Search results for "POPULATION DYNAMICS"
showing 10 items of 281 documents
Interactions between willows and insect herbivores under enhanced ultraviolet-B radiation
2002
We studied the effects of elevated ultraviolet-B radiation on interactions between insect herbivores and their host plants by exposing two species of phytochemically different willows, Salix myrsinifolia and S. phylicifolia, to a modulated increase in ultraviolet radiation in an outdoor experiment and monitoring the colonisation of insect herbivores on these willows. We examined the effect of increased ultraviolet-B (UV-B) radiation on (1) the quality of willow leaves, (2) the distribution and abundance of insect herbivores feeding on these willows, (3) the resulting amount of damage, and (4) the performance of insect larvae feeding on the exposed plant tissue. Six clones of each of the two…
Ancient human genomes suggest three ancestral populations for present-day Europeans
2014
We sequenced the genomes of a ∼7,000-year-old farmer from Germany and eight ∼8,000-year-old hunter-gatherers from Luxembourg and Sweden. We analysed these and other ancient genomes1,2,3,4 with 2,345 contemporary humans to show that most present-day Europeans derive from at least three highly differentiated populations: west European hunter-gatherers, who contributed ancestry to all Europeans but not to Near Easterners; ancient north Eurasians related to Upper Palaeolithic Siberians3, who contributed to both Europeans and Near Easterners; and early European farmers, who were mainly of Near Eastern origin but also harboured west European hunter-gatherer related ancestry. We model these popula…
Ancient human DNA.
2011
The contribution of palaeogenetic data to the study of various aspects of hominin biology and evolution has been significant, and has the potential to increase substantially with the widespread implementation of next generation sequencing techniques. Here we discuss the present state-of-the-art of ancient human DNA analysis and the characteristics of hominin aDNA that make sequence validation particularly complex. A brief overview of the development of anthropological palaeogenetic analysis is given to illustrate the technical challenges motivating recent technological advancements.
Transmission Heterogeneity and Control Strategies for Infectious Disease Emergence
2007
Background The control of emergence and spread of infectious diseases depends critically on the details of the genetic makeup of pathogens and hosts, their immunological, behavioral and ecological traits, and the pattern of temporal and spatial contacts among the age/stage-classes of susceptible and infectious host individuals. Methods and Findings We show that failing to acknowledge the existence of heterogeneities in the transmission rate among age/stage-classes can make traditional eradication and control strategies ineffective, and in some cases, policies aimed at controlling pathogen emergence can even increase disease incidence in the host. When control strategies target for reduction…
Population dynamics in Daphnia magna as modified by chronic tetradifon stress.
2000
Two Daphnia magna offsprings (animals from the first and third brood) whose parentals (F0-generation) were exposed during 21 days to different tetradifon (4-chlorophenyl 2,4,5-trichlophenyl sulfone) concentrations, were transferred to a pesticide free medium during 21 days (recovery period). The algae Nannochloris oculata (5 x 10(5) cells/mL) was used as food. In this recovery study, survival, growth and reproduction (mean total young per female, mean brood size, onset of reproduction and mean number broods per female) were assessed as individual parameters and the intrinsic rate of natural increase (r) as population parameter, for F1 generation (1st and 3rd broods). Reproduction was still …
Population structure in Atlantic cod in the eastern North Sea-Skagerrak-Kattegat: early life stage dispersal and adult migration.
2015
Background In marine fish species, where pelagic egg and larvae drift with ocean currents, population structure has been suggested to be maintained by larval retention due to hydrographic structuring and by homing of adult fish to natal areas. Whilst natal homing of adults has been demonstrated for anadromous and coral reef fishes, there are few documented examples of philopatric migration in temperate marine fish species. Results Here, we demonstrate temporally stable genetic differentiation among spawning populations of Atlantic cod (Gadus morhua L.), and present genetic and behavioural evidence for larval drift and philopatric migration in the eastern North Sea-Skagerrak-Kattegat area. W…
Species cohesion despite extreme inbreeding in a social spider.
2011
Colonial social spiders experience extreme inbreeding and highly restricted gene flow between colonies; processes that question the genetic cohesion of geographically separated populations and which could imply multiple origins from predecessors with limited gene flow. We analysed species cohesion and the potential for long-distance dispersal in the social spider Stegodyphus dumicola by studying colony structure in eastern South Africa and the cohesion between this population and Namibian populations previously published. Data from both areas were (re)analysed for historic demographic parameters. Eastern South African S. dumicola were closely related to an east Namibian lineage, showing coh…
Effect of cropping systems on species dynamics and gene flow at the landscape level. A modelling approach
2008
International audience
Survival after pathogen exposure in group-living insects: don't forget the stress of social isolation!
2016
A major cost of group-living is its inherent risk of pathogen infection. To limit this risk, many group-living animals have developed the capability to prophylactically boost their immune system in the presence of group members and/or to mount collective defences against pathogens. These two phenomena, called density-dependent prophylaxis and social immunity, respectively, are often used to explain why, in group-living species, individuals survive better in groups than in isolation. However, this survival difference may also reflect an alternative and often overlooked process: a cost of social isolation on individuals' capability to fight against infections. Here, we disentangled the effect…
Inferring genetic connectivity in real populations, exemplified by coastal and oceanic atlantic cod
2018
Significance Estimates of migration are important for understanding the dynamics of natural populations. A statistic known as FST is often used to measure levels of genetic differentiation among natural populations. Equations that translate FST into estimates of migration are based on “ideal” populations, which are subject to many simplifying assumptions compared with real populations. Therefore, theoretical estimates of migration might not be realistic. We modeled populations of Atlantic cod in the North Sea and the adjacent Skagerrak region to compare how migration is related to the complexities of real populations, and how actual migration compares with predictions based on theory. Resul…