Summary1. Arboreal ants are both diverse and ecologically dominant in the tropics. Such ecologically important groups are likely to be particularly useful in ongoing empirical efforts to understand the processes that regulate species diversity and coexistence. 2. Our study addresses how access to tree-based resources and the diversity of pre-existing nesting cavities affect species diversity and coexistence in tropical arboreal ant assemblages. We focus on assemblage-level responses to these variables at local scales. We first surveyed arboreal ant diversity across three naturally occurring levels of canopy connectivity and a gradient of tree size. We then conducted whole-tree experimental manipulations of canopy connectivity and the diversity of cavity entrance sizes. All work was conducted in the Brazilian savanna or 'cerrado'. 3. Our survey suggested that species richness was equivalent among levels of connectivity. However, there was a consistent trend of lower species density with low canopy connectivity. This was confirmed at the scale of individual trees, with low-connectivity trees having significantly fewer species across all tree sizes. Our experiment demonstrated directly that low canopy connectivity results in significantly fewer species coexisting per tree. 4. A diverse array of cavity entrance sizes did not significantly increase overall species per tree. Nevertheless, cavity diversity did significantly increase the species using new cavities on each tree, the species per tree unique to new cavities, total species using new cavities, and total cavity use. The populations of occupied cavities were consistent with newly founded colonies and new nests of established colonies from other trees. Cavity diversity thus appears to greatly affect new colony founding and colony growth. 5. These results contribute strong evidence that greater resource access and greater cavity diversity have positive effects on species coexistence in local arboreal ant assemblages. More generally, these positive effects are broadly consistent with niche differentiation promoting local species coexistence in diverse arboreal ant assemblages. The contributions of this study to the understanding of the processes of species coexistence are discussed, along with the potential of the focal system for future work on this issue.

The fungus‐growing ants and their fungal cultivars constitute a classic example of a mutualism that has led to complex coevolutionary dynamics spanning c. 55–65 Ma. Of the five agricultural systems practised by fungus‐growing ants, higher‐attine agriculture, of which leaf‐cutter agriculture is a derived subset, remains poorly understood despite its relevance to ecosystem function and human agriculture across the Neotropics and parts of North America. Among the ants practising higher‐attine agriculture, the genus Trachymyrmex Forel, as currently defined, shares most‐recent common ancestors with both the leaf‐cutter ants and the higher‐attine genera Sericomyrmex Mayr and Xerolitor Sosa‐Calvo et al. Although previous molecular‐phylogenetic studies have suggested that Trachymyrmex is a paraphyletic grade, until now insufficient taxon sampling has prevented a full investigation of the evolutionary history of this group and limited the possibility of resolving its taxonomy. Here we describe the results of phylogenetic analyses of 38 Trachymyrmex species, including 27 of the 49 described species and at least 11 new species, using four nuclear markers, as well as phylogenetic analyses of the fungi cultivated by 23 species of Trachymyrmex using two markers. We generated new genetic data for 112 ants (402 new gene sequences) and 95 fungi (153 new gene sequences). Our results corroborate previous findings that Trachymyrmex, as currently defined, is paraphyletic. We propose recognizing two new genera, Mycetomoellerius gen.n. and Paratrachymyrmex gen.n., and restricting the continued use of Trachymyrmex to the clade of nine largely North American species that contains the type species [Trachymyrmex septentrionalis (McCook)] and that is the sister group of the leaf‐cutting ants. Our fungal cultivar phylogeny generally corroborates previously observed broad patterns of ant–fungus association, but it also reveals further violations of those patterns. Higher‐attine fungi are divided into two groups: (i) the single species Leucoagaricus gongylophorus (Möller); and (ii) its sister clade, consisting of multiple species, recently referred to as Leucoagaricus Singer ‘clade B’. Our phylogeny indicates that, although most non‐leaf‐cutting higher‐attine ants typically cultivate species in clade B, some species cultivate L. gongylophorus, whereas still others cultivate fungi typically associated with lower‐attine agriculture. This indicates that the attine agricultural systems, which are currently defined by associations between ants and fungi, are not entirely congruent with ant and fungal phylogenies. They may, however, be correlated with as yet poorly understood biological traits of the ants and/or of their microbiomes.

