Populations 101 welcomes absolute beginners into the living logic of population change, using vivid, real-world examples instead of jargon. Across twelve chapters, readers learn what a 'population' is, how births, deaths, arrivals, and departures shape growth and decline, and why time, space, and life history strategies matter. The book teaches how to observe and count responsibly, interpret simple graphs and maps, and recognize environmental drivers—from weather and resources to predators, partners, and people. By the end, readers can connect careful field notes to clear, humane decisions, and "read" population stories with confidence in parks, farms, cities, and coasts.