Natural Selection and Speciation Terms

# of offspring produced by an individual that survive to reproduce

# of offspring surviving to reproduce in comparison to other individuals in the population

a trait that confers increased relative fitness on organisms that possess that trait

occurs when natural selection favors phenotypes at one end of the distribution

occurs when natural selection favors phenotypes in the center of the distribution

occurs shen natural selection favors phenotypes at both extremes of the distribution; the mean phenotype has the lowest fitness

one sex, for Ex. females, can act as an agent of selection for the morphology of the other sex (not discussed in lecture)

species arise from subdivion of a lineage

a group of organisms that are related by descent from a common ancestor

a species is a group of naturally or potentially interbreeding population that are reproductively isolated from other such groups

an irreducible (basal) cluster of organisms, diagnosably distinct from other clusters, and within which there is a parental pattern of ancestry and descent. (Notice that this def. emphasizes the criterion of common descent. An advantage of this def. over the biological species concept is that it includes both asexually and sexually reproducing animals).

a unit of a species containing those organisms that are actually interbreeding

NO CHANGE in a lineage over time

a lineage changes over time (e.g. due to natural selection of genetic drift), but these changes do not lead to a splitting of the lineage

a lineage ends; has no living descendents