Type Of Population Structure Research Articles

Optimization of institutional incentives for cooperation in structured populations.

The application of incentives, such as reward and punishment, is a frequently applied way for promoting cooperation among interacting individuals in structured populations. However, how to properly use the incentives is still a challenging problem for incentive-providing institutions. In particular, since the implementation of incentive is costly, to explore the optimal incentive protocol, which ensures the desired collective goal at a minimal cost, is worthy of study. In this work, we consider the positive and negative incentives for a structured population of individuals whose conflicting interactions are characterized by a Prisoner's Dilemma game. We establish an index function for quantifying the cumulative cost during the process of incentive implementation, and theoretically derive the optimal positive and negative incentive protocols for cooperation on regular networks. We find that both types of optimal incentive protocols are identical and time-invariant. Moreover, we compare the optimal rewarding and punishing schemes concerning implementation cost and provide a rigorous basis for the usage of incentives in the game-theoretical framework. We further perform computer simulations to support our theoretical results and explore their robustness for different types of population structures, including regular, random, small-world and scale-free networks.

Effects of single nucleotide polymorphism ascertainment on population structure inferences.

Single nucleotide polymorphism (SNP) data are widely used in research on natural populations. Although they are useful, SNP genotyping data are known to contain bias, normally referred to as ascertainment bias, because they are conditioned by already confirmed variants. This bias is introduced during the genotyping process, including the selection of populations for novel SNP discovery and the number of individuals involved in the discovery panel and selection of SNP markers. It is widely recognized that ascertainment bias can cause inaccurate inferences in population genetics and several methods to address these bias issues have been proposed. However, especially in natural populations, it is not always possible to apply an ideal ascertainment scheme because natural populations tend to have complex structures and histories. In addition, it was not fully assessed if ascertainment bias has the same effect on different types of population structure. Here, we examine the effects of bias produced during the selection of population for SNP discovery and consequent SNP marker selection processes under three demographic models: the island, stepping-stone, and population split models. Results show that site frequency spectra and summary statistics contain biases that depend on the joint effect of population structure and ascertainment schemes. Additionally, population structure inferences are also affected by ascertainment bias. Based on these results, it is recommended to evaluate the validity of the ascertainment strategy prior to the actual typing process because the direction and extent of ascertainment bias vary depending on several factors.

Population structure of Laurus nobilis L. in Central Italian forests: evidence for its ongoing expansion

During the last decades, an ongoing spread of broad-leaved evergreen laurophyllous species has been reported for forests of Southern Europe. Several factors were suggested as the main drivers of the phenomenon, namely global warming, land-use change, evolutionary history, and increase in atmospheric CO2. Among laurophylls, Laurus nobilis L. is considered one of the most prominent from the morphological, evolutionary, and ecological point of view. We studied the population structure of L. nobilis in Central Italy in its natural habitat to investigate its regeneration and potential expansion along with the influence biotic and abiotic factors. To define types of population structures, we collected proportions of six growth classes of L. nobilis in 16 sites. We obtained three types of population structure, i.e., (1) stable, (2) dynamic, and (3) regressive. The first two types are the most frequent, suggesting a potential increase of L. nobilis abundance within forests of Central Italy. The regressive population type occurs mainly in sites with heavy ungulate impact. High propagule pressure along with shaded and moist environmental conditions favor L. nobilis regeneration. Accordingly, we found evidence of a recent L. nobilis spread in Central Italian forests. We suggest the increase of forest cover and age, due to the abandonment of traditional rural practices, as key factors for the regeneration of this apparently late-successional laurophyll. In conclusion, the recent expansion of L. nobilis that we observed in the Italian forest stands can therefore be ascribed to a process of natural recover of a potential niche following land-use change.

Population structure of Alnus jorullensis , a species used as firewood by five rural communities in a natural protected area of Mexico

