Abstract: Changes in global and regional precipitation regimes are among the most pervasive components of climate change. Intensification of rainfall cycles, ranging from frequent downpours to severe droughts, could cause widespread, but largely unknown, alterations to trophic structure and ecosystem function. We conducted multi-site coordinated experiments to show how variation in the quantity and evenness of rainfall modulates trophic structure in 210 natural freshwater microcosms (tank bromeliads) across Central and South America (18°N to 29°S). The biomass of smaller organisms (detritivores) was higher under more stable hydrological conditions. Conversely, the biomass of predators was highest when rainfall was uneven, resulting in top-heavy biomass pyramids. These results illustrate how extremes of precipitation, resulting in localized droughts or flooding, can erode the base of freshwater food webs, with negative implications for the stability of trophic dynamics. © 2020, The Author(s).

Abstract: The majority of variation in six traits critical to the growth, survival and reproduction of plant species is thought to be organised along just two dimensions, corresponding to strategies of plant size and resource acquisition. However, it is unknown whether global plant trait relationships extend to climatic extremes, and if these interspecific relationships are confounded by trait variation within species. We test whether trait relationships extend to the cold extremes of life on Earth using the largest database of tundra plant traits yet compiled. We show that tundra plants demonstrate remarkably similar resource economic traits, but not size traits, compared to global distributions, and exhibit the same two dimensions of trait variation. Three quarters of trait variation occurs among species, mirroring global estimates of interspecific trait variation. Plant trait relationships are thus generalizable to the edge of global trait-space, informing prediction of plant community change in a warming world. © 2020, Crown.

Abstract: Group hunting, nomadism, wingless queens and colony fission characterize army ants, allowing them to have become the main tropical arthropod predators, mostly of other social insects. We studied the reactions of different ant species to the New World army ants Eciton burchellii (WESTWOOD, 1842) and E. hamatum (FABRICIUS, 1782) (Ecitoninae). We compiled our results with those already known in a synthetic appendix. A wide range of ant species react to the ap-proach of army ant raids by evacuating their nests with several workers transporting brood. The Eciton plunder a large part of the brood but rarely kill workers or queens, so that the latter return to their nest and resume colony activity. One exception is Paratrechina longicornis (LATREILLE, 1802) colonies that quickly evacuate their nest, so that the entire col-ony can generally escape a raid. Another is Leptogenys mexicana (MAYR, 1870) that leave their nests in columns while some nestmates resist the attack; they therefore lose only a few larvae. We noted that colonies can avoid being raided if the army ants ignore them (Atta cephalotes (LINNAEUS, 1758)), or if the workers produce a repellent substance (Azteca associated with myrmecophytic Cecropia) or are repellent themselves (Pachycondyla villosa (FABRICIUS, 1804), Ec-tatomma spp.). In the other cases, a part of the brood is lost. When an Eciton raid approached the base of their host-tree trunk, Azteca andreae GUERRERO, DELABIE and DEJEAN, 2010 workers dropped a part of their brood on the ground. While numerous Eciton workers were gathering up this brood, the front of the column advanced, so that the Azteca andreae nests were not plundered. Pheidole megacephala (FABRICIUS, 1793) nests were partly plundered as the workers reacted aggressively, blocking the Eciton inside their nests during a long time. When the latter returned toward their bivouac, they were attacked and killed by their nestmates whether or not they had retrieved Pheidole brood. Consequently, the front of the column turned away from the Pheidole nest.

Abstract: Mutualistic interactions between ants and plants are important features of many ecosystems, and they can be divided into three main categories: dispersal and protective mutualisms and myrmecotrophy. In both the Neotropics and the Southeastern Asian Paleotropics, ant gardens (AGs), a particular type of ant-plant interaction, are frequent. To initiate AGs, ants integrate the seeds of certain epiphyte species into the carton of their nest. The development of the plants leads to the formation of a cluster of epiphytes rooted in the carton. They have been defined as one of the most complex associations between ants and plants known because of the plurispecific, but also specialized nature of the association involving several phylogenetically-distant ant and plant species. The aim of this review is to provide a synthesis of the diversity and ecology of AGs, including the outcomes experienced by the partners in the interaction and the direct and indirect impacts ant-garden ants have on the plant and arthropod communities.

Abstract: The purpose of this study was to test the capacity of the ectomycorrhizal (ECM) fungus, Scleroderma bermudense, to alleviate saline stress in seagrape (Coccoloba uvifera L.) seedlings. Plants were grown over a range (0, 200, 350 and 500 mM) of NaCl levels for 12 weeks, after 4 weeks of non-saline pre-treatment under greenhouse conditions. Growth and mineral nutrition of the seagrape seedlings were stimulated by S. bermudense regardless of salt stress. Although ECM colonization was reduced with increasing NaCl levels, ECM dependency of seagrape seedlings increased. Tissues of ECM plants had significantly increased concentrations of P and K but lower Na and Cl concentrations than those of non-ECM plants. Higher K concentrations in the leaves of ECM plants suggested a higher osmoregulating capacity of these plants. Moreover, the water status of ECM plants was improved despite their higher evaporative leaf surface. The results suggest that the reduction in Na and Cl uptake together with a concomitant increase in P and K absorption and a higher water status in ECM plants may be important salt-alleviating mechanisms for seagrape seedlings growing in saline soils.