Chapter 4.3: How Species Form Pages 136 - 142
What is a species? • Biological species consists of populations that can interbreed and produce a group of viable offspring, which can also reproduce in nature. • They are reproductively isolated from other species. • Populations that breed at different times are reproductively isolated. • Biological species that are geographically isolated cannot interbreed.
What is a species? • - Lions and tigers are a different species. • - Lions are savannah cats • Tigers are jungle cats • These species are separated by biological barriers (different behaviors, habitats) and geographic barriers.
Female Lion + Male Tiger = Liger It's pretty much my favorite animal. It's like a lion and a tiger mixed... bred for its skills in magic. - Napoleon Dynamite (2004)
Forming a new species • Speciation: the formation of a new species • Two pathways can lead to the formation of a new species. • Transformation • Divergence
Forming a new species • Transformation – a new species gradually develops as a result of mutation and adaptation to changing environmental conditions, and the old species is gradually replaced. • Evolution of mammoths – the ancestral mammoth slowly evolved into the steppe mammoth than slowly evolved into the woolly mammoth that lived up to 10 000 yrs ago.
Forming a new species • Divergence – one or more species arise from a parent species that continues to exist. • The small hoofed Hyracothermium is thought to be the ancestor of modern horses, tapirs, and rhinoceroses.
Keeping populations separate • For speciation to occur, two populations must be prevented from interbreeding. • If the populations remain isolated long enough, speciation will eventually occur because of changes accumulated in the population due to natural selection, which affects reproduction. • Types of separation • Geographical Barriers • Biological Barriers
Geographical Barriers • Geographical barriers prevent interbreeding and result in speciation because they keep population physically separated. • a peninsula becoming an island • Canyons can separate populations • Powerful storms can transport animals (birds) to islands • The geographic isolation does not have to occur indefinitely, just long enough for speciation to occur. West Coast Salamanders – Ring Species
The Kaibab squirrel (Sciurusabertikaibabensis, left) became geographically isolated from the common ancestor with its closest relative, the Abert squirrel (Sciurusabertiaberti, right) in the North Rim of the Grand Canyon about 10,000 years ago. Since then, several distinguishing features, such as the black belly and forelimbs have gradually evolved
Biological Barriers • Behaviour is a biological barrier that will keep individuals separate. • Courtship songs of birds; some bird calls are similar (if they shared a recent common ancestor) but are different enough to provide a biological barrier to reproduction. • Temporal barriers – species breed during different seasons. • Similar organism use different habitats; two species of garter snake – one lives near water, the other lives in open areas.
reproductive isolation • When populations become reproductively isolated – even when they have not become geographically isolated – speciation can occur. • Example: cichlids (fish) in Africa’s Lake Victoria
Adaptive radiation • Adaptive radiation : the diversification of a common ancestral species into a variety of species all of which are differently adapted. • Finches in the Galapagos • The fruit fly Drosophila • Marsupials in Australia • Marsupials of Madagascar
The pace of evolution • Gradualism • That evolution/speciation proceeds by imperceptibly small, cumulative steps over long periods of time rather than by abrupt, major changes. • Punctuated Equilibrium • That evolution amongst sexually reproducing species takes place in rapid bursts, separated by long periods in which little change occurs.
The Theory of Evolution by Natural Selection: • Life forms have developed from ancestral forms. • All living things are related to one another by varying degrees through common ancestry. • All living things on Earth have a common origin (share a common ancestor) • The mechanism by which populations change is natural selection
The process of natural section: • Random heritable genetic mutations (variations) exist within populations • Some mutations result in a survival advantage • Organisms with an advantage are more likely to pass on the trait to offspring • The frequency (occurrence) of the mutation increases in the population; the population as a whole starts to change.
Chapter 3-4 Review Questions • Page 110 - #1,6,9, 11, 14 • Page 144 - #1, 2, 4, 7-10 • Answer to the questions are posted on the wikispace.