Chapter 5Evolution

How did life become so diverse on earth?

What does natural selection mean?

Is it possible to observe these processes in action?

Evolution Change in a population over time Usually caused by changes in an environment If there is a critical change in environment…

AdaptMigrateBecome extinct

What’s needed? Genetic variation

Sexual reproductionMutations

Random Breeding

Natural Selection

When the environment changes, those who are best adapted to the new environment are the ones that survive and reproduce, thus passing their genes onto the next generation.

Adaptation- any heritable trait that enable organisms to better survive and reproduce under prevailing environmental conditions

Explains why life has changed over time and why life is so diverse

Natural

SelectIon

Unknown finch ancestor

Insect and nectar eatersFruit and seed eaters

Greater Koa-finch

Kona Grosbeak

Maui Parrotbill

Kuai Akialoa

Amakihi

Crested Honeycreeper

Apapane

Darwin’s finches displayed natural variations, a resultof sexual reproduction.

Because there is variationsome finches were bettersuited, or more fit, for theenvironment.

Finches that were ableto find food lived longenough to reproduce.

Finches that reproducedpassed their traits totheir offspring.

Nature “selects” organisms ina population that are morefit for a particular set ofenvironmental factors.

Early foxpopulation

Spreadsnorthwardandsouthwardandseparates

Adapted to heatthrough lightweightfur and long ears, legs, and nose, whichgive off more heat.

Adapted to cold through heavier fur, short ears,short legs, short nose. White fur matches snow for camouflage.

Gray Fox

Arctic Fox

Different environmentalconditions lead to differentselective pressures and evolutioninto two different species.

Northernpopulation

Southernpopulation

Other Ways Evolution Happens

Artificial Selection- human determine which organisms breed

GMO’s- human genetically alter genes to produce a wanted outcome

D. What is coevolution? Changes in the gene pool of one species can

lead to changes in the gene pool of the otherPredators and prey take turns in having the upper

hand

Evolution shapes ecological niches and determines species distributions

Range of tolerance- all species have an optimal environment in which it performs well. The limit to the abiotic conditions they can tolerate is known as the range of tolerance.

Fundamental niche- the ideal conditions for a species.

This is not what actually happens! Realized niche – the part of the

fundamental niche that the species actually occupies

Competition is usually the factor that keeps an organism from parts of its niche

When niches of species compete intensely for scarce resources, the species will evolve with different adaptations to reduce competition – this is evolutionary divergence

Black skimmerseizes small fishat water surface

Flamingofeeds on minuteorganismsin mud

Scaup and otherdiving ducks feed onmollusks, crustaceans,and aquatic vegetation

Brown pelican dives for fish,which it locates from the air

Avocet sweeps bill throughmud and surface water in search of small crustaceans,insects, and seeds

Louisiana heron wades intowater to seize small fish

Oystercatcher feeds onclams, mussels, and other shellfish into which it pries its narrow beak

Dowitcher probes deeplyinto mud in search ofsnails, marine worms,and small crustaceans

Knot (a sandpiper) picks upworms and small crustaceansleft by receding tide

Herring gull is atireless scavenger

Ruddy turnstone searchesunder shells and pebbles for small invertebrates

Piping plover feedson insects and tinycrustaceans on sandy beaches

Specialized feeding niches of birds in a coastal wetland. Reduces competition and allows sharing of limited resources.

The Five Global Mass Extinctions

Mass extinction- when large numbers of species went extinct over a relatively short period of time.

The Sixth Mass Extinction

Scientists feel that we are in our sixth mass extinction, occurring in the last two decades.

Estimates of extinction rates vary widely, from 2 % to 25% by 2020.

In contrast to previous mass extinctions, scientists agree that this one is caused by humans.