The population biology ofPlanaria torva (Müller) (Turbellaria,Tricladida)

Summary 1. A quantitative study of the population biology ofPlanaria torva (Müller) living in a productive lake, based on monthly samples over a period of 20 months, is presented. 2. Samples of triclads, their cocoons and other organisms were taken from bricks placed at a shallow depth in the lake. They provided relative information on changes in population size structure and demonstrated the temporal breeding of this triclad. 3. Cocoon production byP. torva began in January and reached a peak in March–April. This was followed by a peak in recently-hatched young during May–June. Adults reached a maximal proportion of the total population in January and most had died by July. 4. Changes in size structure suggest that intra-specific competition occurred during June–July following the recruitment of young. This hypothesis is supported by other independent evidence. 5. Attempts to measure fecundity based on cocoons and young gave very different results attributed to the sampling technique.     

Genetic diversity and population viability in translocated North?Island saddleback (

Genetic variation in two translocated populations of North Island saddleback (Philesturnus rufusater) on Kapiti Island and at Zealandia was investigated using five microsatellite loci and compared with the source populations in the Hauraki Gulf. Although the absolute number of alleles in the two populations was low (3 alleles per locus), both populations carried all the alleles found in their immediate source populations, but lacked one rare allele found in only one individual from the original remnant population on Hen Island. Overall heterozygosity was high and inbreeding coefficients were low. Population viability analyses showed that these populations will likely reach carrying capacity by the middle of this decade, and genetic simulations predicted that they should retain between 90% (Kapiti) and 95% (Zealandia) of the heterozygosity of their sources. The difference between the two populations is most likely due to the prolonged post-translocation bottleneck on Kapiti when rats were still present on the island. While our results suggest that additional top-up translocations would be unnecessary and unwarranted at this time, further work on potentially selected loci or inbreeding depression could justify this decision to be revisited.     

α1 (Pi) types and subtypes in the Tyrolean population

Since nine patients with infantile liver cirrhosis or hepatopathy associated with the Pi ZZ phenotype had been observed in recent years in the Children's Hospital of the University of Innsbruck, Tyrol, the distribution of the Pi types and the PiM subtypes was determined in the Tyrolean population. Apparently healthy blood donors (868) from different regions of Tyrol were examined. Isoelectricfocusing was used for classification of Pi types. The frequency of the allele PiZ was 0.0138, which corresponded to the range observed in other Middle European populations. The frequencies for the suballeles of PiM were PiM1 = 0.7062, PiM2 = 0.1480, and PiM3 = 0.1037. PiS had a frequency of 0.0225, the other rare alleles occurred with a combined frequency of 0.0058.     

The anatomy of population change in a black grouse population 1992–2008

We interrogate an 18-year-long dataset containing counts of displaying male black grouse Tetrao tetrix and incidental counts of females within an 800-km² region of Perthshire, Scotland. We examine the trends in the population and investigate how different components of the population might act as signposts of different stages of overall population change. We found statistical evidence for a decline in black grouse numbers between 1992 and 2000, and then a recovery from 2002 to 2008, but little evidence for a link between population change and weather during the decline phase. There was some evidence for a positive relationship between male and female counts. The two main components of male population size, lek size and lek frequency followed the overall population trend while it was increasing, but during the earlier decline, the two became uncoupled, to expose a complex structure within the data. During the decline, when black grouse numbers were approaching their minimum, mean lek size was actually increasing. Small leks lost proportionally more birds than did large leks, and lek longevity was positively correlated with lek size, indicating that maintenance of large leks is crucial in buffering the population against serious declines. During the decline, the spatial arrangement of leks changed, with remnant leks showing tight clustering at larger spatial scales, before expanding out to fill the large areas of unoccupied landscape during the population increase. We discuss these findings in terms of species monitoring and suggest that counts of young males may add much useful demographic information with little extra effort.     

How do SNP ascertainment schemes and population demographics affect inferences about population history?

