Unit 02 · Biodiversity & Populations
A community is more than a species list. This unit separates richness from evenness, puts a number on diversity with the Simpson and Shannon indices, and tracks how populations grow — the runaway curve of exponential growth against the S-shaped logistic curve that levels off at carrying capacity. You’ll sort r-strategists from K-strategists, read survivorship curves, and estimate a population you can’t count directly by mark and recapture in the field. Mastery means you can measure the health of a community and predict where its populations are headed.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Species richness & evenness | Confuses how many species there are with how evenly they’re spread. | Counts species (richness) but ignores whether one dominates. | Distinguishes richness from evenness and explains why both shape a community’s biodiversity. |
| Diversity indices (Simpson & Shannon) | Cannot put a number on diversity at all. | Plugs data into an index but cannot interpret the result. | Calculates a Simpson or Shannon index from survey data and explains what a higher value means. |
| Population growth models | Assumes every population just keeps growing. | Names exponential and logistic growth but cannot tell which fits a dataset. | Distinguishes exponential from logistic growth and predicts which a population follows from its limiting factors. |
| Carrying capacity & life strategies | Has no sense of an environment’s population limit. | Defines carrying capacity but cannot link it to r- and K-strategists. | Uses carrying capacity (K), survivorship curves, and r- vs K-selection to predict a population’s trajectory. |
| Field technique (quadrat & mark-recapture) | Places the quadrat carelessly or botches the recapture count. | Runs the survey but records or tags samples inconsistently. | Runs a clean biodiversity survey and estimates population size by mark-recapture, defending the sampling design. |
| Integration (cross-domain) | Treats the science as isolated facts; makes no cross-domain connection. | Names a link to history, reading, or writing but cannot defend why it matters. | Connects the unit to its anchor across History · Reading · Writing (plus chosen electives) and defends why the connection matters. |
“The pond had high richness but low evenness — one duckweed swamped everything, so the Shannon index came out low. I estimated the frog population by marking forty, releasing them, and recapturing: the fraction that were tagged scales up to the whole. It’s leveling off near carrying capacity, not still climbing.”
“There were a lot of species, so diversity is high, I guess. The population just grows until… something? I’m not sure how you’d count all the frogs.”
You demonstrate this unit through a quadrat biodiversity survey and a mark-recapture population estimate, computing a diversity index and defending your sampling design aloud — not a multiple-choice test. A criterion counts as mastered only when you can both gather clean field data and justify the population math behind it. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.