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276 results for “Small population”
Niche partitioning within a population of seasnakes is constrained by ambient thermal homogeneity and small prey size
<p>In many populations of terrestrial snakes, an individual's phenotype (e.g. body size, sex, colour) affects its habitat use. One cause for that link is gape-limitation, which can result in larger snakes eating prey that are found in different habitats. A second factor involves thermoregulatory opportunities, whereby individuals select habitats based upon thermal conditions. These ideas predict minimal intraspecific variation in habitat use in a species that eats small prey and lives in a thermally uniform habitat – such as the seasnake <i>Emydocephalus annulatus</i>, that feeds on tiny fish eggs and lives in inshore coral-reefs. To test that prediction, we gathered data on water depths and substrate attributes for 1475 sightings of 128 free-ranging <i>E. annulatus</i> in a bay near Noumea, New Caledonia. Habitat selection varied among individuals, but with a preference for coral-dominated substrates. A snake's body size and reproductive state affected its detectability in deep water, but overall habitat use was not linked to snake body size, colour morph, sex, or pregnancy. A lack of ontogenetic shifts in habitat use allows extreme philopatry in <i>E. annulatus</i>, thereby reducing gene flow among populations and potentially, delaying recolonization after local extirpation events.</p>
Data from: Population structure, gene flow, and historical demography of a small coastal shark (Carcharhinus isodon) in US waters of the Western Atlantic Ocean
Patterns of population structure, genetic demographics, and gene flow in the small coastal shark Carcharhinus isodon (finetooth shark) sampled from two discrete nurseries along the southeastern US coast (Atlantic) and three nurseries in the northern Gulf of Mexico (Gulf), were assessed using 16 nuclear-encoded microsatellites and 1077 base pairs of the mitochondrial DNA (mtDNA) control region. Significant heterogeneity in microsatellite allele distributions was detected among all localities except between the two in the Atlantic. Significant heterogeneity in mtDNA haplotypes was not detected, a result likely due to extremely low mtDNA diversity. The genetic discontinuities combined with seasonal movement patterns, a patchy distribution of appropriate nursery habitat, the apparent absence of sex-biased gene flow, and the occurrence of mating in the vicinity of nursery areas, suggest that both male and female finetooth sharks display regional philopatry to discrete nursery areas. Global and local tests of neutrality, using mtDNA haplotypes, and demographic model testing, using Approximate Bayesian Computation of microsatellite alleles, supported a range-wide expansion of finetooth sharks into US waters occurring less than ∼9000 years ago. These findings add to the growing number of studies in a variety of coastally distributed marine fishes documenting significant barriers to gene flow around peninsular Florida and in the eastern Gulf. The findings also provide further evidence that the traditional model of behavioural ecology, based on large coastal sharks, may not be appropriate for understanding and conserving small coastal sharks.
Genetic diversity of Horsfieldia tetratepala (Myristicaceae), an endangered plant species with extremely small populations to China: implications for its conservation
<p>Genetic variation determines the evolutionary potential of a species and is vital for fully understanding the evolution of a species, as well as for developing optimal conservation strategies. <i>Horsfieldia tetratepala</i> is an economically important rainforest tree which has declined steadily, mainly though habitat destruction, and an endangered, narrow endemic in China where it is also classified as a Plant Species with Extremely Small Populations (PSESP). Effective conservation strategies for <i>H. tetratepala</i> are required urgently, but limited information about its<i> </i>genome is available. Accordingly, restriction site-associated DNA sequencing (RAD_seq) was used to sequence sixty-three <i>H. tetratepala</i> trees covering ten isolated populations to assess genome-level diversity and population structure, generating 8,103 high-quality SNPs. Low genetic diversity and moderate genetic differentiation was observed among populations, but Bayesian clustering divided the sampled <i>H. tetratepala</i> populations into two genetic clusters, though with some populations from Guangxi and Yunnan intermixed. Because of increasing of habitat fragmentation and human disturbance, conservation priority should be placed on populations with higher genetic variation (e.g., BB, TKH, DWS, and GLQ). Overall, our study provides valuable genomic resources for <i>H. tetratepala</i> that will significantly advance the formulation of effective conservation strategies.</p>
Micro-endemic species of snails and amphipods show population genetic structure across very small geographic ranges
