6 Ex: Northern Elephant Seals Bottleneck EffectEx: Northern Elephant SealsLarge population overhunting 20 TotalPopulation eventually recovered in sizeLoss of genetic variationCould hurt long-term survival of species
8 Mechanisms of Evolution Remember mutations?A random change in a sequence of DNA.A small population with a lot of mutations has the greatest potential for evolution
9 Mechanisms of Evolution Natural SelectionHow does it alter phenotypes?
10 Mechanisms of Evolution Stabilizing selection: selection against extreme expressions of a trait, selection for the averageEx: birth weight in human babies
11 Mechanisms of Evolution Directional selection: selection toward one extreme of a traitEx: Galapagos finches - large beaks during droughtPeppered moths - color
12 Mechanisms of Evolution Disruptive selection: selection against the average, selection for both extremesEx: Cichlid fish size - males
13 Mechanisms of Evolution Sexual selection: selection of a trait in males to attract a mate and intimidate other malesEx: peacocks
14 Isolation Reproductive Isolation Some members of a population change so much that they can no longer produce offspring with members of the original population.
15 Different mating patterns Eastern meadowlarkandWestern meadowlarkDifferent mating patternsLigerSterile
16 Isolation Geographic Isolation A separation of population by a barrier Ex: mountains, rivers, the Grand Canyon
17 SpeciationFor speciation to happen, a population has to move away and then be reproductively isolated.
18 Speciation Allopatric Speciation A physical barrier divides one population into 2 or more populationsAbert squirrelSouth RimKaibab SquirrelNorth Rim
19 Speciation Sympatric Speciation A species evolves into a new species without a physical barrierThe old species and new species live side by side during speciation
20 Patterns of Evolution Adaptive Radiation (Divergent Evolution) The evolution of a new species in a relatively short period of timeone species evolves into several different forms that live in different habitatshomologous structures
24 Patterns of Evolution Convergent Evolution Unrelated species evolve similar traits even though they live in environments that are really far apartsimilar ecology and climateanalogous structures
25 3. Convergent EvolutionUnrelated species evolve similar adaptations, due to environmental pressures (natural selection)These adaptations may look similar from the outside, but actually evolve independently from each otherEx: sharks, dolphins, seals, penguins
26 Analogous structuresSimilar in appearance and function, but are developed from anatomically different partsEvidence for convergent evolutionEx: octopus eye versus vertebrate eye (both complex eyes