Effects Of Landscape Compositions On Predator-prey Qualitative Food Web In Wheat And Cotton Fields

In this study,we choose wheat and cotton in northern China as the research crop,system monitoring the main preys and predators in those two field.Four landscape scales of the selected test sites are 0.5 km,1 km,1.5 km,and 2 km,we make a detailed investigation about planting situation and all kinds of noncrop habitat distribution.The qualitative food network of predators and preys was constructed and the effects of landscape structure on the qualitative food network were analyzed.The results of the study are as follows:The increase of wheat proportion in northern China will lead to interaction richness,linkage density and connectance reduced,this is associated with a decrease in the habitat diversity of natural enemies.Meanwhile,the woodlot and other crops have a positive correlation with interaction richness,linkage density and connectance on all four scales.This indicates that diverse habitats,such as woodland,wasteland and grassland,will provide food and shelter for natural enemies,which will be conducive to the complexity and stability of food network.Generality under the smaller landscape scale(0.5,1.0 km),vulnerability to the larger landscape scale(1.0,2.0 km)was inversely proportional to the proportion of wheat planting ratio,and proportional to the proportion of woodlot and other crops.It shows that woodlot and other crops will increase the diversity and stability of predator-prey food relations.Landscape diversity is conducive to the maintenance of food web relationship.The fitting results of the predator-prey qualitative food network in cotton field and landscape metrics showed that in all four landscape scale,the proportion of secondary crops is positively related to interaction richness,generality and linkage density.More secondary crops means more habitats,which can provide more food sources,facilitate the establishment and stabilization of food web,and enhance the intensity of predator to pest.Meanwhile,the proportion of maize in the landscape is negatively correlated with the interaction richness,linkage density and generality.In larger landscape scales(1 km,1.5 km,and 2 km),the proportion of cotton was positively related to connectance.Which suggest that large area single planting of main crops such as corn,will reduces the complexity of food relationship,and is not conducive to the biological control function of natural enemies.This study provides ideas for the study of the predator-prey food network structure of major crops in northern China from the perspective of landscape structure change.It also provides a reference for optimizing the farmland landscape structure,protecting the natural enemy habitat,giving full play to the ecosystem service function of natural enemies and improving the management level of pests.