Competing, helping and harming

Besides eating one another, organisms also compete for shared resources: food, water, physical space or sunlight.

Competition isn't simply bad. It controls population size and keeps the ecosystem balanced. Without it, one species could multiply too much and push everything else out. Many deer and limited grass, for example, means the deer population can't grow without end.

There are other relationships too, and the book sorts them by who gains and who loses.

Mutualism: both benefit. Honeybees and flowers: the bee gets nectar, and the flower gets pollinated. Both win.

Commensalism: one benefits and the other is unaffected. An orchid growing on a tree branch gets physical support; the branch is neither helped nor harmed.

Parasitism: one benefits and the other is harmed. Ticks on a dog feed on its blood and benefit; the dog gets itchy, irritated skin.

All of these are part of the web of life. The Indian wildlife biologist Asir Jawahar Thomas Johnsingh helped us see forests through animals' eyes and pioneered the study of wildlife with modern tracking. Working in Bandipur National Park, Karnataka, he showed that predators such as tigers and leopards rely on prey like deer and wild boar, and that a healthy prey population is the key to predator survival. To save the tiger, you have to save the deer, and the grass the deer eat.