BIOL120 - Lecture 17: Ecology, Interactions & Biodiversity

Ecology Overview

  • Ecology = study of interactions, relationships, distributions of organisms and their environment (from Ancient Greek "oîkos" house + "logía" study)
  • Focus: processes influencing abundance & distribution; reciprocal ecological ↔ evolutionary change
  • Modern relevance: central to solving 21st-century environmental problems

Scales of Organization

  • Population: individuals of one species in same area, interacting
  • Community: multiple populations of different species interacting in same area
  • Ecosystem: flows of energy & materials among communities and abiotic environment

Species Interactions (General)

  • Effects coded as positive (+)(+), negative (−)(-), neutral (0)(0) at individual & population levels
  • Interaction types alter local distribution, abundance, dominance, and food-web structure

Direct Interspecific Interactions

  • Exploitation (+/−)(+/-): predation, herbivory, parasitism, pathogens
  • Competition (−/−)(-/-): use of shared, limiting resources
  • Facilitation: mutualism (+/+)(+/+), commensalism (+/0)(+/0)

Trophic Interactions (Energy Transfer)

  • Herbivory: plant defenses vs herbivore adaptations; recruits of third parties (e.g., ants)
  • Predation: regulates consumers, maintains diversity; predators can be omnivores
  • Parasitism / Pathogens: host usually survives initially; include endo/ecto parasites, brood parasites, disease vectors
  • Decomposition: nutrient cycling (detritivores, fungi, microbes)

Ecological Niches & Competition

  • Fundamental niche: nn-dimensional set of abiotic & biotic conditions for survival/reproduction without other species
  • Realised niche: portion actually occupied in presence of competitors, predators, etc.
  • Outcomes:
    • Competitive exclusion if niches completely overlap
    • Resource partitioning (spatial, temporal, trophic) reduces overlap (e.g., Anolis lizard micro-habitats; forest geophytes flowering before canopy closure)

Facilitation & Indirect Effects

  • Mutualism: pollination, seed dispersal, nitrogen fixation, mycorrhizae
  • Commensalism: e.g., cattle egrets following livestock, epiphytes on trees
  • Indirect facilitation: one species alters environment benefiting others (e.g., Juncus reduces soil salinity)
  • Ecosystem engineers modify abiotic environment (beavers, dung beetles)

Biodiversity Levels

  1. Genetic diversity: variation within/between populations → adaptive capacity
  2. Species diversity: number of species in ecosystem/biosphere → extinction cascades
  3. Ecosystem (trophic) diversity: variety of ecosystems & energy pathways
  4. Interaction diversity: diversity of species interactions; emerging metric for ecosystem stability

Human Impacts

  • Anthropogenic drivers: habitat loss, agriculture, urbanisation, pollution, climate change, invasive species
  • Result: unprecedented global decline in biodiversity & ecosystem function (IPBES 2019)
  • Human disturbance reshapes communities, alters interactions, and disrupts ecosystem services

Key Takeaways

  • All organisms in a community are linked by direct or indirect interactions
  • Interactions can be (+)(+), (−)(-), or (0)(0) and determine community structure
  • Predation, herbivory, competition, and facilitation are core processes shaping niches and biodiversity
  • Biodiversity comprises genetic, species, ecosystem, and interaction dimensions; loss at any level weakens resilience
  • Understanding ecological interactions is essential for mitigating human impacts and conserving biodiversity