Nitrogen addition and experimental drought simplified arthropod network in temperate grassland

Changes in species interactions due to species loss are threatening ecological networks. To explore the responses of arthropod networks to global changes, we conducted a multifactorial field experiment in temperate grassland, in which nitrogen (N) deposition, drought and snowmelt timing were manipulated. We constructed modular networks for arthropod functional groups and assessed their complexity by connectance, interaction diversity and interaction strength. Specifically, the pattern of reduction of network complexity was different in N and drought conditions: (a) increased foliar N strengthened single pathway and weakened the net effect of other pathways in N treatment; (b) filtered plant species and changed micro-habitats in drought conditions. Whereas delayed snowmelt increased arthropod abundance only in early spring, but its interaction with N treatment or drought showed various impacts on functional groups. Therefore, it is suggested that the co-effect of multiple global change factors, occurring in different seasons, should be considered as a panorama.