Ecology — BIOL 3340 cheat sheet · Bragg · UNomaha Fall 2026

Hierarchy

Organism → population → community → ecosystem → biome → biosphere.
Adaptation = inherited (NS-produced); Acclimation = reversible within lifetime; Plasticity = one genotype, many phenotypes.

Climate

• Insolation max at equator; tilt 23.5° → seasons.
• Hadley cell: equator rainforest, ~30° desert.
• Coriolis: deflects winds R (N hem), L (S hem).
• Rain shadow: rain on windward, dry leeward.
• Albedo = reflected fraction; snow ~0.8.
• Greenhouse gases: H₂O, CO₂, CH₄, N₂O, O₃.

Aquatic

• Ice floats — water densest at 4 °C.
• Lake layers: epilimnion (warm, O₂↑) · thermocline (steep T drop) · hypolimnion (cold, low O₂).
• Spring/fall turnover: when surface = 4 °C, wind mixes.
• Oligotrophic = nutrient-poor; eutrophic = nutrient-rich.
• Salinity ppt: fresh <0.5 · brackish 0.5–30 · marine 30–37.
• Carbonate: CO₂ + H₂O ⇌ HCO₃⁻ + H⁺ ⇌ CO₃²⁻ + 2H⁺ (pH ~8.1). Acidification ↓ CO₃²⁻ for shells.

Soil

• Horizons: O · A · E · B · C · R.
• Texture: sand+silt+clay; loam = best.
• CEC = cation exchange capacity (clay+humus hold cations).
• Field capacity → wilting point = plant-available water.
• CLORPT: Climate, Organisms, Relief, Parent material, Time.

Plant adaptations

Path	Where	Trade-off
C3	Most temperate	Cool/wet; loses CO₂ to photoresp.
C4	Tropical grasses, corn	PEPC concentrates CO₂; hot/sunny.
CAM	Cacti, agave	Stomata open at night; deserts.

Animal thermal

• Ectotherm body T = environment; behavioral.
• Endotherm generates heat metabolically.
• Bergmann: bigger in cold (less SA:V).
• Allen: shorter appendages in cold.
• Countercurrent: antiparallel arteries+veins recycle heat.

Population growth

• Density · dispersion (uniform, random, clumped).
• Survivorship: I humans · II birds · III fish.
• Exponential dN/dt = rN (J-curve, no limits).
• Logistic dN/dt = rN(1−N/K) (S-curve, → K).
• r-selected: small, many offspring, disturbed.
• K-selected: large, few offspring, stable.

Regulation

• Density-dependent: competition, disease, predation.
• Density-independent: weather, fire, floods.
• Allee effect: per-capita rate ↓ at very low N.
• Metapopulation: source-sink connected by dispersal.
• Semelparity 1× → die · Iteroparity repeated.

Competition

• Exploitation indirect via resource · interference direct.
• Gause: identical niches can't coexist.
• Fundamental → Realized niche (after competition).
• Resource partitioning (MacArthur warblers).
• Character displacement: traits diverge in sympatry.
• Lotka-Volterra: dN₁/dt = r₁N₁(K₁−N₁−α₁₂N₂)/K₁.

Predation

• FRs: I linear · II saturating · III sigmoid (switching).
• Optimal foraging: max E gained / time.
• Lynx-snowshoe hare ≈10 yr cycle.
• Aposematism warning · Batesian tasty mimic of toxic · Müllerian toxic mimic toxic.
• Plant defenses: tannins, alkaloids, glucosinolates.
• Parasitoid = larva kills host (wasps).

Mutualism

• +/+; obligate or facultative.
• Mycorrhizae: arbuscular (in cells, ~80% plants) · ecto (sheath, trees).
• Pollination syndromes: bee, hummer, bat, fly, wind.
• Coevolution — reciprocal change.
• Coral-zooxanthellae provide ~90% energy; bleaching = expulsion.

Community

• S=richness; evenness=balance; H'=−Σpᵢln(pᵢ).
• α/β/γ: within / turnover / regional.
• Keystone = big effect, low abundance (Pisaster).
• Engineer = physical modifier (beavers).
• Top-down vs bottom-up control; trophic cascade (wolves → elk → willow).

Succession + FIRE (Bragg)

• Primary bare substrate · secondary soil intact.
• Pioneer → climax (or non-equilibrium).
• Models: facilitation · inhibition · tolerance.
• IDH: diversity peaks at moderate disturbance.
• Pyrogenic: serotinous cones (jack/lodgepole), thick bark (oak/ponderosa), basal sprout.
• Tallgrass prairie: 3–5 yr fire return; suppresses woody, recycles N, stimulates C4.
• Loess Hills (W. Iowa) prairie — fire-dependent.
• Bragg: prescribed-burn timing/freq experiments at Glacier Creek Preserve.

Ecosystem flow

• GPP − resp = NPP; 10% rule limits chains to 4–5.
• Pyramid: energy always ↓; biomass occasionally inverted (open ocean).
• Detritus chains often >50% energy flow.
• N: fix → ammonify → nitrify (NH₄→NO₂→NO₃) → denitrify.
• P: NO atmosphere; rock weathering → soil → biota.
• Liebig: limited by minimum nutrient.
• Eutrophication: N/P → bloom → hypoxic.
• Biomagnification: DDT, Hg up food chain.

Biomes

Biome	Climate
Trop. rainforest	Warm + wet year-round.
Trop. savanna	Warm, seasonal rain; fire.
Desert	Low precip; hot or cold.
Temperate grassland (NE!)	Hot summer, cold winter, mod rain. Fire.
Temp. decid. forest	4 seasons, 75–150 cm rain.
Boreal/taiga	Long cold winter; conifers.
Tundra	Permafrost; mosses.
Mediterranean	Hot dry summer, mild wet winter; fire.

Conservation

• Island biogeography: S = balance of immigration (↓ distance) + extinction (↓ area).
• S = cA^z; doubling area +10–25% S.
• Fragmentation → edge effects, gene flow ↓.
• MVP: smallest population with ~95% persistence.
• Hotspot = high endemism + threat.
• Sixth extinction: human-driven, ~100–1000× background.