🌍 1. Island Theory and Species Richness

• Island Theory 🏝️ says: The number of species increases with the size of an island.
  • Big islands → many species
  • Small islands → fewer species
• Used for plants and animals, but… 🦠 Does it apply to microbes?
  • Microbes are microscopic and easily dispersed (dust, air, water).
  • Hypothesis: “Everything is everywhere.”
  • But: even microbes may have distinct distributions depending on niches and environmental constraints.
  • Testing this helps determine if ecological patterns found in large organisms also apply to microbes.

🌐 2. Biogeography

• Biogeography = distribution of life across space.
  • Example: palms grow in tropical zones, not in Denmark 🌴🇩🇰 (unless planted).
  • For microbes, it’s unclear whether the same patterns hold true.
• Understanding microbial biogeography matters for applications (e.g., biogas in Denmark vs China). If microbial communities differ, experimental results may not transfer directly between locations.

🧫 3. Niche Theory

• A niche is the environmental range where a species can survive and grow.
  • Factors: 🌡️temperature, 💧salinity, 🧂nutrient concentration, 🧪substrate type, and uptake capacity.
• Microbial niches are complex because microbes vary in metabolism and substrate use.
• Each species has an “optimal zone,” beyond which it can’t thrive.
• In diverse systems, many microbes coexist because they occupy different niches — splitting available resources (“resource partitioning”).

📊 4. Species Richness & Sampling

• Species richness = total number of distinct species in a system.
• More sampling → more species found (until a plateau is reached).
  • Called a rarefaction curve.
  • Works the same with DNA sequencing: more reads = more species discovered until saturation.

♻️ 5. Ecosystem Stability Concepts

Microbial communities, like macro ecosystems, can respond differently to disturbances (e.g., heat, antibiotics, pollution).

🔁 Key Properties:

1. Resistance
   • System remains unchanged despite disturbance.
   • e.g., gut microbiome stays balanced after mild stress.
2. Resilience
   • System changes but returns to original state afterward.
3. Functional Redundancy
   • Multiple species perform the same role.
   • So if one species dies, others fill the gap → function maintained.
4. Functional Shift
   • If both community and function change permanently.

🧠 Example: Human gut microbiome

• Healthy gut → high diversity → functional redundancy.
• Antibiotics or poor diet → loss of species → harder to recover.
• Lesson: maintain diversity for stability and health.

🛡️ 6. The Insurance Hypothesis

• High diversity = high “insurance.”
  • If one species fails, another can take over its role.
• 🌊 Example: Wastewater treatment plants
  • One nitrifying species → system collapse if it dies.
  • Many nitrifiers → stable process even under stress.
• Rule of thumb: more diversity → more stability → better ecosystem function.

🪸 7. Keystone Species

• A keystone species has a disproportionately large effect on ecosystem structure and function.
  • Removal causes major disruption.
  • Often not the most abundant species.
• 🦑 Examples:
  • Starfish controlling coral reef structure.
  • Nitrogen-fixing microbes → essential for nitrogen cycle.
  • Nitrifying bacteria → crucial for wastewater nitrification.
• Without them, nutrient cycles collapse.

🤝 8. Microbial Interactions

Microbes interact constantly — positively, negatively, or neutrally.

• Some bacteria even exchange electrons directly through conductive structures (nanowires).
• These interactions can be visualized via network analysis, where co-occurrence patterns reveal potential symbioses or competition.

🧬 9. From Genotype to Ecosystem

• Each microbe has:
  • Genotype (DNA) → determines expressed proteins → leads to a measurable phenotype.
• But ecosystems consist of many interacting phenotypes.
• The grand challenge: integrate molecular biology (genes, proteins, metabolites) with community ecology (interactions, networks).
• This is the frontier of microbial ecology research 🔬✨ — predicting ecosystem behavior from molecular data.

🧩 10. Big Picture

• Microbial ecosystems follow similar ecological laws as plant/animal systems but with added complexity due to:
  • Horizontal gene transfer
  • Tiny size and rapid evolution
  • Metabolic interdependence
• Understanding these patterns helps design stable engineered systems (biogas, wastewater, soil remediation) and protect natural ones.