Observed average beak depth: 9.5 mm
Beak size categories: Size 6 and Size 12
Significance of beak depth: 1 or 2 mm difference can impact survival and reproduction drastically.
Key point: If a trait is not heritable, it cannot undergo natural selection.
Example: Flamingos turning pink due to carotenoid food, showing environmental influence on a trait that's not genetic.
Heritability measures how much of the phenotype variation is attributed to the genotype.
Definition of phenotype: Includes environmental and genetic factors influencing traits.
Heritability formula: H^2 = Vg / Vp
Vg = variance due to genotype
Vp = total variance in phenotype
Decomposition of Vp into Vg and Ve helps understand phenotype variance.
Broad sense heritability includes all genetic variance; narrow is more specific.
Highly heritable traits (closer to 1) can change rapidly in populations while low heritable traits (closer to 0) evolve more slowly.
Importance of heritability in understanding trait transmission across generations.
Uses line of best fit to analyze phenotype data between parent and offspring.
Example: Average beak depth of parents versus their offspring plotted to show correlation.
Closer clustering of data points to the line indicates more genetic influence.
Dots above or below the line reflect environmental impacts on phenotype.
More spread indicates higher environmental influence.
The correlation between phenotype and environmental factors is a critical part of understanding natural selection.
52 years of bird data on Daphne Major Island showed populations fluctuated significantly (from 1400 to 200 during drought).
Bird population survival directly linked to seed availability affected by environmental conditions.
Larger beaks tended to benefit survival at times, while smaller beaks benefitted at other times.
Selection pressures are not static; they change with environmental factors.
Example: Average beak size increased from 9.5 mm to 10.2 mm post-drought.
Natural selection does not aim for perfection but rather adapts traits based on fluctuating environments.
Trade-offs observed: larger beak size may enhance survival but impact other traits negatively (like speed).
Individuals may engage in altruistic behaviors (e.g., alarm calling) to benefit their relatives, enhancing shared gene transmission.
Kin selection emphasizes survival of shared genes over individual risk.
Genetic variation is crucial for adaptability in changing environments.
New adaptations can emerge from persistent selection pressures over generations.
Natural selection acts on individuals, not populations, assessing fitness relative to environmental contexts.
Examples of artificial versus natural selection illustrate the underlying principles of heritability and adaptive change.
Key takeaway: Natural selection does not lead to perfection; it produces a multitude of traits optimized for survival in specific environments.