What regulate and limit reindeer populations in Norway?

An understanding of how species are affected by top-down and bottom-up processes in food webs, and how these forces interact with climatic conditions is crucial for how ecosystems should be managed. In Norway large carnivores are effectively removed from extensive areas to protect livestock, leaving human harvesting as the only significant top-down force on ungulate populations. We examined the relative role of top-down and bottom-up processes for 58 semi-domesticated reindeer populations in Norway subjected to contrasting climatic regimes over the period 1981–2005. Intensive herding and international agreement have resulted in a situation where some populations are unable to undertake seasonal migration to the interior to escape the unfavourable climatic conditions that rule the coastal region in the winter, a critical season for northern ungulates. We used this natural manipulation to contrast between populations with 'poor' and 'good' winter conditions. For populations with good winter conditions, average body size increased with harvesting, suggesting that some top-down process was necessary to avoid food limitation. Time-series analyses revealed that direct regulation of population size was only evident in populations subjected to intensive harvesting. The lack of direct regulation in populations subjected to low harvesting resulted in high vulnerability to harsh winter weather. The body size and climate vulnerability of populations with poor winter conditions was unaffected of harvesting, but average densities was positively related to overall vegetation productivity as indexed by satellite images (NDVI). Top-down processes appeared to be necessary to dampen the effect of harsh winters in populations with generally good winter conditions. Conversely, populations subjected to generally poor winter conditions appeared to be more influenced by bottom-up processes and buffered climatic perturbations by increasing body size.     

Is colour polymorphism advantageous to populations and species?

I am writing in response to an article by Bolton, Rollins and Griffith (2015) entitled ‘The danger within: the role of genetic, behavioural and ecological factors in population persistence of colour polymorphic species’ that was recently published as an Opinion under the NEWS AND VIEWS section in Molecular Ecology. Bolton et al. (Molecular Ecology, 2015, 24 , 2907) argue that colour polymorphism may reduce population fitness and increase extinction risk and emphasize that this is contrary to predictions put forward by Forsman et al. (Ecology, 89 , 2008, 34) and Wennersten & Forsman (Biological Reviews 87 , 2012, 756) that the existence of multiple colour morphs with co‐adapted gene complexes and associated trait values may increase the ecological and evolutionary success of polymorphic populations and species. Bolton et al. (Molecular Ecology, 2015, 24 , 2907) further state that there is no clear evidence from studies of ‘true polymorphic species’ that polymorphism promotes population persistence. In response, I (i) challenge their classifications of polymorphisms and revisit the traditional definitions recognizing the dynamic nature of polymorphisms, (ii) review empirical studies that have examined whether and how polymorphism is associated with extinction risk, (iii) discuss the roles of trait correlations between colour pattern and other phenotypic dimensions for population fitness and (iv) highlight that the causes and mechanisms that influence the composition and maintenance of polymorphisms are different from the consequences of the polymorphic condition and how it may impact on aspects of ecological success and long‐term persistence of populations and species.     

Temporal processes and duck populations: examples from Mývatn

Studies of temporal processes at Lake Mývatn, Iceland, on three scales, millennial, centennial and decadal, are reviewed and a summary is presented of the main results of waterfowl population monitoring studies conducted during the past three decades. The characteristics of shallow, subarctic Lake Mývatn and its volcanic environment, are outlined, as well as recent conflicts between development and conservation. Mining of the bottom sediment of Lake Mývatn has been a major agent causing habitat destruction and damage to the food web. Population limitation of waterbirds at Mývatn is discussed, as three research questions and emerging answers: (1) How is reproductive output determined? All species studied showed positive correlations of production of young with levels of aquatic insects, catastrophic weather was rarely important; (2) How is the dispersion of breeding ducks determined? Densities of migratory species are determined mainly by resource levels on the breeding ground in the year before they return to the breeding area; a year-round resident species, Bucephala islandica, adjusts its density to the current availability of insect food in each of two main habitats used; (3) How are flyway populations of ducks determined? For most species, there is not enough information on total numbers and the state of the habitat on a flyway scale. In B. islandica, there are indications that the total population is limited by resources in winter. The Mývatn study area is dominated by a single, shallow and eutrophic lake and for many waterbird species the area seems to form a single functional unit. This leads to significant correlations when comparing demography with environmental conditions, such as food resources.     

