EVOLUTION MECHANISMS

NATURAL SELECTION Environment favors the individuals that have the better adapted traits Those that lack traits that help them survive will decrease in number EX: peppered moths

DIVERGENT EVOLUTION Several species evolve from a single ancestral species Individuals migrate long distances over time and adapt to different environments EX: horses; donkeys; zebra EX: black bear; grizzley bear; polar bear

ADAPTIVE EVOLUTION Several species evolve from a single ancestral species but within close proximity to each other Become adapted to specific environmental conditions within similar habitats EX: finches of Galapagos islands

CONVERGENT EVOLUTION Unrelated species adapt similar features because they have adapted to similar environments EX: sharks; fish; dolphins Different ancestors ANALGOUS STRUCTURES: fins for swimming in aquatic environment

COEVOLUTION

STABILIZING SELECTION Individuals with average traits are favored over individuals with extreme traits EX: clutch size in birds…birds that lay an “intermediate” amount of eggs have the highest survival rate…if mother bird lays too many eggs…some will starve…too few and lower number that will survive to reproduce themselves

DIRECTIONAL SELECTION One extreme trait is favored EX: wood peckers with longer beaks can reach deeper into tree bark & most likely to get enough food EX: faster cheetah most likely to catch its prey

DISRUPTIVE SELECTION Individuals at both extremes favored over the intermediate trait EX: smallest spider & largest spider population increase over medium spiders…largest spiders too big for many birds to eat…smallest spiders harder to find/not worth the effort…but medium spiders just right!

Identify the type of selection… 1. DIRECTIONAL SELECTION 2. STABILIZING SELECTION 3. DISRUPTIVE SELECTION