Arboreal twig-nesting ants form dominance hierarchies over nesting resources.

Interspecific dominance hierarchies have been widely reported across animal systems. High-ranking species are expected to monopolize more resources than low-ranking species via resource monopolization. In some ant species, dominance hierarchies have been used to explain species coexistence and community structure. However, it remains unclear whether or in what contexts dominance hierarchies occur in tropical ant communities. This study seeks to examine whether arboreal twig-nesting ants competing for nesting resources in a Mexican coffee agricultural ecosystem are arranged in a linear dominance hierarchy. We described the dominance relationships among 10 species of ants and measured the uncertainty and steepness of the inferred dominance hierarchy. We also assessed the orderliness of the hierarchy by considering species interactions at the network level. Based on the randomized Elo-rating method, we found that the twig-nesting ant species Myrmelachista mexicana ranked highest in the ranking, while Pseudomyrmex ejectus was ranked as the lowest in the hierarchy. Our results show that the hierarchy was intermediate in its steepness, suggesting that the probability of higher ranked species winning contests against lower ranked species was fairly high. Motif analysis and significant excess of triads further revealed that the species networks were largely transitive. This study highlights that some tropical arboreal ant communities organize into dominance hierarchies

Twig-Nesting Ants: The Hidden Predators of the Coffee Berry Borer in Chiapas, Mexico

Coffee is a globally important crop that is subject to numerous pest problems, many of which are partially controlled by predatory ants. Yet several studies have proposed that these ecosystem services may be reduced where agricultural systems are more intensively managed. Here we investigate the predatory ability of twig-nesting ants on the main pest of coffee, the coffee berry borer ( Hypothenemus hampei ) under different management systems in southwest Chiapas, Mexico. We conducted both laboratory and field experiments to examine which twig-nesting ant species, if any, can prey on free-living borers or can remove borers embedded in coffee fruits and whether the effects of the twig-nesting ant community differ with habitat type. Results indicate that several species of twig-nesting ants are effective predators of both free-living borers and those embedded in coffee fruits. In the lab, Pseudomyrmex ejectus, Pseudomyrmex simplex , and Pseudomyrmex PSW-53 effectively removed free-living and embedded borers. In the field, abundance, but not diversity, of twig-nesting ant colonies was influenced by shade management techniques, with the highest colony abundance present in the sites where shade trees were recently pruned. However, borer removal rates in the field were significant only in the shadiest site, but not in more intensively managed sites. This study provides evidence that twig-nesting ants can act as predators of the coffee berry borer and that the presence of twig-nesting ants may not be strongly linked to shade management intensity, as has been suggested for other arthropod predators of the borer.Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btpPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78620/1/j.1744-7429.2009.00603.x.pd

Pseudacteon

Three new species of the genus Pseudacteon are described, all from Chiapas, Mexico, and all of which are parasitoids of the ant Azteca instabilis. Sternite 6 of Pseudacteon dorymyrmecis Borgmeier is illustrated for the first time, and P. confusus Disney is synonymized with this species. The natural history of the Azteca-Pseudacteon interaction is described

Agroforests as Model Systems for Tropical Ecology1

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117179/1/ecy2008894913.pd

Changes in arboreal ant populations following pruning of coffee shade-treesin Chiapas, Mexico

Reducing or eliminating shade cover in coffee ( Coffea arabica L.) agroforestry systems affects fungal disease and pest outbreaks, coffee yields, and can result in biodiversity loss of important predators, such as ants. Less dramatic changes in shade structure or composition may also affect ants. Shade tree pruning, a common management practice in shaded coffee systems, has unknown consequences for ant communities. The effects of pruning on arboreal ant communities were investigated by measuring ant abundance, distribution, and species richness in the short (1 week) and long-term (6 months) after shade tree pruning in one 25×50 m plot. Shade tree pruning significantly affected the distribution and abundance of two of the most common ant species ( Azteca instabilis F. Smith and Camponotus senex textor Forel), and in general did not affect other ants. After pruning, C. senex textor ants were 80% more abundant on coffee plants and shade trees, whereas A. instabilis abundance dropped by 40% on coffee plants and 73% on shade trees after pruning. Additionally, C. senex textor were significantly more widespread, whereas A. instabilis distributions were more restricted. The effects of pruning were strong over the short-term, but were not evident over the long-term. Shade tree pruning did not affect ant diversity. Thus shade tree pruning largely affected certain aspects of arboreal ant communities in one coffee agroforestry system, with important implications for biological control.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41767/1/10457_2004_Article_2372.pd

