Influence of host phylogeny, geographical location and seed harvesting diet on the bacterial community of globally distributed Pheidole ants.

The presence of symbiotic relationships between organisms is a common phenomenon found across the tree of life. In particular, the association of bacterial symbionts with ants is an active area of study. This close relationship between ants and microbes can significantly impact host biology and is also considered one of the driving forces in ant evolution and diversification. Diet flexibility of ants may explain the evolutionary success of the group, which may be achieved by the presence of endosymbionts that aid in nutrition acquisition from a variety of food sources. With more than 1,140 species, ants from the genus Pheidole have a worldwide distribution and an important role in harvesting seeds; this behavior is believed to be a possible key innovation leading to the diversification of this group. This is the first study to investigate the bacterial community associated with Pheidole using next generation sequencing (NGS) to explore the influences of host phylogeny, geographic location and food preference in shaping the microbial community. In addition, we explore if there are any microbiota signatures related to granivory. We identified Proteobacteria and Firmicutes as the major phyla associated with these ants. The core microbiome in Pheidole (those found in >50% of all samples) was composed of 14 ASVs and the most prevalent are family Burkholderiaceae and the genera Acinetobacter, Streptococcus, Staphylococcus, Cloacibacterium and Ralstonia. We found that geographical location and food resource may influence the bacterial community of Pheidole ants. These results demonstrate that Pheidole has a relatively stable microbiota across species, which suggests the bacterial community may serve a generalized function in this group.

Are all patches worth exploring? Foraging desert birds do not rely on environmental indicators of seed abundance at small scales.

BACKGROUND: Consumers should show strong spatial preferences when foraging in environments where food availability is highly heterogeneous and predictable. Postdispersal granivores face this scenario in most arid areas, where soil seed bank abundance and composition associates persistently with vegetation structure at small scales (decimetres to metres). Those environmental features should be exploited as useful pre-harvest information, at least to avoid patches predicted to be poor. However, we did not find the expected spatial association in the algarrobal of the central Monte desert by observing foraging seed-eating birds, a field technique influenced by how much they exploit visited patches. In this work we tested if the first stage of foraging by granivorous birds (patch visit, encounter or exploration) is positively associated with environmental indicators of patch quality by recording the removal of single seeds from 300 scattered experimental devices during seasonal trials. Spatial selectivity was analysed by comparing the structural characteristics of used vs. available microhabitats, and evaluated against bottom-up and top-down hypotheses based on our previous knowledge on local seed bank abundance, composition and dynamics. Their foraging activity was also explored for spatial autocorrelation and environmental correlates at bigger scales. RESULTS: Postdispersal granivorous birds were less selective in their use of foraging space than expected if microhabitat appearance were providing them relevant information to guide their search for profitable foraging patches. No microhabitat type, as defined by their vegetation structure and soil cover, remained safe from bird exploration. Analyses at bigger temporal and spatial scales proved more important to describe heterogeneity in seed removal. CONCLUSIONS: Closeness to tall trees, probably related to bird territoriality and reproduction or to their perception of predation risk, seemed to determine a first level of habitat selection, constraining explorable space. Then, microhabitat openness (rather than seed abundance) exerted some positive influence on which patches were more frequently visited among those accessible. Selective patterns by birds at small scales were closer to our predictions of a top-down spatial effect, with seed consumption creating or strengthening (and not responding to) the spatial pattern and dynamics of the seed bank.

Effects of Introduced Plants on Diet and Seed Preferences of Pogonomyrmex carbonarius (Hymenoptera: Formicidae) in the Patagonian Steppe.

