A close and often lifelong ecological relationship between species is calledMultiple choice question.succession.species richness.a keystone.a symbiosis.

Break Down the Problem

1. Identify the terms presented in the multiple choice options:
   • Succession
   • Species richness
   • A keystone
   • A symbiosis

Relevant Concepts

2. Define each of the terms mentioned in the options:
   • Succession: The process by which ecosystems change and develop over time.
   • Species Richness: A measure of the number of different species present in an ecological community.
   • A Keystone: A species that has a disproportionately large effect on its environment relative to its abundance.
   • A Symbiosis: A close and often lifelong interaction between two different biological species.

Analysis and Detail

3. Analyze the definitions:
   • The question specifies a "close and often lifelong ecological relationship," which corresponds most closely with the definition of symbiosis.
   • Although keystone species play a critical role in their communities, the term does not specifically denote an ecological relationship.
   • Succession and species richness address broader ecological concepts rather than specific relationships.

Verify and Summarize

4. Verify the relationship:
   • Symbiosis specifically denotes interaction types such as mutualism, commensalism, and parasitism, all of which can be lifelong relationships, while other options do not reflect this specificity.

Final Answer

The correct answer is a symbiosis.