archipelago have been explained primarily by landbridge formation and the opening of two straits in the Pliocene, namely the Tokara and Kerama gaps. These old straits have been considered to be the barriers most likely to determine genetic boundaries. To test this, we conducted a molecular analysis of the herb Ophiorrhiza japonica. We discuss the causes of and processes involved in its phylogeographical structure and explore aspects of island separation other than the duration of the straits to explain genetic boundaries at the gaps. Location Ryukyu Archipelago, Japan. Methods Plants were collected from 40 localities in the archipelago and vicinity. Non‐coding regions of chloroplast DNA were sequenced. The genealogical relationships among haplotypes were estimated using a statistical parsimony network. To examine the phylogeographical structure, we compared two parameters of population differentiation, namely G_ST and N_ST, and conducted correlation analysis of genetic and geographical distances. Genetic boundaries were identified using Monmonier’s maximum difference algorithm. To test vicariance–dispersal hypotheses, that is, vicariance after migration via the Pliocene landbridge or over‐sea dispersal in the Pleistocene, molecular dating analysis was conducted. Results A statistical parsimony network revealed that the haplotypes from the Ryukyu Archipelago and northwards coalesce to one ancestral haplotype in Taiwan. A clear phylogeographical structure was observed: plants within the same population and populations in geographical proximity were phylogenetically close. A genetic boundary was recognized across the Kerama Gap, but not across the Tokara Gap. Dating analysis suggested that population divergence across the Kerama Gap occurred in the early to late Pleistocene. Main conclusions The statistical parsimony network suggests migration from Taiwan and northward range expansion in the archipelago. Based on the divergence time, over‐sea dispersal in the Pleistocene is likely, although migration via a Pliocene landbridge is not totally rejected. Negligible genetic differentiation across the Tokara Gap suggests recent over‐sea dispersal, possibly facilitated by the small geographical width of the gap. Conversely, the large genetic differentiation across the Kerama Gap is probably explained by the large geographical distance across it. The past splitting of a landbridge would have had a significant influence on population differentiation after a certain geographical distance was reached.     

Representing genetic variation as continuous surfaces: an approach for identifying spatial dependency in landscape genetic studies

Landscape genetics, an emerging field integrating landscape ecology and population genetics, has great potential to influence our understanding of habitat connectivity and distribution of organisms. Whereas typical population genetics studies summarize gene flow as pairwise measures between sampling localities, landscape characteristics that influence population genetic connectivity are often continuously distributed in space. Thus, there are currently gaps in both the ability to analyze genotypic data in a continuous spatial context and our knowledge of expected of landscape genetic structure under varying conditions. We present a framework for generating continuous “genetic surfaces”, evaluate their statistical properties, and quantify statistical behavior of landscape genetic structure in a simple landscape. We simulated microsatellite genotypes under varying parameters (time since vicariance, migration, effective population size) and used ancestry (q) values from STRUCTURE to interpolate a genetic surface. Using a spatially adjusted Pearson's correlation coefficient to test the significance of landscape variable(s) on genetic structure we were able to detect landscape genetic structure on a contemporary time scale (≥5 generations post vicariance, migration probability ≤0.10) even when population differentiation was minimal (F_ST≥0.00015). We show that genetic variation can be significantly correlated with geographic distance even when genetic structure is due to landscape variable(s), demonstrating the importance of testing landscape influence on genetic structure. Finally, we apply genetic surfacing to analyze an empirical dataset of black bears from northern Idaho USA. We find black bear genetic variation is a function of distance (autocorrelation) and habitat patch (spatial dependency), consistent with previous results indicating genetic variation was influenced by landscape by resistance. These results suggest genetic surfaces can be used to test competing hypotheses of the influence of landscape characteristics on genetic structure without delineation of categorical groups.     

