Abstract: In the interspecific relationship, one organism may supply the other with some material and energy produced in metabolism. This is the“costs” that one species paid for the another. The “costs” may be rewarded or not, rewarded more or less. The insect-pollinated plants need to pay pollination costs for pollen transfer. The pollination costs of the general insect-pollinated plants are confined to providing nectar sources and some structures favored for nectar collecting. In general, the plants needn't to provide nutrition and shelters to the pollinators. But the fig trees need to; otherwise they should have no seeds. The present paper dealt with the trees of dioecious Ficus pumila L.. It is showed that each gall tree bears about 43,000 pollinators(Wiebesia pumilae(Hill)Wieb.), and when the gall trees paid economically, the female trees were rewarded efficiently by the reasonable arrangement of inflorescences and flowers.

Key words: watershed, water quality, ecological health assessment, environment protection.