AP Biology Notes: Biodiversity, Behavior, and Ecology

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Three Things to Know about Biodiversity: 

  1. A phylogenetic tree is a diagram indicating evolutionary relationships between taxa of organisms. It depicts an ancestral species with other species branching off from it. More closely related taxa are nearer to one another in the diagram. Phylogenetic trees are intended to show ancestral connections between species and some include information about the timescale of species divergences.
  2. A cladogram is typically a simplified version of a phylogenetic tree, which shows degrees of relatedness without necessarily offering information about the ancestral relationships between species or the timescale of divergences.
  3. Phylogenetic trees and cladograms can show anagenetic evolutionary changes (which do not lead to speciation), as well as cladogenetic evolutionary changes (which do).


Five Things to Know about Behavior: 

  1. Behaviors in organisms are responses that are triggered by stimuli (internal and external), and the behaviors that promote reproduction and survival are favored by natural selection.
  2. Innate behaviors are inherited and instinctive, whereas learned behaviors are acquired through interactions with the environment. The behaviors are not mutually exclusive.
  3. Cooperation involves organisms working together for mutual benefits, while competition involves organisms contending with each other for limited resources.
  4. Both environmental changes (such as deforestation and earthquakes) and invasive species (nonnative species introduced into an ecosystem) disrupt the balance of an ecosystem and affect the behavior of native populations.
  5. Communication among organisms involves the transmission of signals to produce changes in behavior that are vital to reproductive success, natural selection, and evolution.


Six Things to Know about Ecology: 

  1. Populations with infinite resources increase exponentially in a J-shaped curve. Usually, the environment has a carrying capacity, the maximum number of individuals it will support. Factors affecting population size can be density-dependent (overcrowding) or density-independent (a storm wipes out part of a population).
  2. Species that are r-selected have many offspring and provide almost no parental care (fish, insects). They succeed best in new habitats with many resources. K-selected species have few offspring and care for them for an extended period (elephants, humans). Those species do best in stable environments near carrying capacity.
  3. A biome is a climatic zone with associated animals and vegetation (tundra, desert, etc.). An ecosystem comprises a community of living organisms and its habitat. Different populations of organisms make up the community. Each organism is adapted to a specific niche or role.
  4. Food webs trace energy flow in a community. Different trophic levels consist of primary producers (plants), primary consumers (herbivores), secondary consumers (carnivores), and decomposers (bacteria).
  5. Materials such as water, nitrogen, carbon, and phosphorus travel through the environment and are recycled in biogeochemical cycles involving different life forms.
  6. Human activity has affected the environment significantly (e.g., ozone depletion, habitat destruction, and global warming).


Key Topics–Biodiversity, Behavior, and Ecology


Remember that the AP Biology exam tests you on the depth of your knowledge, not just your ability to recall facts. While we have provided brief definitions here, you will need to know these terms in even more depth for the AP Biology exam.

Biodiversity: Phylogenetic Trees

  • Monera: The kingdom of bacteria (no longer used under the three domain system)
  • Protoctista: Kingdom composed of eukaryotic microorganisms and their immediate descendants, such as slime molds and protozoa
  • Fungi: Kingdom of eukaryotic organisms that lack vascular tissues and chlorophyll, possessing chitinous cell walls; reproduction occurs through spores
  • Plantae: Kingdom containing all extinct and living plants
  • Animalia: Kingdom that includes all extinct and living animals
  • Domains: Biological classification of prokaryotes and eukaryotes into Bacteria, Archaea, and Eukarya
  • Archaea: Domain comprised of an ancient group of microorganisms (prokaryotes) that are metabolically and genetically different from bacteria; they came before the eukaryotes
  • Bacteria: Domain of single-celled organisms that reproduce by fission and can be spiral, rod, or spherical shaped; often pathogenic organisms that rapidly reproduce
  • Eukarya: Domain containing all eukaryotic organisms
  • Species: A group of populations that can interbreed to produce fertile, viable offspring
  • Genus: In taxonomy, a classification between species and family; a group of very closely related species (e.g., Homo, Felis)
  • Phylum: A category of taxonomic classification that is ranked above class; kingdoms are divided into phyla
  • Kingdom: Second-highest taxonomic classification of organisms, after domain

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Full Biodiversity, Behavior, and Ecology Notes

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