Population and evolutionary dynamics in spatially structured seasonally varying environments

Increasingly imperative objectives in ecology are to understand and forecast population dynamic and evolutionary responses to seasonal environmental variation and change. Such population and evolutionary dynamics result from immediate and lagged responses of all key life‐history traits, and resulting demographic rates that affect population growth rate, to seasonal environmental conditions and population density. However, existing population dynamic and eco‐evolutionary theory and models have not yet fully encompassed within‐individual and among‐individual variation, covariation, structure and heterogeneity, and ongoing evolution, in a critical life‐history trait that allows individuals to respond to seasonal environmental conditions: seasonal migration. Meanwhile, empirical studies aided by new animal‐tracking technologies are increasingly demonstrating substantial within‐population variation in the occurrence and form of migration versus year‐round residence, generating diverse forms of ‘partial migration’ spanning diverse species, habitats and spatial scales. Such partially migratory systems form a continuum between the extreme scenarios of full migration and full year‐round residence, and are commonplace in nature. Here, we first review basic scenarios of partial migration and associated models designed to identify conditions that facilitate the maintenance of migratory polymorphism. We highlight that such models have been fundamental to the development of partial migration theory, but are spatially and demographically simplistic compared to the rich bodies of population dynamic theory and models that consider spatially structured populations with dispersal but no migration, or consider populations experiencing strong seasonality and full obligate migration. Second, to provide an overarching conceptual framework for spatio‐temporal population dynamics, we define a ‘partially migratory meta‐population’ system as a spatially structured set of locations that can be occupied by different sets of resident and migrant individuals in different seasons, and where locations that can support reproduction can also be linked by dispersal. We outline key forms of within‐individual and among‐individual variation and structure in migration that could arise within such systems and interact with variation in individual survival, reproduction and dispersal to create complex population dynamics and evolutionary responses across locations, seasons, years and generations. Third, we review approaches by which population dynamic and eco‐evolutionary models could be developed to test hypotheses regarding the dynamics and persistence of partially migratory meta‐populations given diverse forms of seasonal environmental variation and change, and to forecast system‐specific dynamics. To demonstrate one such approach, we use an evolutionary individual‐based model to illustrate that multiple forms of partial migration can readily co‐exist in a simple spatially structured landscape. Finally, we summarise recent empirical studies that demonstrate key components of demographic structure in partial migration, and demonstrate diverse associations with reproduction and survival. We thereby identify key theoretical and empirical knowledge gaps that remain, and consider multiple complementary approaches by which these gaps can be filled in order to elucidate population dynamic and eco‐evolutionary responses to spatio‐temporal seasonal environmental variation and change.     

Exploring the role of Micronesian islands in the maintenance of coral genetic diversity in the Pacific Ocean

Understanding how genetic diversity is maintained across patchy marine environments remains a fundamental problem in marine biology. The Coral Triangle, located in the Indo‐West Pacific, is the centre of marine biodiversity and has been proposed as an important source of genetic diversity for remote Pacific reefs. Several studies highlight Micronesia, a scattering of hundreds of small islands situated within the North Equatorial Counter Current, as a potentially important migration corridor. To test this hypothesis, we characterized the population genetic structure of two ecologically important congeneric species of reef‐building corals across greater Micronesia, from Palau to the Marshall Islands. Genetic divergences between islands followed an isolation‐by‐distance pattern, with Acropora hyacinthus exhibiting greater genetic divergences than A. digitifera, suggesting different migration capabilities or different effective population sizes for these closely related species. We inferred dispersal distance using a biophysical larval transport model, which explained an additional 15–21% of the observed genetic variation compared to between‐island geographical distance alone. For both species, genetic divergence accumulates and genetic diversity diminishes with distance from the Coral Triangle, supporting the hypothesis that Micronesian islands act as important stepping stones connecting the central Pacific with the species‐rich Coral Triangle. However, for A. hyacinthus, the species with lower genetic connectivity, immigration from the subequatorial Pacific begins to play a larger role in shaping diversity than input from the Coral Triangle. This work highlights the enormous dispersal potential of broadcast‐spawning corals and identifies the biological and physical drivers that influence coral genetic diversity on a regional scale.     

