Natural History of Ants: What We (do not) Know About Trophic and Temporal Niches of Neotropical Species

Our understanding of the natural history of Neotropical ants is still limited, both due to a lack of detailed descriptive efforts and the widespread use of morphospecies in community studies. Use of trophic resources and period of activity are two central niche aspects little explored for most species. This work aims to review the literature and provide empirical field data on these aspects for several species. The fieldwork was carried out in the Atlantic forest of southern Brazil. Trophic and temporal niches were assessed with pitfall traps and seven kinds of bait representing natural resources available to ants. Crushed insects were the preferred resource, whereas bird feces and living prey were less exploited overall. Most of the species occupied a broad trophic niche, using several resources, but with pronounced quantitative differences. Odontomachus chelifer (Latreille, 1802) and Pachycondyla striata Smith, 1858 were the only species that consistently used large prey, and avoided trisaccharides. Wasmannia auropunctata (Roger, 1863) differed remarkably from previous accounts, using feces as its sole trophic resource. Pheidole species had no previous records and use resources in different ways. Most species had no strong preference for period of activity. Camponotus zenon Forel, 1912 was nocturnal and Crematogaster nigropilosa Mayr, 1870, Linepithema iniquum (Mayr, 1870) and Linepithema pulex Wild, 2007 were diurnal. Complementary methods, context-dependence and descriptive studies have a central role in the understanding of ant natural history. Community assessments can contribute significantly to this knowledge if researchers also pay attention to the individual species involved

From field to fat – Integrating approaches to unveil use of trophic resources by tropical and temperate ant species (Hymenoptera: Formicidae)

The use of food resources is one of the most important aspects of ecosystem functioning. Trophic relationships determine fluxes of matter and energy, shape interactions between organisms and ultimately direct the evolution of the species themselves. Competition is a fundamental biotic interaction, and niche partitioning constitutes an important mechanism to allow species coexistence. However, many other factors influence community structuring, and may change or supplant the outcomes of competition. Ants are one of the most abundant, widespread and ecologically relevant terrestrial organisms. On the ground of tropical forests, dozens of species may coexist, which raises the question: how similar are they? Behavioral and environmental mechanisms of coexistence have been proposed for ants, but the use of resources itself is surprisingly understudied, and the trophic niches of most species is unknown. In this thesis, I used three complementary methods, representing a gradient of source-specificity/time-representativity, to describe patterns of resource use in a tropical and a temperate ant community. In the first study, I reviewed the available literature on resource use for the identified tropical species and compared it to field data obtained with baiting. Previous information was scant or inexistent for most species. Ants broadly used most resources available, but with quantitative differences between species. Wasmannia auropunctata has the most specialized niche, using only feces, a new behavior for the species. In the second study, my coauthors and I performed a laboratory experiment to describe fatty acid assimilation in ants. Two temperate ant species (Formica fusca and Myrmica rubra) displayed similar patterns and dynamics in composition, although amounts were influenced by their reproductive status. The main fatty acids (C16:0, C18:0 and C18:1n9) were extensively synthesized from sugars, but we observed some diet-specific ones that might work as biomarkers (C18:2n6, C18:3n3, C18:3n6). The experiment fulfilled a basic knowledge gap and set the ground for application of fatty acid analysis in an ecological context. In the third study, we put together field observations, fatty acid and stable isotope analyses to describe overall patterns of resource use and species’ niches in both communities. We observed a consistent picture of high, and quantitatively equivalent, generalism in both communities, regardless of species richness. Temperate species presented fatty acid patterns distinct from tropical ones, which may be related to environmental factors. Similarities in bait attendance, fatty acid compositions and isotope signatures were all correlated in Brazil, thus all methods corresponded in their characterization of species’ niches to some extent, and were robust enough to detect differences even in a highly generalized community. Method complementarity was particularly important to understand the behavior of the most specialized species. In Germany, no correlations were observed, likely due to the small number of species available. Fatty acid analysis emerges as a powerful tool and may be applied to answer many questions related to resource use in ants, but use of fatty acids as biomarkers seems to be limited. In general, the results of this thesis agreed with the recent view that specialization does not increase with species richness towards the tropics. Several coexistence mechanisms may act to structure ant communities, with trophic niche partitioning playing a relatively small role in the ones we studied. No mechanism appears to be universal and community structure may be better understood on a case-by-case basis, at local scale

From field to fat – Integrating approaches to unveil use of trophic resources by tropical and temperate ant species (Hymenoptera: Formicidae)

