Only 10% of energy passes to the next trophic level
Energy is lost as heat at each trophic level. Only ~10% transfers up. 1000 kcal of plants → 100 kcal of herbivores → 10 kcal of carnivores. This is why food chains are short.
🧬 Ecology
CHON = Life's building blocks
Most Common Elements in Living Things
Carbon, Hydrogen, Oxygen, Nitrogen — the elements of life
CHON makes up ~96% of all living matter. Carbon is the backbone of all organic molecules. The other elements form water, proteins, nucleic acids.
🧬 Ecology
Producers → Primary → Secondary → Tertiary
Food Chain Levels
Trophic levels in order — always start with producers
All 5 ecological relationships — who wins and who loses
Mutualism (+/+), Commensalism (+/0), Parasitism (+/−), Competition (−/−), Predation (+/−). Remember: the sign shows what each organism gains or loses.
+/+
Mutualism — both benefit (e.g., bees and flowers)
+/0
Commensalism — one benefits, other unaffected
+/−
Parasitism — parasite gains, host loses
−/−
Competition — both lose resources
+/−
Predation — predator gains, prey loses
🧬 Ecology
"Biome = Climate determines community"
What Defines a Biome
Biomes are defined by climate, not by species
Temperature and precipitation determine biome type. Tropical rainforests: hot + wet. Deserts: hot or cold + dry. Tundra: cold + dry. Species are a consequence, not the definition.
Nitrogen Cycle Steps
Nitrogen cycle: FAND — Fixation, Ammonification, Nitrification, Denitrification
Nitrogen Cycle Steps
Four key processes that cycle nitrogen through ecosystems
Fixation: N₂ gas → ammonia (by bacteria or lightning). Ammonification: dead organisms → ammonia (decomposers). Nitrification: ammonia → nitrites → nitrates (soil bacteria). Denitrification: nitrates → N₂ gas back to atmosphere (anaerobic bacteria).
F
Fixation — N₂ to ammonia
A
Ammonification — dead matter to ammonia
N
Nitrification — ammonia to nitrates
D
Denitrification — nitrates back to N₂
K vs r Selection
K-selected species: few offspring, lots of parental care (elephants). r-selected: many offspring, little care (insects).
K vs r Selection
Two reproductive strategies — opposite ends of the spectrum
r-selected (r for rate): many small offspring, little parental investment, short lifespan, opportunistic. Thrive in unstable environments. Bacteria, insects, weeds. K-selected (K for carrying capacity): few large offspring, heavy parental investment, long lifespan. Stable environments. Elephants, humans, whales.
Ecological Succession
Succession: Pioneer species → gradual change → Climax community
Ecological Succession
How ecosystems change and develop over time
Primary succession: bare rock → lichen → moss → grass → shrubs → forest. Starts where no soil exists (after volcano, glacier retreat). Secondary succession: soil already exists (after fire or flood) — faster. Pioneer species (lichen, moss) modify the environment enabling others to follow.
Carrying Capacity
Carrying capacity (K): maximum population an environment can sustainably support
Carrying Capacity
The ceiling on population growth — set by available resources
When population hits K, growth slows and levels off (logistic growth, S-curve). Below K: resources plentiful, population grows fast (J-curve). Limiting factors: food, water, space, predation, disease. Overshoot: population exceeds K → crash.
Food Chain vs Food Web
Food web vs food chain: chain = one path, web = all paths combined
Food Chain vs Food Web
The difference between a simplified model and the real picture
Food chain: linear sequence (grass → grasshopper → frog → snake → hawk). Simple but unrealistic. Food web: all feeding relationships in an ecosystem interlocked. More accurate. Remove one species from a web and the effects ripple through many chains.
Three types of close species interactions — who benefits and who doesn't
Mutualism: both benefit (clownfish + sea anemone, bees + flowers). Commensalism: one benefits, other unaffected (barnacles on whales, birds nesting in trees). Parasitism: one benefits, other harmed (tapeworm + host, mosquito + human). Parasites rarely kill hosts — better to keep them alive.
Mutualism
+/+ both benefit
Commensalism
+/0 one benefits, one unaffected
Parasitism
+/- one benefits, one harmed
Climate Change Ecology
Greenhouse effect: CO₂ traps heat → global warming → more extreme weather, rising seas
Climate Change Ecology
How the greenhouse effect drives ecological change
Sun's energy enters atmosphere as light, warms Earth, Earth radiates heat back as infrared. Greenhouse gases (CO₂, CH₄, N₂O) trap that infrared. More GHGs → more heat trapped → warming. Ecological effects: species range shifts, coral bleaching, phenological mismatches.