Biohistory Journal, Autumn, 2005

Research: Index > The meaning of the existence of predators in the natural world

The meaning of the existence of predators in the natural world

Takayoshi Nishida, Kyoto University Graduate School of Agriculture

In a Southeast Asian botanical garden, I found a one-to-one predator-prey relationship established in an independent environment. The stinkbug eats the fruit of the Hydnocarpus anthelmintica Pierre, a fruit tree used in Chinese herbal medicine, and the predator stinkbug eats only that stinkbug. In ordinary conditions, very few stinkbugs become prey, and their deaths through predation amount to only a few percentage points of the population. This is in accordance with the conventional wisdom of ecology.     We then raised the ratio of the predators and observed the result. This developed the activity of evasion by the prey, and there was almost no change in the death rate. The success rate for reproduction fell by half. A decline in the number born has the same meaning for the ecology as the death of most of the prey. This indeed was the effect of a natural enemy.

The prey that encounters the predator will try to survive even at the expense of reproduction. The ecosystem is the result of this relationship between species, and the existence of the predator is important for maintaining the balance of nature, even when the predator does not feed on the prey. Do the locusts of the rice paddies avoid reproductive opportunities so they will not be eaten by frogs and birds? A study of this question is underway right now.

Takayoshi Nishida The raxa nishidai lives exclusively on the shield bug, but successfully captures one while hunting only once every several hundred times.     Completed work for a doctorate at Kyoto University’s Graduate School of Agriculture in 1988. After serving as an associate professor at the entomology lab at the Kyoto University Faculty of Agriculture, he has since 1998 been an assistant at the Kyoto University Graduate School of Agriculture, Division of Applied Biosciences/Plant Protection Section

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