The use of food resources is one of the most important aspects of ecosystem functioning. Trophic relationships determine fluxes of matter and energy, shape interactions between organisms and ultimately direct the evolution of the species themselves. Competition is a fundamental biotic interaction, and niche partitioning constitutes an important mechanism to allow species coexistence. However, many other factors influence community structuring, and may change or supplant the outcomes of competition. Ants are one of the most abundant, widespread and ecologically relevant terrestrial organisms. On the ground of tropical forests, dozens of species may coexist, which raises the question: how similar are they? Behavioral and environmental mechanisms of coexistence have been proposed for ants, but the use of resources itself is surprisingly understudied, and the trophic niches of most species is unknown. In this thesis, I used three complementary methods, representing a gradient of source-specificity/time-representativity, to describe patterns of resource use in a tropical and a temperate ant community. In the first study, I reviewed the available literature on resource use for the identified tropical species and compared it to field data obtained with baiting. Previous information was scant or inexistent for most species. Ants broadly used most resources available, but with quantitative differences between species. Wasmannia auropunctata has the most specialized niche, using only feces, a new behavior for the species. In the second study, my coauthors and I performed a laboratory experiment to describe fatty acid assimilation in ants. Two temperate ant species (Formica fusca and Myrmica rubra) displayed similar patterns and dynamics in composition, although amounts were influenced by their reproductive status. The main fatty acids (C16:0, C18:0 and C18:1n9) were extensively synthesized from sugars, but we observed some diet-specific ones that might work as biomarkers (C18:2n6, C18:3n3, C18:3n6). The experiment fulfilled a basic knowledge gap and set the ground for application of fatty acid analysis in an ecological context. In the third study, we put together field observations, fatty acid and stable isotope analyses to describe overall patterns of resource use and species’ niches in both communities. We observed a consistent picture of high, and quantitatively equivalent, generalism in both communities, regardless of species richness. Temperate species presented fatty acid patterns distinct from tropical ones, which may be related to environmental factors. Similarities in bait attendance, fatty acid compositions and isotope signatures were all correlated in Brazil, thus all methods corresponded in their characterization of species’ niches to some extent, and were robust enough to detect differences even in a highly generalized community. Method complementarity was particularly important to understand the behavior of the most specialized species. In Germany, no correlations were observed, likely due to the small number of species available. Fatty acid analysis emerges as a powerful tool and may be applied to answer many questions related to resource use in ants, but use of fatty acids as biomarkers seems to be limited. In general, the results of this thesis agreed with the recent view that specialization does not increase with species richness towards the tropics. Several coexistence mechanisms may act to structure ant communities, with trophic niche partitioning playing a relatively small role in the ones we studied. No mechanism appears to be universal and community structure may be better understood on a case-by-case basis, at local scale

Formigas de solo e de bromélias em uma área de Mata Atlântica, Ilha de Santa Catarina, sul do Brasil: Levantamento de espécies e novos registros

A mirmecofauna em uma área de Mata Atlântica da Ilha de Santa Catarina foi inventariada utilizando métodos diversos para formigas de solo e de bromélias. Foram feitas amostragens mensais entre março de 2002 e agosto de 2004, utilizando o extrator de Winkler, armadilhas de interceptação e queda, além de coleta de bromélias. Foram encontradas 124 espécies, divididas em nove subfamílias e 33 gêneros. Os gêneros com maior riqueza foram Pheidole, Solenopsis, Crematogaster, Acromyrmex e Camponotus. Encontrou-se mais espécies no solo que nas bromélias, com 8% do total ocorrendo nos dois hábitats. Foram obtidos 11 registros novos para o estado de Santa Catarina e 20 para a região da Grande Florianópolis. Tais resultados estão relacionados com o uso de metodologias novas para a região, e mostram que a fauna de formigas desta ainda precisa ser mais bem estudada

The cephalic anatomy of workers of the ant species Wasmannia affinis (Formicidae, Hymenoptera, Insecta) and its evolutionary implications

Despite the ecological significance of ants and the intensive research attention they have received, thorough treatments of the anatomy and functional morphology are still scarce. In this study we document the head morphology of workers of the myrmicine Wasmannia affinis with optical microscopy, μ-computed tomography, scanning electron microscopy, and 3D reconstruction, providing the first complete anatomical treatment of an ant head with a broad array of modern techniques. We discuss the potential of the applied methods to generate detailed and well-documented morphological data sets with increased efficiency. We also address homology problems, particularly in the context of the cephalic digestive tract. According to our analyses the “pharynx” of previous ant studies is homologous to the prepharynx of other insects. We also discuss the phylogenetic potential and functional significance of the observed characters, with internal features such as tentorium and musculature discussed for the first time. Our investigation underlines that detailed anatomical data for Formicidae are still very fragmentary, which in turn limits our understanding of the major design elements underlying the ant bauplan. We attempt to provide a template for further anatomical studies, which will help to understand the evolution of this fascinating group on the phenotypic level

Simple does not mean poor: grasslands and forests harbor similar ant species richness and distinct composition in highlands of southern Brazil

Several studies addressed ant communities in the dense Atlantic Forest that runs along the Brazilian coast. However, comparatively little is known about the mixed forests and grasslands that occur in the southern range of the Atlantic Forest domain. In this study we performed the first standardized assessment of ants in the forest- grassland mosaic found in the highlands of the state of Santa Catarina. We aimed to investigate and compare ant richness and composition between mixed forests and grasslands in the main mountain range of south Brazil. Ants were collected in two years with ground pitfalls, tree pitfalls and litter samples. Sixty ant species were recorded, resulting in 22 new records for “Planalto Serrano” region and three for the state of Santa Catarina: Eurhopalothrix depressa , Pheidole radoszkowskii and Wasmannia williamsoni . There was significant dissimilarity in ant species composition between grasslands and forests, but no difference in ant species richness, even considering the higher number of strata in mixed forests. Similar richness and low number of arboreal species suggest that this ant community is structured similarly to temperate ones. Both habitats presented a large proportion of exclusive species. The fact that species composition between grassland and forest areas differed, coupled with the similarity in species richness between habitats and the record of new ant species for the region, calls for strong conservation efforts in grasslands of southern Brazil, which still are little protected by conservation areas