The Living World: Biodiversity
What you must know
Biodiversity has three levels: genetic, species, and ecosystem/habitat diversity. Understand species richness (count) versus species evenness (relative abundance) and how both shape diversity indices. Learn the types of speciation (allopatric via geographic isolation, sympatric without it) and extinction (background vs. mass). Know ecosystem services - provisioning, regulating, supporting, cultural - and the difference between generalist and specialist species. Island biogeography predicts richness from island size and distance to mainland. Ecological tolerance and range of tolerance explain why species distribution is limited by abiotic factors; indicator species signal environmental quality.
Traps
- Equating high richness with high diversity - evenness matters; a community dominated by one species can be less diverse despite many species.
- Confusing habitat diversity with species diversity.
- Misreading island biogeography: larger and closer = more species.
- Assuming specialists adapt better; generalists tolerate disturbance but specialists are more extinction-prone.
Worked example / rule of thumb
Two plots each have 5 species. Plot A: 90% one species, 2% each of four others. Plot B: 20% each of five species. Both richness = 5, but Plot B has higher evenness and therefore higher diversity. Rule: richness counts names; evenness weighs balance.