What does the 'logistic model for population variation' actually mean. Can someone give a simple explanation.
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P(n+1) - P(n) is the change in population over one period. \n\nrP is the rate of growth of population, tempered by (1-P(n)/E). \n\nBasically, imagine P(n) is very small compared to the equilibrium population. P(n)/E would be small, and 1-P(n)/E would be close to one. Thus, the growth of population rP(n)*(1-P(n)/P) would be close to rP. \n\nHowever, the model takes into account other factors, e.g. environment, that limits population growth. As P(n) grows, P(n)/E gets closer to 1. If P(n) is almost exactly E, (1-P(n)/E) approaches 0. Thus rP(1-P(n)/E) approaches 0, and the population growth P(n+1) - P(n) approaches 0. \n\nAs a result, the population starts growing very fast, and then slows down as it approaches equilibium value. This relationship would also hold if the population started out too high, and decreased towards equilibrium.
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NatBoCheck: Well for starters even creationists believe in microevolution, but then you probably don't know what that is.\n\nGive me a few mins...\n\n"The process of evolution can be summarized in three sentences: Genes mutate. [gene: a hereditary unit] Individuals are selected. Populations evolve."\n\n"The mechanisms of evolution are mutation, natural selection, genetic drift, recombination and gene flow."\n\nMutation\n\nThe cellular machinery that copies DNA sometimes makes mistakes. These mistakes alter the sequence of a gene. This is called a mutation. There are many kinds of mutations. A point mutation is a mutation in which one "letter" of the genetic code is changed to another. Lengths of DNA can also be deleted or inserted in a gene; these are also mutations. Finally, genes or parts of genes can become inverted or duplicated. Typical rates of mutation are between 10-10 and 10-12 mutations per base pair of DNA per generation. \n\nNatural Selection\n\nSome types of organisms within a population leave more offspring than others. Over time, the frequency of the more prolific type will increase. The difference in reproductive capability is called natural selection. Natural selection is the only mechanism of adaptive evolution; it is defined as differential reproductive success of pre- existing classes of genetic variants in the gene pool.\n\nThe most common action of natural selection is to remove unfit variants as they arise via mutation. [natural selection: differential reproductive success of genotypes] In other words, natural selection usually prevents new alleles from increasing in frequency. This led a famous evolutionist, George Williams, to say "Evolution proceeds in spite of natural selection."\n\nNatural selection can maintain or deplete genetic variation depending on how it acts.\n\nGenetic Drift\n\nAllele frequencies can change due to chance alone. This is called genetic drift. Drift is a binomial sampling error of the gene pool. What this means is, the alleles that form the next generation's gene pool are a sample of the alleles from the current generation. When sampled from a population, the frequency of alleles differs slightly due to chance alone.\n\nAlleles can increase or decrease in frequency due to drift. The average expected change in allele frequency is zero, since increasing or decreasing in frequency is equally probable. A small percentage of alleles may continually change frequency in a single direction for several generations just as flipping a fair coin may, on occasion, result in a string of heads or tails. A very few new mutant alleles can drift to fixation in this manner.\n\nRecombination\n\nEach chromosome in our sperm or egg cells is a mixture of genes from our mother and our father. Recombination can be thought of as gene shuffling. Most organisms have linear chromosomes and their genes lie at specific location (loci) along them. Bacteria have circular chromosomes. In most sexually reproducing organisms, there are two of each chromosome type in every cell. For instance in humans, every chromosome is paired, one inherited from the mother, the other inherited from the father. When an organism produces gametes, the gametes end up with only one of each chromosome per cell. Haploid gametes are produced from diploid cells by a process called meiosis.\n\nIn meiosis, homologous chromosomes line up. The DNA of the chromosome is broken on both chromosomes in several places and rejoined with the other strand. Later, the two homologous chromosomes are split into two separate cells that divide and become gametes. But, because of recombination, both of the chromosomes are a mix of alleles from the mother and father.\n\nRecombination creates new combinations of alleles. Alleles that arose at different times and different places can be brought together. Recombination can occur not only between genes, but within genes as well. Recombination within a gene can fo
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Seems like you answered your own question.  Population distribution is strongly depend on the population's ability to survive at their location.  So, predators, food availability, climate, all have a role.  There is also alot of randomness in population distribution.
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There is a phrase that scientists use called Carrying Capacity which is the amount of a species that the environment can hold due to limiting factors which are any biotic (living factors) or Abiotic (nonliving factors)factors that restrict the existence, reproduction, or distribution of organisms. When the number of a species reaches or exceeds the carrying capacity then limiting factors begin to take effect such as the amount of food available. Also when the carrying capacity is exceeded competition begins for food, shelter, and reproductive rights. There are three types of growths: stable  growth, rapid growth, and slow growth.An example of stable growth would be the U.S. an example of rapid growth would be China. Since not all countries have the same growth rate it is hard to say whether there are too many people in the world. So really it is a matter of opinion. In some countries there are to many people, such as third world countries, but in other countries there are not too many people. As for what we can do about it, there is nothing we really can do besides what China does (limits each household to one child). What happens is when the carrying capacity is exceeded there is not enough food, shelter, etc. for all the individuals in a population. As a result those individuals die and the population's size eventually falls below the carrying capacity(which is what happens in most third world coutries). This is referred to as 'Survival of the Fittest'. It's horrible to imagine but it's the truth and theres not much we can do about it.