Demography of source—sink populations and the evolution of ecological niches

Summary The demography of populations living in variable environments is an important factor molding the evolution of ecological niches, for it determines the relative strength of selection pressures on adaptations to different habitats. Here I consider a coarse-grained environment consisting of two habitat types and investigate how the selection pressure on reproductive success in different habitats depends on their quality and frequency and the dispersal pattern. The results suggest that selection on adaptations to optimal habitats will usually be stronger than on adaptations to poor habitats and the ecological niche will thus tend to be an evolutionarily conservative character. It is because under the habitat choice or limited dispersal that seem to prevail in natural populations, more individuals encounter the better habitat than would be expected solely on the basis of its relative area. This bias results in reduced selection pressure on reproductive success in the poorer habitat. With habitat choice or limited dispersal, selection pressure on reproductive success in the poorer habitat may exceed that on reproductive success in the better habitat only if the poorer habitat is much more frequent in the environment than the better habitat and the difference in their quality is not large.     

Plankton populations of Lake Leake and Tooms Lake—Oligotrophic Tasmanian Lakes

The characteristic feature of Lake Leake and Tooms Lake is their great similarity in physical and chemical limnology. This similarity extends to the plankton populations in general terms, both lakes being dominated by Cyclotella stelligera Cleve et Grun. and having few other species. Floristic differences are minimal. Despite this floristic similarity distinct differences exist in plankton periodicity, principally in that of Cyclotella stelligera. The extreme oligotrophy of the lakes, already suspected from their low nutrient levels, is confirmed by the extremely meagre standing crops.     

Trade-off between plant growth and defense? A comparison of sagebrush populations

We used ecotypic variation in big sagebrush (Artemisia tridentata) to examine potential trade-offs between inherent growth rate and tolerance or resistance to herbivory. Seeds were obtained from seven geographic populations, and 1,120 seedlings were established in a common garden. In one set of plots, plants were subjected to five treatments: control, regular insecticide spray, moderate browsing, severe browsing, or moderate browsing plus insecticide. Plants in a second set of plots were all untreated, and were used to estimate ambient growth, flower production, and susceptibility to herbivorous insects. In the first growing season, population differences in relative growth rate produced approximately seven-fold variation in mean biomass. Two populations of basin big sagebrush (A. tridentata tridentata) and one population of mountain big sagebrush (A. tridentata vaseyana) grew fastest; those of Wyoming big sagebrush (A. tridentata wyomingensis) showed the slowest growth. Bi-weekly application of insecticide for two growing seasons had no effect on the growth of either browsed or unbrowsed plants. All populations showed compensatory growth (but not overcompensation) in response to browsing, but the degree of compensation was unrelated to inherent growth rate. Similarly, there was no consistent relationship between plant growth rate and flower production in the second growing season. Some insects colonized fast-growing populations more frequently than slow-growing ones, but patterns of insect colonization were species-specific. At the level of geographic populations and subspecies, we found little evidence of a built-in trade-off between inherent growth rate and the ability to tolerate or resist herbivory. Because population ranks for growth rate changed substantially between seasons, attempts to correlate growth and defense characters need to account for differences in the growth trajectories of perennial plants.     

Physiological and mutagenic effects of N-methyl-N′-nitro-N-nitrosoguanidine in populations of chlorococcal algae

The suitability was evaluated of MNNG as a mutagen inducing increased frequencies of mutations in the cell populations of three strains of chlorococcal algae for the purposes of selection. MNNG has proved to be highly toxic to those algae as it produces severe physiological responses of the affected cells. The mutagenic effect of MNNG was relatively small in comparison with the recorded toxic effect. From these results it has been concluded that in reverse to NEU, MNNG can hardly be applied with such good an effect in the mutation breeding of chlorococcal algae that are suitable for mass cultivation.     

