Life History Strategies
⭐ MacArthur & Wilson Model Core
7 Parameters
Life History Strategies: r-Selected vs K-Selected Species
Comparative matrix of reproductive investment, survivorship curves, body size, population fluctuation, and ecological stability.
| Trait / Parameter | r-Selected Species ('Opportunistic') | K-Selected Species ('Equilibrium') |
|---|---|---|
| Environmental Stability | Unstable, variable, unpredictable; frequent disturbances | Stable, predictable; resource-limited near carrying capacity (K) |
| Body Size & Lifespan | Small body size; short lifespan (< 1 year) | Large body size; long lifespan (decades) |
| Offspring Number & Frequency | Semelparous or massive clutches (thousands of tiny eggs/seeds) | Iteroparous (few offspring per reproductive event, repeated over lifetime) |
| Parental Investment / Care | Minimal to absent; high juvenile mortality | Extensive and prolonged parental care; high juvenile survival |
| Survivorship Curve Type | Type III (steep early mortality followed by high adult survival) | Type I (high survival through youth/adulthood; steep drop in old age) |
| Population Growth Model | Exponential / J-shaped boom-and-bust cycles | Logistic / S-shaped sigmoidal stabilizing near carrying capacity (K) |
| Representative Examples | Bacteria, weeds (dandelion), insects (aphids, locusts), oysters | Elephants, humans, whales, parrots, oak trees |
Strategy Comparison
Key Point
Strategy: r-Selected
Growth Mode: Exponential (J)
Survivorship: Type III
Parental Care: None
Key Point
Strategy: K-Selected
Growth Mode: Logistic (S)
Survivorship: Type I
Parental Care: Extensive
Ecological Succession
⭐ Ecosystem Dynamics Benchmark
5 Parameters
Ecological Succession: Primary vs Secondary Succession
Comparative matrix of starting substratum, pioneer species, soil presence, duration to climax community, and disturbance types.
| Feature | Primary Succession | Secondary Succession |
|---|---|---|
| Initial Starting Substratum | Sterile, barren area where NO living organisms or soil previously existed | Disturbed area where previous biological community existed but was partially destroyed |
| Pre-existing Soil & Propagules | Completely ABSENT (bare rock, hardened volcanic lava, sand dune, retreated glacier) | PRESENT (soil already formed with buried seeds, spores, mycorrhizae, dormant roots) |
| Pioneer Colonizers | Crustose lichens, mosses (acid-secreting weathering agents) | Fast-growing annual weeds, grasses, pioneer shrubs (seeds already in soil bank) |
| Time Duration to Climax Community | Extremely long (hundreds to thousands of years; e.g. 1000+ years to build soil) | Much faster (50 to 200 years to reach mature climax forest) |
| Triggering Events | Volcanic eruption creating new island, glacial retreat, newly deposited sand dune | Forest fire, hurricane blowdown, abandoned agricultural farmland, clear-cut logging |
Soil & Rate Comparison
Primary
Starting Soil: Absent
Pioneers: Lichens / Mosses
Timeline: 1000+ Years
Secondary
Starting Soil: Present
Pioneers: Grasses / Weeds
Timeline: 50-200 Years
Trophic Dynamics & Pyramids
⭐ High-Yield Ecology Trap
4 Parameters
Ecological Pyramids: Energy vs Biomass vs Numbers (Upright vs Inverted)
Diagnostic table of pyramid geometry across grassland, forest, open ocean, and parasitic ecosystems.
| Ecosystem | Pyramid of Energy | Pyramid of Biomass | Pyramid of Numbers |
|---|---|---|---|
| Grassland Ecosystem | Always Upright (10% trophic transfer law) | Upright (Producers >> Herbivores >> Carnivores) | Upright (Massive grass count supports few carnivores) |
| Pond / Marine Open Ocean | Always Upright (thermodynamic entropy rule) | INVERTED (Phytoplankton turnover is rapid; standing biomass < Zooplankton < Whales) | Upright (Millions of phytoplankton support fewer zooplankton) |
| Single Tree Ecosystem (Forest) | Always Upright | Upright (Single giant tree biomass outweighs all insects) | Spindle-shaped / Inverted (1 giant oak tree supports 100,000 herbivorous insects) |
| Parasitic Food Chain | Always Upright | Inverted / Spindle-shaped | INVERTED (1 Host deer supports hundreds of ticks, which support millions of protozoa) |
Inverted Pyramid Traps
Key Point
Parameter: Energy
Can Be Inverted: NEVER (Always Upright)
Rule: Second Law of Thermodynamics
Key Point
Parameter: Biomass
Can Be Inverted: YES (Open Ocean / Pond)
Rule: Rapid phytoplankton turnover
Key Point
Parameter: Numbers
Can Be Inverted: YES (Tree & Parasite Chains)
Rule: Few large hosts support many parasites
