Small fortis ate small seeds forced to feed on the

Small fortis ate small seeds
 Forced to feed on the dreaded tribulus
The dreaded Tribulus (caltrop)
 usually ignored by the finches
 only fortis and magnirostris can break open its hard spines
 extremely sharp spines
Differing Strategies for eating Tribulus
Magnirostris
 crushes the seeds with its beak
 requires 200 newtons of force

 can often eat all the seeds in one mericarp
 gets 2.5x more energy per minute than fortis
 but magnirostris is larger and needs more food
 even then they come out on top (2.5 -1 = 1.5x more energy)
Fortis
 too small to crush the seeds
 braces it against a rock to split it open
 requires only 54 newtons
 cost= fewer seeds obtained per mericarp
 some even steal from magnirostris
Small fortis have a marked disadvantage
 Cannot open tribulus
 Had to eat Chamaesyce
 Herb with small soft seeds
 But exudes a sticky, milky latex
 Similar to milkweed
 Gets stuck to their heads
 Feathers on their heads fall off
 Bald birds die in the hot sun
Decline in population size = Decrease in seed abundance = Increase in seed hardness
Survival is not random; larger birds are more likely to survive than small birds
Role of adaptations (morphology and behavior) may be evident only during times of stress and
competition
Good years:
 Variation fills in
 Less selection on the adaptations
Tough years:
 Adaptations become important
 Increased selection
 Reduction in variation
Genetics of beak morphology
 Bmp4
 candidate gene from chicken
 known to influence beak depth
 finches with deeper beaks have stronger expression of Bmp4
Evidence for Evolution: Part 1
Chapter 17
Evolution is just a theory, not a fact
 Scientific theory is different from our everyday use
 theory is not a guess or a hunch
 well- established, well- supported, well- documented explanations for our observations
 Theory > Law

Theories and Laws
 Law of gravity- if you drop something it will fall to the ground
 Only a description, it does not say why
 Theories to explain why: Newton’s Theory of Gravity and also Einstein’s Theory of Relativity
 Laws described, Theories explain
 Gravity is real, it is true, it can be observed. It can be tested
Evolution
 Things evolve : populations change over time
 Evolution usually happens gradually : populations change over hundreds to thousands of years
 Speciation occurs : one species splits into two or more species
 All species share common ancestry : splitting of lineages from one ancestral form
 Much of evolution change was caused by natural selection : the sole process producing
adaptation, the appearance of design
Predictions based on evolution
 If life originated on Earth in the distant past and then evolved, we should see evidence in the
fossil record
 If evolution occurred within lineages, and those lineages sometimes split then we should see
change in species or morphology through the fossil record
 If creatures share a common ancestry, then we should see transitional forms
 We should see evidence of retrodictions and vestigial characters