Background: Ilite (Alnus jorullensis ) is a very important pioneer species for the regeneration of temperate forests but also the source of fuel for the inhabitants of the Cofre de Perote National Park in Veracruz, Mexico.
 Questions: How much ilite is consumed by families in the Cofre de Perote National Park? What type of population structure is exhibited by Alnus jorullensis ? Are there differences in population structure of this species between years? What is the diameter of the individuals extracted for firewood?
 Study site and dates: The population structure of ilite was evaluated during April 2016 and April 2017 in five localities of the Cofre de Perote National Park.
 Methods: Eighty families in these localities were interviewed about the use of firewood. Eighteen permanent plots of 20 × 50 m were established in order to record total height and diameter at breast height (130 cm) of standing trees of A. jorullensis and the basal diameter of its stumps.
 Results: Families in the study area indicated that they use in average 2 loads of ilite as firewood per week and extract adult individuals. Population density of ilite decreased from 2016 to 2017, in both years juvenile individuals were predominant, with a low presence of seedlings. Population structure did not differ between years. The basal diameters of stumps measured between 6 and 214 cm.
 Conclusions: Extraction of A. jorullensis did not change its population structure between years, however local inhabitants perceive that this activity and clandestine logging are affecting their availability.

Seed germination and population structure of two endangered tree species: Magnolia perezfarrerae and Magnolia sharpii

Background: Due to habitat fragmentation many Magnolia species are at risk of extinction in Mexico.Question: What type of population structure is exhibited by Magnolia perezfarrerae and M. sharpii, endemic species of Chiapas, Mexico? Does the extreme reduction in the population of both Magnolia affect their reproductive capacity? What is the propagation potential in both species of Magnolia ? Is it necessary to use pregerminative treatments for Magnolia species propagation?Studied species: Magnolia perezfarrerae A. Vázquez & Gómez-Domínguez and Magnolia sharpii Miranda.Study sites and years of study: Highlands and Central Depression of Chiapas, Mexico, from 2015 to 2017.Methods: In this study, the density and distribution of diametric sizes of M. perezfarrerae and M. sharpii were assessed in natural populations. Their reproductive capacity and the ex-situ germination of both species was analyzed.Results: The population density in M. perezfarrerae was 40-53 ind. ha-1, and 24-83 ind. ha-1 in M. sharpii . Size structure varied between populations of each species: one apparently without problems of regeneration, and another with discontinuous distribution in several size categories. The seeds presented physical, chemical and mechanical dormancy. The pre-germination treatments applied proved mostly effective for M. sharpii by 73 % and by 64 % for M. perezfarrerae .Conclusions: The current condition of Magnolia species is critical and their persistence is compromised. Any viable conservation option would need to identify potential sites for the reintroduction of new populations.

Parent-preferred dispersal promotes cooperation in structured populations.

Dispersal is a key process for the emergence of social and biological behaviours. Yet, little attention has been paid to dispersal's effects on the evolution of cooperative behaviour in structured populations. To address this issue, we propose two new dispersal modes, parent-preferred and offspring-preferred dispersal, incorporate them into the birth-death update rule, and consider the resultant strategy evolution in the prisoner's dilemma on random-regular, small-world, and scale-free networks, respectively. We find that parent-preferred dispersal favours the evolution of cooperation in these different types of population structures, while offspring-preferred dispersal inhibits the evolution of cooperation in homogeneous populations. On scale-free networks when the strength of parent-preferred dispersal is weak, cooperation can be enhanced at intermediate strengths of offspring-preferred dispersal, and cooperators can coexist with defectors at high strengths of offspring-preferred dispersal. Moreover, our theoretical analysis based on the pair-approximation method corroborates the evolutionary outcomes on random-regular networks. We also incorporate the two new dispersal modes into three other update rules (death-birth, imitation, and pairwise comparison updating), and find that similar results about the effects of parent-preferred and offspring-preferred dispersal can again be observed in the aforementioned different types of population structures. Our work, thus, unveils robust effects of preferential dispersal modes on the evolution of cooperation in different interactive environments.

Extremely Low Genomic Diversity of Rickettsia japonica Distributed in Japan.

Rickettsiae are obligate intracellular bacteria that have small genomes as a result of reductive evolution. Many Rickettsia species of the spotted fever group (SFG) cause tick-borne diseases known as “spotted fevers”. The life cycle of SFG rickettsiae is closely associated with that of the tick, which is generally thought to act as a bacterial vector and reservoir that maintains the bacterium through transstadial and transovarial transmission. Each SFG member is thought to have adapted to a specific tick species, thus restricting the bacterial distribution to a relatively limited geographic region. These unique features of SFG rickettsiae allow investigation of how the genomes of such biologically and ecologically specialized bacteria evolve after genome reduction and the types of population structures that are generated. Here, we performed a nationwide, high-resolution phylogenetic analysis of Rickettsia japonica, an etiological agent of Japanese spotted fever that is distributed in Japan and Korea. The comparison of complete or nearly complete sequences obtained from 31 R. japonica strains isolated from various sources in Japan over the past 30 years demonstrated an extremely low level of genomic diversity. In particular, only 34 single nucleotide polymorphisms were identified among the 27 strains of the major lineage containing all clinical isolates and tick isolates from the three tick species. Our data provide novel insights into the biology and genome evolution of R. japonica, including the possibilities of recent clonal expansion and a long generation time in nature due to the long dormant phase associated with tick life cycles.

