95,679 research outputs found
Asymptotic Validity of the Bayes-Inspired Indifference Zone Procedure: The Non-Normal Known Variance Case
We consider the indifference-zone (IZ) formulation of the ranking and
selection problem in which the goal is to choose an alternative with the
largest mean with guaranteed probability, as long as the difference between
this mean and the second largest exceeds a threshold. Conservatism leads
classical IZ procedures to take too many samples in problems with many
alternatives. The Bayes-inspired Indifference Zone (BIZ) procedure, proposed in
Frazier (2014), is less conservative than previous procedures, but its proof of
validity requires strong assumptions, specifically that samples are normal, and
variances are known with an integer multiple structure. In this paper, we show
asymptotic validity of a slight modification of the original BIZ procedure as
the difference between the best alternative and the second best goes to
zero,when the variances are known and finite, and samples are independent and
identically distributed, but not necessarily normal
Clonal Interference, Multiple Mutations, and Adaptation in Large Asexual Populations
Two important problems affect the ability of asexual populations to
accumulate beneficial mutations, and hence to adapt. First, clonal interference
causes some beneficial mutations to be outcompeted by more-fit mutations which
occur in the same genetic background. Second, multiple mutations occur in some
individuals, so even mutations of large effect can be outcompeted unless they
occur in a good genetic background which contains other beneficial mutations.
In this paper, we use a Monte Carlo simulation to study how these two factors
influence the adaptation of asexual populations. We find that the results
depend qualitatively on the shape of the distribution of the effects of
possible beneficial mutations. When this distribution falls off slower than
exponentially, clonal interference alone reasonably describes which mutations
dominate the adaptation, although it gives a misleading picture of the
evolutionary dynamics. When the distribution falls off faster than
exponentially, an analysis based on multiple mutations is more appropriate.
Using our simulations, we are able to explore the limits of validity of both of
these approaches, and we explore the complex dynamics in the regimes where
neither are fully applicable.Comment: 24 pages, 5 figure
Inferring introduction routes of invasive species using approximate Bayesian computation on microsatellite data
Determining the routes of introduction provides not only information about the history of an invasion process, but also information about the origin and construction of the genetic composition of the invading population. It remains difficult, however, to infer introduction routes from molecular data because of a lack of appropriate methods. We evaluate here the use of an approximate Bayesian computation (ABC) method for estimating the probabilities of introduction routes of invasive populations based on microsatellite data. We considered the crucial case of a single source population from which two invasive populations originated either serially from a single introduction event or from two independent introduction events. Using simulated datasets, we found that the method gave correct inferences and was robust to many erroneous beliefs. The method was also more efficient than traditional methods based on raw values of statistics such as assignment likelihood or pairwise F(ST). We illustrate some of the features of our ABC method, using real microsatellite datasets obtained for invasive populations of the western corn rootworm, Diabrotica virgifera virgifera. Most computations were performed with the DIYABC program (http://www1.montpellier.inra.fr/CBGP/diyabc/)
Rate of Adaptation in Large Sexual Populations
Adaptation often involves the acquisition of a large number of genomic
changes which arise as mutations in single individuals. In asexual populations,
combinations of mutations can fix only when they arise in the same lineage, but
for populations in which genetic information is exchanged, beneficial mutations
can arise in different individuals and be combined later. In large populations,
when the product of the population size N and the total beneficial mutation
rate U_b is large, many new beneficial alleles can be segregating in the
population simultaneously. We calculate the rate of adaptation, v, in several
models of such sexual populations and show that v is linear in NU_b only in
sufficiently small populations. In large populations, v increases much more
slowly as log NU_b. The prefactor of this logarithm, however, increases as the
square of the recombination rate. This acceleration of adaptation by
recombination implies a strong evolutionary advantage of sex
Phase Transition in Sexual Reproduction and Biological Evolution
Using Monte Carlo model of biological evolution we have discovered that
populations can switch between two different strategies of their genomes'
evolution; Darwinian purifying selection and complementing the haplotypes. The
first one is exploited in the large panmictic populations while the second one
in the small highly inbred populations. The choice depends on the crossover
frequency. There is a power law relation between the critical value of
crossover frequency and the size of panmictic population. Under the constant
inbreeding this critical value of crossover does not depend on the population
size and has a character of phase transition. Close to this value sympatric
speciation is observed.Comment: 13 pages, 8 figure
Used-habitat calibration plots: a new procedure for validating species distribution, resource selection, and step-selection models
âSpecies distribution modelingâ was recently ranked as one of the top five âresearch frontsâ in ecology and the environmental sciences by ISI's Essential Science Indicators (Renner and Warton 2013), reflecting the importance of predicting how species distributions will respond to anthropogenic change. Unfortunately, species distribution models (SDMs) often perform poorly when applied to novel environments. Compounding on this problem is the shortage of methods for evaluating SDMs (hence, we may be getting our predictions wrong and not even know it). Traditional methods for validating SDMs quantify a model's ability to classify locations as used or unused. Instead, we propose to focus on how well SDMs can predict the characteristics of used locations. This subtle shift in viewpoint leads to a more natural and informative evaluation and validation of models across the entire spectrum of SDMs. Through a series of examples, we show how simple graphical methods can help with three fundamental challenges of habitat modeling: identifying missing covariates, non-linearity, and multicollinearity. Identifying habitat characteristics that are not well-predicted by the model can provide insights into variables affecting the distribution of species, suggest appropriate model modifications, and ultimately improve the reliability and generality of conservation and management recommendations
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