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part A\nfind the limit as t->infinity = 2000\n\npart B\nthe first derivative tells the rate at which the population grows.  you want to know when the rate was highest, i.e use the second derivative.\nfind p"(t)=0\nt=13.25 years\n\npart C\nthe inflection point is at t=13.25 years, which is what we found in the previous problem.  this is the time when the rabbit population grew the fastest.  to find the size of the population, evaluate p(13.25)=1000\n\npart D\nlack of food, lack of genetic variability causing imbreeding, lack of space
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c is the right answer.\n\nA makes no sense in relation to the question\nB natural selection has a bit of randomness in it of course but is basically not random. I mean, the fastest critter in the herd may have had an unlucky day and so he will not procreate, oops. But otherwise, the slowest are intentionally selected by the lion and that is never random.\nD just isn't true, plenty of proof there.
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EEEEH. I'm not really good with this mumbojumbo stuff but here is a site on genotypes and stuff. -> http://janis7hepc.com/Genotypes.htm <-
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Your argument has some assumptions, assertions, and logic that are not sound.\n\nFirst of all, you only multiply probabilities together when they are independent variables - it would be easy to argue that many of the items that you mentioned are interdependent.\n\nAlso, I think you misunderstand what evolution of species is proposing.  Evolution does NOT depend on luck - it is instead an observation that lucky organisms survive and pass on their properties to their descendants.\n\nConsider bacteria - almost all mutations are harmful but a few bacteria have lucky mutations that make them immune to penicillin.  If penicillin is used on bacteria, only these lucky ones survive - and most of their descendants inherit the the same immunity-mutation.  \n\nThe original mutation is luck - the environment then selects and a small set of traits due to beneficial mutations persists.  And THAT is not luck, that is selection.  That's why the process is called "Natural Selection".  \n\nSadly, this is why almost all bacteria were zapped by the early antibiotics, and now (only 60 years later) we have hundreds of resistant strains.
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This is Darwin's Theory of Evolution known as natural selection:\n\n1. Species have great fertility. They make more offspring than can grow to adulthood. \n\n2. Populations remain roughly the same size, with modest fluctuations. \n\n3. Food resources are limited, but are relatively constant most of the time. From these three observations it may be inferred that in such an environment there will be a struggle for survival among individuals. \n\n4. In sexually reproducing species, generally no two individuals are identical. Variation is rampant. \n\n5. Much of this variation is heritable.
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WilliamLCB is correct about the when.  The why is described in some detail at the Mathworld link below.  The summary is that dividing by (n-1) for the sample variance is required to give you a *unbiased* estimator for the population variance.
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Binomial (or binary) logistic regression is a form of regression which is used when the dependent is a dichotomy and the independents are of any type. Multinomial logistic regression exists to handle the case of dependents with more classes than two. When multiple classes of the dependent variable can be ranked, then ordinal logistic regression is preferred to multinomial logistic regression. Continuous variables are not used as dependents in logistic regression. Unlike logit regression, there can be only one dependent variable. \n\nDoes this answer it?
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Please take the time to\nvote for the best answer\n\nThank You!!\n\nI know this is for take yr pick\n\nConditions for natural selection\n\nThe excess fecundity, and consequent competition to survive, in every species provides the precondition for the process Darwin called natural selection. Natural selection is easiest to understand as a logical argument, leading from premises to conclusion. The argument requires the four conditions listed below.\n\n1. Reproduction. Entities must reproduce to form a new generation.\n\n2. Heredity. The offspring must tend to resemble their parents: roughly speaking, 'like must produce like'. This condition is provided by Mendelian inheritance.\n\n3. Variation in characteristics of the members of the population. \n\n4. Variation in the fitness of organisms associated with these characteristics. \n\nProvided these conditions are met for any property of a species, natural selection automatically results, as in the case of the peppered moth. If any are not, it does not. Thus entities, like planets, that do not reproduce cannot evolve by natural selection. But when the four conditions apply, the organisms with the property conferring higher fitness will leave more offspring, and the frequency of that type of organism will increase in the population. \n\nThe biologist Richard Dawkins argues that there is possibly only one condition for natural selection.
