BIOL 3130 Lecture Notes - Lecture 6: Disruptive Selection, Directional Selection, Habitat Destruction
23 Feb 2018
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Types of selection: directional: selection against phenotype at one extreme, stabilizing: means fitter than extremes, disruptive: extremes fitter than mean. Stabilizing: means fitter than the extremes, ex: babies too small or too large not as likely to survive as average-sized babies. Loss of variability can be bad b/c it will reduce ability to respond to future problems. Disruptive: extremes favored over the mean- force for speciation (parapatric speciation, ex: pop on peninsula vs. pop on mainland, ex: black, white, grey rabbits with black and white rocks to hide- grey die off. Study: golden-winged and blue-winged warblers in southern ontario forest fragments (disruptive & directional selection) Disruptive selection: extremes favored (although they interbreed) Isolating mechanisms (hybrids suboptimal compared to adults: how species separated, gla(cid:272)ial separatio(cid:374) . Followed by habitat separation in post-glacial areas: hybrid: poor competitor against gww in edge areas, and against bww in forest areas. Golden-winged warblers disappear from a given breeding site, within fifty years of blue-winged.
