This video segment from Evolution: "Evolutionary Arms Race" tells the story of the leafcutter ant and the fungus it farms -- an example of mutually beneficial symbiosis. [4:59]

Biology 2e is designed to cover the scope and sequence requirements of a typical two-semester biology course for science majors. The text provides comprehensive coverage of foundational research and core biology concepts through an evolutionary lens. Biology includes rich features that engage students in scientific inquiry, highlight careers in the biological sciences, and offer everyday applications. The book also includes various types of practice and homework questions that help students understand—and apply—key concepts. The 2nd edition has been revised to incorporate clearer, more current, and more dynamic explanations, while maintaining the same organization as the first edition. Art and illustrations have been substantially improved, and the textbook features additional assessments and related resources.

By the end of this section, you will be able to do the following:

Discuss the predator-prey cycle
Give examples of defenses against predation and herbivory
Describe the competitive exclusion principle
Give examples of symbiotic relationships between species
Describe community structure and succession

By the end of this section, you will be able to do the following:

Understand the nutritional adaptations of plants
Describe mycorrhizae
Explain nitrogen fixation

Travel underground for an up-close look at the ants, amoebas, and bacteria that maintain healthy soil. Glimpse this microscopic world and learn about the symbiotic relationship between fungi and tree roots. [2:49] Support materials for students is provided.

This lesson will introduce the three types of symbiotic relationships and give examples of each. It is 4 of 4 in the series titled "Symbiotic Relationships."

A variety of symbiotic relationships exist between sharks and other marine species in this segment from Nature. [2:03]