Community Ecology — Structure, Interactions, and Dynamics Explained | Chapter 54 of Campbell Biology

How do species interact to shape the structure and function of their communities? In Chapter 54 of Campbell Biology, we explore the core concepts of community ecology, including the diverse interactions between species, the impact of keystone and ecosystem engineer species, and the factors driving community structure and succession. This chapter provides a vital framework for understanding the dynamics of real-world ecosystems and the role of both living and nonliving components.

Watch the full podcast summary below, then read on for detailed concepts, glossary terms, and modern insights into community ecology and environmental science.

Interspecific Interactions: The Web of Life

Communities are shaped by many types of interspecific interactions—relationships between species that influence their survival and reproduction:

• Competition: Two species vie for the same resources, which can lead to competitive exclusion or resource partitioning (dividing resources to minimize conflict).
• Predation: One organism kills and consumes another, often leading to the evolution of defensive adaptations.
• Herbivory: Animals feed on plants or algae, prompting the evolution of plant defenses.
• Mutualism: Both species benefit (e.g., pollinators and flowering plants).
• Commensalism: One species benefits while the other is unaffected.
• Symbiosis: A broad term covering any close and long-term interaction between species, including mutualism, commensalism, and parasitism.

Trophic Structure and Food Webs

Trophic structure describes the feeding relationships in a community:

• Primary producers: Plants and other photosynthetic organisms that form the base of the food web.
• Consumers: Organisms that feed on producers and each other (herbivores, carnivores, omnivores).
• Decomposers: Organisms that recycle nutrients by breaking down dead matter.

Keystone species and ecosystem engineers (like beavers) have a disproportionately large effect on community structure and ecosystem function relative to their abundance.

Community Diversity and Biogeography

Community diversity is measured by:

• Species richness: The total number of species present.
• Shannon Diversity Index (H): A metric that incorporates both richness and the relative abundance of each species.

Diversity is influenced by abiotic factors (climate, soil, disturbance) and biotic factors (interactions among organisms). Larger, more diverse communities are often more stable and resilient to disturbances.

Disturbance and Ecological Succession

Disturbances—events that change community structure, such as fires, storms, or human activity—play a key role in shaping communities. The process of ecological succession follows disturbance:

• Primary succession: Occurs in lifeless areas where soil has not yet formed (e.g., after a volcanic eruption).
• Secondary succession: Occurs where an existing community has been cleared but soil remains (e.g., after a forest fire).

Succession moves through a series of stages, from pioneer species to a more stable climax community.

Key Glossary Terms

• Abiotic Factors: Nonliving components (temperature, sunlight, water, soil).
• Biotic Factors: Living components (other organisms).
• Community: Different populations living and interacting in an area.
• Competitive Exclusion: Two species with identical niches cannot coexist indefinitely.
• Keystone Species: Species with a large impact relative to their abundance.
• Mutualism: (+/+) Interaction where both benefit.
• Predation: (+/-) Interaction where one organism consumes another.
• Symbiosis: Close relationship between two species.
• Trophic Structure: Feeding relationships and energy flow.
• Succession: Community change and development over time.
• Ecosystem Engineers: Species that create or modify habitats.
• Species Richness: Number of different species present.
• Shannon Diversity Index (H): Measure of community diversity.
• Resource Partitioning: Division of resources to reduce competition.
• Top-down/Bottom-up Control: Regulation of community structure from consumers/resources, respectively.

Conclusion: Why Community Ecology Matters

Understanding community ecology helps explain the intricate web of life, from species interactions and food webs to how disturbances shape ecosystems. This knowledge is crucial for conservation, managing invasive species, and preserving biodiversity in a changing world.

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