Human-managed ecosystems are incubators of novel interactions. In human-managed ecosystems, species interactions can provide various ecosystem functions. The variation of human management intensity, however, may hinder or facilitate ecosystem functions, such as pest control. Changes in pest control, for example, may result from cascading trophic or non-trophic interactions in response to the population change of an organism sensitive to environmental perturbation. In this study, we investigate how management intensity of an agroecosystem affects the density or activity of organisms in an interaction network associated with a pest in the coffee agroecosystem. We combined signed digraphs, qualitative modeling and time averaging analyses with field data to test if (1) population density or activity change of any organism within the network would lead to a change in the density equilibria of any of the organisms in the network, and if this differ with levels of intensification, and (2) if higher-order (non-trophic) interactions are important in regulating such changes. We further explore how changes in population dynamics of the sensitive species affect the pest control function in the agroecosystem.
Results/Conclusions
Field data reveals that organism density or activity in the coffee agroecosystem under two levels of intensification have reached two different alternative stable states. The qualitative modeling and time averaging approaches suggest that a far-flung parasitoid species is responsible for the density and activity changes of organisms in the network, and non-trophic higher-order interactions are essential for such changes. Along with the qualitative modeling, quantitative analyses suggest that the less intensified coffee agroecosystem is under a different pest control regime than the more intensified agroecosystem. While the less intensive agroecosystem shows pest control that is disease-dominant, pest control in the more intensive agroecosystem is predator-dominant, a result emerging from the change of species alternative stable states due to the environmental sensitivity of a far-flung parasitoid fly.