Different species have different potentials for population growth, known as life-history strategies. A species’ biology may place it anywhere along a continuum between two extremes—the r- and K-selected species.

From left: Norbert Rosing/National Geographic Stock; © Wayne Lynch/AGE fotostock; © Juniors Bildarchiv GmbH/Alamy; Tom Reichner/Shutterstock; John W. Bova/Science Source; Taylor S. Kennedy/National Geographic Stock