Species concepts, reproductive isolation, speciation modes, macroevolutionary tempo.
Speciation And Macroevolution
Species concept
Operational definition of species. Biological species concept (Mayr): reproductively isolated populations. Phylogenetic: smallest…
Reproductive isolation
Barriers preventing interbreeding. Prezygotic: temporal, behavioural, mechanical, gametic isolation. Postzygotic: hybrid…
Allopatric speciation
Divergence in geographically separated populations accumulating genetic incompatibilities. Dominant mode in animals (Mayr). Classical:…
Sympatric speciation
Divergence within a single geographic area via ecological differentiation, sexual selection, or polyploidy. Documented in cichlid fish,…
Adaptive radiation
Rapid diversification of a lineage into multiple ecological niches. Canonical: Darwin's finches, Hawaiian honeycreepers, African rift-lake…
Mass extinction
Short interval of elevated extinction rate across many taxa. Big Five: Ordovician-Silurian, Late Devonian, Permian-Triassic (~96% marine…
Cambrian explosion
~540 Mya rapid diversification of most animal phyla. Causes debated: O2 rise, Hox-gene innovation, predation. Burgess Shale + Chengjiang…
Cope's rule & Dollo's law
Cope: lineages tend toward larger body size over time. Dollo: complex lost traits rarely re-evolve (irreversibility). Both are tendencies…
Background vs mass extinction
Raup & Sepkoski 1982: baseline extinction rate punctuated by ~5 mass-extinction peaks (end-Permian wiped ~95% of marine species).…
Hybrid zone
Geographic region where two diverged populations meet + interbreed. Tension zones maintained by selection against hybrids; can lead to…