Do island plant populations really have lower genetic variation than mainland populations? Effects of selection and distribution range on genetic diversity estimates

Ecological and evolutionary studies largely assume that island populations display low levels of neutral genetic variation. However, this notion has only been formally tested in a few cases involving plant taxa, and the confounding effect of selection on genetic diversity (GD) estimates based on putatively neutral markers has typically been overlooked. Here, we generated nuclear microsatellite and plastid DNA sequence data in Periploca laevigata, a plant taxon with an island–mainland distribution area, to (i) investigate whether selection affects GD estimates of populations across contrasting habitats; and (ii) test the long‐standing idea that island populations have lower GD than their mainland counterparts. Plastid data showed that colonization of the Canary Islands promoted strong lineage divergence within P. laevigata, which was accompanied by selective sweeps at several nuclear microsatellite loci. Inclusion of loci affected by strong divergent selection produced a significant downward bias in the GD estimates of the mainland lineage, but such underestimates were substantial (>14%) only when more than one loci under selection were included in the computations. When loci affected by selection were removed, we did not find evidence that insular Periploca populations have less GD than their mainland counterparts. The analysis of data obtained from a comprehensive literature survey reinforced this result, as overall comparisons of GD estimates between island and mainland populations were not significant across plant taxa (N = 66), with the only exception of island endemics with narrow distributions. This study suggests that identification and removal of markers potentially affected by selection should be routinely implemented in estimates of GD, particularly if different lineages are compared. Furthermore, it provides compelling evidence that the expectation of low GD cannot be generalized to island plant populations.     

Sympatric Epichloë species and chemotypic profiles in natural populations of Lolium perenne

The distribution of different Epichloë species within eight natural populations of Lolium perenne was studied. In total, 40.2% of the asymptomatic plants were infected by Epichloë festucae var. lolii or by Epichloë typhina. Both species occurred in sympatry in seven grass populations, and some plants had dual infections by both taxa. No hybrid taxa such as Epichloë hybrida were detected. Epichloë festucae strains were classified into two morphotypes, M1 and M3, according to culture characters, both morphotypes occurred in sympatry in seven populations. Plants bearing stromata produced by Epichloë typhina were observed, but asymptomatic plants infected by this species also occurred in seven populations. The alkaloid profile of Lolium perenne plants was related to the morphotype of their infecting strains: most plants infected by M3-strains were characterized by lolitrem, and those with M1-strains contained either ergovaline or lolitrem. Plants infected by Epichloë typhina were characterized by high peramine content.     

Association of TNF-α and IL-10 polymorphisms with tuberculosis in Tunisian populations

Cytokine Th1/Th2 balance is known to play a key role in controlling Mycobacterium tuberculosis infection. Based upon the functional role of the TNF-α [-308 G(low)?→?A(high) (rs1800629)] and IL-10 [-1082 A(low)?→?G(high) (rs1800870), -819 T(low)?→?C(high) (rs1800871) and -592 A(low)?→?C(high) (rs1800872)] single nucleotide polymorphisms (SNPs) on production levels, we genotyped 76 patients with pulmonary tuberculosis (TB) (pTB), 55 patients with extrapulmonary TB (epTB) and 95 healthy blood donors by polymerase chain reaction fragment length polymorphism (PCR-RFLP). We observed that -308 A allele was associated with increased risk susceptibility to epTB (OR?=?1.96; 95% CI, 1.04-3.71; P?=?0.024). The -1082 AG genotype was significantly associated with increased risk development of epTB (odds ratio [OR]?=?3.69; 95% confidence intervals [CI], 1.73-7.92; P corrected for the number of genotypes [Pc]?=?0.0003). By contrast, -1082 AA genotype appeared to be associated with resistance to pTB (OR?=?0.38; 95% CI, 0.19-0.74; Pc?=?0.006) and epTB (OR?=?0.22; 95% CI, 0.1-0.48; Pc?=?0.00006). High-producer IL-10 GCC haplotype seemed to be associated with 2.11-fold (95% CI, 1.28-3.46; Pc?=?0.003) and 2.57-fold (95% CI, 1.5-4.4; Pc?=?0.0006) increased susceptibility to pTB and epTB, respectively. Combination of TNF-α/IL-10 high producer genotypes was associated with increased 3.13-fold (95% CI, 1.23-8.05; Pc?=?0.028) susceptibility to epTB. However, combined TNF-α/IL-10 low producer genotypes appeared to have protect effect to pTB (OR?=?0.44, 95% CI, 0.21-0.89; Pc?=?0.04) and epTB (OR?=?0.26, 95% CI, 0.1-0.62; Pc?=?0.0028). Collectively, our results showed that analysed SNPs in the TNF-α and IL-10 gene polymorphisms play key role in susceptibility to or protection against TB development in Tunisian populations.     