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You’re probably asking yourself why we spent so much time on HWE since it never happens in the real world. Why did I spend time on this?\n\nIt provides us with a baseline or null model to assess the impacts of different factors (each eliminated by one of the assumptions)\n\nIE\nThe organism is diploid\nReproduction is sexual\nGenerations are non-overlapping\nMating is random\ndoes not allow inbreeding and assortative mating\nPopulation size is very large\nremoves sampling error (genetic drift)\nMigration is negligible\nMutation can be ignored\nNatural selection does not affect the allele in question
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The term comes from oldish genetics vocabulary and it refers to the most common allele (in terms of proportion) for a given gene in a population. \nBefore modern population genetics research, it was believed that most genes (and associated characteristics) usually had one "normal" form (that would be the wild-type allele, present in most individuals) and another "mutant" form (the least common one). \nNow we know that natural populations are polymorphic (have usually several alleles) for any given gene, and there may be one or more than one more frequent alleles.
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The opposite to this:\n\nhttp://www.statsdirect.com/help/regression_and_correlation/conditional_logistic_regression.htm
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The exponential graph does not take into account that eventually a population will reach a point where it has fully exploited its resources.  It rises slowly at first, but then increasingly steeply, because as the population grows, there are more organisms reproducing. However, the rate of reproduction per organism is constant.  If the graph is drawn on semi-log paper, it will be a straight line.\n\nThe S-shaped curve considers that as a population fills its habitat, resources become scarce, and the population can only then grow slowly.   The initial portion is very similar to the exponential curve.\n \nAs the population fills its habitat, the rate of growth declines, until eventually, the population is stable at some maximum, called the carrying capacity.  This is called the stationary phase.\n\nIf populations grow quickly, they can exceed the carrying capacity, degrade the environment and experience swift decline.   After the population crashes, the environment can rebound.  \n\nThis is illustrated in some population of predators versus prey.  Where populations cycle between growth and decline.
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Microevolution is a change in a population's alleles over a period of time.\n\nIt is very difficult to detect changes that occur on the microscopic level. These changes must manifest themselves in the organisms phenotype. Since individuals do not evolve, one must keep a close eye on the individuals population to detect any change in genotypic modification. Biologists have a way to help them detect such changes; it is called the Hardy -Weinberg theorem.   This idea was developed to determine if a population was evolving. The authors of the theorem set up a series of parameters, which do not exist in nature, to be followed when determining the allele frequencies of any population. These guide lines are as follows:\nThe population must be very large in size.\nIt must be isolated from other populations. ( no gene flow)\nNo mutations.\nRandom mating.\nNo natural selection.\nAs one can see, these characteristics cannot be eliminated from nature. \n\nThere are 5 basic causes of microevolution:\n1. Genetic Drift: This represents random changes in small gene pools due to sampling errors in propagation of alleles. The bottleneck effect and founder effect are prime examples of genetic drift. In either case the number of individuals in a population is drastically reduced distorting the original allelic frequencies.\n2. Gene Flow: The movement of alleles into and out of a gene pool. Migration of an organism into different areas can cause the allelic frequencies of that population to increase. Most populations are not isolated, which is contrary to the Hardy-Weinberg Theorem.\n3. Mutations: These changes in the genome of an organism are an important source of natural selection.\n4. Nonrandom mating: Inbreeding is a popular form of nonrandom mating. Individuals will mate more frequently with close individuals than more distant ones. Assortive mating, is another form of nonrandom mating. Here the individuals will mate with partners that closely resemble themselves in certain characteristics.\n5. Natural Selection: Populations vary in the types of individuals and their reproductive success. Those individuals who leave more offspring behind than others, pass on more of their alleles and have a better success rate in dominating the population.\n\nMacroevolution can be defined simply as evolution above the species level, and its subject matter includes the origins and fates of major novelties such as tetrapod limbs and insect wings, the waxing and waning of multi-species lineages over long time-scales, and the impact of continental drift and other physical processes on the evolutionary process. \nFossils: any preserved remnant or impression left by organisms that lived in the past.\nThese remnants of the past are only meaningful in the context of macroevolution only if their vintages relative to other fossils can be determined by methods we shall now discuss.\n \nGeological Time Scale:\n \nRelative dating: Superimposition of sedimentary rocks tells the relative age of fossils. The fossils in each layer are a local sampling of the organisms that existed when that sediment was deposited. Younger strata are superimposed on the top of older ones , and the succession of fossil species is a story of macroevolution that can be read by paleobiologists.\n \nAbsolute dating: This does not mean errorless dating. The age is given in years and not in relative terms such as early , before , and after. Radioactive dating is the method often used to determine the age of the fossils and rocks . Fossils contain isotopes of elements accumulated in the organism when they were alive. Because each radioactive isotope has a fixed rate of decay, half-life, it can be used to date the species. Half-life is unaffected by pressure, temperature, or other environmental variables.\n \nExamples of half-life:\n\nPotassium 40 -- 1.3 x 109\nRubidium 87 -- 4.9 x 1010\nUranium 238 -- 4.5 x 109\nCarbon 14 -- 5.7 x 103\n \nAnother form of dating is called the "clock". Am