bio lecture 03/11

Ecological Interactions Overview

• Importance of ecological interactions in understanding relationships among organisms in their environments.

Types of Ecological Interactions

Competition

• Definition: Interaction where individuals compete for the same resources (food, space, light).

• Even if one species wins, both exert energy, leading to potential negative effects on fitness.

Consumption

• Definition: Interaction benefiting one organism while costing another.

  • Types:

    • Predator-Prey: Classic example involving predators consuming prey.

    • Herbivory: Herbivores consuming plant material.

    • Parasitism: One organism benefits at the expense of another, causing harm to the host.

Commensalism

• Definition: Interaction where one organism benefits and the other is not significantly affected.

  • Example: Orchids attracting flies by mimicking scents without providing nectar; the fly may be distracted from reproduction.

Environmental Influences on Interactions

• Shift in Ecological Interactions: Environmental changes can lead to shifts in interactions, e.g., mutualism becoming parasitism when conditions become unfavorable.

• Microorganisms: Microbial populations can shift from mutualistic to pathogenic due to environmental stressors like:

  • Changes in resources.

  • Changes in host condition (e.g., diet, health status).

  • Changes in physical conditions (e.g., pH, temperature).

Case Study: Environmental Shifts in Microorganisms

Opportunistic Pathogen Example

• Biofilms: Free-floating bacteria can become pathogenic when nutrients increase, leading to a shift from a non-adherent to an adherent state.

• Skin Damage: An injury allows bacteria to enter; changes in the skin environment lead to potential pathogenic relationships.

Human Host Interactions

• Impact of Diet: Changes in diet can alter microbiota diversity and interactions.

• Diseases: Conditions like cystic fibrosis can change the host’s interactions with bacteria, enhancing pathogenic potential.

Mutualistic Relationships in Plants and Microbes

Plant Roots and Microbial Interaction

• Roots provide nutrients to beneficial bacteria (e.g., rhizobia) in exchange for nitrogen fixation.

• Nodules Formation: Specialized structures where nitrogen-fixing bacteria reside. Each partner provides essential nutrients:

  • Plants provide sugars (photosynthesis).

  • Bacteria provide fixed nitrogen.

Molecular Signaling in Symbiosis

• Communication occurs through signaling molecules (e.g., rhizobia produce nod factors) that the plant recognizes, leading to a mutualistic relationship.

• Both partners exchange information to establish and maintain their relationship.

Review Concepts

• Resource Regulation: Successful interactions depend on the regulation of available resources and the balance between mutual benefit and competitive exclusion.

• Density and Diversity Trends: As you approach plants roots or gut linings, diversity and density of microbes decrease due to selective pressures from the host.