Analysis of differences in insect communities at different altitudes in Zanthoxylum bungeanum gardens, Yunnan, China

Abstract

Zanthoxylum bungeanum (Rutaceae) is one of the most important economic plants in some areas of China, because Z. bungeanum could be used to mitigate water and soil loss through the reforestation of barren hillsides where cultivation and tree removal has occurred. The mechanisms of insect community dynamics and pest insect outbreaks can be identified through their relationship with environmental factors such as altitude, temperature, humidity and insect community characteristics. This study investigated the relationship between the environmental variables and insect communities in Z. bungeanum gardens near the Jinshajiang River, Yongshan County, Yunnan, China. Insect communities were sampled from seven different gardens at varying altitudes (low 450-750 m; medium 750-1300 m; high 1300-1550 m) from March to September, 2008. All data were analyzed using multivariate analysis of variance (MANOVA) and the level of correlation using the Gray-system theory. The results were: 1) Insect community structure varied with altitude, suggesting altitude is a key factor influencing insect communities in Z. bungeanum gardens; 2) Increases in altitude resulted in higher species diversity, evenness, richness, Ss / Si(the number of species divided by the number of individuals) and Sn / Sp(the number of natural enemy species divided by the number of phytophagous species) at lower altitudes followed by a decline at higher altitudes. However, the species abundance and dominance indices decreased at lower altitudes then increased at higher altitudes; 3) Where Z. bungeanum gardens grew under more extreme climatic conditions, such as higher temperatures and lower humidity at lower altitudes, or lower temperatures and higher humidity at higher altitudes, there were less diverse insect communities. Thus, insect community characteristics such as species diversity, evenness, richness, Ss / Si and Sn / Sp indices were lower and more unstable in gardens at lower and higher altitudes. The seasonal dynamics of insect communities at lower and higher altitudes changed more quickly compared with those at medium altitudes. The climatic conditions at the gardens at medium altitudes (750-1300 m) were more suitable for diverse insect communities with ideal temperatures and humidity. Thus, the number of insects at the individual and species level in gardens between 750 and 1300 m (medium altitude) were relatively higher compared with gardens at lower and higher altitudes. The insect communities at medium altitudes indicated better stability based on insect community diversity, evenness, richness, Ss / Si and Sn / Sp indices, which were higher compared with the other two altitudinal groups. In comparison with the gardens at low and high altitudes, the seasonal dynamics of the insect community at medium altitudes changed slightly; 4) The dominance indices for the insect communities were higher at 450-750 m and 1300-1550 m altitude gardens, but lower in the 750-1300 m gardens. Furthermore, the dominance indices at the low and high altitude gardens showed a more significant change among seasons compared with the medium altitude gardens. Overall, insect community dynamics in Z. bungeanum gardens (Yunnan Province) may be influenced by altitudinal factors such as temperature and humidity, affecting insect species and abundance in various sub-communities. The key influencing factors were the extremes of temperature and humidity. The stability of insect communities in Z. bungeanum gardens could be improved under suitable temperature and humidity conditions similar to those found between 750 and 1300 m.