Origins of Biological Diversity Chapter 15: pp 322-351
Concept 15.1The origin of new species. • Essential question: • How do biologists identify species? • How do species arise? • Objectives: • Explain biological species concept. • Compare microevolution and macroevolution. • Describe types of reproductive barriers. • Analyze how adaptive radiation contributes to species diversity.
What is a species? • A distinct form of life. • Biologists use the biological species concept to define a species as a population whose members breed with one another to produce fertile offspring. • Members of one species do not breed with members of another species. • This definition- for sexually reproducing organisms.
How does macroevolution differ from microevolution? • Microevolution is evolution on the smallest scale; generation to generation change in the allele frequencies in a population. • Macroevolution is dramatic changes that are seen in the fossil record. To explain how we evolved from simpler life forms. Includes: • Origin of different species- speciation. • Extinction of species. • Evolution of major features
Key concept- New species leads to biodiversity Figure 15-2 Branching or cladogenic evolution. If one species evolves into two or more surviving species, diversity increases.
Reproductive Barriers: • Reproductive isolation- keeps 2 similar species from breeding. Due to: • Timing- different breeding seasons. Skunk example. • Behavior- different courtship/mating. Ex. Songs of birds • Habitat- adapted to different habitats- Fish ex. • Incompatible reproductive structures. • Infertile hybrids- Horse x Donkey mule.
Geographic Isolation separates populations leading to new species. • Examples include: • mountain ranges- range of ecological zones. • Glaciers and isolated islands • Depends on the organisms’ ability to move about. Examples:deep canyons,wide rivers. Birds, pollen, coyotes vs. antelope squirrels. • Splinter populations-separation of a small portion of the population from the main population. • Crucial event in origin of a new species. • Genetic drift- chance and Natural selection can make the splinter population less and less like the main population.
Do all isolated populations survive and become new species? • No , not all isolated populations survive and become new species. • Speciation only occurs if the two populations can no longer interbreed Not all isolated populations survive and become new species.with each other. • Figure 15.6 model- pg 328.
Adaptive Radiation • Evolution from a common ancestor that results in diverse species adapted to different environments. • Transparency- Figure 15-7 pg. 328. • Islands serve as showcase- ex. Hawaiian islands. • Physically diverse with differences in altitude and rainfall . • New lava flow supports adaptive radiation. • Most native species are found nowhere else.
Figure 15-7Adaptive radiation on an island chain may lead to several new bird species evolving from one founding population.
Tempo of Speciation • Punctuated equilibrium- a model used to address the observation that species often diverge in spurts of rapid change, then exist for long periods of time with little change. • The refining of a scientific theory of gradual change. • Natural selection and adaptation happen, but when the species is “young” . • Major changes are less common once the species is established. • Speciation is rapid in terms of the fossil record. • Most successful species last 1-5 million years.
Figure 15-9In contrast to a more gradual model of evolution, punctuated equilibrium suggests that a new species changes most as it buds from a parent species. There is little change for the rest of the time the species exists.