Effects Of Landscape Corridors On Predators In Fields

An agroecosystem can be understood as a large, landscaped area, which includes a variety of crop habitats and non-crop habitats. Landscape diversity affects the non-crop habitat biodiversity and species migration, which are center issues of landscape ecology. At different scales, corridors can affect the exchanges of species, matter and energy between patches. The inclusion of a reasonable ecological corridor for biodiversity conservation and the implementation of an ecologically based pest management system in the agricultural landscape can play active roles in promoting these exchanges. This study compared different types of landscape corridors that affect the movements of predators in agricultural ecosystems at two scales and assessed the impacts of man-made factors on the abundances of predators and beneficial species for controlling insect pests. The results were as follows:1 Effects of fine scale landscape corridors on predatorsAt the fine scale, we set up three replicate micro-landscape plots, which included weed patches and rice field patches, connected with four different types of corridors. We found that the different types of corridors had similar predator groups and dominant species. There were no significant differences in the diversity indices, evenness indices or dominant concentration indices of spiders and carabid predator groups between the different corridors. At different times, the predatory characteristics indices were also similar for the four types of corridors. When comparing the direction of movement, during the early growing season of rice plants, spider groups mostly moved to the rice paddy field patches from the weed patches. In the middle of the growing season, the migration activities in both directions (form rice patches to weed patches, or the converse) were very high. When rice maturation and harvesting were occurring, the predatory spiders returned to the weed patches. However, there were no significant differences in spider species composition and diversity. The population dynamics of carabid beetles exhibited similar trends to the spider groups. According to the corridor types, weed corridors had more spider species and greater spider abundances than other type of corridors. There were significant differences at some time points in spider species and abundance, indicating that weed corridors protected predators to some extent.2 Effects of regional landscape corridors on predatorsAt the regional scale, we selected 6 agricultural landscapes within a 110-m radius that contained different corridors, such as roads for tractor plowing, weedy edges and weedy streams. Every circle agricultural landscape had a different corridor density, circuitry and ratio of node/line, and connectivity. The results show that a higher plant species diversity, more complex vegetation structure and lower extent of human disturbance in a corridor results in a higher abundance of spiders. Simplifications of the vegetation structure and intensive human disturbances may reduce the species composition and abundance of spiders. Physical barriers may affect the species composition and abundance of carabid beetles, but they had little effect on the diversity indices, evenness indices and dominant concentration indices. Judging from their directions of movement between the crop habitats and non-crop habitats, predators did not have significant differences in their species richness and abundance, indicating that predators had no obvious preference for habitat choice. Canonical Correspondence Analysis (CCA) was used to identify correlations between the landscape corridor network structures and the species composition of spiders and carabid beetles. Our results showed that different corridor network structure had different effect on species of spiders and carabid beetles. Indices reflecting the complexity of a corridor network structure, such as the corridor density, had close relationships with the abundance of some spider species such as Lycosa pseudoannulata and Plexippus setipes, whereas the ratio of node/line, connectivity and circuitry correlated with the abundance of other spider species, such as Ummeliata insecticeps, Gnathonarium gibberum, Erigone prominens and Tetragnatha nitens. The corridor density, ratio of node/line, connectivity and circuitry positively correlated with axis 1 of the CCA. Abundance of carabid beetle species such as Chlaenius circumdatus, Stenolophus sp. 1, Stenolophus sp. 2, Harpalus sp. 2 and Dischissus sp. 1 were positively correlated with the ratio of node/line, connectivity and circuitry of corridors. Our results also indicate that the method of CCA analysis was a suitable method to quantitatively assess the relationships between predator species and corridor network structures.