Ecology Chapter on Community Structure

Definition and Structure

• An ecological community is a grouping of interacting populations of different species within a defined area.
• These interactions include predation, competition, mutualism, parasitism, and commensalism.
• Communities are characterized by their species composition, relative abundance, and interactions.

Factors Influencing Community Structure

• Abiotic factors: Temperature, precipitation, sunlight, soil type, and nutrient availability strongly shape the community.
• Biotic factors: Interactions among species, including competition for resources, predation, and mutualism, are key determinants.
• Disturbances: Natural events like fires, floods, and volcanic eruptions significantly alter community composition.
• Succession: The gradual change in species composition over time following a disturbance or habitat creation is called ecological succession.

Types of Communities

• Terrestrial communities: Forests, grasslands, deserts, and tundra are examples, each with its unique plant and animal life.
• Aquatic communities: Freshwater (lakes, rivers, streams) and marine (oceans, coral reefs) communities differ due to salinity, depth, and water flow.
• Specific community categories: Defined by dominant species; examples include coral reefs (dominated by corals), kelp forests (dominated by kelp), and old-growth forests (dominated by long-lived tree species).

Species Interactions

• Competition: Species compete for limited resources (food, water, light, space). This can lead to competitive exclusion or resource partitioning.
• Predation: Predators hunt and consume prey, regulating prey populations and affecting community structure.
• Mutualism: Species benefit from interaction, like pollination by insects.
• Parasitism: One species (parasite) benefits at the expense of the other (host).
• Commensalism: One species benefits, while the other is unaffected.

Community Dynamics

• Population Fluctuations: Species numbers change over time, often due to environmental factors.
• Extinction and Colonization: Species may disappear or join a community based on various conditions, influencing community diversity and composition.
• Community Stability: The ability of a community to resist change and maintain structure and function is called stability. This depends on species richness, complexity of interactions, and resilience.

Keystone Species

• Keystone species significantly impact their communities.
• Removing them drastically alters community structure and function.
• Examples include sea otters or beavers.

Role of Biodiversity

• Biodiversity (species richness and abundance) is vital for community stability.
• Diverse communities are generally more resilient to disturbances.
• Loss of biodiversity weakens the community's ability to adapt and function.

Human Impact

• Human activities strongly influence community structure and dynamics, often negatively.
• Pollution, habitat loss, and climate change are detrimental impacts.
• Invasive species disrupt natural communities.

Explore the intricacies of ecological communities in this quiz. Learn about the factors influencing community structure, including abiotic and biotic elements, as well as the effects of disturbances and succession. Test your knowledge on species interactions and community dynamics.