Response of species diversity to human periodic activities and its forecast
人类周期性活动对物种多样性的影响及其预测

A greatest threat to species diversity worldwide is the loss of suitable habitat. Human activities affect species dynamics and further influence species diversity by changing habitat. We have extended Tilman's n-population model to multi-time scale n-population competition model at the first time by introducing periodic time function, which has been used to simulate and forecast the responses of species diversity to human periodic activities at different time scales. For simplification, we have only simulated the response of species diversity to human activities at millenary scales and carried out a preliminary study on the quantitative forecast of species diversity. The results of simulation and forecast show that: (1) during the first 1/4 cycle (i.e., habitat decreasing), the effects of human-caused habitat loss on superior competitors are more significant than inferior ones. Furthermore, the adaptabilities of inferior competitors to habitat destruction are much stronger than those of superior ones; (2) during 1/4 to 1/2 cycle (i.e., habitat being restored, but decreasing in total area contrast to the initial), the originally most superior competitors such as species 1 and 2 are not sensitive to habitat restoration. Habitat restoration is propitious to the abundances of original superior competitors such as species 3, 4 and 5 to recover and increase, and makes the original inferior competitors such as species 6,7,8,9 and 10 decline; (3) during the former half of a cycle, the amplitudes of the responses of species dynamics are smaller than those during the second half of a cycle. The effects of human periodic activities on species abundance in the process of decreasing in habitat are less significant than those in the process of increasing in habitat; (4) during a full cycle, the responses of species dynamics also oscillate quasi-periodically due to periodic human activities. No species will die out, but the species abundances and the competitive rank will change a lot, which lead to the change of the metapopulation structure; (5) when human periodic activities only persist for 1/4 cycle, the first strongest and second strongest species will go extinct, while other species will oscillate quasi-periodically with small amplitudes. Finally, we have simulated the effects of human periodic activities of different intensities and the results indicate that the higher the intensity of human activities is, the larger the amplitude of species response is. Moreover, the stronger the species is, the bigger the amplitude of species dynamics response is.