Chapter 5 Evolution

 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… Adapt Migrate Become extinct What’s needed?  Genetic variation Sexual reproduction Mutations  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

NaturalSelectIonNaturalSelectIon

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 result of sexual reproduction. Because there is variation some finches were better suited, or more fit, for the environment. Finches that were able to find food lived long enough to reproduce. Finches that reproduced passed their traits to their offspring. Nature “selects” organisms in a population that are more fit for a particular set of environmental factors.

Early fox population Spreads northward and southward and separates Adapted to heat through lightweight fur and long ears, legs, and nose, which give 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 environmental conditions lead to different selective pressures and evolution into two different species. Northern population Southern population

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 other Predators 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 skimmer seizes small fish at water surface Flamingo feeds on minute organisms in mud Scaup and other diving ducks feed on mollusks, crustaceans, and aquatic vegetation Brown pelican dives for fish, which it locates from the air Avocet sweeps bill through mud and surface water in search of small crustaceans, insects, and seeds Louisiana heron wades into water to seize small fish Oystercatcher feeds on clams, mussels, and other shellfish into which it pries its narrow beak Dowitcher probes deeply into mud in search of snails, marine worms, and small crustaceans Knot (a sandpiper) picks up worms and small crustaceans left by receding tide Herring gull is a tireless scavenger Ruddy turnstone searches under shells and pebbles for small invertebrates Piping plover feeds on insects and tiny crustaceans 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  In contrast to previous mass extinctions, scientists agree that this one is caused by humans.