Unit B Ecosystems and Population Change

1. Mechanisms of Population Change Unit B Ecosystems and Population Change

2. Variation among Species • All around us because it’s the differences between living things • Some give organisms a survival advantage, while others cause disadvantage, others have no bearing on survival • Variation that is advantageous=Adaptation • Variability of individuals within same species arise from mutations and sexual reproduction and passed through generations

3. Mutations • Mutations are the random changes in DNA • Caused by chemicals, radiation or errors made while copying • Large populations over long time will have a more substantial number of mutations • Effects can be: • Neutral=no effect on reproductive success (fitness) • Harmful= selective disadvantage • Sickle cell anemia-disorder that cause red blood cells to become crescent shaped instead of round and smooth causing blood clots and other medical problems • Beneficial = selective advantage • Mutation that makes houseflies resistant to DDT in pesticides • California ground squirrel have mutation that makes their blood better able to combat rattlesnake venom

4. Sexual Reproduction • Production of offspring by union of sex cells from 2 DIFFERENT parents and 2 DIFFERENT sets of DNA means: • More traits become available because choices of mates • Different combos of genetic material • Random combos of genetic material 1000 males and 1000 females mean over 1 million different mating possibilities

5. Inherited Characteristics • Variations that arise through sexual reproduction and mutation are then passed on to subsequent generations

6. Evolutionary Biology • Major goal is to understand dramatic changes in populations over time • Compelling scientific theories that explain how organisms are diverse and how they change over time

7. Evolution by Natural Selection • Process whereby the characteristics of a population of organisms change over time because individuals with certain heritable traits survive specific local environmental condition and through reproduction, pass on their traits to their offspring

8. Evidence for Evolution through Natural Selection • What proof is there that present day species evolved from ancestral forms? • To appreciate and judge the validity of a theory it is important to examine the evidence and review how we gain this knowledge • Many lines of investigation • Some direct observation and experiment, some more indirect • Gathered from • Fossil record • Geographic distribution of species • Comparative anatomy and embryology • Biochemistry and genetics

9. Fossil (Paleontology) • Organisms found in different strata (layers of rock), some appear and then never again, not all organisms at same time • Earth slowly geologically changing • fossils found in young rock more similar to species alive today than deeper rock • Fossils found in chronological order so probable ancestors lie in rock beneath species • Transitional fossils show clear link between 2 types of species

11. Biogeography • Study of geographic distribution of life on earth • Close environments populated by related species rather than those environmentally similar and far away • Organisms on islands similar to organisms found on closest mainland • Fossils of same species on coastline of neighboring continents • Closely related species are almost never found in exact location or habitat

13. Anatomy and Embryology • Homologous (similar structure, different function) & vestigial (no useful function) features provide evidence of changes in populations • Similarities in embryo development in related groups point to common ancestors

14. Biochemistry/Molecular Biology • Compare biogeochemical characteristics • Proteins become increasingly different over time in different species • The more two species are related the more patterns in DNA are similarbecause they are inherited from common ancestors

15. Artificial Selection • Process of humans selecting & breeding individuals with desired traits • Use it to produce dramatic changes in relatively short period of time • Provides evidence that this can happen over longer period of time & less dramatically

16. Developing Theories to explain change • Theories can explain evolution on a global scale • Theory • model that accounts for all known scientific evidence as completely as possible • Provides plausible explanation of how things in nature are related • Helps scientists to make testable predictions

17. Lamarck’s Theory • Early 1800s (pre-Darwin) • All individuals are the same, no variation within population • Individuals CAN change and become more complex if the need arises • Use and disuse • Adaptations had a purpose • Acquired characteristics • Organisms had “force” or “desire” that lead them to change • Thought organisms with acquired traits/ characteristics could be passed down generations

18. Darwin’s Theory • Mid 1800s • Individuals of same species are in constant struggle for survival • Descent with modification • Natural Selection • Individuals with more favorable variations are more likely to survive & pass these variations on • Survival of the fittest • survival is not random • Evolution • Individuals with more favorable variations contribute more offspring to succeeding generations their favorable inherited variations become more common

19. Speciation • Theory that explains how new species form • Allopatric speciation • for animals in isolation • 3 step process 1.Physical barrier separates interbreeding therefore they mutate separately 2. Natural selection works on separate populations and they evolve separately 3. In time differences become pronounced and they can no longer be sexually compatible

20. Pace of evolutionary change Gradualism • Change happens slowly, consistently and constantly Punctuated Equilibrium • Change happens in spurts- little change then one or a few HUGE changes • Often because of huge, sudden changes (environment, mutation)