Retrospective Association Analysis of Binary Traits: Overcoming Some Limitations of the Additive Polygenic Model

Case-control genetic association analysis is an extremely common tool in human complex trait mapping. From a statistical point of view, the analysis of binary traits poses somewhat different challenges from the analysis of quantitative traits. Desirable features of a binary trait mapping approach would include (1) phenotype modeled as binary, with appropriate dependence between the mean and variance; (2) appropriate correction for relevant covariates; (3) appropriate correction for sample structure of various types, including related individuals, admixture and other types of population structure; (4) both fast and accurate computations; (5) robustness to ascertainment and other types of phenotype model misspecification, and (6) ability to leverage partially missing data to increase power. We review these challenges and argue, both theoretically and in simulations, for the value of retrospective association analysis as a way to overcome some of the limitations of the phenotype model, including model misspecification due to ascertainment. We give an overview of two recent retrospective methods, CARAT and CERAMIC, that are designed to meet criteria 1-6.

Vegetation structural characteristics and topographic factors in the remnant moist Afromontane forest of Wondo Genet, south central Ethiopia

For forest ecosystem management to be effective, knowledge of the horizontal and vertical structural diversity of a forest is essential. The moist Afromontane highlands of Wondo Genet in south-central Ethiopia present an opportunity to restore and rehabilitate and enhance the ecosystem services to be obtained from this forest sustainably. We focused on the forest structural characteristics to better understand the current forest conditions to assist in the sustainable management of this resource. A total of 75 (20 m × 20 m) quadrats were sampled and diameter at breast height (DBH) ≥ 2 cm and stem height ≥ 2 m were measured. Species identity and abundance, elevation, slope, and aspect were recorded for each plot. Structural characteristics were computed for each plot. Relationship of topographic factors with vegetation characteristics was conducted using R-Software. A total of 72 woody species was recorded. Whereas, the overall diameter distribution shows an inverted J-shaped curve, the basal area followed a bell-shaped pattern. Five types of population structures are revealed. The mean tree density and basal area was 397.3 stems·ha−1 and 31.4 m2·ha−1, respectively. Only 2.8% of the tree species have densities of >25 stems·ha−1 and the percentage distribution of trees show 56.2% in the DBH class 2–10 cm, indicating that the forest is dominated by medium-sized trees. Celtis africana (8.81 m2·ha−1) and Pouteria adolfi-friedericii (5.13 m2·ha−1) make the highest contribution to the basal area and species importance value index. The families/species with the highest importance value index are Ulmaceae, Fabacea and Sapotaceae. Species abundance (r2 =0.32, p <0.001) and species richness (r2 =0.50, p <0.001) are positively related with tree density. Tree density is negatively related with elevation (r2 =−0.36, p <0.001), slope (r2 =−0.15, p <0.001) and aspect (r2 =−0.07, p <0.05). While basal area is negatively related with elevation (r2 =−0.14, p <0.001), it has a positive relationship with tree density (r2 =0.28, p <0.001 and species richness (r2 =0.098). Species with poor population structure should be assisted by restoration tasks and further anthropogenic disturbance such as illegal logging and fuel wood extraction should be restricted.

Estrutura populacional de Symphonia globulifera L. f. (Clusiaceae) em fragmentos de Mata Atlântica de baixada periodicamente alagada

Neste trabalho, avaliou-se a estrutura populacional de Symphonia globulifera em fragmentos florestais periodicamente alagados, nas Reservas Biológicas de Poço das Antas (RBPA) e União (RBU), Rio de Janeiro. Uma análise comparativa entre o papel das estratégias reprodutivas (via semente ou via vegetativa) na estrutura populacional foi também realizada. Para a amostragem, foram selecionadas três áreas na RBPA (PORT, CM e ARI) e uma área na RBU. Foram encontrados dois tipos de estrutura populacional para S. globulifera: 1) populações PORT e ARI com baixo recrutamento e predominância de indivíduos oriundos de sementes que podem estar em fase de senescência e 2) populações CM e RBU com grande número de recrutas oriundos de reprodução vegetativa. Plântulas e jovens apresentaram, em geral, um maior número de indivíduos de via vegetativa. Em relação aos adultos, ocorreu um predomínio de indivíduos oriundos de sementes. Esses padrões parecem estar relacionados ao regime hídrico de cada ambiente. A predominância nos pântanos de plântulas e jovens de via vegetativa e árvores oriundas de semente sugere a existência de uma forte mortalidade diferenciada nas fases de plântula e jovens de indivíduos oriundos de reprodução vegetativa.

