Divergent Evolution: shared ancestry, different behavior.
Describe a strength and a weakness of the observational approach?
Strength: it costs less money
Weakness: you don't have a control
Natural Selection: the differential survival and reproduction of individuals due to differences in heritable phenotypes.
Conditions for Natural Selection:
Variation
Differential Reproductive Success
Heritability
Variation: members of a population differ in characteristics.
Differential reproductive success depends on that variation, some individuals with particular characteristics have more offspring than others.
Heritability: parents can pass on characteristics to their offspring.
How do we Know Variation is Heritable?
1.Parents Offspring Regression
2. Selection Experiments
Parent Offspring Regression: examines the similarity between parents and their offspring. If a trait is heritable, the trait values of offspring should be similar to the trait values of the parents.
Selection Experiments: individuals are subjected to differential selection of a trait. If this results in a change in average trait value in later generations, the trait is heritable.
Variability is due to differences in genetic composition and environmental conditions.
Variability shows up when traits:
do not affect fitness
are subjected to certain types of selection
are influenced by learning
Adaptation: traits that result from natural selection and confer higher fitness than alternative traits.
How do we measure Fitness?
Direct: the number of progeny that go on to reproduce
Indirect: survivorship, number of maters, body size and growth, etc.
Eastern screech-owls show great variation in dispersal direction with no coincident differences in reproductive success, indicating fitness is not associated with dispersal's compass direction.
Honeybee foraging performance increases due to trial and error learning.
Directional Natural Selection:
Individuals in a population with an extreme trait value at one end of the spectrum posses the highest fitness.
Ex: Galapagos medium ground finches with the median beak size have the best chance of survival
Disruptive Natural Selection:
Individuals with extreme trait values have the best chance of survival.
In Spadefoot tadpoles, the detritus and carnivore morphs have the highest chance of survival bc they can feed efficiently.
Stabilizing Natural Selection:
Individuals in a population with intermediate trait values have the highest fitness.
Cooperative Behavior: many social animals help others to survive and reproduce.
only works when everyone gets involved
Group Selection: selection operates at the level of the group. Groups that contain too many individuals maximizing individual gain will have lower fitness, than groups that work together.