Adaptive Radiation (Cambrian Explosion)
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7 terms
Terms | Definitions |
|---|---|
 adaptive radiation | genetic and ecological diversification of a single, ancestral species into multiple derived and at least partially coexisting species, involving new ecological and/or geological zones - accounts for the cladogenetic (brancing) pattern of evolution, as opposed to the anagenetic (non-branching change) w/in a lineage |
| three fundamental components of all adaptive radiations | 1. ecological opportunities (niches) 2. genetic isolation, differentiation of populations --> multiple speciation events 3. ecological differentiation --> coexistence of new speceis (necessary? still debated) |
| three ecological situations favorable to adaptive radiation | 1. new general adaptation opens new adaptive zone (e.g., angiosperm plant radiation starting in cretaceous, facilitated by seeds, plant chemistry protection from herbivore. bird adaptive radiation once flight evolved) 2. new environment opens up adaptive zone after disturbance - e.g., radiation of birds & mammals after dinosaur extinction 3. species colonizes new environment with few competitors |
| whats so dramatic about cambrian explosion? | - diverse species in short time - origin of essentially all modern groups of animals - 1st hard-shelled invertebrates |
| complications of cambrian explosion idea | - molecular data suggests many groups arose in proterozioc eon (if so then took way longer than previously thought) - |
| predation theory on cambrian explosion | posits that the first predators on invertebrates arose during cambrian, creating selection for diverse anti-predator adaptations, and predator-prey arms race - some predators in cambrian explosion were large, voracious, formidable - e.g. multiple species of Anomalocaris up to 2m in length, "terror of the trilobites" - biting mechanism using models of anomalocaris to simulate jaw mechanism matched by "bites" out of fossil trilobites = experimental validation |
| evidecne for predation hypothesis | - many prey species well armored against biting predator - dorsal eyes to detect predators (opabinia) - diverse ways to hide from predators - e.g., diverse burrowing priapulids and other worms that could retract into holes - diverse means of locomotion (evasion?) |
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