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AP Course

AP Biology

Updated for the AP Biology framework effective fall 2025, with concept lessons, data reasoning, quizzes, and practice problems.

Explore life from molecules and cells to evolution and ecosystems through the official AP Biology unit sequence.

Lessons
Structure of Water and Hydrogen BondingElements of LifeIntroduction to MacromoleculesCarbohydratesLipidsNucleic AcidsProteinsCell Structure and FunctionCell SizePlasma MembraneMembrane PermeabilityMembrane TransportFacilitated DiffusionTonicity and OsmoregulationMechanisms of TransportCell CompartmentalizationOrigins of Cell CompartmentalizationEnzymesEnvironmental Impacts on Enzyme FunctionCellular EnergyPhotosynthesisCellular RespirationCell CommunicationIntroduction to Signal TransductionSignal Transduction PathwaysFeedbackCell CycleRegulation of Cell CycleMeiosisMeiosis and Genetic DiversityMendelian GeneticsNon-Mendelian GeneticsEnvironmental Effects on PhenotypeDNA and RNA StructureDNA ReplicationTranscription and RNA ProcessingTranslationRegulation of Gene ExpressionGene Expression and Cell SpecializationMutationsBiotechnologyIntroduction to Natural SelectionNatural SelectionArtificial SelectionPopulation GeneticsHardy–Weinberg EquilibriumEvidence of EvolutionCommon AncestryContinuing EvolutionPhylogenySpeciationVariations in PopulationsOrigins of Life on EarthResponses to the EnvironmentEnergy Flow Through EcosystemsPopulation EcologyEffect of Density on PopulationsCommunity EcologyBiodiversityDisruptions in Ecosystems
Quizzes
Practice Problems Lab design, data analysis, and FRQ practice resources can be added here.

AP Biology · Unit 8 · Topic 8.3

Population Ecology

Energy flow, interactions, population limits, and disturbance shape ecological patterns across scales.

1. Topic Lens

Population Ecology is studied through ecology. Connect the system boundary, interacting parts, and measurable evidence before applying a formula.

\[\frac{dN}{dt}=rN\left(1-\frac{N}{K}\right)\]

2. Why the Formula Works

The relationship is built from definitions and conservation reasoning:

  1. Exponential growth gives the baseline rate rN.
  2. Resource limitation is represented by the remaining-capacity fraction 1-N/K.
  3. Multiplication makes growth approach zero as N approaches carrying capacity K.
\[\text{growth}=\text{intrinsic growth}\times\text{unused capacity}\]

3. Detailed Visual Model

Pixel diagram for Population EcologyOriginal schematic connecting Population Ecology to Ecology.
Population Ecology: an original pixel-style model. Use it as a schematic, not a literal scale drawing.

4. Worked Example and Lab Link

For r=0.4/year, K=1000, and N=500, what does the logistic model predict for dN/dt?

Answer: The predicted growth is 0.4(500)(1-0.5)=100 individuals per year.

Investigation idea: Use quadrat samples from contrasting microhabitats to estimate abundance and quantify sampling uncertainty.

Common trap: Carrying capacity can change; it is not a permanent maximum, and energy is not recycled like matter.

Checkpoint · Topic 8.3

Explain how population ecology supports or limits this conclusion: The predicted growth is 0.4(500)(1-0.5)=100 individuals per year.

Official curriculum reference: College Board AP Biology course page. The explanation and worked example are independently written for this study site.