Accounting for Population Stratification in Practice: A Comparison of the Main Strategies Dedicated to Genome-Wide Association Studies

Genome-Wide Association Studies are powerful tools to detect genetic variants associated with diseases. Their results have, however, been questioned, in part because of the bias induced by population stratification. This is a consequence of systematic differences in allele frequencies due to the difference in sample ancestries that can lead to both false positive or false negative findings. Many strategies are available to account for stratification but their performances differ, for instance according to the type of population structure, the disease susceptibility locus minor allele frequency, the degree of sampling imbalanced, or the sample size. We focus on the type of population structure and propose a comparison of the most commonly used methods to deal with stratification that are the Genomic Control, Principal Component based methods such as implemented in Eigenstrat, adjusted Regressions and Meta-Analyses strategies. Our assessment of the methods is based on a large simulation study, involving several scenarios corresponding to many types of population structures. We focused on both false positive rate and power to determine which methods perform the best. Our analysis showed that if there is no population structure, none of the tests led to a bias nor decreased the power except for the Meta-Analyses. When the population is stratified, adjusted Logistic Regressions and Eigenstrat are the best solutions to account for stratification even though only the Logistic Regressions are able to constantly maintain correct false positive rates. This study provides more details about these methods. Their advantages and limitations in different stratification scenarios are highlighted in order to propose practical guidelines to account for population stratification in Genome-Wide Association Studies.

CORRELATIONS BETWEEN HETEROZYGOSITY AND REPRODUCTIVE SUCCESS IN THE BLUE TIT (CYANISTES CAERULEUS): AN ANALYSIS OF INBREEDING AND SINGLE LOCUS EFFECTS

To understand the mechanisms behind heterozygosity-fitness correlations (HFC), it is necessary to employ large numbers of markers with known function and independently estimate the variation in inbreeding in the population. Here we genotyped 794 blue tits with 79 microsatellites that were distributed across 25 chromosomes and that were classified either as "functional" (N= 58) or "neutral" (N= 21). We found a positive effect of individual heterozygosity at multiple loci on clutch size, on the number of eggs sired by males, and on the number of recruits produced by males and females. We documented the occurrence of some consanguineous matings and found evidence for a particular type of population structure that can contribute to the occurrence of inbreeding. As the set of "neutral" loci provided more power to detect HFC and identity disequilibrium, we argue that "neutral" markers are better predictors of the effects of inbreeding. The number of significant effects at single loci did not exceed the expected number of false positives and no strong effects were associated with heterozygosity at "functional" markers. Thus, the HFC found here cannot be attributed to strong effects of the loci under study.

Integral projection models for finite populations in a stochastic environment

Continuous types of population structure occur when continuous variables such as body size or habitat quality affect the vital parameters of individuals. These structures can give rise to complex population dynamics and interact with environmental conditions. Here we present a model for continuously structured populations with finite size, including both demographic and environmental stochasticity in the dynamics. Using recent methods developed for discrete age-structured models we derive the demographic and environmental variance of the population growth as functions of a continuous state variable. These two parameters, together with the expected population growth rate, are used to define a one-dimensional diffusion approximation of the population dynamics. Thus, a substantial reduction in complexity is achieved as the dynamics of the complex structured model can be described by only three population parameters. We provide methods for numerical calculation of the model parameters and demonstrate the accuracy of the diffusion approximation by computer simulation of specific examples. The general modeling framework makes it possible to analyze and predict future dynamics and extinction risk of populations with various types of structure, and to explore consequences of changes in demography caused by, e.g., climate change or different management decisions. Our results are especially relevant for small populations that are often of conservation concern.

