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.