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