<p class="MsoNormal"><span>Understanding variation in population genetic structure, even across small distances and for species with extremely limited ranges, is critical for conservation planning and the development of effective management strategies for imperiled species. Organisms that occupy the same geographic extent can maintain different population structures, ranging from highly diverged to panmictic. Such differences can result from differences in biological characteristics such as dispersal ability or demographic history. We used microsatellite loci to evaluate population genetic structure and variation of four desert spring invertebrates having high to low dispersal ability: the lung snail <em>Physa acuta</em>, two species of gilled snails (<em>Juturnia kosteri</em> and <em>Pyrgulopsis roswellensis</em>; family Hydrobiidae) and the amphipod <em>Gammarus desperatus</em>. The study location represents entire species ranges for the micro-endemic hydrobiids and <em>G. desperatus</em>, while <em>P. acuta</em> is ubiquitous throughout much of North America. We found little evidence of significant population genetic structure for <em>P. acuta</em><span> and </span><em>J. kosteri</em><span>,</span></span><em><span> </span></em><span>but much more for</span><em><span> </span></em><em><span>P. roswellensis </span></em><span>and </span><em><span>G. desperatus.</span></em><span> Our results demonstrate differences in habitat preference and/or dispersal ability between the species. While significant isolation-by-distance was detected in the two hydrobiids, dispersal is likely more limited in <em>P. roswellensis</em> than <em>J. kosteri</em>. This information provides insight into how gene flow shapes varying population genetic structure between species across small spatial scales (<100 km<sup>2</sup>). Most importantly, our results suggest that conservation agencies should not consider these microendemic species to be composed of single populations, but rather, that management plans for such species should account for population genetic variation across the species' ranges.</span></p>
A three-weight surface modeling approach for optimizing small-scale population disaggregation
<p><span>In recent decades, gridded population data at fine scales has become a popular data source for assessing and monitoring the Sustainable Development Goals (SDGs). However, current population disaggregation methods are facing challenges in generating high-precision population grids for small areas with limited data. To fill this gap, we proposed a lightweight population gridding method that combines basic dasymetric mapping and point-based surface modeling, named three-weight surface modeling. In this method, there are three weights designed to describe the population spatial heterogeneity from different perspectives. The first weight is building-volume weight, which is equivalent to the preliminary results of population assignment based on building volume information. The second weight, POI-center weight, incorporates POI categories and aggregation patterns to express the centers with high population density, which is calculated based on the neighborhood accumulation rule of Spearman's correlation coefficients between POIs and population size. The third weight called POI-distance weight, indicates different rates of population decay with distance from high-density centers. The three-weight surface model allows us to dynamically adjust the parameters so as to correct the building-volume weight according to the remaining two POI-related weights for a more accurate population surface. After analyzing the census population and the disaggregation results of 544 villages in three counties (Huishui, Luodian and Pingtang) in southern Guizhou Province, China, we found that the customized three-weight model constructed using the local parameter groups demonstrated better accuracy performance compared to separate dasymetric mapping or point-based surface modeling. Meanwhile, the 10-m population grid generated by the local parameter model (LPTW-POP) exhibited higher resolution and lower errors (RMSE, MAE and MRE) than widely used gridded population datasets like LandScan, WorldPop and GHS-POP.</span></p>
Supplementary material 4 from: Davoli F, Cozzo M, Angeli F, Groff C, Randi E (2018) Infanticide in brown bear: a case-study in the Italian Alps – Genetic identification of perpetrator and implications in small populations. Nature Conservation 25: 55-75. https://doi.org/10.3897/natureconservation.25.23776
Table S1. Detailed results of the biological model (consensus and composite) :
Supplementary material 1 from: Davoli F, Cozzo M, Angeli F, Groff C, Randi E (2018) Infanticide in brown bear: a case-study in the Italian Alps – Genetic identification of perpetrator and implications in small populations. Nature Conservation 25: 55-75. https://doi.org/10.3897/natureconservation.25.23776
Text S1. Parameters used for parentage analysis :
Supplementary material 3 from: Davoli F, Cozzo M, Angeli F, Groff C, Randi E (2018) Infanticide in brown bear: a case-study in the Italian Alps – Genetic identification of perpetrator and implications in small populations. Nature Conservation 25: 55-75. https://doi.org/10.3897/natureconservation.25.23776
Text S3. Detailed results of LRmix STUDIO for each suspected male: Global Composite (ADO 0.55) :
Supplementary material 1 from: Hong Qu H, Wang C-J, Zhang Z-X (2018) Planning priority conservation areas under climate change for six plant species with extremely small populations in China. Nature Conservation 25: 89-106. https://doi.org/10.3897/natureconservation.25.20063
Table S1, S2; Figure S1, S2 : Explanation note:
Supplementary material 2 from: Davoli F, Cozzo M, Angeli F, Groff C, Randi E (2018) Infanticide in brown bear: a case-study in the Italian Alps – Genetic identification of perpetrator and implications in small populations. Nature Conservation 25: 55-75. https://doi.org/10.3897/natureconservation.25.23776
Text S2. Detailed results of LRmix STUDIO for each suspected male: Global Consensus (ADO 0.65) :
Figures 5-6 from: Gentile R, Cardoso TS, Costa-Neto SF, Teixeira BR, D'Andrea PS (2018) Community structure and population dynamics of small mammals in an urban-sylvatic interface area in Rio de Janeiro, Brazil. Zoologia 35: 1-12. https://doi.org/10.3897/zoologia.35.e13465
Figures 5-6 Small mammal community structure in CFMA and Pau da Fome, Rio de Janeiro, Brazil, for the (5) 2001 and (6) 2012–2015 samplings. (A, B, C, D, E, F, G, H, K, L) CFMA transects, (C1, D1, E1, F1, G1) Pau da Fome transects.
