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Population Evolution

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speciation-
the formation one or more new species from a single ancestral species. Process by which a new species is formed from an existing one
cladistics-
a taxonomic approach that classifies organisms according to the order in time that branches arose in the evolutionary history of the taxa.
ingroup-
the group of species (or taxa) that is being analyzed using cladistics
outgroup-
a species (or taxa) that is closely related to the ingroup, but not as closely-related as the members of the ingroup are to each other (earlier common ancestor of the cladogram)
primitive characters (plesiomorphy)-
describes a character that is present in the outgroup. [but arose prior to the common ancestor (outgroup)]
derived characters (apomorphy)-
describes a character that is present in the ingroup, but not in the outgroup. [arose after the common ancestor (outgroup)]
genetic
drift- Random changes in the allele frequencies of a population due to chance happenings (events). This generally occurs in small populations (large populations tend to be able to withstand these events without significant effect on their allele frequencies). Unlike natural selection, an individual's fitness generally does not have great influence on whether or not it is removed from the gene pool during genetic drift (it is a non selective event). The small population is not representative of the larger "parent population" (certain alleles may be lost, over-represented, or under-represented). There tends to be less genetic diversity.
founder effect
- a small number of individual's from a large population migrate and colonize a new habitat. Ex. "Mutiny on the Bounty" and Pitcairn Island, Darwin's finches and the Galapagos Islands
bottleneck effect
- occurs when catastrophic events (volcanic eruption, earthquake, fire, flood, over-hunting) decimate a population so that only a small percentage of the population survives and are left to repopulate the community (or the world, in sever instances) Ex. Cheetahs and the ice age, Northern Elephant Seals and over-hunting
divergent evolution
(similar populations or species evolving in different environments)- process in which once-related populations evolve independently (often because of geographic isolation). Two (or more) related species becoming more and more dissimilar. The presence of homologous structures in different species is an indication of divergent evolution. Ex. polar and brown bear, red and knit fox.
convergent evolution
(different population or species evolving in similar environments)- process by which unrelated organisms independently evolve similarities. Evolution of similar traits in distantly related organisms. Leads to production of analogous structures. Ex. wings of birds and butterflies, insect mimicry, streamlined shape of fish and small whales
adaptive radiation
- type of divergent evolution in which ancestral species develop into an array of species, each specialized to fit into a different niche. Process by which a species )or small group of species) rapidly evolves into several different forms. Relatively rapid evolution of many diversely adapted species from a common ancestor.
analogous structures-
structures in two different species that serve the same function, but are not derived from a common ancestor
homologous structures-
- structures that are related because they came from a common ancestor
coevolution-
process in which two species evolve in response to changes in each other. A change in one species acts as a selective force on another species. Ex. Flowers (shape, scent, or color) and their Pollinators (feeding structures of insects, birds, bats), Predators and Prey
gene pool
- the combined genetic material for all the members of a population (all the genes in a population)
allele frequency
- the number of times a specific allele occurs in a population divided by the total number of alleles present (for a gene) in that population. Ex. A population of 500 people each have two alleles for blood type (1000 alleles) Alleles There are 300 IA, 100 I B , and 600 i Allele frequency IA=30%, IB=10%, and i-60%
geneticequilibrium
- a condition in which the allele frequencies of a population remain constant from generation to generation no evolution would be occurring.
niche-
the habitat and role that a population plays in that habitat.