Transcript File
Chapter 5 Evolution of Biodiversity • Dung of the Devil 1918-1920: Flu epidemic (Spanish flu). • • • Caused by H1N1 (closely related to the 2009-2010 virus: swine flu) Extracts from the “dung of the devil” used 80 years previous for the Spanish flu showed potential to fight the swine flu. • • 20mill-100mill people die. 600,000 in the US Found only in the tropical rainforests of Madagascar. Of the most promising current candidates for new drugs, 70% were first discovered in plants animals and microbes. • Unfortunately many being lost to deforestation, agriculture, and other human activities. Earth is home to a tremendous diversity of species • We can think about Biodiversity on three scales: • • • Ecosystem diversity- the variety of ecosystems within a given region. Species diversity- the variety of species in a given ecosystem. Genetic diversity- the variety of genes within a given species. p. 121 How many species? • Species: a group that is distinct from other groups in terms of size, behavior, or biochemical properties and can interbreed to produce viable offspring. • The number of species in a given area is the most common measure of biodiversity (the quantity and variety within an ecosystem). • Scientists have named about 2 million species and approximate there are 5-100 million on Earth. The accepted estimate is set at 10 million. • • Species richness- the number of species in a given area. Species evenness- the measure of whether a particular ecosystem is numerically dominated by one species or are all represented by similar numbers of individuals. Community 1 has Good evenness Both have same richness p. 122 Phylogenic Tree How do you determine how closely related two species are to the original ancestor or to each other? Another example P.126 • • • Evolution is the mechanism underlying biodiversity Evolution- a change in the genetic composition of a population over time. Microevolution- evolution below the species level. • Gives rise to diversity within a species. Macroevolution- Evolution which gives rise to new species or new genera, family, class or phyla. • Gives rise to new species, genus, class, family, etc. • • • Creating Genetic Diversity Genes- physical locations on chromosomes within each cell of an organism. Genotype- the complete set of genes in an individual. Mutation- a random change in the genetic code. • • • • • First way that diversity is created. Most mutations are detrimental. Some mutations improve an organisms chances of survival and reproduction. Phenotype- the actual set of traits expressed in an individual. Recombination-occurs as chromosomes are duplicated during meiosis and mitosis. • • Second way diversity is created. Piece of one chromosome breaks off and attaches to another chromosome. Evolution • Occurs by 3 primary mechanisms: • Artificial selection • Natural selection • Random processes. Evolution by artificial and natural selection • • Evolution by artificial selection- when humans determine which individuals breed. Evolution by natural selection- the environment determines which individuals are most likely to survive and reproduce. Darwin’s theory of evolution by natural selection • • • • • Individuals produce an excess of offspring. Not all offspring can survive. Individuals differ in their traits. Differences in traits can be passed on from parents to offspring. Differences in traits are associated with differences in the ability to survive and reproduce. • Fitness: Ability to survive and reproduce. • Adaptation: Traits that improve an individual’s fitness. All species produce an excess number of offspring. Only those offspring having the fittest genotype will pass their genes on to the next generation. P. 128 • • • • Evolution by Random Processes Mutation- occur randomly and can add to the genetic variation of a population. Genetic drift- change in the genetic composition of a population over time as a result of random mating. Bottleneck effect- a reduction in the genetic diversity of a population caused by a reduction in its size. Founder effect- a change in a population descended from a small number of colonizing individuals. P. 129 Speciation and extinction determine biodiversity • Allopatric speciation- when new species are created by geographic or reproductive isolation. • River changes course, etc. • Sympatric speciation- the evolution of one species into two species in the absence of geographic isolation, usually through the process of polyploidy, an increase in the number of sets of chromosomes. Once they become polyploid, they generally can not interbreed with their diploid ancestor. Four things that influence the pace of evolution Change in a species’ genotype or phenotype such as an adaptation. Can take 100’s to millions of years. Average global rate of evolution is approximately 1 every 3 million years. If a species can not adapt quickly enough it will go extinct. Evolution shapes ecological niches and determines species distributions • • Range of tolerance- all species have an optimal environment in which it performs well. The limit to the abiotic conditions they can tolerate is known as the range of tolerance. Fundamental niche- the ideal conditions for a species. p. 135 Mix of all abiotic conditions that is perfect for the organism. Limit of tolerance Niches • • • Realized niche- the range of abiotic and biotic conditions under which a species lives. This determines the species distribution, or areas of the world where it lives. Niche generalist- species that live under a wide range of conditions. Niche specialist- species that live only in specific habitats. • • • The Fossil Record Fossils- remains of organisms that have been preserved in rock. Much of what we know about evolution comes from the fossil record. The average life span of a species appears to be only about 1 million years. Extinctions may occur because: • • No favorable environment to move to. Favorable environment may already be occupied. • The Five Global Mass Extinctions Mass extinction- when large numbers of species went extinct over a relatively short period of time. Better known extinction happened during the cretaceous period wiping out 50% of all species including the dinosaurs. Consensus among scientists says it was a meteorite that hit Earth, formed a giant dust ball that blocked out the sun for many years. Greatest on record ~90% of marine and 70% terrestrial vertebrates went extinct. 250 million years ago. The Sixth Mass Extinction • • • Scientists feel that we are in our sixth mass extinction, occurring in the last two decades. Estimates of extinction rates vary widely, from 2 % to 25% by 2020. In contrast to previous mass extinctions, scientists agree that this one is caused by humans.