Figures 2-4 from: Gentile R, Cardoso TS, Costa-Neto SF, Teixeira BR, D'Andrea PS (2018) Community structure and population dynamics of small mammals in an urban-sylvatic interface area in Rio de Janeiro, Brazil. Zoologia 35: 1-12. https://doi.org/10.3897/zoologia.35.e13465
Figures 2-4 Plots of the Non-metric Multidimensional Scaling Analysis between the two periods and areas studied (● CFMA and Pau da Fome) for the small mammal species: (2) comparison between 2001 and 2012-2015 samplings including all transects pulled; (3) comparison among transects in 2001 (transects from A to D in disturbed forests and from E to H in peridomicile areas of CFMA; transects from C1 to G1 in disturbed forest of Pau da Fome); (4) comparison among transects for the 2012-2015 period (transects A, B, K, L in disturbed forest areas of CFMA; E1 in disturbed forest areas of Pau da Fome; C, D in peridomicile areas of CFMA; C1 and D1 in peridomicile areas of Pau da Fome; E and F in preserved forest areas of CFMA).
Figure 7 from: Gentile R, Cardoso TS, Costa-Neto SF, Teixeira BR, D'Andrea PS (2018) Community structure and population dynamics of small mammals in an urban-sylvatic interface area in Rio de Janeiro, Brazil. Zoologia 35: 1-12. https://doi.org/10.3897/zoologia.35.e13465
Figure 7 Canonical correspondence analysis (CCA) and relationship among species, transects (A, B, C, D, E, F) and habitat variables (CANO – percentage of canopy cover; TREE – number of trees with diameter at breast height ≥ 5; VCS – percentage of vegetation cover on the soil; VVO – vertical vegetation obstruction) for the 2012–2015 period in CFMA, Rio de Janeiro, Brazil.
Figure 9 from: Gentile R, Cardoso TS, Costa-Neto SF, Teixeira BR, D'Andrea PS (2018) Community structure and population dynamics of small mammals in an urban-sylvatic interface area in Rio de Janeiro, Brazil. Zoologia 35: 1-12. https://doi.org/10.3897/zoologia.35.e13465
Figure 9 Age structure of the marsupial Didelphis aurita for the 2012–2015 period in CFMA and Pau da Fome, Rio de Janeiro, Brazil.
Figure 1 from: Gentile R, Cardoso TS, Costa-Neto SF, Teixeira BR, D'Andrea PS (2018) Community structure and population dynamics of small mammals in an urban-sylvatic interface area in Rio de Janeiro, Brazil. Zoologia 35: 1-12. https://doi.org/10.3897/zoologia.35.e13465
Figure 1 Map of the study area indicating the sampling localities in CFMA and Pau da Fome region, State of Rio de Janeiro, Brazil. 1) CFMA – Peridomicile, 2–3) CFMA – Disturbed Forest, 4) CFMA – Preserved Forest, 5) Pau da Fome – Peridomicile, 6) Pau da Fome – Disturbed Forest.