β-Globin gene linked DNA haplotypes and frameworks in three South-East Asian populations

Summary DNA haplotypes and frameworks (numbers in parenthesis) linked to the -globin gene were determined by restriction fragment analysis using eight restriction endonucleases on 86 (97) chromosomes bearing the normal -globin gene (HBB^*A) and 108 (118) chromosomes bearing HBB^*E in subjects homozygous for HBB^*A or HBB^*E from three South-East Asian populations with high HBB^*E frequencies (northern Thailand, north-eastern Thailand and Cambodia). A systematic nomenclature for -globin gene-linked haplotype characterized by six polymorphic sites is introduced. In all populations, HBB^*A occurred preferentially (>80%) in linkage with the haplotype 41 (+----+) and all three frameworks described by Antonarakis et al. (1982). In contrast, almost 80% of the HBB^*E genes occurred with the haplotype 27 (-+-+++). In northern and north-eastern Thailand, HBB^*E was present almost exclusively in framework 2; HBB^*E in framework 3 (Asian) was limited to the Khmer population of Cambodia, and the frequency of HBB^* E-linked framework 3 increased from the west to the east in this country.     

How to ‘catch’ floating populations? Research and the fixing of migration in space and time

Abstract

The recent ‘mobilities turn’ in the social sciences suggests that research always fixes mobility somehow in time and space, in order to understand it. Migration, being a form of mobility, has to be fixed on certain times and spaces in order to make it possible to define and research it. Being a geographer, I build on this insight in the first part of the article to re-read the critiques on post-war methodological nationalism. Reflecting on my own past research practice, I argue in the second part that leaving behind the methodological nationalism paradigm does not mean leaving behind the necessity to fix migration in time and space, on either the ontological or the practical methodological level. New ways of fixing are chosen and, out of recurring ontological and methodological choices, new migration stereotypes are developing such as what might be called ‘methodological ruralism’ in the case of Romanian migration.     

Are bottlenecks associated with colonization? Genetic diversity and diapause variation of native and introduced Rhagoletis completa populations

The success of invasive species appears to be a paradox: despite experiencing strong population bottlenecks, invasive species are able to successfully establish in new environments. We studied how the walnut husk fly, Rhagoletis completa, was able to successfully colonize California from the Midwestern United States, by examining genetic diversity and diapause variation of native and introduced fly populations. Climate plays an important role in the successful establishment of introduced insects, because insect diapause is highly dependent upon external climatic conditions. We examined if: (1) fly populations show signs of a population bottleneck, (2) native and introduced flies differ in diapause length when exposed to California and Midwestern climatic conditions, and (3) population genetic diversity is related to variation in diapause length. We assessed if fly diapause conformed more to a model of establishment by local adaptation or to a model of a highly plastic “general-purpose genotype”. Our results indicate that only two populations close to the original introduced location showed signs of a population bottleneck, and native and introduced populations did not differ in genetic diversity. Genetic diversity increased in the northern introduced populations, suggesting that multiple introductions have occurred. Flies emerged about 2 weeks earlier under the Midwestern treatment than the California treatment, and introduced flies emerged about a week earlier than native flies. All flies emerged when walnuts are typically available in California. Although variance in diapause length differed between populations, it did not vary between populations or regions. Furthermore, genetic diversity was not associated with diapause variation. Therefore, multiple introductions and a “general-purpose genotype” appear to have facilitated the fly’s invasion into California.     

Invasive and native Rhododendron ponticum populations: is there evidence for genotypic differences in germination and growth?