Invasive species may interact with resident species and disrupt previously established interactions, with effects on the whole community. If introduced seeds are selectively consumed by native granivores, this could limit the establishment or spread of invasive plants (biotic resistance), and reduce the predation pressure upon native seeds. We determined if the presence of introduced plants affects the diet and the seed preferences of the ant Pogonomyrmex carbonarius (Mayr) in a Patagonian steppe. We expected a higher proportion of introduced seeds in the diet of nests located in areas with a high abundance of introduced species (roadsides) than in nests located in low invaded areas. Diet composition was obtained by collecting items retrieved by workers to colonies and compared between areas of contrasting abundance of introduced species. Field-based choice experiments were performed to evaluate whether exotic seeds were preferred to native ones under a paired comparisons design. Native seeds predominated in the diet. A low proportion of introduced species were included only in colonies close to the road. Ants preferred native seeds to introduced ones, and showed a marked preference for seeds of the native grass Pappostipa speciosa (Trin. & Rupr.) Romasch. (Poaceae), typical of the Patagonian steppe. The presence of introduced plants had little influence on interactions of P. carbonarius with seeds in the Patagonian steppe. Therefore, this ant species would not exert a control on the studied introduced plants, illustrating a case of low biotic resistance to invasion by these species.

Seed removal in a tropical North American desert: an evaluation of pre- and post-dispersal seed removal in Stenocereus stellatus.

To determine seed removal influence on seed populations, we need to quantify pre- and post-dispersal seed removal. Several studies have quantified seed removal in temperate American deserts, but few studies have been performed in tropical deserts. These studies have only quantified pre- or post-dispersal seed removal, thus underestimating the influence of seed removal. We evaluated pre- and post-dispersal seed removal in the columnar cactus Stenocereus stellatus in a Mexican tropical desert. We performed selective exclosure experiments to estimate percentage of seeds removed by ants, birds and rodents during the pre- and post-dispersal phases. We also conducted field samplings to estimate abundance of the most common seed removers. Birds (10-28%) removed a higher percentage of seeds than ants (2%) and rodents (1-4%) during pre-dispersal seed removal. Melanerpes hypopolius was probably the main bird removing seeds from fruits. Ants (62-64%) removed a higher percentage of seeds than birds (34-38%) and rodents (16-30%) during post-dispersal seed removal. Pogonomyrmex barbatus was probably the main ant removing seeds from soil. Birds and ants are the main pre- and post-dispersal seed removers in S. stellatus, respectively. Further studies in other S. stellatus populations and plants with different life forms and fruit types will contribute to evaluate seed removal in tropical American deserts.

Toward reliable estimates of seed removal by small mammals and birds in the Neotropics

Birds are often considered seed predators of less importance when compared to rodents or granivorous ants in studies of seed predation using selective exclosures. However, it is possible that the role of granivorous birds interacting with seeds on the floor of Neotropical forests is being underestimated, if the selective exclosures designed to allow exclusive access to small rodents do not work properly in the Neotropics. We used an experimental approach to evaluate whether birds could remove seeds from selective exclosures designed to allow exclusive access to rodents. We compared seed removal from two paired treatments in the field: an open treatment (control) allowing the access to all vertebrates, and a selective exclosure treatment, where seeds were placed under a cage staked to the ground and covered on top and on the laterals by wire mesh of varying sizes. Treatments were placed in the center of a sand quadrat in order to record the visit of vertebrates from their footprints. Although the selective exclosures are used to tell apart the small mammal seed removal from that of other animals, birds could persistently remove seeds from selective exclosures. Thus, the role of birds interacting with seeds on the floor of tropical forests may be underestimated for some plant species, due to an artifact of the exclosure method employed. Exclosures of 40 x 40 x 40 cm should be efficient to deter the removal of seeds by birds, allowing the consumption of the seeds by small mammals at the same time.