Complejidad ecológica y el control de plagas en un cafetal orgánico: Develando un servicio ecosistémico autónomo

Those who practice organic or traditional agricuture have the sense that the biodiversity within their farms offers ecosystem services that contribute to the stability, productivity and sustainability of their systems. However, due to their complexity, ecological interactions are very dificult to tease out empirically,especially when these interactions are embedded in complex networks.The science of complexity offers a new platform to help us tease out those complex intercations and their consequences for agroecosystems. Recent studies that incorporate complex networks, non-linearities, stochasticity and, in particular, an added spacial dimension, reveal persistant ecological systems that generate ecosystem services as a result of ecological interactions. Here we describe our theoretical and empirical research of a complex interaction network that has an effect on at least four coffee pests, the coffee berry borer, the gree coffee scale, the coffee rust and the coffee leafminer.Los que practican la agricultura orgánica o la agricultura tradicional perciben que la biodiversidad que se encuentra en sus fincas ofrece servicios ecosistémicos que contribuyen a la estabilidad, productividad y sostenibilidad de sus sistemas. Sin embargo, por su complejidad, las interacciones ecológicas en sistemas muy diversos son muy difíciles de discernir empíricamente, en especial cuando están embebidas en redes complejas. La ciencia de la complejidad nos ofrece una nueva plataforma para discernir esas interacciones ecológicas complejas y sus consecuencias para los sistemas agroecológicos. Estudios recientes que incorporan elementos de estructura de redes complejas, no-linearidades, estocastisidad y, en particular, una dimensión especial, revelan sistemas ecológicos que persisten y que generan servicios ecosistémicos como resultado de las interacciones ecológicas. En este artículo, describimos nuestras investigaciones teóricas y empíricas de una red compleja de interacciones que tiene un efecto en por lo menos tres plagas de café, la broca, la escama verde (cochinilla o quereza) y la roya

The Importance of Ants and High-Shade Management to Coffee Pollination and Fruit Weight in Chiapas, Mexico

Recent reports show importance of pollinators to coffee and importance of ants as pollinators or floral protectors in many systems. Arthropod and pollinator diversity, however, declines with management intensification of coffee ( Coffea arabica ) agroecosystems. We investigated influences of both flying pollinators and ants on coffee fruit set and fruit weight in one high-shade (high-biodiversity) and one low-shade (low-biodiversity) coffee farm in Chiapas, Mexico through exclusion experiments. Contradictory to previous reports, flying pollinators alone did not affect coffee fruit set or fruit weight. Individual fruit weights, however, were higher on branches with both ants and flying pollinators (1.78 g ± 0.312 (SE)) compared to branches without ants (1.03 ± 0.029) or branches without ants or flying pollinators (1.05 ± 0.049), but only in the high-shade site. Although the mechanisms producing higher fruit weights are unknown, we discuss how ants or ant-flying pollinator interactions under high-shade coffee management may contribute to increased fruit weight and the implications of high-shade management for both sustainable coffee production and biodiversity conservation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42430/1/10531_2005_Article_0602.pd

Effects of Management Intensity and Season on Arboreal Ant Diversity and Abundance in Coffee Agroecosystems

Agricultural intensification decreases arthropod predator diversity, abundance and population stability, and may affect interactions between top predators and their arthropod prey – ultimately affecting ecosystem services. Coffee management intensification (reduction or removal of shade trees) reduces diversity of arthropod predators (ground-foraging ants). Because ants provide ecosystem services by controlling pests, influences of intensification on arboreal, coffee-foraging ant diversity and abundance are important. We here address how coffee intensification affects: (1) coffee-foraging ant diversity and abundance and (2) seasonal fluctuations in ant abundance. In each of four coffee sites of varying management intensity in Chiapas, Mexico, we sampled vegetation and using two methods, sampled ant diversity and abundance over two years. Sites significantly differed in vegetation and management intensity. Coffee-foraging ant diversity generally decreased with increasing management intensity (16–26% fewer species observed in the most intensively-managed site). Ant abundance was higher in the wet season. Management intensity, however, did not influence ant abundance or seasonal fluctuations in abundance. Our results highlight the importance of diverse agricultural systems in maintaining arthropod predator diversity, and point to one model system in which we may effectively test how diversity per se affects ecosystem services.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42427/1/10531_2004_Article_4247.pd