Evolution, Biodiversity, & Population Ecology Chapter 3

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

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

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

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

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

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

Directional selection = drives a feature in one direction

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

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

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

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

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)

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