Transcript Slide 1
Evolution Part III “Speciation through Isolation, Patterns in Evolution, Fossil record, Geologic Time, and Cladistics” Speciation through Isolation Main Idea: New species can arise when populations are isolated – Isolation – if gene flow between species stops for any reason, the populations are “isolated” – Speciation – is the rise of two or more species from one existing species – Four types of Isolation: Reproductive isolation Behavioral isolation Geographic isolation Temporal isolation Reproductive Isolation Reproductive isolation occurs when members of different populations are no longer able to mate successfully with each other Two cases: – Not physically able to mate – They cannot produce offspring able to survive Reproductive isolation between populations is the final step in speciation Behavioral Isolation A large part of the mating process involves rituals, chemical signals, songs, and courtship dances Behavioral isolation occurs when members of a population are not “accepted” because of their behavior or improper courtship rituals – Example – the flashing patterns in male and female fireflies – Example – the courtship song and dance of the lyre bird in South Australia Geographic Isolation In geographic isolation there are physical barriers that divide a population into two or more groups – Rivers, mountains, dried lake beds, or man-made barriers – When populations are separated long enough, they may evolve different adaptations and undergo speciation Temporal Isolation A temporal barrier is one that prevents reproduction because of “timing” – Bird migrations are often governed by changing of the seasons and food availability for their young Patterns in Evolution As new species arise they are under pressure to survive. Adaptive traits are kept in a population through natural selection but, sudden changes in an environment can eliminate one or more species In science, the terms chance and random refer to how easily an outcome can be predicted – Mutation and genetic drift cannot be predicted so they are considered random events Patterns in Evolution Natural selection, which acts on diversity, is not random. Individuals with traits that adapt them to their environment better have a better chance of surviving and passing on those adaptations to future generations. It is important to remember that it is the environment that controls the direction of natural selection Convergent Evolution Different species around the world adapt to similar environments When evolution towards similar traits in unrelated organisms develops it is called convergent evolution – The habitat will favor those best adapted for survival (natural selection) Divergent Evolution When closely related species evolve in different directions, they become increasingly different through divergent evolution As time passed in different habitats, several species of primates evolved from a common ancestor Species Evolution Main Idea: Species can shape each other over time – As species interact they form relationships – Close species interaction is called symbiosis – As species compete, cooperate, and interact in various ways their evolutionary paths may become connected Two types of these interactions: – Coevolution – the process by which two or more species evolve in response to changes in the other – “Evolutionary arms race” – a type of coevolution where species respond to other species they are competing with Often times this occurs in predator-prey relationships where the prey evolves to escape the evolving predator as the predator evolves to better catch its prey Species Coevolution One such relationship in nature is between ants and aphids – Ants prefer nectar and “herd” the aphids like sheep to the most succulent parts of a plant for the aphids to eat – The aphids produce a nectar from their abdomen which the ants love! – In return for the nectar, the ants protect the aphids from their most feared predator – the ladybug! Species Extinction Extinction – the elimination of a species from the Earth – Background extinctions - extinctions that occur continuously at a very low rate caused by many reasons – Mass extinctions – sudden, rare events that cause hundreds, thousands, and sometimes millions of species to become extinct Adaptive Radiation As one species diversifies into many descendent species it is called adaptive radiation – This type of speciation usually follows a mass extinction and creates a Huge diversity of species in a relatively short period of time The diagram shows a Species A that moves to an island displaying the founder effect and Species A undergoes adaptive radiation inhabiting a range of islands and habitats. Geologic Time Scientific evidence shows us that the Earth is about 4.5 billion years old! There are many tools scientists use to discover this Index fossils are fossils of organisms that existed only during a specific time period – The trilobite to the right is one of the most abundant fossils during the Paleozoic Era Geologic Time There are a couple methods for determining the age of fossils – Relative dating gives you an estimate of the time period of an organism based upon the rock layer in which it is found This method is not very accurate for exact measurements – Radiometric dating uses isotopes of organic elements to determine a fairly exact age of a substance relative to the decay of the organic elements found in a sample (usually Carbon-14) This is accurate to a few hundred years or less Radiometric Dating Species Classification based upon Evolutionary Relationships As we look at animals it is apparent that similar animals have a lot in common – Example: modern dogs and wolves share a common ancestor The phylogeny of a species is the evolutionary history of that species The most common way to make an evolutionary tree is through cladistics which is a classification based on common ancestry Cladistics A cladogram is an evolutionary tree that proposes how species may be related through a common ancestor Clade Node Branch that represents the most recent common ancestor Group of organisms that share traits derived from a common ancestor Derived Character Trait that organisms share AFTER the hash mark showing a new trait