In this section, you will explore the following questions:
- What are the pathways of species evolution in hybrid zones?
- What are the two major theories on rates of speciation?
Connection for AP® Courses
Speciation can both occur gradually over time in small steps or in bursts of change known as punctuated equilibrium. With punctuated equilibrium, a species may remain unchanged for long periods of time. The primary influencing factor on changes in speciation rate is environmental change.
Information presented and the examples highlighted in the section support concepts outlined in Big Idea 1 of the AP® Biology Curriculum Framework. The AP® Learning Objectives listed in the Curriculum Framework provide a transparent foundation for the AP®Biology course, an inquiry-based laboratory experience, instructional activities, and AP® exam questions. A learning objective merges required content with one or more of the seven science practices.
|Big Idea 1||The process of evolution drives the diversity and unity of life.|
|Enduring Understanding 1.C||Life continues to evolve within a changing environment.|
|Essential Knowledge||1.C.1 Speciation and extinction have occurred throughout Earth’s history.|
|Science Practice||5.1 The student can analyze data to identify patterns or relationships.|
|Learning Objective||1.20 The student is able to analyze data related to questions of speciation and extinction throughout the Earth’s history.|
Speciation occurs over a span of evolutionary time, so when a new species arises, there is a transition period during which the closely related species continue to interact.
- stability, fusion, reinforcement
- allopatric speciation, sympatric speciation, fusion
- convergent evolution, divergent evolution, no evolution
- natural selection, genetic drift, gene flow
Varying Rates of Speciation
Scientists around the world study speciation, documenting observations both of living organisms and those found in the fossil record. As their ideas take shape and as research reveals new details about how life evolves, they develop models to help explain rates of speciation. In terms of how quickly speciation occurs, two patterns are currently observed: gradual speciation model and punctuated equilibrium model.
- There is a significant change in the environment over time, such as the breakup of a supercontinent due to tectonic activity.
- A species that has a competitor outcompetes it and drives it to extinction, freeing up more resources.
- There is a sudden and significant change in the environment, such as a volcanic eruption that divides a population that once shared a habitat.
- There is a stable and unchanging environment in which a species can flourish.
The primary influencing factor on changes in speciation rate is environmental conditions. Under some conditions, selection occurs quickly or radically. Consider a species of snails that had been living with the same basic form for many thousands of years. Layers of their fossils would appear similar for a long time. When a change in the environment takes place—such as a drop in the water level—a small number of organisms are separated from the rest in a brief period of time, essentially forming one large and one tiny population. The tiny population faces new environmental conditions. Because its gene pool quickly became so small, any variation that surfaces and that aids in surviving the new conditions becomes the predominant form.
Visit this website to continue the speciation story of the snails.