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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 Magnirostriscrushes 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