Numerous mechanisms promoting assembly and maintenance of diversity have been identified, from disturbance to structure of species interaction networks. Understanding which mechanisms are operating and how they are interacting in the field is crucial for maintaining functional diversity and important ecosystem services. This is particularly true in managed ecosystems such as agroecosystems where effective biocontrol often relies on associated biodiversity such as insect predators and parasitoids. Here we examined the impact of habitat complexity on the response of an arboreal foraging ant community to disturbance in a coffee agroecosystem in Chiapas, Mexico. The primary disturbance in this system is driven by an entomopathogenic fungus (Lecanicillium lecanii) infecting the green coffee scale (Coccus viridis), an important food resource for its mutualist partner, Azteca instabilis, a dominant ant species. We hypothesize the disruption of this mutualism forces a shift in foraging of the dominant competitor and thus has cascading effects on the arboreal foraging ant community. Furthermore, we hypothesize that increasing habitat complexity, in this case shade tree density, serves to dampen the effect of this disturbance by providing refugia and alternative foraging resources for the keystone dominant, thus altering the aggregate effect of disturbance on the community. To test these hypotheses, we induced an artificial fungal epizootic in four experimental sites by spraying a suspended spore mixture on coffee bushes surrounding A. instabilis nest-sites in which the ant/scale mutualism was strong. Surveys of activity of all arboreal foraging ant species present were undertaken before and after the epizootic. These surveys were undertaken in both coffee bushes and shade trees within the experimental plots and were compared to identical analyses undertaken in a control site.
Results/Conclusions
We found a significant shift in foraging activity of other species of ants in two of four experimental sites after the artificial epizootic. This response was significantly related to shade tree density; as density increased, activity of other ants increased in coffee bushes post-epizootic. Additionally, we found a significant decrease in A. instabilis foraging activity in coffee bushes and corresponding increase in foraging activity in shade trees in the same two sites. These results suggest that increasing habitat complexity allowed A. instabilis to adapt to disturbance and the fluctuation in foraging location of the dominant competitor opened niche space for other arboreal foraging ants, promoting maintenance of ant diversity. This has implications for management of shade tree density specifically promoting predatory ants and thus biocontrol of coffee.
