Community Level Interactions

• Biotic interactions within an ecosystem include predation, competition, and symbiosis
• Knowledge of energy transfers and community interactions involving both biotic and abiotic factors is important to understand ecological impacts
• Co-evolution: Organisms' behaviors and physical characteristics are an evolutionary response to interactions with the environment and other community members
• Predator/Prey Interactions:

  • Co-evolutionary arms race
  • Predator adaptations to capture prey
  • Prey adaptations to avoid predators
• Limiting Factors:

  • Abiotic factors that limit population density within a community
  • At least one abiotic factor, such as water, limits energy production (NPP) within an ecosystem
  • Examples of abiotic limiting factors vary from system to system
• Niche Concept:

  • Every organism fills a niche in the community
  • Niche includes habitat and all community level interactions
  • Keystone species play a critically important role in the ecology of the system
• Competitive Interactions:

  • Result from limiting factors and competition for resources
  • Survival of the fittest principle
  • Law of Competitive Exclusion
  • Types of competitive interactions: Intra-specific and Inter-specific competition
• Resource or Niche Partitioning:

  • Organisms develop behaviors and traits to avoid competition
  • Competition is always a negative in evolutionary terms
• Symbiosis:

  • Symbiotic interactions involve interactions between organisms within a biological community
  • Types of symbiotic interactions: Mutualism, Commensalism, Parasitism
• Ecological Succession:

  • Describes how biological communities change over time
  • Important concept for the AP exam
• Producers in ecosystems use energy from the sun to produce sugar which supports both terrestrial and marine food webs
• Organisms utilize inorganic matter from the air, water, and soil to build and maintain their bodies
• Organisms cycle matter back to the environment in biogeochemical cycles
• Distinct ecosystems are adapted to specific abiotic conditions such as rainfall patterns, nutrient cycling, temperature, and soil conditions found in certain geographic locations (Biomes)
• Each ecosystem will have at least one limiting factor that limits NPP or species diversity within the ecosystem
• Organisms must have physical or behavioral adaptations to the limiting factor in order to exist in that ecosystem
• Organisms within a given ecosystem look and act the way they do partly in response to the main limiting factor present in that biome
• Abiotic factors such as sunlight and temperature act as natural selective forces on organisms within an ecosystem
• Organisms found in ecosystems are shaped by community interactions including predation, competition, and symbiosis
• Organisms enter into co-evolutionary relationships with other members of the ecosystem
• Co-evolutionary relationships have evolved over millions of years and shape how ecosystems function
• Predator/Prey Interactions
• Fundamental law of nature: "eat or be eaten"
• Herbivores defend their calories by growing larger, running faster, or producing toxins to avoid predators
• Predators have highly developed sense organs, are intelligent, fast, and sometimes venomous to capture prey
• The more adaptations predators develop, the more adaptations prey must develop and vice-versa
• Ecosystem function is dependent on predator/prey relationships
• Keystone species play critical roles in ecosystems, and if lost, the entire system can be lost
• Niche concept: Each organism fills a niche in a community
• Organisms compete for limited resources, and the best adapted individuals will win the competition
• Law of Competitive Exclusion: No two organisms can occupy the same niche at the same time
• Competition is essential but comes at a cost for organisms
• Species have evolved mechanisms to avoid competitive interactions
• Symbiotic interactions are essential to how ecosystems function
• Symbiotic relationships can be mutualistic, commensalism, or parasitic
• Mutualistic relationships benefit both organisms involved, like pollination
• Commensalism benefits one organism while the other is neither harmed nor helped
• Parasitic relationships benefit one organism at the expense of another
• Primary succession involves pioneer species like lichens, moss, and weeds establishing in new habitats
• Ecological succession describes how ecosystems change over time