Selection Pressure Adaptive Radiation Selection Pressure What pushes

Selection Pressure & Adaptive Radiation

Selection Pressure What pushes giraffes to have really long necks? Why do peacocks have long elaborate tails? Why do moths blend in with tree trunks and branches? External agents which affect an organism’s ability to survive in a given environment Can be negative (decreases the occurrence of a trait) or positive (increases the proportion of a trait)

Selection Pressure Predators Individuals with adaptations to escape a predator will have a higher chance of producing more offspring Example: speed, defense, camouflage, mimicry Prey/Food Individuals with adaptations to obtain more food will have a higher chance of producing more offspring Example: speed, senses for finding prey/food, weaponry for killing food, camouflage for stealth

Selection Pressure Climate Individuals with adaptations to survive new climates will have a higher chance of producing more offspring Example: Mates more blubber in cold temperatures or Sexual Selection Individuals with adaptations to attract mates will have a higher chance of producing more offspring Example: strong, attractive, good provider, songs, antlers Others: Disease, availability of shelter & more

Selection Pressure

Selection Pressure Directional Selection Natural selection favours one extreme of a population for that trait Often happens when environment changes in a consistent way Example: Neck of giraffe, camouflage, mimicry

Selection Pressure Disruptive Selection Natural selection favours both extremes Causes species to diverge; two new species made Occurs when there are two different types of resources found in an area Example: Darwins finches

Selection Pressure Stabilizing Selection Natural selection favours the average of the population Extremes are not well suited for organism Example: bird clutch size, deer antlers

Niche An organism's role in an ecosystem Includes: a The environment that a given organism lives in The organism's "job" in that environment What the organism eats How it interacts with other living (biotic) elements How it interacts with the nonliving (abiotic) aspects of the environment

Adaptive Radiation Describes the evolutionary diversification of a single ancestral line It occurs when members of a single species occupy a variety of niches with different environmental conditions Members evolve different phenotypic features (adaptations) in response to the different selection pressures An example of adaptive radiation can be seen in the variety of beak types seen in the finches of the Galapagos Islands These finches have specialised beak shapes depending on food resource