Analysis of vertebral counts of the tropical anguillids, Anguilla megastoma, A. obscura, and A. reinhardtii, in the western South Pacific in relation to their possible population structure and phylogeny

The population structures of three tropical eel species, Anguilla megastoma, A. obscura, and A. reinhardtii, collected from several localities of each species range in the western South Pacific Ocean were evaluated using statistical analyses of total number of vertebrae (TV) data, which also included previously published data. There was a significant difference in TV values between Samoa and French Polynesia specimens of A. megastoma, while no significant difference was observed in TV data of A. obscura, despite the two species having similar overlapping species distribution ranges. There also was no significant difference found in the TV data of A. reinhardtii. These results suggest that A. megastoma may be separated into eastern and western populations in the western South Pacific, but there was no statistical evidence using the TV data that A. obscura and A. reinhardtii have population structure in the western South Pacific. These possible types of population structures are discussed in relation to the phylogeography and life histories of other tropical anguillid eels.

Patterns of genetic differentiation in Thamnophis and Taricha from the Pacific Northwest

AbstractAim The co‐evolutionary interaction between the common garter snake, Thamnophis sirtalis, and the rough‐skinned newt, Taricha granulosa, takes place throughout much of the Pacific Northwest (North America). The biogeography of the Pacific Northwest has been heavily influenced by the last Pleistocene glaciation, which reached a maximum as late as 14,000 yr bp. We researched: (1) what type of population structure is present for garter snakes and newts, (2) whether the population structure of these species is consistent with a Pleistocene glaciation hypothesis, and (3) how population structure and migration possibly affect co‐evolution between these species.Location The Pacific Northwest of North America, specifically northern California, Oregon and Washington in the USA.Methods We sampled approximately 20 populations for each species from three different transects. Using microsatellite markers and tissue samples from both species, we quantified the population structure for both species. Individual‐based assignment tests were used to estimate contemporary migration rates.Results Both Th. sirtalis and Ta. granulosa exhibited little genetic differentiation among our study sites, even among those separated by large distances. Significant population structure was detected on multiple geographic scales. Differences in population structure were observed among transects and between garter snake and newt transects. Contemporary migration rate estimates indicate high levels of genetic exchange between populations.Main conclusions Prior to this study, little was known about the fine‐scale population structure of either species in this region. Patterns of population structure for garter snakes and newts reflect a shared biogeographical history affected by the Pleistocene glaciation in the Pacific Northwest. Both species apparently migrate frequently between populations, thus potentially retarding the process of adaptive co‐evolution. We find that populations from a northern coastal transect (Washington) are most likely to be locally adapted.

Historical population demography of red snapper (Lutjanus campechanus) from the northern Gulf of Mexico based on analysis of sequences of mitochondrial DNA

We evaluated stock structure and demographic (population) history of red snapper (Lutjanus campechanus) in the northern Gulf of Mexico (Gulf) via analysis of mitochondrial (mt)DNA sequences from 360 individuals sampled from four cohorts (year classes) at three localities across the northern Gulf. Exact tests of genetic homogeneity and analysis of molecular variance both among cohorts within localities and among localities were non-significant. Nested clade analysis provided evidence of different temporal episodes of both range expansion and restricted gene flow due to isolation by distance. A mismatch distribution of pairwise differences among mtDNA haplotypes and a maximum-likelihood coalescence analysis indicated a population expansion phase that dated to the Pleistocene and probably represents (re)colonization of the continental shelf following glacial retreat. The spatial distribution of red snapper in the northern Gulf appears to have a complex history that likely reflects glacial advance/retreat, habitat availability and suitability, and hydrology. Habitat availability/suitability and hydrology may partially restrict gene flow among present-day red snapper in the northern Gulf and give rise to a metapopulation structure with variable demographic connectivity. This type of population structure may be difficult to detect with commonly used, selectively neutral genetic markers.

Group founding and breeding structure in the subsocial spider stegodyphus lineatus (Eresidae)

Co-operative behaviour may evolve by enhancing the genetic similarity of group members. Increased group similarity is thought to be the basis for the 'subsocial route' of social evolution in the spider family Eresidae. Two processes may promote the similarity of individuals within populations or breeding groups, namely philopatry in stable environments and founder events in a stochastic environment. We show that both processes led to genetic differentiation within and among populations of the subsocial spider Stegodyphus lineatus. Within populations we distinguished between the genetic structure caused by random mating and philopatry in old breeding groups and that caused by newly founded groups consisting of sibs. Such sib-groups suggest that new breeding groups are established primarily by single females. The different gene coancestries among breeding groups resulted in high variances among single-locus data. The results imply that sex-specific dispersal behaviour (random male mating-dispersal or female group founding) had different impacts on the population structure. This type of population structure, where within-population philopatry and founder events may lead to differential proliferation of breeding groups, is very similar to that presumed for social spiders, and is also one that could provide the conditions for interdemic selection.

