Explain carrying capacity and limiting factors, and interpret a population graph showing exponential growth, leveling off, or a population crash.
A population is all the members of one species living in a given area. Populations grow when births and arrivals outnumber deaths and departures. With unlimited food, space, and no predators, a population can grow exponentially, meaning it grows faster and faster, producing a graph that curves sharply upward. Real environments, though, are not unlimited: limiting factors like food, water, space, disease, and predators eventually slow growth down.
The largest population size an environment can support long-term is called its carrying capacity. As a population approaches carrying capacity, growth typically levels off, producing an S-shaped graph instead of an ever-rising curve. If a population overshoots its carrying capacity, for example after a run of good weather produces extra food temporarily, resources can run short and a sharp population crash can follow, dropping the population back down, sometimes below its original level, until conditions stabilize again.
Mastery looks like: They can read a population graph and correctly identify exponential growth, leveling off near carrying capacity, and a population crash, explaining a likely cause for each.
Common stumbles: Assuming populations always grow in a smooth, ever-rising line; describing a crash as random instead of connecting it to a specific limiting factor being exceeded.