Fire is an important agent of disturbance in tropical savannas, but relatively few studies have analyzed how soil-and-litter dwelling arthropods respond to fire disturbance despite the critical role these organisms play in nutrient cycling and other biogeochemical processes. Following the incursion of a fire into a woodland savanna ecological reserve in Central Brazil, we monitored the dynamics of litter-arthropod populations for nearly two years in one burned and one unburned area of the reserve. We also performed a reciprocal transplant experiment to determine the effects of fire and litter type on the dynamics of litter colonization by arthropods. Overall arthropod abundance, the abundance of individual taxa, the richness of taxonomic groups, and the species richness of individual taxa (Formiciade) were lower in the burned site. However, both the ordinal-level composition of the litter arthropod fauna and the species-level composition of the litter ant fauna were not dramatically different in the burned and unburned sites. There is evidence that seasonality of rainfall interacts with fire, as differences in arthropod abundance and diversity were more pronounced in the dry than in the wet season. For many taxa the differences in abundance between burned and unburned sites were maintained even when controlling for litter availability and quality. In contrast, differences in abundance for Collembola, Formicidae, and Thysanoptera were only detected in the unmanipulated samples, which had a lower amount of litter in the burned than in the unburned site throughout most of our study period. Together these results suggest that arthropod density declines in fire-disturbed areas as a result of direct mortality, diminished resources (i.e., reduced litter cover) and less favorable microclimate (i.e., increased litter desiccation due to reduction in tree cover). Although these effects were transitory, there is evidence that the increasingly prevalent fire return interval of only 1–2 years may jeopardize the long-term conservation of litter arthropod communities.

Fungus-farming (attine) ant agriculture is made up of five known agricultural systems characterized by remarkable symbiont fidelity in which five phylogenetic groups of ants faithfully cultivate five phylogenetic groups of fungi. Here we describe the first case of a lower-attine ant cultivating a higher-attine fungus based on our discovery of a Brazilian population of the relictual fungus-farming ant Apterostigma megacephala, known previously from four stray specimens from Peru and Colombia. We find that A. megacephala is the sole surviving representative of an ancient lineage that diverged ∼39 million years ago, very early in the ∼55-million-year evolution of fungus-farming ants. Contrary to all previously known patterns of ant-fungus symbiont fidelity, A. megacephala cultivates Leucoagaricus gongylophorus, a highly domesticated fungal cultivar that originated only 2-8 million years ago in the gardens of the highly derived and recently evolved (∼12 million years ago) leaf-cutting ants. Because no other lower fungus-farming ant is known to cultivate any of the higher-attine fungi, let alone the leaf-cutter fungus, A. megacephala may provide important clues about the biological mechanisms constraining the otherwise seemingly obligate ant-fungus associations that characterize attine ant agriculture.

Avaliação de Três Métodos para Amostragem de Formigas do Solo no Cerrado BrasileiroRESUMO -Poucos estudos avaliaram a efi ciência de métodos para a coleta de formigas, especialmente em regiões com fi sionomias vegetais bastante variáveis como a do Cerrado. Neste trabalho, foram comparados três métodos para a coleta de formigas do solo: armadilhas de solo, iscas de sardinha e o extrator de serapilheira de Winkler, com o objetivo de determinar o mais apropriado para caracterizar as assembléias de formigas associadas a diferentes tipos de vegetação. Mais espécies foram coletadas com armadilhas de solo e com o extrator de Winkler do que com iscas. As armadilhas de solo coletaram mais espécies nas fi sionomias de cerrado (savânicas), particularmente naquelas com pobre cobertura de serapilheira, enquanto o extrator de Winkler foi mais efi ciente nas fi sionomias fl orestais, com exceção daquela sujeita a inundações periódicas. Houve baixa similaridade na composição de espécies entre as fi sionomias de cerrado e fl orestais, e esse padrão foi observado com qualquer dos três métodos de coleta. Portanto, mesmo o uso de um único método pode ser sufi ciente em estudos que comparam condições ou hábitats bastante distintos. Entretanto, se o propósito da amostragem for produzir um inventário mais completo, sugerimos o uso de uma combinação de métodos, em particular as armadilhas de solo e o extrator de Winkler. Desse modo, o Protocolo para Amostragem de Formigas da Serapilheira (ALL Protocol) parece ser adequado para a amostragem de formigas na ameaçada região do Bioma Cerrado. PALAVRAS-CHAVE: Inventário de formigas, isca, Formicidae, armadilha de solo, extrator de Winkler ABSTRACT -Few studies have evaluated the effi ciency of methods for sampling ants, especially in regions with highly variable vegetation physiognomies such as the Cerrado region of central Brazil. Here we compared three methods to collect ground-dwelling ants: pitfall traps, sardine baits, and the Winkler litter extractor. Our aim was to determine which method would be most appropriate to characterize the ant assemblages inhabiting different vegetation types. More species were collected with pitfall traps and with the Winkler extractor than with sardine baits. Pitfall traps collected more species in the cerrado (savanna) physiognomies, particularly in those with a poor litter cover, whereas the Winlker extractor was more effi cient in the forest physiognomies, except the one subject to periodic inundations. There was a low similarity in species composition between forest and cerrado physiognomies, and this pattern was detected regardless of the method used to sampling ants. Therefore, even the use of a single, relatively selective method of collection can be enough for studies comparing highly distinct habitats and/or conditions. However, if the purpose of the sampling is to produce a more thoroughly inventory of the ant fauna, we suggest the use of a combination of methods, particularly pitfall traps and the Winkler extractor. Therefore, the Ants of the Le...