V. Evolution by Natural Selection

▪ Biological Evolution: the process whereby earth’s life changes over time through changes in genetic characteristics of populations. All species descended from earlier, ancestral species.

▪ Proposed by Charles Darwin-On the Origin of Species by Means of Natural Selection. Change in populations (not individuals) genetic makeup over successive generations. Major driving force of adaptation

Darwin’s Theory

▪ Individuals produce an excess of offspring▪ Not all offspring can survive▪ Individual differ in their traits (Genetic Variability )▪ Differences in traits can be passed from parent –

offspring (differential reproduction)▪ Natural Selection: environmental conditions favor

some individuals over others ▪ Fitness: Ability to survive and reproduce▪ Adaptation/Adaptive Traits: any heritable trait that

improves the ability of an individual organism to survive and to reproduce at a higher rate than other individuals in a population under prevailing environmental conditions.

▪ Differential reproduction: individuals with the trait are able to survive and reproduce at a higher rate than other individuals in the population

▪ Natural Selection at work: Genetic Resistance=ability of one or more organisms in a population to tolerate a chemical designed to kill it. Antibiotic Resistance/Pesticide Resistance

▪ Limitations to adaptation through natural selection▪ Change in enviro condition can lead to adaptation

only for genetic traits already present in a population’s gene pool or for traits resulting from mutations, which occur randomly

▪ Ability to adapt limited by reproductive capacity▪ Natural Selection acts on individuals but occurs

in populations

▪ Example of Evolution by Natural SelectionPeppered Moth 

▪ Coevolution: Populations of two different species interact over a long period of time, change in gene pool of one can lead to change in gene pool of another.

▪ http://www.biotopics.co.uk/newgcse/naturalselection.html

IV. Evolution by Random Processes

▪ Genetic Drift: Change in allele frequency in a population due to random sampling. Some organisms, by chance, leave behind more offspring

▪ genetic drift with marbles▪ Population Bottleneck: an evolutionary event in

which a significant percentage of a population or species is killed or otherwise prevented from reproducing; some genotypes will be lost and genetic composition of survivors will differ from original group

▪ Founder Effect: The founder effect is a special case of a population bottleneck, occurring when a small group in a population splinters off from the original population and forms a new one, taking with it only limited alleles from the original population

Summary

▪ Earth’s biodiversity is the product of evolution, a change in the genetic composition of a population over time

▪ Evolution below the species level is microevolution-variety of apples or potatoes

▪ Genetic changes that give rise to new genera, families, classes in macroevolution

▪ Extinction and speciation are what leads to biodiversity

VII. Speciation and Extinction Determine Biodiversity

▪ Process of Speciation- Two PhasesGeographic Isolation: groups from same population become physically isolatedReproductive Isolation: When sexually reproductive organisms becomes so genetically different they cannot mate 

Pace of Evolution

▪ Hundreds to millions of years

▪ Average global rate 1 species every 3 million years.

▪ If populations cannot adapt quickly enough they go extinct

▪ To survive a rapid environmental change, a population must evolve quickly.

VIII. What Role Do Species Play in an Ecosystem?

▪ Ecological Niche: role of an organism in ecosystem; its way of life

▪ Niche includes adaptations acquired through evolution, range of tolerance, types and amounts of resources the species uses and interactions with other organisms. Competition limits niche

▪ Limits to Adaptation-ability to adapt limited to gene pool and how fast it can reproduce.

Resource Partitioning: Some species competing for same resource develop special adaptations: hunt day vs. night

Survival of fittest-fitness is a measure of reproductive success, leaving the most descendants-not strength

Niche

▪ All species has an optimal environment in which it performs particularly well-a range of tolerance or limit to abiotic conditions they can tolerate.

▪ Fundamental Niche: full potential range of conditions if there were no competition

Realized Niche: the portion of niche fulfilled

▪ A generalist species: Broad Niches able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources

▪ A specialist species: Narrow Niches can only thrive in a narrow range of environmental conditions or has a limited diet. Often prone to extinction.▪ Endemic Species: found only in one area; are most

vulnerable to extinction

▪ Most organisms do not all fit neatly into either group

IX. Environmental Changes-Physical Evolution

▪ Movement of tectonic plates has determined location of continents and ocean basins▪ Location/latitude of continents determines

climate and thus where plants and animals live

▪ Movement of continents has allowed species to move, adapt to new environments and form new species.

▪ Movement of tectonic plates has allowed species to move, adapt to new climates and form new species

▪ Volcanic Eruptions: Mt. Saint Helens: Destroy habitat and wipe out populations

▪ Earthquakes: create fissures that separate and isolate populations

▪ Climate Change and Natural Selection: Grizzly and Polar Bear

▪ Divergence: One species becomes two▪ Convergence: The evolution of species from

different taxonomic groups toward a similar form.

▪ Extinction: Species ceases to exist. They can be ecologically extinct-number are so small they cannot fulfill their role. Over 99 % of all species that have ever lived are now extinct.

Background Extinction-normally occurring in nature

Mass Extinction-large percent of species across the genera