Background

The selection of variable sites for inclusion in genomic analyses can influence results, especially when exemplar populations are used to determine polymorphic sites. We tested the impact of ascertainment bias on the inference of population genetic parameters using empirical and simulated data representing the three major continental groups of cattle: European, African, and Indian. We simulated data under three demographic models. Each simulated data set was subjected to three ascertainment schemes: (I) random selection; (II) geographically biased selection; and (III) selection biased toward loci polymorphic in multiple groups. Empirical data comprised samples of 25 individuals representing each continental group. These cattle were genotyped for 47,506 loci from the bovine 50 K SNP panel. We compared the inference of population histories for the empirical and simulated data sets across different ascertainment conditions using F_ST and principal components analysis (PCA).

Results

Bias toward shared polymorphism across continental groups is apparent in the empirical SNP data. Bias toward uneven levels of within-group polymorphism decreases estimates of F_ST between groups. Subpopulation-biased selection of SNPs changes the weighting of principal component axes and can affect inferences about proportions of admixture and population histories using PCA. PCA-based inferences of population relationships are largely congruent across types of ascertainment bias, even when ascertainment bias is strong.

Conclusions

Analyses of ascertainment bias in genomic data have largely been conducted on human data. As genomic analyses are being applied to non-model organisms, and across taxa with deeper divergences, care must be taken to consider the potential for bias in ascertainment of variation to affect inferences. Estimates of F_ST, time of separation, and population divergence as estimated by principal components analysis can be misleading if this bias is not taken into account.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1469-5) contains supplementary material, which is available to authorized users.     

Is the brown shrimp Crangon crangon (L.) population of the Vaccarès lagoon (Camargue, France, Rhône delta) an annual population?

To study the population dynamics of Crangon crangon in the Vaccarès lagoon in the Camargue (Rh?ne delta), the age of brown shrimp was determined using the method of Tiews (1954). This method consists in counting the number of segments of the outer branch of the first antenna. This number is correlated with the number of moults already accomplished by the shrimp. The duration of the intermoult depends on water temperature. Adapting this model to our environmental data, we determined the age of the brown shrimp. Hatching of larvae occurs in the sea in May, and juveniles enter the lagoon from June to September. Our results showed that Crangon crangon in the Vaccarès lagoon reached sexual maturity between 6 and 11 months, and individuals are 1 year old when they leave the lagoon. A few adults from the previous year (1+) migrate back to the lagoon the following year, but these older individuals represent only a very small part of the population, and have only been observed occasionally. The Vaccarès brown shrimp population can therefore be considered as annual, in contrast to northern European populations.     

What does population structure analysis reveal about the Pterostylis longifolia complex (Orchidaceae)?

Morphologically similar groups of species are common and pose significant challenges for taxonomists. Differences in approaches to classifying unique species can result in some species being overlooked, whereas others are wrongly conserved. The genetic diversity and population structure of the Pterostylis longifolia complex (Orchidaceae) in Tasmania was investigated to determine if four species, and potential hybrids, could be distinguished through genomic AFLP and chloroplast restriction‐fragment‐length polymorphism (RFLP) markers. Analysis of molecular variance (AMOVA) results indicated that little genetic variation was present among taxa, whereas PCoA analyses revealed genetic variation at a regional scale irrespective of taxa. Population genetic structure analyses identified three clusters that correspond to regional genetic and single taxon‐specific phenotypic variation. The results from this study suggest that “longifolia” species have persisted throughout the last glacial maximum in Tasmania and that the complex may be best treated as a single taxon with several morphotypes. These results could have serious evolutionary and conservation implications as taxonomic changes could result in the instatement of a single, widespread taxon in which rarer morphotypes are not protected.     

