SAT / PSAT
SAT / PSAT Prep
History & Social Science
AP World History AP US History AP European History AP Human Geography AP US Government & Politics AP Psychology AP Macroeconomics AP Microeconomics
English
AP English Language & Composition AP English Literature & Composition
Math & Computer Science
AP Calculus AB/BC AP Precalculus AP Statistics AP Computer Science A AP Computer Science Principles
Sciences
AP Biology AP Chemistry AP Environmental Science AP Physics 1 AP Physics 2
World Languages & Arts
AP Spanish Language AP Art History AP Music Theory Start studying →
Unit 8 · Ecology Flashcards Cheat Sheet Essentials Visual Review MC Practice FRQ Practice

AP Biology Unit 8 Visual Review

A topic-by-topic visual walkthrough of Ecology — behavior, energy flow, population and community ecology, biodiversity, and disruptions to ecosystems.

← Back to Unit 8 hub
TOPIC 8.1 Responses to the Environment Innate vs. learned behavior Innate — instinctive, genetically programmed, present from birth (reflexes, fixed action patterns, migration). Learned — modified by experience (habituation, imprinting, conditioning, trial-and-error). Movement responses Taxis — directed movement toward or away from a stimulus (e.g., a moth toward light = positive phototaxis). Kinesis — a change in the SPEED or turning of movement, but not directed (e.g., pill bugs in dry vs. moist areas). Communication & signaling Animals signal with sound, chemicals (pheromones), visuals, and touch — for mating, warning, and finding food (e.g., the honeybee "waggle dance"). Cooperation & rhythms Cooperative behavior (herding, cooperative hunting, altruism) can raise survival. Circadian rhythms are internal ~24-hour cycles cued by light. Behavior is shaped by natural selection Behaviors that improve survival and reproduction are favored and passed on. Both innate and learned responses help organisms respond to changing conditions and maintain homeostasis. Organisms respond to their environment with innate and learned behaviors shaped by selection. The Review Hub · AP Biology Unit 8 TOPIC 8.2 Energy Flow Through Ecosystems tertiary secondary consumers primary consumers herbivores producers (autotrophs) only ~10% of energy passes up each level The 10% rule Only about 10% of the energy at one trophic level is passed to the next. The other ~90% is lost as heat, used for life processes, or never eaten. Who's who Producers make their own food (photosynthesis). Consumers eat others. Decomposers (bacteria, fungi) recycle nutrients from dead matter back to producers. Energy flows, matter cycles Energy enters as sunlight and EXITS as heat — it flows one way and is never recycled, so ecosystems need a constant energy input. Because so much energy is lost, food chains rarely have more than 4–5 levels. Gross primary productivity = total energy fixed; net (NPP) = what's left after producers' own respiration. Only ~10% of energy transfers up each trophic level — which limits food chains to a few links. The Review Hub · AP Biology Unit 8 TOPIC 8.3 Population Ecology — Growth Models K exponential (J) logistic (S) population size time → Exponential growth (J-curve) Unlimited resources → the population grows faster and faster with no ceiling. Rare and temporary in nature (new habitat, few predators, abundant food). Logistic growth (S-curve) Growth slows as resources run low and levels off at the carrying capacity (K) — the max population an environment can sustain long-term. The realistic model. r-selected vs. K-selected species r-strategists: many offspring, little care, short lives, boom-and-bust (insects, weeds, bacteria). K-strategists: few offspring, lots of care, long lives, stable near K (elephants, humans, whales). Real populations follow the logistic S-curve, leveling off at carrying capacity (K). The Review Hub · AP Biology Unit 8 TOPIC 8.4 Density & Population Limits Density-DEPENDENT stronger as the population gets denser • Competition for food, water, space • Predation (predators focus on dense prey) • Disease & parasites (spread faster) • Accumulation of waste/toxins These factors regulate the population TOWARD its carrying capacity (K). Density-INDEPENDENT affect the population regardless of density • Natural disasters (fire, flood, drought) • Extreme weather & temperature • Seasonal changes • Human habitat destruction A flood kills the same FRACTION whether the population is large or small. How to tell them apart Ask: "Does crowding make this factor stronger?" If YES → density-dependent (biological: competition, disease). If NO → density-independent (usually physical/environmental). Both together shape real population sizes over time. Density-dependent factors intensify with crowding; density-independent ones don't. The Review Hub · AP Biology Unit 8 TOPIC 8.5 Community Ecology SPECIES INTERACTIONS (+ = helped, − = harmed) Competition (− / −) Both species need the same limited resource, so both are harmed. Predation (+ / −) One organism (predator or herbivore) eats another — drives defenses & mimicry. Mutualism (+ / +) Both species benefit — e.g., bees & flowers, gut bacteria & you. Commensalism (+ / 0) One benefits, the other is unaffected — e.g., barnacles on a whale. Parasitism (+ / −) Parasite benefits at the host's expense — e.g., ticks, tapeworms. Niche & keystone A niche is a species' role. A keystone species has an outsized effect (e.g., sea otter). Ecological succession Communities change over time. Primary succession starts on bare rock (no soil) with pioneer species like lichens; secondary succession follows a disturbance (fire) where soil remains — it's faster. Species interact through competition, predation, and symbiosis — shaping the whole community. The Review Hub · AP Biology Unit 8 TOPIC 8.6 Biodiversity THREE LEVELS OF BIODIVERSITY Genetic diversity Variety of alleles WITHIN a species. More alleles = a better chance of surviving disease or change. Species diversity Number AND evenness of species in a community. Higher diversity = more stable ecosystem. Ecosystem diversity Variety of habitats and ecosystems in a region — forests, wetlands, reefs, grasslands. Why biodiversity matters Diverse ecosystems are more stable and resilient, and provide "services": food, medicine, clean water, pollination. Keystone species A single species that holds a community together. Remove it (e.g., sea otters, wolves) and the whole system collapses. The link back to evolution Genetic diversity is the raw material for natural selection. A population with more diversity has more ways to adapt when the environment changes — tying ecology directly back to Unit 7. Biodiversity (genetic, species, ecosystem) makes ecosystems more stable and resilient. The Review Hub · AP Biology Unit 8 TOPIC 8.7 Disruptions in Ecosystems Invasive species Non-native species with no natural predators outcompete natives (e.g., zebra mussels, kudzu, Burmese pythons). Human impact Habitat destruction, deforestation, pollution, overharvesting, and fragmentation of habitats. Climate change Rising CO₂ and temperature shift ranges, melt ice, and acidify oceans — stressing coral reefs and polar species. How ecosystems respond A disruption to any one part ripples through the whole system. Removing a keystone species can collapse a community. Ecosystems can sometimes recover through succession, or shift permanently to a new stable state. Populations may adapt (if they have the genetic diversity and time), migrate to new areas, or go extinct. Conservation matters Protecting habitats, controlling invasive species, and preserving genetic diversity all help ecosystems stay resilient — because a diverse ecosystem is far better equipped to absorb and recover from disruptions. Invasive species, human impact, and climate change disrupt ecosystems — diversity aids recovery. The Review Hub · AP Biology Unit 8
1 / 7

How to use the visual review

Spend 30 seconds per slide before clicking next. Look at the diagram, then ask yourself: "Could I draw this from memory and explain it?"

Use the fullscreen button () on desktop for the best experience. Use arrow keys to navigate. Tap "Show all slides" to jump around.

This is great for review the night before the exam — fast, visual, and covers everything you need to remember about Unit 8's ecology content.