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| 2 Conditions of Natural Selection |
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Variation occurs among individuals
Variations result in differences |
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Measured by the proportional contribution to a future generation
under a given set of environmental conditions, individual traits are selected for or against |
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| the change in the properties of population (species) over the course of generations |
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| Darwin presents the theory of natural selection designed to enable them to survive and reproduce (fit over unfit) |
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| genetically determined characteristic that improves an organisms ability to survive and reproduce under prevailing environmental conditions |
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| occurs because most traits have more than one gene affecting them |
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| most traits are affected by |
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| species are usually composed of |
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| interbreeding subpopulations linked by movement of individuals |
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| the total genetic variation of alleles within a population |
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| the most common measure of genetic variation (genotype frequency) |
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| a change in the mean or variance of a phenotypic trait across generations due to changes in allele frequencies |
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| natural selection acts on the phenotype by |
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| altering both genotype and allele frequencies within a population |
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| 3 general types of natural selection |
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directional selection
stabilizing section
disruption |
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| favors individuals at one extreme of phenotype |
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| favors 2 extremes of phenotypes in a population which have greater fitness that the intermediate |
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| the phenotypic trait that natural selection acts upon |
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| the environmental cause of fitness differences among individuals in a population |
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| do all phenotypic traits represent adaptations? |
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| heritable traits in a gene or chromosome |
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| migration (as related to genes) |
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| results in transfer of genes between local populations (gene flow) |
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| change in allele frequencies due to random chance |
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| each generation represents |
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| a subset or sample of the previous generations gene pool |
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| genotypic ratios remain unchanged generation to generation provided that 1)natural selection doesn't occur 2) genetic drift is insignificant 3) mutations are absent 4) mating is random |
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| Hardy-Weinberg principal functions as |
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| a null model; deviations give inside into evolutionary forces |
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| individuals choose mates non randomly with respect to genotype; mates selected based on some phenotypic trait |
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| positive assortative mating |
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males are more phenotypically similar to each other than expected by chance
does not change frequency of individual alleles, but increases proportion of homogeneous individuals |
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| negative assortative mating |
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mates are less phenotypically similar to each other than expected by chance
results in an increase of the frequency of the heterozygous individuals |
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| nonrandom mating of individuals that are more closely related that expected by random chance |
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| inbreeding can by detrimental by: |
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| offspring more likely to inherit rare, recessive deleteroius genes. |
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| species with broad geographic distribution often experience |
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| a broad range of environmental conditions |
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| the greater the distance between populations |
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| the greater the differences |
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| measurable gradual change in a geographic region in the averages of some phenotype |
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| populations that shoe adaptive responses to breaks along a cline |
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| differences in hight based on environment of local populations |
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| free slow of genes among subpopulations is prevented in great part by some sort of barrier |
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| Geographically isolated subpopulations become |
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| evolution from a common ancestor; often rapid |
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| fitness of any phenotype is a function of the |
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| characteristics that enable an individual to maximize fines under one set of conditions |
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| generally limits its ability to do so under a different set of conditions |
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| ability of a genotype to give rise to a range of phenotypic expression under different environmental conditions |
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| Range of phenotypes produced by a particular genotype in different environmental conditions. |
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| occurs during growth and development of an individual and represents an irreversible characteristic |
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| example of developmental plasticity |
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| small size and slow metabolism can facilitate survival in adverse conditions |
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| reversible phenotypic changes in an individual organism in response to environmental changes |
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| Most important property of population |
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| determined by distribution and density |
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| spatial location, area over which a species occupies |
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| area that encompasses the entire population of species |
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| direct climatic limitation |
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| temperature, precipitation |
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| indirect climatic limitation |
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| food production, water supply, habitat, parasites/competitors, geographic barriers |
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| Example: Climate limitation |
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| Red maples limited to north by temp; carolina wrens limited to the east by moisture |
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| Abundance=(distribution area)(population density) |
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1)Random
2)Uniform
3)Clumped |
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caused by natural interactions between individuals in a local environment.
Only occurs in uniform habitats, and is therefore rare |
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| species evenly spaced; antagonistic intraspecific competition |
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| generated by habitat differences; most common type |
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| the number of proportion of individuals in different age groups |
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| Why is age distribution often skewed in plant populations? |
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| older trees outcompete newer organisms |
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| populations of sexually reproducing organisms tend toward a 1:1 ratio |
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more males at birth
males have shorted lifespans, partially due to activities requiring increased risk
females need to survive childbirth |
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| movements of individuals in space |
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| gravity, wind/water, animal, seeds of plants, small animals, fish, shrimp |
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| individual moves out of a subpopulation |
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| individual moves from another area to a new one |
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| a round trip, perhaps involving mating |
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| number of individuals per unit area |
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| the habitat space actually inhabited or utilized by a species |
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