Chapter 5 Evolution and Community Ecology
Feb 22, 2016
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