1. Evolution, Biodiversity, & Population Ecology
Chapter 3

2. This lecture will help you understand:
Natural selection
How evolution influences biodiversity
Reasons for species extinction
Ecological organization
Population characteristics
Population ecology
Conserving biodiversity

4. Evolution: The Source of Earth’s Biodiversity
Species = a population or group of populations whose members share characteristics
They can breed with one another and produce fertile offspring
Population = individuals of the same species that live in an area
Evolution = change over time
Biological evolution = change in populations of organisms over generations
Genetic changes lead to changes in appearance, functioning, or behavior

5. Evolution: The Source of Earth’s Biodiversity
Natural selection = process in which traits that enhance survival and reproduction are passed on more frequently to future generations than those that do not

7. Evolution: The Source of Earth’s Biodiversity
Why environmental scientists need to understand evolution:
Evolutionary processes influence pesticide resistance, agriculture, medicine, health, etc.

8. Natural selection shapes organisms and diversity
In 1858, both Darwin and Wallace proposed natural selection as the mechanism of evolution
Premises of natural selection:
Organisms struggle to survive and reproduce
Organisms produce more offspring than can survive
Individuals of a species vary in their characteristics due to genes and the environment
Some individuals are better suited to their environment and reproduce more effectively
Organisms with better adapted traits will produce more offspring

9. Natural selection shapes organisms and diversity
Adaptation = (traits) that lead to better reproductive success become more common in the population
Adaptive trait (adaptation) = a trait that promotes reproductive success
Mutations = accidental changes in DNA that may be passed on to the next generation
Non-lethal mutations provide the genetic variation on which natural selection acts
Sexual reproduction also leads to variation

10. Directional selection =
drives a feature in one direction

11. Selective pressures from the environment influence adaptation
Divergent evolution = Related species in different environments experience different pressures and evolve different traits
Convergent evolution = unrelated species may acquire similar traits because they live in similar environments

13. Evidence of natural selection is all around us
It is evident in every adaptation of every organism
Artificial selection = the process of selection conducted under human direction
Produced the great variety of dog breeds and food crops

15. Evolution generates biodiversity
Biological diversity (biodiversity) = the variety of life across all levels of biological organization
Species
Genes
Populations
Communities
Scientists have described 1.8 million species
Estimates of the total number of species that exist range from 3 million to 100 million
Biodiversity exists nearly everywhere

16. Speciation produces new types of organisms
The process of generating new species from a single species
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
Natural selection can speed the process

18. We can infer the history of life’s diversification by comparing organisms
How did the major groups of organisms come to be?
Phylogenetic trees = diagrams that show relationships among species, groups, genes, etc.
Scientists can trace how certain traits evolved
Some traits evolved and were passed on
Other traits evolved more than once (e.g., the ability to fly)

20. We can infer the history of life’s diversification by comparing organisms
Knowing how organisms are related to one another helps scientists organize and name them
Categories reflect evolutionary relationships
Scientists use physical and genetic characteristics to organize
Each species gets a two-part Latinized scientific name