Abstract: Water availability is a key determinant of forest ecosystem function and tree species distributions. While droughts are increasing in frequency in many ecosystems, including in the tropics, plant responses to water supply vary with species and drought intensity and are therefore difficult to model. Based on physiological first principles, we hypothesized that trees with a lower turgor loss point (pi-tlp), that is, a more negative leaf water potential at wilting, would maintain water transport for longer into a dry season. We measured sapflux density of 22 mature trees of 10 species during a dry season in an Amazonian rainforest, quantified sapflux decline as soil water content decreased and tested its relationship to tree pi-tlp, size and leaf predawn and midday water potentials measured after the onset of the dry season. The measured trees varied strongly in the response of water use to the seasonal drought, with sapflux at the end of the dry season ranging from 37 to 117% (on average 83 +/- 5 %) of that at the beginning of the dry season. The decline of water transport as soil dried was correlated with tree pi-tlp (Spearman's rho > 0.63), but not with tree size or predawn and midday water potentials. Thus, trees with more drought-tolerant leaves better maintained water transport during the seasonal drought. Our study provides an explicit correlation between a trait, measurable at the leaf level, and whole-plant performance under drying conditions. Physiological traits such as pi-tlp can be used to assess and model higher scale processes in response to drying conditions.

Abstract: Despite ongoing research in food web ecology and functional biogeography, the links between food web structure, functional traits and environmental conditions across spatial scales remain poorly understood. Trophic niches, defined as the amount of energy and elemental space occupied by species and food webs, may help bridge this divide. Here, we ask how the functional traits of species, the environmental conditions of habitats and the spatial scale of analysis jointly determine the characteristics of trophic niches. We used isotopic niches as a proxy of trophic niches, and conducted analyses at spatial scales ranging from local food webs and metacommunities to geographically distant sites. We sampled aquatic macroinvertebrates from 104 tank bromeliads distributed across five sites from Central to South America and compiled the macroinvertebrates’ functional traits and stable isotope values (δ15N and δ13C). We assessed how isotopic niches within each bromeliad were influenced by the functional trait composition of their associated invertebrates and environmental conditions (i.e., habitat size, canopy cover [CC] and detrital concentration [DC]). We then evaluated whether the diet of dominant predators and, consequently, energy pathways within food webs reflected functional and environmental changes among bromeliads across sites. At last, we determined the extent to which the isotopic niches of macroinvertebrates within each bromeliad contributed to the metacommunity isotopic niches within each site and compared these metacommunity-level niches over biogeographic scales. At the bromeliad level, isotopic niches increased with the functional richness of species in the food web and the DC in the bromeliad. The diet of top predators tracked shifts in prey biomass along gradients of CC and DC. Bromeliads that grew under heterogeneous CC displayed less trophic redundancy and therefore combined to form larger metacommunity isotopic niches. At last, the size of metacommunity niches depended on within-site heterogeneity in CC. Our results suggest that the trophic niches occupied by food webs can predictably scale from local food webs to metacommunities to biogeographic regions. This scaling process is determined by both the functional traits of species and heterogeneity in environmental conditions. A plain language summary is available for this article. © 2018 The Authors. Functional Ecology © 2018 British Ecological Society

Abstract: High-speed power-amplification mechanisms are common throughout the animal kingdom. In ants, power-amplified trap-jaw mandibles have evolved independently at least four times, including once in the subfamily Ponerinae which contains the sister genera Odontomachus and Anochetus. In Odontomachus, mandible strikes have been relatively well described and can occur in <0.15 ms and reach speeds of over 60 m s−1. In contrast, the kinematics of mandible strikes have not been examined in Anochetus, whose species are smaller and morphologically distinct from Odontomachus. In this study, we describe the mandible strike kinematics of four species of Anochetus representative of the morphological, phylogenetic, and size diversity present within the genus. We also compare their strikes to two representative species of Odontomachus. We found that two species, Anochetus targionii and Anochetus paripungens, have mandible strikes that overall closely resemble those found in Odontomachus, reaching a mean maximum rotational velocity and acceleration of around 3.7 × 104 rad s−1 and 8.5 × 108 rad s−2, respectively. This performance is consistent with predictions based on body size scaling relationships described for Odontomachus. In contrast, Anochetus horridus and Anochetus emarginatus have slower strikes relative to the other species of Anochetus and Odontomachus, reaching mean maximum rotational velocity and acceleration of around 1.3 × 104 rad s−1 and 2 × 108 rad s−2, respectively. This variation in strike performance among species of Anochetus likely reflects differences in evolutionary history, physiology, and natural history among species. © 2018 The Zoological Society of London

Abstract: Using different techniques to access the canopy of an Amazonian rainforest, we inspected 157 tree crowns for arboreal ants. Diversity statistics showed that our study sample was not representative of the tree and ant populations due to their high diversity in Amazonian rainforests, but permitted us to note that a representative part of territorially dominant arboreal ant species (TDAAs) was inventoried. Mapping of TDAA territories and use of a null model showed the presence of an ant mosaic in the upper canopy, but this was not the case in the sub-canopy. Among the TDAAs, carton-nesting Azteca dominated (52.98% of the trees) whereas ant-garden ants (Camponotus femoratus and Crematogaster levior), common in pioneer formations, were secondarily abundant (21.64% of the trees), and the remaining 25.37% of trees sheltered one of 11 other TDAAs. The distribution of the trees forming the upper canopy influences the structure of the ant mosaic, which is related to the attractiveness of some tree taxa for certain arboreal ant species and represents a case of diffuse coevolution.

Abstract: Azteca brevis Forel, a dolichoderine ant species, builds along the branches of its host plant galleries that bear numerous holes slightly wider than a worker’s head. We noted that the workers hide, mandibles open, beneath different holes, waiting for arthropod prey to walk by or alight. They seize the extremities of these arthropods and pull backwards, immobilizing the prey, which is then spreadeagled and later carved up or pulled into a gallery before being carved up. The total duration of the capture ranges from a few minutes to several hours. This ambush group hunting permits the capture of insects of a wide range of sizes, with the largest being 48.71 times heavier than the workers, something that we compared with other cases of group hunting by ants and trap use by other arthropods. A convergence with myrmicine ants of the genus Allomerus is shown. Thus, this study also shows that the genus Azteca presents the largest panel of group hunting strategies by ants and that there is polyethism related to polymorphism, as hunting workers are larger than their nestmates. We concluded that these gallery-shaped traps correspond to the notion of ‘extended phenotype’.