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NATURAL SELECTION A GENETIC CHANGE IN A POPULATION OF ORGANISM THAT OCCURS OVER TIME. Charles Darwin The Origin of Species by Means of Natural Selection (1859) WHAT DID DARWIN SUGGEST? Inherited traits favorable to survival in a given environment would tend to be preserved and unfavorable ones would be eliminated. Adaptations: Evolutionary modifications that improves the chances of survival and reproductive success of the population in a given environment. WHAT DOES NATURAL SELECTION INVOLVE ? Those individuals with a combination of genetic traits better suited to environmental conditions are most likely to survive and reproduce. Four components of Natural Selection: 1. overproduction 2. variation 3. limits on population growth , or a struggle for existence 4. differential reproductive success MICRO VS. MACRO EVOLUTION Gene pool: The sum total of all genes possessed by the individuals of the population of a species. Microevolution: small genetic changes that occur in a species gene pool over time. Example: Camouflage coloration in the peppered moth REMEMBER THE STORY????? First an environmental change occurred: Soot caused a change in the background color of the tree trunks. Then the environmental change led to a change in selective forces: Predators were able to find and eat the moths with the coloration that no longer blended in with the background. SOOOOOOO…. APPLICATIONS OF DARWIN’S OBSERVATIONS 1. There were two colors forms (Variability in the genes) 2. Color form was genetically based ( heritability of the genes) 3. There was greater survival and reproduction by one of the color forms ( differential reproduction) Microevolution took place!!!! KEYS TO REMEMBER Environmental conditions do not create favorable heritable characteristics… Instead, natural selection favors some individuals over others by acting on inherited genetic variations (alleles) already present in the gene pool of a population. NATURAL SELECTION ACTS ON GENETIC VARIATION Natural selection changes characteristics through: Directional selection = drives a feature in one direction Stabilizing selection = favors intermediate traits Preserving the status quo Disruptive selection = traits diverge in two or more directions EVIDENCE OF NATURAL SELECTION IS EVERYWHERE It is evident in every adaptation of every organism Artificial Selection = the process of selection conducted under human direction Producing the great variety of dog breeds and food crops SPECIES RICHNESS:THE NUMBER OF SPECIES PRESENT IN A COMMUNITY • Tropical Rainforest and coral reefs have extremely high species richness. Isolated islands and mountain tops have low species richness Creates Geographical Isolation BIODIVERSITY: VARIETY OF DIFFERENT SPECIES The number of species in existence at any time is equal to the number added through speciation minus the number removed by extinction. WHAT DETERMINES SPECIES RICHNESS? 1. Abundance of ecological niches Greatest at the margins of adjacent communities ecotone – a transitional zone where two or more communities meet edge effect- the change in species composition produced at ecotones 2. Inverse relationship to the geographical isolation of a community. 3. Reduced when one or more species is dominant in a community (competition) 4. Inversely related to the stress on a habitat 5. Geological history – (climate changes) NICHES Fundamental niche: the potential ecological niche that an organism could have if there were no competition from other species. Realized niche: the life style that an organism actually pursues because of competition from other species. ECOSYSTEM STABILITY • Ecosystems with greater species richness are better able to supply ecosystem services – environmental benefits, such as clean air, clean water, and fertile soil. • Community stability – the ability of a community to withstand environmental disturbances Example: • monocultures and pest vs. blight on a specific trees in a forest of other species MACROEVOLUTION Long term large-scale evolutionary changes among groups of a species. New species are formed from ancestral species and other species are lost through extinctions. Phylogenetic tree (cladogram) MACROEVOLUTION: HOW EVOLUTION TAKES PLACE ABOVE THE LEVEL OF SPECIES AND OVER MUCH LONGER PERIODS THAN MICROEVOLUTION. Macroevolutionary patterns include: 1. Genetic persistence – the inheritance of DNA molecules from the origin of the first cells through all subsequent lines of descent ( basis of the unity of life) 2. Genetic divergence – long-term changes in lineages of species (basis of the diversity of life) 3. Genetic losses – the steady loss through background extinction or mass extinctions (abrupt, catastrophic loss of lineages) GENETIC DRIFT: CHANGES IN THE GENETIC MUTATION: CHANGES IN COMPOSITION OF A DNA OF A CELL POPULATION BY CHANCE. MORE VOCABULARY Gene Flow: Movement of genes between populations. This can lead to changes in the genetic composition of local populations. SPECIATION: THE PROCESS BY WHICH NEW SPECIES ARE GENERATED Allopatric speciation: species formation due to physical separation of populations The main mode of speciation Populations can be separated by glaciers, rivers, mountains Each population gets its own set of mutations GEOGRAPHICAL ISOLATION When two populations of a species or two groups of the same population become physically separated for fairly long periods into areas with different environmental conditions. ANOTHER TYPE OF SPECIATION Sympatric speciation = species form from populations that become reproductively isolated within the same area Feed in different areas Mate in different seasons Hybridization between two species Mutations REPRODUCTIVE ISOLATION: Occurs when species are unable to reproduce because of long term geographical separation. Divergent Evolution: When natural selection operates in two geographically isolated population and change the allele frequencies. SELECTIVE PRESSURES INFLUENCE ADAPTATION Related species in different environments Experience different pressures Evolve different traits Convergent evolution = unrelated species may evolve similar traits Because they live in similar environments COEVOLUTION Organisms evolve together SPECIATION RESULTS IN DIVERSE LIFE FORMS How do major groups diverge over time? Phylogenetic trees (cladograms) = show relationships among species, groups, genes, etc. Scientists can trace how certain traits evolved EXTINCTION: PERMANENTLY GONE! Previous 5 Mass Extinctions: Are we in the 6th Mass Extinction??? MASS EXTINCTION VS. BACKGROUND EXTINCTION In mass extinctions, large numbers of species become extinct each year for tens of thousands to millions of years. The five great mass extinctions have occurred during the past 500 million years and have been 20-60 million years apart. There have also been shorter mass extinctions (loss of 15-24% of all species) in between. A period of mass extinction is often regarded as having a loss of 25-70% of all species. The extinction of the dinosaurs is an example of mass extinction. MASS EXTINCTIONS All mass extinctions have been followed by periods of recovery, known as adaptive radiations. After almost every mass extinction, numerous new species have evolved (speciation) to fill new or vacated ecological niches in the changed environment. The extinction of dinosaurs, for example, was followed by an explosive rise of mammals. Fossil records suggest about 10 million years or more are required for adaptive radiations to rebuild biological diversity after a mass extinction. BACKGROUND EXTINCTION – NATURAL EXTINCTION Background extinction refers to the extinction that occurs naturally in the evolution process. 0.00003% of species become extinct naturally according to fossil records. During the ecological process, the natural extinction occurs following the evolution of the species. If a species cannot succeed in adapting to its surroundings it eventually becomes extinct. FACTORS OF BACKGROUND EXTINCTION INCLUDE 1. gradual changes in temperature 2. predator-prey relationships 3. tectonic plate movements. It is estimated that the average species stays around for 4 -22million years before it becomes extinct and that 99.9 of all the species that have ever existed are now extinct. EXTINCTION IS A NATURAL PROCESS, BUT … Humans profoundly affect rates of extinction Biodiversity loss affects people directly Food, fiber, medicine, ecosystem services