BOIEE 1780 1st Edition Lecture 15Outline of previous lectureI. Darwin’s idea of natural selectionII. Darwin’s finches on DaphneA) 1977 droughtB) El NinoOutline of current lectureI. Finch populationsII. FitnessIII. Back to finchesCurrent lecture*Remember, exam on Thursday… keep an eye out for an email explaining some details about itI. Finch populations*During the El Nino, small seeds became dominant, small-beaked birds also became dominant*Another drought followed… what happens then?-Interestingly, it stays around the same, just a little smaller. This is weird, so why?-It’s because a whole new species of finches came along, and they all ate big seeds, leaving small seeds for the original speciesdrought El Nino droughtthis niche is takenby new competitorav. beak sizeTimeII. Fitness*Fitness depends on the environmental context *Oldfield Mice come in white and brown… they can live on white sand beaches and brown sand beachesMOUSE MOUSE MOUSE MOUSE*Natural selection acts on INDIVIDUALS and can only work for HERITABLE traitsIII. Back to finches*Among medium ground finches, they have a fitness curve (in relation to beak size) with two peaks and a valley in the middle. Why?-Medium ground finches with relatively large beaks can compete with large ground finches for large seeds, and medium ground finches can compete with small ground finches for small seeds. Medium-sized beak birds can’t compete for either resource.*Also, big-beaked birds tend to mate with other big-beaked birds and small-beaked birds tend to mate with other small-beaked birds. Why?-Young female birds choose mates that sing like their dads (therefore have similar beak size)IV. Artificial selection*This is human caused evolution, can cause extraordinary phenotypic variation (like dogs)*Is this a special kind of natural selection or is it fundamentally different-There are valid arguments on both sides-However, this process is supported by all natural selection postulatesV. Examples of natural selection*Scarlet King snakes look very much like venomous Coral snakes in areas where they both live*70% of adults are lactose intolerant. The allele for tolerance is very common in populations where humans have had cattle for hundreds of years*Types of selection:
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