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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RBINS Staff Publications 2020
A restudy of Devonian palynological assemblages of samples from the A1-69 borehole, drilled in the Ghadamis Basin, western Libya, North Africa has led to the discovery of numerous well-preserved megaspores amongst abundant miospores, rare acritarchs and rare chitinozoans. Thirteen samples from base to top, 1496 ft (456 m) up to 965 ft (294 m), contain the richest Devonian megaspore assemblages from northwestern Gondwana. The section is dated by a rich diverse miospore assemblage indicating the presence of the upper part of the AD pre-Lem Biozone up to the lower part of the TCo Oppel Zone, ranging from a latest Eifelian or earliest Givetian age up to a latest Givetian or an earliest Frasnian age. Seventeen megaspore taxa have been identified. Among them, two new species (Biharisporites lugardonii and Lagenicula milleri) and four new varieties (Corystisporites acutispinosus var. acutispinosus and var. bullatus, Heliotriletes longispinosus var. longispinosus and var. radiatus) are described. One new possible megaspore species is also described: Verruciretusispora labiosa sp. nov. One core sample (1293 ft, 394 m) contains several specimens of very large megaspores (ca. 1 mm), the largest known from Devonian localities (except for one specimen observed in the Givetian from Belgium). Among the 17 megaspore taxa from Libya, 6 are present on the Euramerican Continent. This observation is in accordance with previous palynological conclusions that favour the absence of palaeogeographic barriers between the Euramerican and Gondwanan continents that are suggested to be grouped together in a “Pre-Pangea” land mass.
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