BIOL 3445 Lecture Notes - Lecture 13: Medium Ground Finch, Daphne Major, Selective Breeding
BIOL 3445.001 | Lecture #13 | 2/27/2018
Natural Selection
ANNOUNCMENTS
➢ Exam #1
o Pick yours up in her office if you haven’t already
o Feel free to stop by with any questions
➢ Exam #2
o Coming up soon (03/15)
o Study guide and practice questions will go up on Canvas next Thursday
o Not technically cumulative but the information does still build on itself
OBJECTIVES
― Understand how studying selection the wild is complicated
― Explain how selection can vary over time and space
― Explain how selection on a trait can result from different forces acting together
― Understand how we can look for the signs of selection that has happened
EVOLUTION IN A BIRD’S BEAK
― The only difference between natural and artificial selection is who’s doing the
selecting
o It’s harder to calculate some things in the wild because there are more
variables, but it is possible
― Peter and Rosemary grant study the ground finch (Geospiza fortis) on the island
Daphne Major for 30+ years
o Every other scientist said “studying and measuring natural selection in the
wild is too complex” but they said “we just need the right place”
o Studied finches on Daphne Major a literal hell-hole/small island with little
to no human impact so they can capture and mark every bird
o Small and relatively new so it’s perfect for studying a single species
o Absolutely love their job and they get paid a lot of money to do it
▪ Not that the island’s finch inhabitants care too much for money
▪ At least they’ll have an island to retire to
o Know the island inside and out
▪ Can recognize all of the birds and their offspring
― What to Study:
o Population Numbers:
▪ Who survives and who dies?
▪ How many offspring does each bird have?
o Ecological Data:
▪ What is the weather like?
▪ What kinds of foods are available?
o Beak Depth:
▪ Major trait that influences a bird’s survival
find more resources at oneclass.com
find more resources at oneclass.com
BIOL 3445.001 | Lecture #13 | 2/27/2018
― Caltrops (“stickers”, “cackle burs”, etc.) drive a lot of selection
o Seed-cracking capabilities is a very important trait here
▪ These seeds are tiny, so birds have to eat a lot of them to survive
▪ Even if it only takes a few seconds to crack, those seconds add up
o Birds with beak depths of 11mm or greater can crack caltrops (cackle
burs) in 10 seconds
o Birds with beak depths of 10.5mm need 15 seconds
o Birds with beak depths of 8mm or less cannot crack them
o Beak shape/depth is a heritable trait (h2 = 0.90)
― A drought in 1977 resulted in a shift in the foods available
o Only hard caltrops were left because the small, soft seeds had been
eaten or their plants died out
o Completely changed the island and the species who live there
o The finches are small birds that mainly live on the ground and only fly short
distances
▪ They are not strong enough or smart enough to leave the island
o Selection on beak depth has occurred because there are no longer
seeds for small-beaked birds to enjoy. Therefore, they die off and leave
only larger-beaked birds behind, bringing up the average beak depth
▪ S = (after) – (before)
▪ S = 10.2 – 9.5 = 0.7
▪ Natural selection prefers larger beaks
▪ R = (offspring) – (parent)
▪ R = 9.8 – 9.5 = 0.3
▪ Almost never larger than S
― Group Exercise
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Exam #1: pick yours up in her office if you haven"t already, feel free to stop by with any questions. Exam #2: coming up soon (03/15, study guide and practice questions will go up on canvas next thursday, not technically cumulative but the information does still build on itself. Understand how studying selection the wild is complicated. Explain how selection can vary over time and space. Explain how selection on a trait can result from different forces acting together. Understand how we can look for the signs of selection that has happened. The only difference between natural and artificial selection is who"s doing the selecting. It"s harder to calculate some things in the wild because there are more variables, but it is possible. Peter and rosemary grant study the ground finch (geospiza fortis) on the island. Caltrops ( stickers , cackle burs , etc. ) drive a lot of selection: seed-cracking capabilities is a very important trait here.
