Natural Selection How species “adapt” to their environment

Populations evolve over time, not ________ The fate of individuals ______ evolution Unfit individuals _________ Fit individuals live and _________ Natural selection promotes survival of __ individuals They are better suited for the circumstances

Natural selection changes “allele __________” The relative abundance of alleles in a _________ ____-evolution: changes in allele frequency in a population’s gene ____ % of population Here, the recessive allele has become rare Selection increases ________ (“good”) alleles Decreases maladaptive (“_____”) alleles New alleles arise through _________ Alteration of the ________ sequence of genes Causes: radiation, chemicals, replication mistakes Natural selection ______ if new alleles are adaptive

Natural selection can be observed in action Antibiotic resistance in ________ Pesticide resistance in ________ Color change in _________ moths of Britain Before Industrial Revolution: (late 1700s) Trees covered with white _____ Symbiotic fungus & algae White moths were camouflaged Eluded predators Rare black form got _______

After industrial pollution Coal soot killed ________ Tree bark turned black White form of moth _________ Got predated, became rare Black form was better _______ Became the dominant form Today Pollution control saved lichen White form is _____ abundant

Artificial selection speeds the process Animal & plant breeders ______ for certain traits Choose which individuals will _____ gray wolf red junglefowl

Three trends in natural selection:  Time  Neck length Three trends in natural selection: 1. Directional selection Results in change toward one _______ E.g., long necks in giraffes Occurs when environmental change is ___________ Could also lead to increasingly short necks

2. Stabilizing selection  Time  Body size 2. Stabilizing selection Favors an ________ phenotype E.g., body size in lizards Smaller individuals can’t defend territory Larger ones get seen by predators Occurs in _______ environments

Favors ____________over the average Rare 3. Disruptive selection Favors ____________over the average Rare Occurs where 2 types of one _______ are available E.g., small and large seeds  Time  Beak size Result: ____ bird species can have both large- and small-beaked individuals African finch

Several “forces” drive natural selection 1. Competition for limited resources a. _______ species Individuals with adaptive alleles will win b. _______ species E.g., European Starlings vs. Western Bluebirds Both nest in tree cavities – a limited resource Starlings are: - introduced to the U.S. - larger than native bluebirds - win the nest hole competition Bluebirds must _____ or __________

2. Predation When one organism eats another E.g., wolves eat deer Causes biological “___________” Each side keeps evolving better __________ E.g., deer become _____ and more ____ over time Because wolves ate the slower, dumber, deer Wolves become faster over time to catch faster deer An example of _____________ Two species _________ together

3. Symbiosis When different species live in _______________ Also coevolution: if one changes, the other _____ a. Parasitism One species feeds _______ another Lamprey on salmon

One species benefits, the other is __________ b. Commensalism One species benefits, the other is __________ Some animals commensal with humans: house sparrow house fly European cockroach

Both species _________ E.g. ants and swollen-thorn acacias c. Mutualism “cleaner fish” on a shark Both species _________ E.g. ants and swollen-thorn acacias Acacias provide hollow thorns Where ants grow “scale insects” Ants clear away other _______ Acacia has less ________ for water ant swollen thorn

Mates are chosen on ____________ of fitness 4. Sexual selection Mates are chosen on ____________ of fitness argus pheasants Female birds mate with males that: a. Hold good _____________ Ensures a food supply for ________ b. Have “fancy” feathers Make males ________ Only ____ individuals can risk them Each generation, males get more colorful E.g., hummingbirds, peacock Females remain ______________ Best for ________ on nest.