Chapter 5

Chapter 5

1. Earth is home to diversity of species

   • Ecosystem Diversity: the variety of ecosystems within a given region
   • Species Diversity: the variety of species within a given ecosystem
   • Genetic Diversity: the variety of genes within a given species
     • Genes form the blueprints for organism's traits. With genetic diversity, it helps determine the species of diversity and ecosystem diversity

2. How many species?

   • the number of species in any place is the measure of biodiversity
     • It is hard to determine how many species there actually are because many organisms live in inaccessible locations
     • Scientists have estimated around 5 to 100 million species

3. Species Richness and Evenness

   • Species Richness: the number of species in a given area
   • Species Evenness: whether a particular ecosystem is numerically dominated by one species or whether all of its species have similar abundances
     • High species evenness means higher levels of biodiversity while low species evenness is the opposite
   • Species evennes and richness declines after human disturbance

4. Evolutionary relationships

   • organizing species into categories of how closely they are related
   • Phylogenies: the branching patterns of evolutionary relationships
     • determined by the similarity of their traits

5. Evolution is the mechanism underlying biodiversity

   • Evolution: a change in the genetic composition of a population over time
   • Microevolution: evolution below the species level (i.e. different varieties of the same vegetables
   • Macroevolution: genetic changes that create new species, genera, families, classes, or phyla-larger categories of organisms into which species are organized

6. Genetic Diversity

   • Genes: physical locations on chromosomes within each cell of an organism
   • Genotype: complete set of genes in an individual
   • Phenotype: The actual set of traits in an individuals anatomy, physiology and behavior
   • Two processes of genetic diversity:
     • Mutation: occasional mistake in DNA copying process that reduces a random change in genetic code
       • Most are detrimental but some improve chances of survival or reproduction
     • Recombination: as chromosomes are duplicated during reproductive cell division, a piece of a chromosome breaks off and attaches to another chromosome, creating new combinations of genes producing novel traits
       • This can help the immune systems defense

7. Evolution by Artificial Selection

   • Evolution by Artificial Selection: when humans determine which individuals breed, typically with a certain set of traits
     • However it can produce unwanted results (i.e. weeds with mutations repelling herbicides)

8. Evolution by Natural Selection

   • Evolution by Natural Selection: the environment determines which species survive and reproduce
   • Fitness: an individuals ability to survive and reproduce
     • Adaptation: traits that improve an individual's fitness
   • Darwin's Theory
     • not all offspring survive
     • individuals produce an excess of offspring
     • 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

9. Evolution by Random Processes

   • Mutation: occur randomly; if not lethal, they can add to genetic variation of a population
   • Genetic Drift: change in genetic composition of a pop. over time as a result of random mating
   • Bottleneck Effect: a reduction in the genetic diversity of a pop. caused by a reduction in its size
   • Founder Effect: a change in population descended from a small number of colonizing individuals

10. Allopatric versus Sympatric Speciation

    • Geographic Isolation: ex. of evolution creates new species; when a subset of individuals from a bigger pop. colonize in a new area that is physically separated from the rest of the pop.
    • Reproductive Isolation: when two pop.s will be separated over time and will become so different that even if the physical barriers were removed, they couldn't interbreed and produce offspring
    • Allopatric Speciation: speciation requiring geographic isolation
    • Sympatric Speciation: evolution of one species into two species without geographic isolation

11. Pace of Evolution

    • Rate of change: to survive- the pop. must evolve quickly.
    • Genetic Variation: species with high genetic variation contain individuals with a wide variety of phenotypes
    • Pop. Size
      • Genetic Engineering: scientists can copy genes from a species with a certain trait and insert them into another species
      • Genetically Modified Organisms: organisms which have gone through the process of genetic engineering

12. Evolution Shapes Ecological Niches and Determines Species Distributions

    • Range of Tolerance: limits to the abiotic conditions they can tolerate (ex. temp., humidity, salinity, pH)
    • Fundamental Niche: the ideal conditions of the species
    • Realized Niche: the range of abiotic and biotic conditions under which a species actually lives
    • Distribution: the areas of the world in which the species lives
    • Niche Generalists: species which can live in a variety of habitats or feed on a variety of species
    • Niche Specialists: species must live in a specific habitat or feed on a small group of species

13. Environmental Changes and Species Distributions

    • 5 Global Mass Extinctions
      • Mass Extinction: extinction of a large number of species one a short time period
      • Greatest Mass Extinction: 251 million years ago, 90% marine species and 70% land vertebrates went extinct
      • Better known Extinction: end of Cretaceous period (65 million years ago), around one half of Earths species went extinct
      • Currently in the 6th mass extinction, due to harmful human activities, depleting the world from 2-25% of species
    • Fossils: the remains of organisms that have been preserved in rocks
    • Environmental changes: if species cannot adapt to the changes or move to a better environment they they will eventually go extinct
      • The average lifespan of a species is around 1-10 million years