Density‐dependent effects on reproductive performance in a recovering population of White‐tailed Eagles Haliaeetus albicilla

Understanding the mechanisms that shape density‐dependent processes and population dynamics is often essential for species conservation. Two key mechanisms of density‐dependent reductions in reproductive performance are a limited access to foraging habitats (the habitat heterogeneity hypothesis) and territorial aggression towards conspecifics (the interference competition hypothesis) at high population densities. Disentangling the relative importance of these mechanisms within populations below their carrying capacity is important for the evaluation of the success of conservation measures. However, relatively few studies have attempted to quantify the relative importance of both mechanisms for the reproductive performance of a population. Many raptor populations are ideal model systems to investigate density‐dependent effects because they are currently recovering from human‐induced reductions during the last decades. Using a 14‐year dataset, we combined analyses of individual reproductive performance with a mechanistic population model to investigate early signs of density‐dependent regulation in a population of White‐tailed Eagles Haliaeetus albicilla in north‐east Germany. We found a negative effect of the number of neighbouring breeding pairs and a positive effect of water surface area (as a proxy for the availability of favourable foraging habitat) on breeding success and on the average number of nestlings. The mean nearest neighbour distance between breeding pairs has decreased, and the mean distance of nests to the nearest water body has increased over the last 14 years. Moreover, the population model indicates that even though the population is still growing, carrying capacity could be reached at about 500–950 territorial pairs. These results suggest that the selection of nesting sites is determined by a trade‐off between the distance to favourable foraging habitat and the distance to neighbouring breeding pairs. To avoid increasing competition with conspecifics, due to continued population growth, breeding pairs seem to select increasingly suboptimal habitats. Therefore, our results suggest that the habitat heterogeneity and interference competition hypotheses are not necessarily mutually exclusive as mechanisms of density‐dependent population regulation, but can determine the reproductive performance of a raptor population simultaneously. Thus, a future decline in breeding success does not necessarily reflect a decrease in habitat quality but may rather be a consequence of density‐dependent mechanisms. This information may be useful for the interpretation of population trends and for the development of appropriate management strategies for recovering raptor populations.     

Adding energy gradients and long‐distance dispersal to a neutral model improves predictions of Madagascan bird diversity

Macroecological patterns are likely the result of both stochastically neutral mechanisms and deterministic differences between species. In Madagascar, the simplest stochastically neutral hypothesis – the mid‐domain effects (MDE) hypothesis – has already been rejected. However, rejecting the MDE hypothesis does not necessarily refute the existence of all other neutral mechanisms. Here, we test whether adding complexity to a basic neutral model improves predictions of biodiversity patterns. The simplest MDE model assumes that: (1) species' ranges are continuous and unfragmented, (2) are randomly located throughout the landscape, and (3) can be stacked independently and indefinitely. We designed a simulation based on neutral theory that allowed us to weaken each of these assumptions incrementally by adjusting the habitat capacity as well as the likelihood of short‐ and long‐distance dispersal. Simulated outputs were compared to four empirical patterns of bird diversity: the frequency distributions of species richness and range size, the within‐island latitudinal diversity gradient, and the distance‐decay of species compositional similarity. Neutral models emulated empirical diversity patterns for Madagascan birds accurately. The frequency distribution of range size, latitudinal diversity gradient, and the distance‐decay of species compositional similarity could be attributed to stochastic long‐distance migration events and zero‐sum population dynamics. However, heterogenous environmental gradients improved predictions of the frequency distribution of species richness. Patterns of bird diversity in Madagascar can broadly be attributed to stochastic long‐distance migration events and zero‐sum population dynamics. This implies that rejecting simple hypotheses, such as MDE, does not serve as evidence against stochastic processes in general. However, environmental gradients were necessary to explain patterns of species richness and deterministic differences between species are probably important for explaining the distributions of narrow‐range and endemic species.