Distinguish genetic, species, and ecosystem biodiversity, and calculate species richness while reasoning about evenness between two sampled communities.
Biodiversity operates at three levels. Genetic diversity is the variation within a single species (different corn varieties, different human blood types) and matters because it gives a population options for surviving disease or change. Species diversity is the variety of species in an area. Ecosystem diversity is the variety of habitats and ecosystem types across a region. All three matter, and a place can be rich in one while poor in another.
Two communities can have the exact same species richness (the simple count of different species present) yet feel very different in diversity because of evenness -- how evenly individuals are spread across those species. A forest with 40 oaks, 5 maples, and 5 birches has the same richness (3 species) as a forest with 17 oaks, 16 maples, and 17 birches, but the second forest is more genuinely diverse in practice, since no single species dominates it.
Mastery looks like: They can calculate species richness from a sample, reason about evenness between two communities with equal richness, and correctly classify an example into genetic, species, or ecosystem biodiversity.
Common stumbles: Confusing richness (number of different species) with total population size (number of individuals); assuming more individuals automatically means more diversity.