Figure 8 from: Gentile R, Cardoso TS, Costa-Neto SF, Teixeira BR, D'Andrea PS (2018) Community structure and population dynamics of small mammals in an urban-sylvatic interface area in Rio de Janeiro, Brazil. Zoologia 35: 1-12. https://doi.org/10.3897/zoologia.35.e13465
Figure 8 Proportion of reproductively active females of the marsupial Didelphis aurita for the 2012–2015 period in CFMA and Pau da Fome, Rio de Janeiro, Brazil.
Figure 3 in Characterization of a Small Population of the Orangeblack Hawaiian Damselfly (Megalagrion xanthomelas) in Anchialine Pools at Kaloko-Honokōhau National Historical Park, Hawai'i Island
Figure 3. Mean number of male and female Megalagrion xanthomelas observed at the seven core pools (A–G) and at all core pools combined (H) during June 2016–August 2017.
Data from: Evolution of drift robustness in small populations
Most mutations are deleterious and cause a reduction in population fitness known as the mutational load. In small populations, weakened selection against slightly-deleterious mutations results in an additional fitness reduction. Many studies have established that populations can evolve a reduced mutational load by evolving mutational robustness, but it is uncertain whether small populations can evolve a reduced susceptibility to drift-related fitness declines. Here, using mathematical modeling and digital experimental evolution, we show that small populations do evolve a reduced vulnerability to drift, or 'drift robustness'. We find that, compared to genotypes from large populations, genotypes from small populations have a decreased likelihood of small-effect deleterious mutations, thus causing small-population genotypes to be drift-robust. We further show that drift robustness is not adaptive, but instead arises because small populations can only maintain fitness on drift-robust fitness peaks. These results have implications for genome evolution in organisms with small effective population sizes.
Data from: Different evolutionary paths to complexity for small and large populations of digital organisms
A major aim of evolutionary biology is to explain the respective roles of adaptive versus non-adaptive changes in the evolution of complexity. While selection is certainly responsible for the spread and maintenance of complex phenotypes, this does not automatically imply that strong selection enhances the chance for the emergence of novel traits, that is, the origination of complexity. Population size is one parameter that alters the relative importance of adaptive and non-adaptive processes: as population size decreases, selection weakens and genetic drift grows in importance. Because of this relationship, many theories invoke a role for population size in the evolution of complexity. Such theories are difficult to test empirically because of the time required for the evolution of complexity in biological populations. Here, we used digital experimental evolution to test whether large or small asexual populations tend to evolve greater complexity. We find that both small and large—but not intermediate-sized—populations are favored to evolve larger genomes, which provides the opportunity for subsequent increases in phenotypic complexity. However, small and large populations followed different evolutionary paths towards these novel traits. Small populations evolved larger genomes by fixing slightly deleterious insertions, while large populations fixed rare beneficial insertions that increased genome size. These results demonstrate that genetic drift can lead to the evolution of complexity in small populations and that purifying selection is not powerful enough to prevent the evolution of complexity in large populations.
Data from: Genetic signatures of small effective population sizes and demographic declines in an endangered rattlesnake, Sistrurus catenatus
Endangered species that exist in small isolated populations are at elevated risk of losing adaptive variation due to genetic drift. Analyses that estimate short-term effective population sizes, characterize historical demographic processes, and project the trajectory of genetic variation into the future are useful for predicting how levels of genetic diversity may change. Here, we use data from two independent types of genetic markers (single nucleotide polymorphisms [SNPs] and microsatellites) to evaluate genetic diversity in 17 populations spanning the geographic range of the endangered eastern massasauga rattlesnake (Sistrurus catenatus). First, we use SNP data to confirm previous reports that these populations exhibit high levels of genetic structure (overall Fst = 0.25). Second, we show that most populations have contemporary Ne estimates less than 50. Heterozygosity-fitness correlations in these populations provided no evidence for a genetic cost to living in small populations, though these tests may lack power. Third, model-based demographic analyses of individual populations indicate that all have experienced declines, with the onset of many of these declines occurring over timescales consistent with anthropogenic impacts (<200 years). Finally, forward simulations of the expected loss of variation in relatively large (Ne = 50) and small (Ne = 10) populations indicate they will lose a substantial amount of their current standing neutral variation (63% and 99%, respectively) over the next 100 years. Our results argue that drift has a significant and increasing impact on levels of genetic variation in isolated populations of this snake, and efforts to assess and mitigate associated impacts on adaptive variation should be components of the management of this endangered reptile.
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