Chapter 5Evolution and Community Ecology

Section 1 - Evolution

Think About It

• Just a handful of backyard soil may contain an entire miniature world of life.• Insects• Mites• Millipede• Worms• Plant Seeds• Fungi• Bacteria

• Antarctic ice contains living microbes!

• How did life come to be everywhere?

Evolution and Natural Selection

Evolution: change over timeBiological Evolution: a change in a

population’s gene pool over timeGene Pool: all of the genes present in a

populationGene: a sequence of DNA that codes for a

particular traitFor Example: Mouse Population

Today: 40% Brown – 60% TanNext Generation: 28% Brown – 72% Tan

Mechanisms of Biological Evolution

Conditions of Natural Selection

Artificial SelectionArtificial Selection: a human-controlled

process to produce individuals with certain traits

Dogs – “like” breeds with “like” = pureblood, “like” breeds with “non-like” = mutt

Agriculture – to make larger, more successful reproducing, diverse plants

Speciation and ExtinctionScientists estimate that all of the species on

Earth today represent only a fraction of those that have ever lived.

Speciation: the process by which new species are generated

Allopatric Speciation: speciation due to geographic separation

Allopatric Speciation

• Glacial Ice Sheets Move – then Recede

• Major Rivers Change Course – then Return

• Dry Climate Subdivides Lakes – then Refills

• Black Kaibab Squirrel and Gray Abert’s Squirrel

ExtinctionExtinction: the disappearance of a species from

EarthScientists Estimate:

99% of all species that ever lived are now goneAverage time a species spends on Earth is 1

million to 10 million yearsa# of Species on Earth =

(# added by Speciation) – (# removed by Extinction)

ExtinctionBackground Extinction Rate: the rate at which a

gradual, one-species-at-a-time, extinction occursMost ExtinctionEnvironmental Conditions change RapidlyNatural Selection is too slow to adapt

Mass Extinctions: five events that killed off huge numbers of species at onceBest Known = 65 million years ago, wiped out the

dinosaurs