Aves são freqüentemente consideradas predadores de sementes de pouca importância, quando comparadas a roedores e formigas granívoras em estudos sobre predação de sementes que utilizam exclusões seletivas. Contudo, é possível que o papel de aves granívoras que interagem com sementes no solo de florestas Neotropicais vem sendo subestimado, se as exclusões seletivas usadas para permitir o acesso exclusivo a pequenos roedores não funcionam de forma apropriada no Neotrópico. Foi usada uma abordagem experimental para avaliar se aves poderiam remover sementes do interior de exclusões seletivas desenhadas para permitir acesso exclusivo a roedores. Comparou-se a remoção de sementes em dois tratamentos no campo: um tratamento aberto (controle) que permite o acesso a todos os vertebrados, e um tratamento de exclusão seletiva, no qual as sementes eram dispostas sob uma gaiola metálica fixada ao solo e recoberta por tela metálica de tamanhos variados. Os tratamentos foram dispostos no centro de uma parcela de areia de forma a registrar a visita de vertebrados por meio de pegadas. Embora as exclusões seletivas sejam usadas para estimar separadamente a remoção de sementes por pequenos mamíferos daquela praticada por outros animais, aves puderam remover sementes das exclusões seletivas. Assim, o papel de aves interagindo com sementes no solo de florestas tropicais pode estar sendo subestimado para algumas espécies de plantas, devido a um artefato do método de exclusão empregado. Exclusões de 40 x 40 x 40 cm devem ser eficientes para deter a remoção de sementes por aves, permitindo o consumo de sementes por pequenos mamíferos ao mesmo tempo.

Toward reliable estimates of seed removal by small mammals and birds in the Neotropics

Birds are often considered seed predators of less importance when compared to rodents or granivorous ants in studies of seed predation using selective exclosures. However, it is possible that the role of granivorous birds interacting with seeds on the floor of Neotropical forests is being underestimated, if the selective exclosures designed to allow exclusive access to small rodents do not work properly in the Neotropics. We used an experimental approach to evaluate whether birds could remove seeds from selective exclosures designed to allow exclusive access to rodents. We compared seed removal from two paired treatments in the field: an open treatment (control) allowing the access to all vertebrates, and a selective exclosure treatment, where seeds were placed under a cage staked to the ground and covered on top and on the laterals by wire mesh of varying sizes. Treatments were placed in the center of a sand quadrat in order to record the visit of vertebrates from their footprints. Although the selective exclosures are used to tell apart the small mammal seed removal from that of other animals, birds could persistently remove seeds from selective exclosures. Thus, the role of birds interacting with seeds on the floor of tropical forests may be underestimated for some plant species, due to an artifact of the exclosure method employed. Exclosures of 40 x 40 x 40 cm should be efficient to deter the removal of seeds by birds, allowing the consumption of the seeds by small mammals at the same time.

Aves são freqüentemente consideradas predadores de sementes de pouca importância, quando comparadas a roedores e formigas granívoras em estudos sobre predação de sementes que utilizam exclusões seletivas. Contudo, é possível que o papel de aves granívoras que interagem com sementes no solo de florestas Neotropicais vem sendo subestimado, se as exclusões seletivas usadas para permitir o acesso exclusivo a pequenos roedores não funcionam de forma apropriada no Neotrópico. Foi usada uma abordagem experimental para avaliar se aves poderiam remover sementes do interior de exclusões seletivas desenhadas para permitir acesso exclusivo a roedores. Comparou-se a remoção de sementes em dois tratamentos no campo: um tratamento aberto (controle) que permite o acesso a todos os vertebrados, e um tratamento de exclusão seletiva, no qual as sementes eram dispostas sob uma gaiola metálica fixada ao solo e recoberta por tela metálica de tamanhos variados. Os tratamentos foram dispostos no centro de uma parcela de areia de forma a registrar a visita de vertebrados por meio de pegadas. Embora as exclusões seletivas sejam usadas para estimar separadamente a remoção de sementes por pequenos mamíferos daquela praticada por outros animais, aves puderam remover sementes das exclusões seletivas. Assim, o papel de aves interagindo com sementes no solo de florestas tropicais pode estar sendo subestimado para algumas espécies de plantas, devido a um artefato do método de exclusão empregado. Exclusões de 40 x 40 x 40 cm devem ser eficientes para deter a remoção de sementes por aves, permitindo o consumo de sementes por pequenos mamíferos ao mesmo tempo.