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Demographic Fluctuations (demographic + fluctuation)
Selected AbstractsEVOLUTION OF INCOMPATIBILITY-INDUCING MICROBES IN SUBDIVIDED HOST POPULATIONSEVOLUTION, Issue 2 2009Ralph Haygood Many insects, other arthropods, and nematodes harbor maternally inherited bacteria inducing "cytoplasmic incompatibility" (CI), reduced egg hatch when infected males mate with uninfected females. Although CI drives the spread of these microbes, selection on alternative, mutually compatible strains in panmictic host populations does not act directly on CI intensity but favors higher "effective fecundity," the number of infected progeny an infected female produces. We analyze the consequences of host population subdivision using deterministic and stochastic models. In subdivided populations, effective fecundity remains the primary target of selection. For strains of equal effective fecundity, if population density is regulated locally (i.e., "soft selection"), variation among patches in infection frequencies may induce change in the relative frequencies of the strains. However, whether this change favors stronger incompatibility depends on initial frequencies. Demographic fluctuations maintain frequency variation that tends to favor stronger incompatibility. However, this effect is weak; even with small patches, minute increases in effective fecundity can offset substantial decreases in CI intensity. These results are insensitive to many details of host life cycle and migration and to systematic outbreeding or inbreeding within patches. Selection acting through transfer between host species may be required to explain the prevalence of CI. [source] Drivers of megaherbivore demographic fluctuations: inference from elephantsJOURNAL OF ZOOLOGY, Issue 1 2009M. J. Trimble Abstract Environmentally induced variation in survival and fecundity generates demographic fluctuations that affect population growth rate. However, a general pattern of the comparative influence of variation in fecundity and juvenile survival on elephant population dynamics has not been investigated at a broad scale. We evaluated the relative importance of conception, gestation, first year survival and subsequent survivorship for controlling demographic variation by exploring the relationship between past environmental conditions determined by integrated normalized difference vegetation index (INDVI) and the shape of age distributions at 17 sites across Africa. We showed that, generally, INDVI during gestation best explained anomalies in age structure. However, in areas with low mean annual rainfall, INDVI during the first year of life was critical. The results challenge Eberhardt's paradigm for population analysis that suggests that populations respond to limited resource availability through a sequential decrease in juvenile survival, reproductive rate and adult survival. Contrastingly, elephants appear to respond first through a reduction in reproductive rate. We conclude that this discrepancy is likely due to the evolutionary significance of extremely large body size , an adaptation that increases survival rate but decreases reproductive potential. Other megaherbivores may respond similarly to resource limitation due to similarities in population dynamics. Knowing how vital rates vary with changing environmental conditions will permit better forecasts of the trajectories of megaherbivore populations. [source] Mitochondrial DNA patterns in the Iberian Northern plateau: Population dynamics and substructure of the Zamora provinceAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2010Luis Alvarez Abstract Several studies have shown the importance of recent events in the configuration of the genetic landscape of a specific territory. In this context, due to the phenomena of repopulation and demographic fluctuations that took place in recent centuries, the Iberian Northern plateau is a very interesting case study. The main aim of this work is to check if recent population movements together with existing boundaries (geographical and administrative) have influenced the current genetic composition of the area. To accomplish this general purpose, mitochondrial DNA variations of 214 individuals from a population located in the Western region of the Iberian Northern plateau (the province of Zamora) were analyzed. Results showed a typical Western European mitochondrial DNA haplogroup composition. However, unexpected high frequencies of U5, HV0, and L haplogroups were found in some regions. The analyses of microdifferentiation showed that there are differences between regions, but no geographic substructure organization can be noticed. It can be stated that the differences observed in the genetic pool of the sampled area at regional level results from the mixture of different populations carrying new lineages into this area at different points in history. Am J Phys Anthropol 142:531,539, 2010. © 2010 Wiley-Liss, Inc. [source] | ||||||||||