Search results for "Population"
showing 10 items of 9945 documents
Fitness differences and persistent founder effects determine the clonal composition during population build-up in Daphnia
2014
During the initial stages of population build-up in new habitats, the time at which immigrants arrive may infl uence their contribution to the population and thus determine population genetic structure. While the numerical advantage associated with founder eff ects may promote dominance of the off spring of early colonizers, fi tness diff erences associated with ecological diff erences among genotypes may potentially overwhelm these founder eff ects. We conducted an outdoor mesocosm experiment to test whether the sequence of arrival determines the relative contribution of genetic lineages (clones) to populations of the water fl ea Daphnia . A set of D. galeata clones was inoculated pairwise…
Ornithophily on the Canary Islands
1984
(1) On the Canary Islands and Madeira typical bird-flowers occur in at least twelve species of six genera, although true flower-birds are absent. This inconsistency is in part elucidated by field observations on exotic and wild plants of Tenerife. —(2) In the Botanical Garden of Orotava it could be observed that various ornithophilous plants, which were introduced there, were visited by indigenous birds for nectar and in one case (Orthostemon) for food tissue. Of the three bird species involved, an endemic race of Chiffchaff (Phylloscopus collybita) and resident Blackcaps (Sylvia atricapilla) exploit, and pollinate, flowers legitimously, while the Wild Canary (Serinus canaria) is predominan…
Breeding suppression in the bank vole as antipredatory adaptation in a predictable environment
1994
In northern Fennoscandia, microtine rodent populations fluctuate cyclically. The environment of an individual vole can be considered to be predictable when the risks of predation and intra- and interspecific competition change with the cycle, such that both are high during the population highs of voles. The risk of predation is also high during the vole crash. After the crash, the vole population is characterized by low intra- and interspecific competition and low predation pressure. The main predators affecting voles during the crash are the small mustelids, least weasel and stoat. The density of these specialist predators declines drastically during the winter after the vole crash. We stu…
Genetic population structure of two cryptic Gammarus fossarum types across a contact zone
1998
Previous studies have revealed inconsistent results about the taxonomic status of European Gammarus fossarum forms. The variability in morphology and hybridization ability has not shown clear geographic patterns, whereas on a genetical basis two Central European G. fossarum forms have been proposed. In the present study the genetic structure of G. fossarum populations was investigated across a natural contact zone. For the first time direct comparisons of allotopic versus syntopic populations were feasible. 24 Populations of G. fossarum plus 4 populations of G. pulex (as outgroup) were sampled along 2 transects across the contact zone. The genotypes of about 60 individuals per population we…
Leaf shape variation and taxonomic boundaries in two sympatric rupicolous species of Helichrysum (Asteraceae: Gnaphalieae), assessed by linear measur…
2012
Quantifying and understanding the causes of population differentiation in plants are critical for assessing the taxonomic structure of species, as the level of differentiation among populations may correspond to incipient speciation. Using linear and geometric morphometric approaches, phenotypic variation and associations between leaf traits and geographic and environmental characteristics were investigated in Helichrysum crassifolium and the widespread and sympatric Helichrysum pendulum: two species exhibiting conspicuous leaf variation in size and shape. The morphometric results show that both species have distinct patterns of leaf shape variation. However, overlapping values link the ran…
Population trends of birds across the iron curtain: Brain matters
2011
One approach to assess human impact on species’ population dynamics is to correlate ecological traits of species with their long-term population trends. Yet, few studies investigated population trends in multiple regions that differ in human impact to reveal which traits explain population trends over larger geographic areas and which only regionally. We examined the relationship between various species traits and long-term population trends of 57 common passerine bird species from 1991 to 2007 in three adjacent regions in central Europe that experienced differences in socioeconomic history: North-Western Germany, Eastern Germany and the Czech Republic. We tested effects of habitat, dietary…
Do not disturb the family: roles of colony size and human disturbance in the genetic structure of lesser kestrel
2015
Dispersal and philopatry are fundamental processes influencing the genetic structure and persistence of populations, and might be affected by isolation and habitat perturbation. Habitat degradation induced by human activities could have detrimental consequences on the genetic structure of populations. Therefore, it is crucial to understand the role of human impact in promoting or disrupting the genetic structure. Here, we conducted a genetic analysis using 12 polymorphic microsatellite markers of 70 lesser kestrels Falco naumanni from 10 breeding colonies of two subpopulations in Sicily (southern Italy). Genetic differentiation between the two subpopulations was negligible, and linear dista…
Food for flight: pre-migratory dynamics of the Lesser Kestrel Falco naumanni.
2014
Capsule The post-reproductive stage of Lesser Kestrel is crucial for migratory fuelling and survival. Aims To describe the summer pre-migratory ecology of the Lesser Kestrel in Sicily and review existing data in Southern Europe. Methods We identified the main summer roosts and then made roost counts every ten days from 2010 to 2012. We used case-sensitive modelling procedures to detect biases in counts (generalized linear mixed models), assess the annual population trends from 2005 to 2012 (TRends and Indices for Monitoring); and to model habitat preferences (generalized linear model). We sampled pellets to describe the birds’ diet during the peak month prior to migration. Results We discov…
New Polymorphic Microsatellite Loci for the Zebra MusselDreissena polymorpha(Pallas, 1771), a Common Bioindicator
2011
ABSTRACT To investigate the influence of environmental pollution on the population genetics of Dreissena polymorpha, we developed five new polymorphic micro satellite loci for the zebra mussel. This mussel is widely distributed and is a common bioindicator in the field of ecotoxicology. The amplification of the microsatellite loci was tested on a single population of 24 individuals. In this population, the number of alleles per locus ranged from 3–14, and the observed heterozygosity ranged from 0.545–0.909 (mean, 0.772). All loci followed Hardy-Weinberg expectations, suggesting no evidence for null alleles. There was no significant genetic linkage disequilibrium, neither between the aforeme…
Host‐parasite relationships between two seal populations and two species of Corynosoma (Acanthocephala) in Finland
1988
Ringed seals (Phoea hispida botnica), from the Bothnian Bay, north-eastern Baltic Sea were examined for acanthocephalan parasites in 1977-1982, and specimens from Lake Saimaa in south-eastern Finland (P. h. saimensis) were examined in 1980-1981. The two seal stocks have been isolated from Arctic stock for 11,000 years and from each other for 8,000 years. Corynosoma strumosum and C. semerme were found in the Baltic seals, but only C. strumosurn in those from the lake. Eighty two of the ringed seals caught in the Bothruan Bay were infected with both Corynosoma species, one with a single infection of C. strumosum and one with C. semerme inautumn. The total number of C. semerme increased in rel…