Ecology Of Riparian Arthropod Communities Of The Three Gorges Reservoir

The water level of the Three Gorges Reservoir rose to 175 m in 2010 since fully operational of the Three Gorges Dam.The Three Gorges Reservoir regulates its water level by impounding in winter and draining in summer.Therefore,the terrestrial ecosystem between 145 m and 175 m in the upstream of the Yangtze River and its tributaries was flooded,forming a new riparian zone with an area of 348.93 km~2 and a vertical height of 30 m.Riparian zones are important ecological interfaces between aquatic and terrestrial ecosystems.They are biodiversity-rich.In this paper,we samples riparian arthropods from the whole Three Gorges Reservoir and its typical areas,studied the arthropod diversity and its distribution patterns from the longitudinal,vertical and temporal scales,and identified the key factors influencing arthropod diversity in riparian zone.Finally,we illustrated the effects of impoundment on riparian arthropods by comparing arthropod communities of natural and regulated sections.The main conclusions of this paper are as follows:The composition and structure of riparian arthropod community showed apparently changes along the longitudinal gradient.There were significant differences in arthropod community composition between the midstream and the upstream.Riparian arthropod community composition of the Yangtze River is also significant different from its tributaries.The longitudinal gradient had a significant effect on riparian arthropod community of The Three Gorges Reservoir.The abundance and richness of riparian arthropods was highest in midstream,and the biomass decreased from upstream to downstream.The abundance,richness and biomass of riparian arthropods in tributaries were higher than those in the Yangtze River.Flooding depth determined the arthropod communities and its distribution pattern along longitudinal gradient.The community composition and structure of riparian arthropods were significantly varied with elevation.The richness and abundance of arthropods and the relative abundance of omnivores and detritivores increased with the elevation,while the predators decreased with the elevation.Flooding duration is the main factor affecting the community structure and distribution pattern of riparian arthropods.Riparian arthropod communities can be established rapidly after the flood recedes.Riparian arthropods may come from aquatic,terrestrial and upstream ecosystems.Of these,93 percent of arthropod species were from terrestrial ecosystems,6 percent from aquatic ecosystems,and 65 species may only migrated from associated terrestrial ecosystems.The richness and abundance of arthropods reached the highest level on the10th day after the flood recedes,and then decreased slowly.Most of the pioneer species of riparian arthropods were predatory beetles,and their relative abundance decreased at first and then increased.Herbivores showed an opposite tendencies.The richness and abundance of riparian beetles in the frequently flooded areas were higher than those in the non-flooded areas.There was a significant positive correlation between the flooding time and the richness and abundance of riparian beetles.Flood disturbance induced by the Three Gorges Reservoir was beneficial to the riparian beetles on a long term effects and unfavorable on a short period.Plant communities in riparian zone of the Three Gorges Reservoir had an large effect on the arthropod community.Plant community composition can reflect the community characteristics of riparian arthropods better than plant structure and diversity.Under different degrees of flooding stress,the different response of plants and arthropods lead to obvious spatial variation of the effects of plant communities on arthropod communities.Plant community composition in upstream and non-flooded areas could accurately predict the riparian arthropod community of the Three Gorges Reservoir.Plant community heterogeneity and productivity in midstream and downstream of the Three Gorges Reservoir and the regions with low elevation had a significant positive effect on the richness and abundance of riparian arthropods.The impoundment of the Three Gorges Reservoir changed the habitat conditions of riparian arthropods,resulting disappearance of many arthropod species.The community composition,structure and distribution pattern of arthropods changed significantly.More than 20%of taxa disappeared,indicating that arthropod communities were inclined to simplification due to the impoundment of the Three Gorges Reservoir.Impoundment increased total richness and abundance of riparian arthropods.Omnivores showed a negative response to impoundment,as their abundance in the riparian habitat in the regulated section was significantly lower than in the natural section.Predators,detritivores,and herbivores showed a positive response,but omnivores did not.Our results also showed impoundment had a strong effect on the spatiotemporal variability of community composition of riparian arthropods.These results indicated that impoundment lowered the species diversity and that uplands might become a permanent habitat for riparian species under the new environmental conditions.Arthropod diversity is an important component of riparian biodiversity and plays critical ecological functions in riparian ecosystems.The research on riparian arthropod communities can provide basic theoretical support for riparian biodiversity conservation and restoration,and also is important for the integrated ecosystem management of riparian zones and the safe operation of the Three Gorges Reservoir.