RAPD marker estimation of genetic structure among isolated northern leopard frog populations in the south‐western USA

Amphibians in the south-western United States are currently experiencing population declines. Causal explanations for these population changes as well as the implementation of sound management practices requires an understanding of the genetic structure of natural amphibian populations. To this end, we estimated genetic differences within and among seven isolated populations of northern leopard frogs, Rana pipiens, from Arizona and southern Utah using random amplified polymorphic DNA (RAPD) analyses. Fourteen arbitrarily designed primers detected 38 polymorphic loci in 85 individual frogs. Three types of population structure were observed in this study. (i) Two populations showed low genetic diversity (D = 0.10 and 0.04) and may have been established by relatively recent events. (ii) Two were not genetically distinct and exhibited a high degree of within-population diversity (D = 0.35). The possibility of gene flow between these populations is high due to their geographical proximity and their shared genetic structure. (iii) Three populations were genetically distinct from each other and the other populations, and exhibited intermediate within-population variation (D = 0.19, 0.17, 0.14). Genetic distances among the seven populations ranged from 0.00 to 0.20, suggesting that some of these leopard frog populations are genetically distinct. Although based on relatively small samples, these data suggest that leopard frog populations in the south-west are likely to represent unique genetic entities worthy of conservation. The management implications of these results are that isolated leopard frog populations should be evaluated on an individual basis to best preserve them.

RAPD marker estimation of genetic structure among isolated northern leopard frog populations in the south‐western USA

Amphibians in the south‐western United States are currently experiencing population declines. Causal explanations for these population changes as well as the implementation of sound management practices requires an understanding of the genetic structure of natural amphibian populations. To this end, we estimated genetic differences within and among seven isolated populations of northern leopard frogs, Rana pipiens, from Arizona and southern Utah using random amplified polymorphic DNA (RAPD) analyses. Fourteen arbitrarily designed primers detected 38 polymorphic loci in 85 individual frogs. Three types of population structure were observed in this study. (i) Two populations showed low genetic diversity (D= 0.10 and 0.04) and may have been established by relatively recent events. (ii) Two were not genetically distinct and exhibited a high degree of within‐population diversity (D= 0.35). The possibility of gene flow between these populations is high due to their geographical proximity and their shared genetic structure. (iii) Three populations were genetically distinct from each other and the other populations, and exhibited intermediate within‐population variation (D= 0.19, 0.17, 0.14). Genetic distances among the seven populations ranged from 0.00 to 0.20, suggesting that some of these leopard frog populations are genetically distinct. Although based on relatively small samples, these data suggest that leopard frog populations in the south‐west are likely to represent unique genetic entities worthy of conservation. The management implications of these results are that isolated leopard frog populations should be evaluated on an individual basis to best preserve them.

Age‐states, population structure, and seedling regeneration of Chionochloa pallens in Canterbury alpine grasslands, New Zealand

Abstract. Age‐states, population structure, and seedling regeneration of the grass Chionochloa pallens were investigated in eight alpine grassland stands representing the range of canopy cover (ca. 5–75 %) and basal area (112 ‐ 3889 m2/ha‐1) in the headwaters of the Avoca catchment, Canterbury, New Zealand. In open‐canopy stands (&lt; 50 % canopy cover, &lt; 2000 m2/ha‐1 basal area) C. pallens individuals were clearly distinguishable. Rela‐tionshipsbetweenbasal diameter, number of tillers, height, and % crown death suggested four putative age‐states: ‘seedlings‘, ‘juvenile tussocks’, ‘mature tussocks’ and ‘senescent tussocks’. Four types of population structure were identified depending onthe proportions of seedlings and juvenile and mature tussocks. C. pallens seedlings were present in seven stands at densities ranging from 0.6 to 123.4 / m2. They were most frequent on microsites protected from frost‐heave by short herbaceous vegetation or litter, but with little competition from taller vegetation. Differences in seedling densities between stands partly reflected the proximity and abundance of seed sources and degree of protection from frost‐heave. C. pallens population structures appear to be influenced by the frequency and magnitude of geomorphic disturbances and browsing by introduced animals.