The role of food in the population dynamics of Orchesella cincta (Linné) (Collembola)

Summary The feeding activity of the collembolan species Orchesella cincta (Linné) was studied in the laboratory and in the field. In the laboratory it was shown that at any one time only about 50–60% of the animals were feeding; the remainder were occupied with molting activities. Most of the time similar values were obtained in the field but during winter and during dry summer periods high percentages of empty guts could be demonstrated, indicating an absence or inaccessability of food. When favorable weather returned, a high feeding activity was again observed. Laboratory experiments and field observations indicate that temporary starvation periods are followed by synchronization of the molting and reproductive rhythms and an apparent increase in longevity. These phenomena are important for the restoration of the population after unfavorable periods but reduce the stabilizing force of food scarcity.     

Evolution of birth intervals in a french rural population (1840–1950)

This study presents the first results concerning the evolution of the birth intervals since 1840 among a rural population of the centre of France, where birth control appeared as far back as the end of the 18th Century. We observe the absence of variation of the average interval between successive briths in relation to the period of marriage, family size and socio-economic status of spouses. This confirms that child spacing does not play a part in the constitution of family. The average intervals between marriage and first birth are associated with most of the variables, essentially due to the marrying age and to a lesser extent to the family size. This rural population, in spite of a modern profile by the widespread practice of birth control, still presents traditional attitudes in the structure of its fertility as is indicated by the absence of birth spreading and the important part which seems to be played by the marriage age of women.     

Statistical indicators and state–space population models predict extinction in a population of bobwhite quail

Early warning systems of extinction thresholds have been developed for and tested in microcosm experiments, but have not been applied to populations of wild animals. We used state–space population models and a statistical indicator to detect a transcritical bifurcation extinction threshold in a population of bobwhite quail (Colinus virginianus) located in an agricultural region experiencing habitat deterioration and loss. The extinction threshold was detectible using two independent data sets. We compared predictions from state–space population models to predictions from a statistical indicator and found that predictions were corroborated. Using state–space population models, we estimated that our study population crossed the extinction threshold in 2010 (2002–2036; 95 % confidence intervals [CI]) using the whistle count (WC) data set and in 2008 (1999–2064; 95 % CI) using the Breeding Bird Survey (BBS) data. With the statistical indicator, we estimated that the extinction threshold will be crossed in 2018 (2004–2031; 95 % CI) using the WC data and will be crossed in 2012 (2006–2018; 95 % CI) using the BBS data. We expect extinction in our study population soon after crossing the extinction threshold, but the time to extinction and potential reversibility of the threshold are unknown. Our results suggest that neither small nor decreasing population size will warn of the transcritical bifurcation extinction threshold. We suggest that managers of wildlife populations in regions experiencing land use change should try to predict extinction thresholds and make management decisions to ensure the persistence of the species.     

Four variants of human plasma α2-glycoprotein (ZAG) in the Japanese population

Summary Zn-₂-glycoprotein (ZAG) of plasma from the general Japanese adult population (n=1224) was studied by polyacrylamide gel isoelectric focusing (IEF) followed by immunoblotting with specific antiserum to ZAG. Most of the plasmas showed a common band pattern, while 16 samples showed four other patterns. These ZAG band patterns were easily differentiated by desialyzing the samples prior to IEF. The asialo form of ZAG commonly showed a single band. The 16 plasma samples presenting double bands were classified into four types containing the common single band. The differences in ZAG phenotypes may be suggested to be due to amino acid substitutions of the ZAG molecule. The statistical frequencies of five alleles, which we proposed to designate ZAG^*1, ZAG^*2, ZAG^*3, ZAG^*4, and ZAG^*5, were 0.9935, 0.0025, 0.0016, 0.0004, and 0.0020, respectively. The genetic transmission of the rare alleles ZAG^*3 and ZAG^*4 was confirmed by two family studies.     

α-Thalassemia haplotypes in the Algerian population

Summary DNA mapping was performed in seven unrelated HbH patients and nine carriers for -thalassemia trait originating from Algeria. This study has allowed us to identify four -thalassemia haplotypes: the (–^3.7) haplotype, which is the most frequent (18 of 23 -thalassemic chromosomes), the (–()^20.5) haplotype, a (--) haplotype, and an ()^T haplotype. Our results also show that the (–^3.7) haplotypes encountered in the Algerian population are heterogeneous and differ by the site of the unequal crossover responsible for the 3.7-kb deletion and the size of the interzeta fragment. In addition, during this survey we observed that normal chromosomes bearing a polymorphic BglII site are associated with different interzeta fragments.     

