Impacts of organic and conventional orange orchard management on ant biodiversity in the Amazon

Background/Question/Methods   Environment impacts in the Amazon region are caused primarily by the expansion of cattle ranching and agriculture. Despite the evidence of impacts caused by deforestation, new areas are cleared of trees and new agricultural systems are introduced on a daily basis. However, studies have shown that some agroecosystems can sustain elevated levels of biodiversity depending on the type and the intensity of the management employed. Conventional orange orchards in the Amazon are intensively managed including high levels of mechanization and a conventional protocol of agrochemicals use. The goal of this study was to evaluate ant species richness and composition in orange orchards under organic and conventional management. Ants were sampled in orange orchards in the districts of Capitão Poço and Garrafão do Norte, PA, Brazil. Twenty pitfall traps were placed in each of three replicates for each management type and left for 48 hours before collecting specimens. Vegetation and other environmental variables were measured at each sampling point. Differences in ant species richness with management systems were examined using smoothed species accumulation curves. The effect of the explanatory variables on the richness of ant species was investigated using a GLM complete model with all the variables and interactions.

Results/Conclusions   Overall, eighty-five species of ants were collected. In the organic orange orchards 69 species of ants were sampled, and 65 species were sampled in conventional orchards. Pheidole (13 spp) and Camponotus (11 spp) were the most speciose genera. Smoothed species sample curves show no significant differences on species richness between systems. However, higher ant richness was found in areas with greater litter biomass and plant height and litter biomass interaction had positive effects over ant species richness. Under conventional management, plant species richness, plant density, the interactions among plant species richness and distance from the forest, plant species richness and litter biomass, distance from the forest and litter biomass had a significant effect on ant species richness. Litter biomass was the most important environmental variable that explained ant species richness in organic orange orchards, while herbaceous plant species richness and plant density were the most important variables in conventional orchards. The results suggest that agricultural areas with higher plant diversity provide more resources to the ant communities and fostering higher species diversity. Furthermore, this study has broader implications to agricultural intensification in the Amazon region.