Patterns and processes of Evolution Section 19.2

Why do some organisms live but others die? Some changes occur within a species Others can be over much larger scales When changes occur in clades greater than a single species they are referred to as Macroevolutionary patterns Creation of species through speciation Disappearance through extinction Emergence of large clades – dinosaurs, mammals – examples of macro evolutionary patterns

Classification of fossils Fossils can be classified into clades Either clades only containing extinct organisms Or clades also containing living organisms Cladograms illustrate how closely related organisms are Relation does not mean direct ancestor

Why do species go extinct? They fail to adapt to a changing environment Some clades appear more susceptible to extinction than others - why? The rate of speciation within a clade must equal to or greater than the rate of extinction for a clade to continue to survive over the long term Reptillia is an example of a highly successful clade Living organisms continue to adapt and thrive Most species in clade dinosauria are extinct, but birds survived because they adapted to the new environment

What drives extinction of a species? Two types of extinction Extinction due to Natural selection – always occurring (background extinction) Extinction due to a mass Extinction A mass extinction is when a many species become extinct over a short period of time. Entire ecosystems vanish, food webs collapse… Earth has experiences many of these throughout it’s history

What causes mass extinctions?

Is there a good side to a mass extinction? Yes, there can be. It creates many new opportunities for survivors to adapt and speciate Recovery takes about 5 – 10 million years

Does evolution always occur at the same rate? No! Some organisms change consistently through time – gradualism Some organisms do not really change over time, until something happens to upset their equilibrium – ‘punctuated equilibrium’. It has been proposed that most new species are produced during this period of rapid change

Why does evolution occur at different rates? Rapid evolution may occur if a small population gets separated from the main populations Small population will evolve faster as there are fewer individuals to spread change to Migration to a new environment Eg. Galapagos Islands Mass extinctions create many new ecological niches Organisms that survive will fluorish

Macroevolution There are two main types of macroevolution Adaptive Radiation One ancestral species (or small group) evolves to produce a number of different species that live in different ways Can be caused by migration, extinctions Species can also evolve a new feature allowing them to take advantage of the environment Example – dinosaurs and mammals Mammals were around during dinosaurs but were not successful After dinosaur extinction, an adaptive radiation of mammals began. Convergent Evolution Unrelated organisms in different places but similar environments evolve similar features Emus, Rheas and Ostriches

What is Coevolution? The process by which two species evolve in response to changes in each other over time Often they become so intertwined that neither can live without the other If one has an evolutionary change so will the other Examples Specific flowers and pollinators Plants and herbivores Plants produce poisons to stop themselves being eaten But insects resistant to the poisons will flourish Often these insects use the poisons to their advantage

Key Points Macro-evolutionary patterns are changes that affect many species of entire clades Examples – speciation and extinction Earth has experienced a number of mass extinctions Evolution can occur at different rates Gradualism vs punctuated equilibrium Paleontologists have identified patterns of macroevolution Adaptive radiation and convergent evolution