Animal Behavior/Natural Selection

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Natural Selection[edit]

More offspring are produced than finite resources can support. Individuals thus can be viewed as in a constant struggle for existence. Individuals within a population are rarely clones, they commonly show variation in phenotypes as well as genotypes. Some of this variation in behavioral phenotypes is heritable. As successful variants are more likely to survive and reproduce, their genotypes will be become overrepresented in the next generation

Density-independent and density-dependent growth models: Exponential Model: a species can potentially increase in numbers according to a geometric series -- Thomas Robert Malthus (1766-1834) Logistic Model: the rate of population increase may be limited, i.e. it may depend on population density -- Pierre Verhulst (1838). Carrying Capacity (K): an environment's maximum persistently supportable load (Catton 1986).

Natural selection is the process by which environmental effects lead to varying degrees of reproductive success among individuals of a population of organisms with different hereditary characters, or traits. The characters that inhibit reproductive success decrease in frequency from generation to generation. It is the process whereby certain genes (alleles) gain greater representation in the following generations compared to other alleles. Adaptations are the complement of traits that increases the fitness of the owner. An individual's Fitness or Reproductive Success is the relative probability that an animal of a particular genotype and phenotype will manage to contribute its genes to the next generation

Aside from Natural Selection, changes in gene frequencies within a population may also arise from a variety of other sources including:

  • Mutations: changes to individual nucleotide bases along the DNA to large scale rearrangements of chromosomes
  • Gene flow: Emigration, Immigration
  • Genetic drift: Changes in the genetics of the population as a result of chance. Bottlenecks and Founder Effect: Ellis-van Creveld Syndrome is an autosomal recessive skeletal dysplasia that results in short limbed disproportionate dwarfism. The syndrome most commonly occurs in the Amish population of Lancaster, Pa. The incidence is approximately 5 per 1000 live births and 2 per 1000 living persons. No case had been described in the Amish of Ohio, Indiana, or other Amish areas at the time of an extensive search performed by McKusick, et al. The genealogy of the disorder in the Amish of Lancaster, Pa. can be traced back to the immigrants Samuel King and his wife

Example: H.B.D. Kettlewell's work on Industrial Melanism