Every ecosystem has a specific carrying capacity for plants, which provides the food source for animals. Let’s consider an example: a deer requires 2 kg of grass and grains annually to sustain itself, while a mouse needs 1/2 a kilogram of the same resources. If a square mile of grassland can produce 10 kilograms of grass and grains per year for animal consumption, then only 5 deer (10 kg / 2 kg) can find enough resources to survive. Additionally, due to their smaller size and lower resource requirements, 20 mice (10 kg / 0.5 kg) can thrive in the same area.

The concept is simple: larger mammals need more sustenance to meet their energy needs. For instance, an elephant consumes a significantly greater amount of food compared to a human because of its larger size.

This principle also extends to carnivores that prey on herbivores. In our example, if the mile-square section of land can sustain 5 deer, and a wolf requires 2 1/2 deer annually to survive (note that these numbers are simplified for illustrative purposes), then only two wolves can find sufficient prey to survive in that specific area. It’s important to note that these calculations are not precise reflections of real-world dynamics but rather serve as a simplified explanation of the concept.