Abstract: Because territoriality is energetically costly, territorial animals frequently respond less aggressively to neighbours than to strangers, a reaction known as the “dear enemy phenomenon” (DEP). The contrary, the “nasty neighbour effect” (NNE), occurs mainly for group-living species defending resource-based territories. We studied the relationships between supercolonies of the pest fire ant Solenopsis saevissima and eight ant species able to live in the vicinity of its nests plus Eciton burchellii, an army ant predator of other ants. The workers from all of the eight ant species behaved submissively when confronted with S. saevissima (dominant) individuals, whereas the contrary was never true. Yet, S. saevissima were submissive towards E. burchellii workers. Both DEP and NNE were observed for the eight ant species, with submissive behaviours less frequent in the case of DEP. To distinguish what is due to chemical cues from what can be attributed to behaviour, we extracted cuticular compounds from all of the nine ant species compared and transferred them onto a number of S. saevissima workers that were then confronted with untreated conspecifics. The cuticular compounds from three species, particularly E. burchellii, triggered greater aggressiveness by S. saevissima workers, while those from the other species did not. © 2013 Elsevier B.V.

Abstract: Beta diversity is among the most employed theoretical concepts in ecology and biodiversity conservation. Up to date, a self-contained definition of it, with no reference to alpha and gamma diversity, has never been proposed. Using Kullback-Leibler divergence, we present the explicit formula of Shannon's β entropy, a bias correction for its estimator and a confidence interval. We also provide the mathematical framework to decompose Shannon diversity into several hierarchical nested levels. From botanical inventories of tropical forest plots in French Guiana, we estimate Shannon diversity at the plot, forest and regional level. We believe this is a complete and usefulness toolbox for ecologists interested in partitioning biodiversity. © 2011 The Authors. Oikos © 2012 Nordic Society Oikos.

Abstract: Biodiversity continues to decline in the face of increasing anthropogenic pressures such as habitat destruction, exploitation, pollution and introduction of alien species. Existing global databases of species' threat status or population time series are dominated by charismatic species. The collation of datasets with broad taxonomic and biogeographic extents, and that support computation of a range of biodiversity indicators, is necessary to enable better understanding of historical declines and to project – and avert – future declines. We describe and assess a new database of more than 1.6 million samples from 78 countries representing over 28,000 species, collated from existing spatial comparisons of local-scale biodiversity exposed to different intensities and types of anthropogenic pressures, from terrestrial sites around the world. The database contains measurements taken in 208 (of 814) ecoregions, 13 (of 14) biomes, 25 (of 35) biodiversity hotspots and 16 (of 17) megadiverse countries. The database contains more than 1% of the total number of all species described, and more than 1% of the described species within many taxonomic groups – including flowering plants, gymnosperms, birds, mammals, reptiles, amphibians, beetles, lepidopterans and hymenopterans. The dataset, which is still being added to, is therefore already considerably larger and more representative than those used by previous quantitative models of biodiversity trends and responses. The database is being assembled as part of the PREDICTS project (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems – www.predicts.org.uk). We make site-level summary data available alongside this article. The full database will be publicly available in 2015. The collation of biodiversity datasets with broad taxonomic and biogeographic extents is necessary to understand historical declines and to project – and hopefully avert – future declines. We describe a newly collated database of more than 1.6 million biodiversity measurements from 78 countries representing over 28,000 species, collated from existing spatial comparisons of local-scale biodiversity exposed to different intensities and types of anthropogenic pressures, from terrestrial sites around the world.

Abstract: Biological nitrogen fixation (BNF) is a fundamental part of nitrogen cycling in tropical forests, yet little is known about the contribution made by free-living nitrogen fixers inhabiting the often-extensive forest canopy. We used the acetylene reduction assay, calibrated with 15N2, to measure free-living BNF on forest canopy leaves, vascular epiphytes, bryophytes and canopy soil, as well as on the forest floor in leaf litter and soil. We used a combination of calculated and published component densities to upscale free-living BNF rates to the forest level. We found that bryophytes and leaves situated in the canopy in particular displayed high mass-based rates of free-living BNF. Additionally, we calculated that nearly 2 kg of nitrogen enters the forest ecosystem through free-living BNF every year, 40% of which was fixed by the various canopy components. Our results reveal that in the studied tropical lowland forest a large part of the nitrogen input through free-living BNF stems from the canopy, but also that the total nitrogen inputs by free-living BNF are lower than previously thought and comparable to the inputs of reactive nitrogen by atmospheric deposition.

Abstract: Both gene flow and historical events influence the genetic diversity of natural populations. One way to understand their respective impact is to analyze population genetic structure at large spatial scales. We studied the distribution of genetic diversity of 17 populations of Vouacapoua americana (Caesalpiniaceae) in French Guiana, using nine micro satellite loci. Low genetic diversity was observed within populations, with a mean allelic richness and gene diversity of 4.1 and 0.506, respectively, which could be due to low effective population size and/or past bottlenecks. Using the regression between F-st/(1-F-st), estimated between pairs of populations, and the logarithm of the geographical distance, the spatial genetic structure can partly be explained by isolation-by-distance and limited gene flow among populations. This result is in agreement with the species' biology, including seed and pollen dispersal by rodents and insects, respectively. In contrast, no clear genetic signal of historical events was found when examining genetic differentiation among populations in relation to biogeographical hypotheses or by testing for bottlenecks within populations. Our conclusion is that nuclear spatial genetic structure of V. americana, at the geographic scale of French Guiana, is better explained by gene flow rather than by historical events.