Understanding the drivers of ant diversity and co-occurrence in agroecosystems is fundamental because ants participate in interactions that influence agroecosystem processes. Multiple local and regional factors influence ant community assembly.We examined local factors that influence the structure of a twig-nesting ant community in a coffee system in Mexico using an experimental approach. We investigated whether twig characteristics (nest entrance size and diversity of nest entrance sizes) and nest strata (canopy shade tree or coffee shrub) affected occupation, species richness, and community composition of twig-nesting ants and whether frequency of occupation of ant species varied with particular nest entrance sizes or strata.We conducted our study in a shaded coffee farm in Chiapas, Mexico, between March and June 2012. We studied ant nest colonization by placing artificial nests (bamboo twigs) on coffee shrubs and shade trees either in diverse or uniform treatments. We also examined whether differences in vegetation (no. of trees, canopy cover and coffee density) influenced nest colonization.We found 33 ant species occupying 73% of nests placed. Nest colonization did not differ with nest strata or size. Mean species richness of colonizing ants was significantly higher in the diverse nest size entrance treatment, but did not differ with nest strata. Community composition differed between strata and also between the diverse and uniform size treatments on coffee shrubs, but not on shade trees. Some individual ant species were more frequently found in certain nest strata and in nests with certain entrance sizes.Our results indicate that twig-nesting ants are nest-site limited, quickly occupy artificial nests of many sizes, and that trees or shrubs with twigs of a diversity of entrance sizes likely support higher ant species richness. Further, individual ant species more frequently occupy nests with different sized entrances promoting ant richness on individual coffee plants and trees.

Vegetation connectivity is an essential aspect of the habitat complexity that impacts species interactions at local scales. However, agricultural intensification reduces connectivity in agroforestry systems, including coffee agroecosystems, which may hinder the movement of natural enemies and reduce the ecosystem services that they provide. Ants play an important role in regulating the coffee berry borer (CBB), which is the most damaging coffee pest. For arboreal ant communities, the connections between trees are important structures that facilitate ant mobility, resource recruitment, foraging success, and pest control ability. To better understand how connectivity impacts arboreal ants in coffee agroecosystems, we conducted an experiment to assess the impact of artificial (string) and naturally occurring vegetation (vines, leaves, branches) connectivity on Azteca sericeasur behavior on coffee plants. We compared ant activity, resource recruitment, and CBB removal rates across three connectivity treatments connecting coffee plants to A. sericeasur nest trees: vegetation connectivity, string, and control (not connected) treatments. We found higher rates of ant activity, resource recruitment, and CBB removal on plants with naturally occurring vegetation connections to A. sericeasur nest trees. Artificial connectivity (string) increased the rates of resource recruitment and CBB removal but to a lesser extent than vegetation connectivity. Moreover, vegetation connectivity buffered reductions in ant activity with distance from the ant nest tree. These results reinforce how habitat complexity in the form of vegetation connectivity impacts interspecific interactions at the local scale. Our results also suggest that leaving some degree of vegetation connectivity between coffee plants and shade trees can promote ant-mediated biological pest control in coffee systems.

In natural and managed systems, connections between trees are important structural resources for arboreal ant communities with ecosystem‐level effects. However, ongoing agricultural intensification in agroforestry systems, which reduces shade trees and connectivity between trees and crop plants, may hinder ant recruitment rates to resources and pest control services provided by ants. We examined whether increasing connectivity between coffee plants and shade trees in coffee plantations increases ant activity and enhances biological control of the coffee berry borer, the most devastating insect pest of coffee. Further, we examined whether artificial connections buffer against the loss of vegetation connectivity in coffee plants located at larger distances from the nesting tree. We used string to connect Inga micheliana shade trees containing Azteca sericeasur ant nests to coffee plants to compare ant activity before and after placement of the strings, and measured borer removal by ants on coffee plants with and without strings. Ant activity significantly increased after the addition of strings on connected plants, but not on control plants. Borer removal by ants was also three times higher on connected plants after string placement. Greater distance from the nesting tree negatively influenced ant activity on control coffee plants, but not on connected plants, suggesting that connections between coffee plants and nest trees could potentially compensate for the negative effects that larger distances pose on ant activity. Our study shows that favoring connectivity at the local scale, by artificially adding connections, promotes ant activity and may increase pest removal in agroecosystems. Abstract in Spanish is available with online material.

Understanding the ecology of mutualisms becomes a particularly important task when considering agroecosystems, as many ecosystem services are associated with mutualistic interactions. Here we report on experiments associated with an indirect pest control mutualism between the arboreal nesting ant Azteca sericeasur and coffee. This system is particularly interesting because the indirect Azteca-Coffea mutualism emerges from an Azteca-scale insect mutualism that takes place on the coffee plant. We describe this interaction structure as a mutualism-dependent mutualism and ask whether the density of intermediary mutualist (scale insects, Coccus) that benefits Azteca also influences the benefits provided to coffee plants. We found that indeed Azteca’s benefit to Coffea is consistent when Coccus density is high. Furthermore, we also found that at low Coccus density Azteca only benefits Coffea in the beginning of the rainy season, and this effect is likely due to the fact that Coccus produces less sugars with higher precipitation. We suggest a framework for thinking about context-dependency in agroecosystem mutualisms that may provide a more mechanistic way to tease apart the prevalent context-dependent results in ecological literature. Finally, we address some past recommendations as it pertains to the management of the Azteca-Coffea-Coccus complex in coffee agroecosystems.

Abstract: Whether an ecological community is controlled from above or below remains a popular framework that continues generating interesting research questions and takes on especially important meaning in agroecosystems. We describe the regulation from above of three coffee herbivores, a leaf herbivore (the green coffee scale, Coccus viridis), a seed predator (the coffee berry borer, Hypothenemus hampei), and a plant pathogen (the coffee rust disease, caused by Hemelia vastatrix) by various natural enemies, emphasizing the remarkable complexity involved. We emphasize the intersection of this classical question of ecology with the burgeoning field of complex systems, including references to chaos, critical transitions, hysteresis, basin or boundary collision, and spatial self-organization, all aimed at the applied question of pest control in the coffee agroecosystem.