Abstract Discussion of the vertical stratification of organisms in tropical forests has traditionally focused on species distribution. Most studies have shown that, due to differences in abiotic conditions and resource distribution, species can be distributed along the vertical gradient according to their ecophysiological needs. However, the network structure between distinct vertical strata remains little-explored. To fill this gap in knowledge, we used baits to sample ants in the canopy and understorey trees of a Mexican tropical rain forest to record the ant?tree co-occurrences. We examined the ant?tree co-occurrences in the canopy and understorey using complementary network metrics (i.e., specialization, interaction diversity, modularity, and nestedness). In addition, we evaluated co-occurrence patterns between ant species on trees, using C-score analysis. In general, we found no differences in the network structure, although the interaction diversity was greater in the understorey than in the canopy networks. We also observed that co-occurrence networks of each vertical stratum featured four ant species in the central core of highly co-occurring species, with three species unique to each stratum. Moreover, we found a similar trend toward ant species segregation in the both strata. These findings reveal a similar pattern of ant?ant co-occurrences in both vertical strata, probably due to the presence of arboreal-nesting ants in the understorey. Overall, we showed that despite the marked differences in species composition and environmental conditions between understorey and canopy strata, ant?tree co-occurrences in these habitats could be governed by similar mechanisms, related to dominance and resource monopolization by ants. Abstract in Spanish is available with online material.
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We describe an assemblage of 54 avian bones from early Eocene marine sediments of the Ampe quarry near Egem in Belgium. The fossils belong to at least 20 species in more than 11 higher-level taxa. Well-identifiable specimens are assigned to the Odontopterygiformes, Galliformes, Messelornithidae, Apodiformes, Halcyornithidae, Leptosomiformes (cf.Plesiocathartes), and Coraciiformes (cf. Septencoracias). Further specimens are tentatively referred to the phaethontiform Prophaethontidae and to the Accipitridae, Masillaraptoridae, and Alcediniformes. The threedimensionally preserved fossils from Egem provide new data on the osteology of taxa that are otherwise mainly known from compression fossils with crushed bones. The material also includes specimens that further knowledge of the composition of early Eocene avifaunas of the North Sea Basin. The comparatively well-represented small galliform species is clearly distinguished from the early Eocene Gallinuloididae and most closely resembles Argillipes aurorum, a largely ignored galliform species from the London Clay. The tentatively identified fossils of Accipitridae and Alcediniformes would represent the earliest fossil records of these clades. The bird assemblage from Egem includes relatively few seabirds (Odontopterygiformes, cf. Prophaethontidae) and is dominated by remains of terrestrial species (Galliformes, Messelornithidae). Arboreal birds (Halcyornithidae, Leptosomiformes, cf. Alcediniformes, Coraciiformes) are less abundant and aerial insectivores (Apodiformes) very scarce, which either indicates a taphonomic bias in the composition of the avifauna or particular paleoenvironmental characteristics of the nearshore habitats in that area of the southern North Sea Basin.
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RBINS Staff Publications 2019