نتایج جستجو برای: species selection
تعداد نتایج: 844002 فیلتر نتایج به سال:
The relationship between sexual selection and extinction risk has rarely been investigated. This is unfortunate because extinction plays a key role in determining the patterns of species richness seen in extant clades, which form the basis of comparative studies into the role that sexual selection may play in promoting speciation. We investigate the extent to which the perceived risk of extinct...
Gradual evolutionary change by natural selection operates so slowly within established species that it cannot account for the major features of evolution. Evolutionary change tends to be concentrated within speciation events. The direction of transpecific evolution is determined by the process of species selection, which is analogous to natural selection but acts upon species within higher taxa...
BACKGROUND Species distribution models require selection of species, study extent and spatial unit, statistical methods, variables, and assessment metrics. If absence data are not available, another important consideration is pseudoabsence generation. Different strategies for pseudoabsence generation can produce varying spatial representation of species. METHODOLOGY We considered model outcom...
this research concentrates on the lithostratigraphy, biostratigraphy, microfacies and sedimentary environment of the asmari and gachsaran formations at southwest firuzabad. the thickness of the studied section in all 608.95 meters that 220.8 meters belong to the asmari formation and 387.95 meters belong to the gachsaran formation (champe and mol members). in the study area, the asmari formation...
In Salmonella typhimurium seven tRNA species specific for leucine, proline and arginine have 1-methylguanosine (m1G) next to and 3' of the anticodon (position 37 of tRNA), five tRNA species specific for phenylalanine, serine, tyrosine, cysteine and tryptophan have 2-methylthio-N-6-(cis-hydroxy)isopentenyladenosine (ms2io6A) in the same position of the tRNA, and four tRNA species, specific for l...
Habitat selection is a fundamental component of community ecology, population ecology, and evolutionary biology and can be especially important to species with complex annual habitat requirements, such as migratory birds. Resource preferences on the breeding grounds may change during the postfledging period for migrant songbirds, however, the degree to which selection changes, timing of change,...
Shifting prey selection has been identified as a mechanism potentially regulating predator-prey interactions, but it may also lead to different outcomes, especially in more complex systems with multiple prey species available. We assessed changing prey selection by lions, the major predator for 12 large herbivore species in South Africa's Kruger National Park. The database was provided by recor...
Recent documentation of a few compelling examples of sympatric speciation led to a proliferation of theoretical models. Unfortunately, plausible examples from nature have rarely been used to test model predictions, such as the initial presence of strong disruptive selection. Here I estimated the form and strength of selection in two classic examples of sympatric speciation: radiations of Camero...
For an old-growth forest edge in the Sierra Nevada, we quantified the extent of edge effects from a group selection harvest. Across transects from the interior of the old-growth forest through the group selection opening, we quantified changes in resource availability (light, soil moisture, and seedbed) and vegetation composition (cover, richness). We found a steep change in light availability ...
cause of mortality. However, another hemoglobin allele C has recently been estimated to have even higher fitness, and now appears to be replacing allele S, suggesting that the sickle-cell polymorphism may be evolutionarily short-lived. When alleles are maintained by balancing selection for a long evolutionary time and are consequently shared by related species, it is referred to as 'trans-speci...
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