Previous studies have shown that the invasive spread of Rhododendron ponticum in the British Isles is influenced by the more favourable environmental conditions in the new territory than in the species' home range. In this study, we asked whether the species' invasion success might also involve a genotypic background for higher growth and germination rates in invasive populations. We tested the hypotheses that invasive populations have higher absolute germination rates, germinate faster and exhibit higher growth rates. We present data from greenhouse and climate chamber experiments with seed material and Rhododendron cuttings from six populations each of native Georgian, native Spanish and invasive Irish populations subjected to different temperature environments.
There were no differences in the maximum germination rate and optimum germination temperature between native and invasive origins. We found significant differences in germination velocity with the Irish seeds responding most rapidly to all germination treatments. Accordingly, in the growth experiment the invasive Irish origins had the highest relative growth rates in all environments tested.
Our results provide evidence for a genetic shift in invasive populations towards an increased investment in growth and towards a faster germination rate. Both traits would contribute to explaining this species' range expansion. The underlying evolutionary mechanisms for this shift are discussed, including the possibility of hybridisation or of an ecological release from hitherto experienced constraints in the native area.     

The effect of reintroductions on the genetic variability in Eurasian lynx populations: the cases of Bohemian–Bavarian and Vosges–Palatinian populations

Over the past ~40 years, several attempts were made to reintroduce Eurasian lynx to suitable habitat within their former distribution range in Western Europe. In general, limited numbers of individuals have been released to establish new populations. To evaluate the effects of reintroductions on the genetic status of lynx populations we used 12 microsatellite loci to study lynx populations in the Bohemian–Bavarian and Vosges–Palatinian forests. Compared with autochthonous lynx populations, these two reintroduced populations displayed reduced genetic diversity, particularly the Vosges–Palatinian population. Our genetic data provide further evidence to support the status of ‘endangered’ and ‘critically endangered’ for the Bohemian–Bavarian and Vosges–Palatinian populations, respectively. Regarding conservation management, we highlight the need to limit poaching, and advocate additional translocations to bolster genetic variability.     

How fast is fast? Eco‐evolutionary dynamics and rates of change in populations and phenotypes

It is increasingly recognized that evolution may occur in ecological time. It is not clear, however, how fast evolution – or phenotypic change more generally – may be in comparison with the associated ecology, or whether systems with fast ecological dynamics generally have relatively fast rates of phenotypic change. We developed a new dataset on standardized rates of change in population size and phenotypic traits for a wide range of species and taxonomic groups. We show that rates of change in phenotypes are generally no more than 2/3, and on average about 1/4, the concurrent rates of change in population size. There was no relationship between rates of population change and rates of phenotypic change across systems. We also found that the variance of both phenotypic and ecological rates increased with the mean across studies following a power law with an exponent of two, while temporal variation in phenotypic rates was lower than in ecological rates. Our results are consistent with the view that ecology and evolution may occur at similar time scales, but clarify that only rarely do populations change as fast in traits as they do in abundance.     

Allozyme polymorphism of Mdh and α-Gpdh in Ixodes ricinus populations: comparison of borreliae-infected and uninfected ticks

Ixodes ricinus Linnaeus (Acari: Ixodidae) ticks are vectors of numerous infectious diseases in humans and animals. The allozyme variability of MDH and α-Gpdh was detected by native polyacrylamide gel electrophoresis in I. ricinus natural populations in three localities in Serbia. Four alleles of Mdh locus (MDH 1, MDH 2, MDH 3 and MDH X) and four alleles of α-Gpdh locus (VS, S, F and VF) were detected. Interpopulation differences in Mdh and α-Gpdh allele frequencies were statistically insignificant. Significant difference in α-Gpdh allele frequencies between males and females was recorded in the largest sample only. Differences in allele frequencies, detected between borreliae-infected and uninfected I. ricinus ticks, were close to the level of statistical significance, especially for α-Gpdh locus. Clear significant difference appeared in females when sexes were tested separatelly (P = 0.037). It is interesting that genotypes containing rarer alleles (MDH 1 and S) were infected in higher proportion in comparison to other genotypes. Our results point towards a possible role of Mdh and α-Gpdh loci in I. ricinus ticks in the determination of energy requirements for host seeking. Sex differences in α-Gpdh allele frequencies suggest that selective pressure, concerning efficiency of reserve materials utilisation, points to α-Gpdh rather than to Mdh locus.