Dimensions of global population projections: what do we know about future population trends and structures?

The total size of the world population is likely to increase from its current 7 billion to 8–10 billion by 2050. This uncertainty is because of unknown future fertility and mortality trends in different parts of the world. But the young age structure of the population and the fact that in much of Africa and Western Asia, fertility is still very high makes an increase by at least one more billion almost certain. Virtually, all the increase will happen in the developing world. For the second half of the century, population stabilization and the onset of a decline are likely. In addition to the future size of the population, its distribution by age, sex, level of educational attainment and place of residence are of specific importance for studying future food security. The paper provides a detailed discussion of different relevant dimensions in population projections and an evaluation of the methods and assumptions used in current global population projections and in particular those produced by the United Nations and by IIASA.     

β-thalassemia mutations in the Portuguese population

Summary In this study we have carried out haplotype analysis on the -globin gene cluster and characterized the -thalassemia mutation by oligonucleotide hybridization in 14 patients with thalassemia major and 5 with sickle cell/-thalassemia originating from southern Portugal. We found that three mutations, namely the °-39, ° IVS-1 nt 1 and ⁺ IVS-1 nt 110 are prevalent accounting for 53%, 32% and 10% of the -thalassemia chromosomes respectively. In general each mutation was associated with a specific chromosomal haplotype; the ° mutation, however, was linked to three different haplotypes. These results indicate that three oligo-probes complementary to the most common mutations allow prenatal diagnosis by oligonucleotide analysis in 96% of the couples at risk of having offspring with thalassemia major in southern Portugal.     

What limits the Serengeti zebra population?

The populations of the ecologically dominant ungulates in the Serengeti ecosystem (zebra, wildebeest and buffalo) have shown markedly different trends since the 1960s: the two ruminants both irrupted after the elimination of rinderpest in 1960, while the zebras have remained stable. The ruminants are resource limited (though parts of the buffalo population have been limited by poaching since the 1980s). The zebras resource acquisition tactics should allow them to outcompete the ruminants, but their greater spatial dispersion makes them more available to predators, and it has been suggested that this population is limited by predation. To investigate the mechanisms involved in the population dynamics of Serengeti zebra, we compared population dynamics among the three species using demographic models based on age-class-specific survival and fecundity. The only major difference between zebra and the two ruminants occurred in the first-year survival. We show that wildebeest have a higher reproductive potential than zebra (younger age at first breeding and shorter generation time). Nevertheless, these differences in reproduction cannot account for the observed differences in the population trends between the zebra and the ruminants. On the other hand, among-species differences in first-year survival are great enough to account for the constancy of zebra population size. We conclude that the very low first-year survival of zebra limits this population. We provide new data on predation in the Serengeti and show that, as in other ecosystems, predation rates on zebras are high, so predation could hold the population in a predator pit. However, lion and hyena feed principally on adult zebras, and further work is required to discover the process involved in the high mortality of foals.     

Does population ecology have general laws?

There is a widespread opinion among ecologists that ecology lacks general laws. In this paper the author argues that this opinion is mistaken. Taking the case of population dynamics, the author points out that there are several very general law-like propositions that provide the theoretical basis for most population dynamics models that were developed to address specific issues. Some of these foundational principles, like the law of exponential growth, are logically very similar to certain law of physics (Newton's law of intertia, for example, is almost a direct analogue of exponential growth). The author discusses two other principles (population self-limitation and resource-consumer oscillations), as well as the more elementary postulates that underlie them. None of the "laws" that the author proposes for population ecology are new. Collectively ecologists have been using these general principles in guiding development of their models and experiments since the days of Lotka, Volterra, and Gause.