Units 7-8 cover evolution (the unifying theory of biology) and ecology — from the mechanisms of evolution and speciation to population dynamics and ecosystem interactions.
Evidence: fossils, biogeography, comparative anatomy (homologous/analogous structures), molecular biology (DNA/protein sequence similarities), embryology. Natural selection: variation → differential survival/reproduction → allele frequency change. Other mechanisms: genetic drift (bottleneck, founder effect), gene flow, mutation. Hardy-Weinberg: p² + 2pq + q² = 1 (genotypes), p + q = 1 (allele frequencies). Conditions for equilibrium: large population, no selection, no migration, no mutation, random mating.
Speciation: allopatric (geographic barrier), sympatric (same location, e.g., polyploidy in plants). Reproductive isolation: prezygotic (habitat, temporal, behavioural, mechanical, gametic) and postzygotic (reduced hybrid viability/fertility). Phylogenetic trees: show evolutionary relationships. Cladograms based on shared derived characters (synapomorphies). Molecular clocks: mutation rate estimates divergence time.
Population ecology: exponential growth (dN/dt = rN) vs logistic (dN/dt = rN(K-N)/K). Carrying capacity K. r-selected (many offspring, little care) vs K-selected (few offspring, much care). Community: interspecific competition, predation, symbiosis (mutualism, commensalism, parasitism). Energy flow: 10% rule between trophic levels. Biogeochemical cycles: carbon, nitrogen, water. Primary productivity: gross (total photosynthesis) vs net (gross - respiration).
Hardy-Weinberg equilibrium (no evolution) requires: (1) Large population — prevents genetic drift. (2) No natural selection — all genotypes equally fit. (3) No migration — no gene flow in or out. (4) No mutation — no new alleles. (5) Random mating — no sexual selection. In reality, no natural population meets ALL conditions, so allele frequencies always change over time (evolution). The model is useful as a null hypothesis: if observed frequencies differ from H-W predictions, at least one condition is violated, indicating evolutionary forces are acting.
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