Abstract: Abstract Wood properties and especially wood density have been used as functional traits organized along major axes of species life history and strategy. Beyond statistical analyses, a better mechanistic understanding of relationships among wood traits is essential for ecologically relevant interpretation of wood trait variations. A set of theoretical relationships mechanistically linking wood basic density with some other wood traits is derived from cellular material physics. These theoretical models picture basic physical constraints and thus provide null hypotheses for further ecological studies. Analysis is applied to data from two original datasets and several datasets extracted from the literature. Results emphasize the strong physical constraint behind the link between basic density and maximal storable water on the one hand, and elastic modulus on the other hand. Beyond these basic physical constraints, the developed framework reveals physically less expected trends: the amount of free water available for physiological needs increases in less dense wood of fast-growing species, and the cell wall stiffness decreases with density in temperate hardwoods and is higher in sapling stages in the rainforest understorey where competition for light is associated with high mechanical risk. We emphasize the use of theoretically independent traits derived from models of cellular material physics to investigate the functional variation of wood traits together with their environmental and phylogenetic variations. Although the current study is limited to basic density, green wood lumen saturation and wood specific modulus, we further emphasize the identification of complementary independent wood traits representing other biomechanical functions, nutrient storage, hydraulic conductance and resistance to drought. A plain language summary is available for this article.

Abstract: Elevational gradients provide an interesting opportunity for studying the effect of climatic drivers over short distances on the various facets of biodiversity. It is globally assumed that the decrease in species richness with increasing elevation follows mainly the decrease in ecosystem productivity, but studies on functional diversity still remain limited. Here, we investigated how resource use and food preferences by both individual ant species and communities foraging in the understory vary with elevation along a complete elevational gradient (200 to 3200 m asl). Five bait types reflecting some of the main ecosystem processes in which ants are involved were tested: mutualism (sucrose and melezitose), predation (live termites), and detritivory (crushed insects and chicken feces). The observed monotonic decrease in both species richness and occurrences with elevation increase was accompanied by changes in some of the tested ecosystem processes. Such variations can be explained by resource availability and/or resource limitation: Predation and bird feces removal decreased with increasing elevation possibly reflecting a decline in species able to use these resources, while insect detritivory and nectarivory were most probably driven by resource limitation (or absence of limitation), as their relative use did not change along the gradient. Consequently, resource attractiveness (i.e., food preferences at the species level) appears as an important factor in driving community structuring in ants together with the abiotic environmental conditions.

Abstract: Abstract Aim Large tropical trees form the interface between ground and airborne observations, offering a unique opportunity to capture forest properties remotely and to investigate their variations on broad scales. However, despite rapid development of metrics to characterize the forest canopy from remotely sensed data, a gap remains between aerial and field inventories. To close this gap, we propose a new pan-tropical model to predict plot-level forest structure properties and biomass from only the largest trees. Location Pan-tropical. Time period Early 21st century. Major taxa studied Woody plants. Methods Using a dataset of 867 plots distributed among 118 sites across the tropics, we tested the prediction of the quadratic mean diameter, basal area, Lorey's height, community wood density and aboveground biomass (AGB) from the ith largest trees. Results Measuring the largest trees in tropical forests enables unbiased predictions of plot- and site-level forest structure. The 20 largest trees per hectare predicted quadratic mean diameter, basal area, Lorey's height, community wood density and AGB with 12, 16, 4, 4 and 17.7% of relative error, respectively. Most of the remaining error in biomass prediction is driven by differences in the proportion of total biomass held in medium-sized trees (50?70 cm diameter at breast height), which shows some continental dependency, with American tropical forests presenting the highest proportion of total biomass in these intermediate-diameter classes relative to other continents. Main conclusions Our approach provides new information on tropical forest structure and can be used to generate accurate field estimates of tropical forest carbon stocks to support the calibration and validation of current and forthcoming space missions. It will reduce the cost of field inventories and contribute to scientific understanding of tropical forest ecosystems and response to climate change.

Abstract: Abstract Aim Seasonally dry tropical forest (SDTF) of the Caribbean Islands (primarily West Indies) is floristically distinct from Neotropical SDTF in Central and South America. We evaluate whether tree species composition was associated with climatic gradients or geographical distance. Turnover (dissimilarity) in species composition of different islands or among more distant sites would suggest communities structured by speciation and dispersal limitations. A nested pattern would be consistent with a steep resource gradient. Correlation of species composition with climatic variation would suggest communities structured by broad-scale environmental filtering. Location The West Indies (The Bahamas, Cuba, Hispaniola, Jamaica, Puerto Rico, US Virgin Islands, Guadeloupe, Martinique, St. Lucia), Providencia (Colombia), south Florida (USA) and Florida Keys (USA). Taxon Seed plants?woody taxa (primarily trees). Methods We compiled 572 plots from 23 surveys conducted between 1969 and 2016. Hierarchical clustering of species in plots, and indicator species analysis for the resulting groups of sites, identified geographical patterns of turnover in species composition. Nonparametric analysis of variance, applied to principal components of bioclimatic variables, determined the degree of covariation in climate with location. Nestedness versus turnover in species composition was evaluated using beta diversity partitioning. Generalized dissimilarity modelling partitioned the effect of climate versus geographical distance on species composition. Results Despite a set of commonly occurring species, SDTF tree community composition was distinct among islands and was characterized by spatial turnover on climatic gradients that covaried with geographical gradients. Greater Antillean islands were characterized by endemic indicator species. Northern subtropical areas supported distinct, rather than nested, SDTF communities in spite of low levels of endemism. Main conclusions The SDTF species composition was correlated with climatic variation. SDTF on large Greater Antillean islands (Hispaniola, Jamaica and Cuba) was characterized by endemic species, consistent with their geological history and the biogeography of plant lineages. These results suggest that both environmental filtering and speciation shape Caribbean SDTF tree communities.

Abstract: ABSTRACT The Black Curassow (Crax alector) is a large game bird with Vulnerable conservation status found in north-central South America. We examined its distributional pattern across French Guiana using a large number of environmental descriptors at 3 scales of analysis: landscape, forest type, and microhabitat. We used a hierarchical model with temporary emigration and imperfect detection for data collected by standard distance sampling methods at 35 study sites. At the landscape scale, Black Curassow density decreased with hunting pressure and increased with steeper slopes in both hunted and unhunted areas. Topography appeared to be a good proxy for Black Curassow ecological requirements and probably reflected habitat quality. At the forest scale, population density was negatively correlated with the abundance of palms and Mimosoideae and positively correlated with the abundance of Lauraceae. Botanical families did not directly influence Black Curassow distribution, but rather determined spatial patterns by being markers of a particular forest type. At the microhabitat scale, Black Curassows used hilltops more frequently than other parts of the local topographical gradient. Our multiscale analysis shows that this species' distribution can be explained by biotic or abiotic conditions, regardless of the scale. For conservation, we recommend maintaining connectivity between Black Curassow populations separated by hunted areas. Our predicted densities could be used to adapt hunting quotas across French Guiana's forests. We show that combining field and remote sensing data helps to understand the ecological processes responsible for Black Curassow habitat relationships.