3.1 Ecosystem structure and function

Ecosystems are complex networks of living organisms and their environment. They're made up of producers, consumers, and decomposers, all interacting with each other and non-living factors like water and soil.

Understanding ecosystem structure and function is crucial for grasping biodiversity. It helps us see how different species work together, compete, and adapt to their surroundings, shaping the natural world around us.

Ecosystem Components and Roles

Biotic and Abiotic Components

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• Ecosystems consist of biotic components (living organisms) and abiotic components (non-living physical and chemical factors) interacting within a defined area
• Producers (plants and algae) form the foundation of ecosystems by converting solar energy into chemical energy through photosynthesis
• Primary consumers (herbivores) feed directly on producers
• Secondary and tertiary consumers (carnivores) feed on other consumers, forming complex food webs
• Decomposers (bacteria and fungi) break down dead organic matter, recycling nutrients back into the ecosystem

Ecosystem Engineers and Keystone Species

• Ecosystem engineers (beavers, earthworms) modify their environment and significantly impact ecosystem structure and function
  • Beavers create dams, altering water flow and creating new habitats
  • Earthworms improve soil structure and nutrient cycling
• Keystone species have a disproportionately large effect on ecosystem structure and function relative to their abundance or biomass
  • Sea otters in kelp forests control sea urchin populations, protecting kelp from overgrazing
  • Prairie dogs in grasslands create burrows that provide habitat for other species and influence vegetation patterns

Interactions Between Organisms

Competition and Predation

• Competition occurs when organisms vie for limited resources, leading to adaptations and niche differentiation
  • Interspecific competition between different species (lions and hyenas competing for prey)
  • Intraspecific competition within the same species (male elephant seals competing for mates)
• Predation involves one organism (predator) consuming another (prey), influencing population dynamics and evolutionary adaptations
  • Predator adaptations (sharp teeth, camouflage)
  • Prey adaptations (speed, defensive structures)

Symbiotic Relationships

• Symbiosis encompasses various long-term interactions between different species
• Mutualism benefits both interacting species
  • Clownfish and sea anemones (protection and nutrient exchange)
  • Pollination (bees and flowers)
• Commensalism benefits one species while having a neutral effect on the other
  • Remora fish attaching to sharks (transportation and food scraps)
  • Epiphytes growing on trees (support without harming the host)
• Parasitism benefits one organism (parasite) at the expense of another (host), often resulting in complex life cycles and host-parasite coevolution
  • Tapeworms in animal intestines
  • Mistletoe on trees
• Amensalism occurs when one species is harmed while the other is unaffected
  • Allelopathic effects of certain plants on surrounding vegetation (black walnut trees inhibiting growth of nearby plants)
  • Larger animals inadvertently trampling smaller organisms

Abiotic Factors and Ecosystem Function

Climate and Physical Factors

• Temperature affects metabolic rates, distribution of organisms, and ecosystem processes such as decomposition and nutrient cycling
  • Ectotherms (reptiles, insects) rely on external heat sources
  • Endotherms (mammals, birds) maintain constant body temperature
• Water availability determines the types of organisms that can survive in an ecosystem and influences primary productivity and nutrient transport
  • Adaptations to water scarcity (cacti, camels)
  • Aquatic ecosystems (freshwater, marine)
• Light intensity and quality impact photosynthesis rates, plant growth, and animal behavior, particularly in aquatic and forest ecosystems
  • Phototropism in plants
  • Diel vertical migration in marine organisms

Soil and Atmospheric Factors

• Soil composition and structure influence plant growth, water retention, and microbial activity, affecting nutrient availability and ecosystem productivity
  • Soil types (clay, sand, loam) affect water retention and nutrient availability
  • Soil pH influences nutrient uptake by plants
• Atmospheric gases, particularly carbon dioxide and oxygen, play crucial roles in photosynthesis, respiration, and global climate regulation
  • Carbon cycle (photosynthesis, respiration, decomposition)
  • Nitrogen cycle (nitrogen fixation, nitrification, denitrification)
• Topography and elevation create microclimates and influence water and nutrient distribution, shaping ecosystem structure and species composition
  • Aspect (north-facing vs. south-facing slopes)
  • Altitudinal zonation in mountain ecosystems

Ecosystem Stability vs Diversity

Biodiversity and Ecosystem Resilience

• Biodiversity encompasses genetic, species, and ecosystem diversity, contributing to overall ecosystem resilience and stability
• The diversity-stability hypothesis suggests that more diverse ecosystems are generally more stable and resistant to perturbations
  • Greater species richness provides more potential responses to environmental changes
  • Diverse ecosystems are less susceptible to invasive species
• Functional diversity, rather than species richness alone, is crucial for maintaining ecosystem processes and services
  • Different functional groups (pollinators, decomposers, predators) contribute to ecosystem stability
• Redundancy in functional groups can provide insurance against ecosystem collapse if some species are lost
  • Multiple species performing similar ecological roles

Ecosystem Dynamics and Stability

• Keystone species and ecosystem engineers play disproportionate roles in maintaining ecosystem stability and function
  • Removal of keystone species can lead to trophic cascades
• Trophic cascades demonstrate how changes in one trophic level can impact ecosystem stability through complex interactions
  • Reintroduction of wolves in Yellowstone National Park affected elk populations and vegetation structure
• Edge effects and habitat fragmentation can reduce ecosystem stability by altering species interactions and reducing population sizes
  • Increased edge habitat in fragmented forests affects microclimate and species composition
• Disturbance regimes (fire, flooding) can reset ecosystem succession and maintain habitat heterogeneity
  • Fire-dependent ecosystems (chaparral, savanna)
  • Flood pulse concept in river ecosystems