Forest stratification shapes allometry and flight morphology of tropical butterflies.

Studies of altitudinal and latitudinal gradients have identified links between the evolution of insect flight morphology, landscape structure and microclimate. Although lowland tropical rainforests offer steeper shifts in conditions between the canopy and the understorey, this vertical gradient has received far less attention. Butterflies, because of their great phenotypic plasticity, are excellent models to study selection pressures that mould flight morphology. We examined data collected over 5 years on 64 Nymphalidae butterflies in the Ecuadorian Chocó rainforest. We used phylogenetic methods to control for similarity resulting from common ancestry, and explore the relationships between species stratification and flight morphology. We hypothesized that species should show morphological adaptations related to differing micro-environments, associated with canopy and understorey. We found that butterfly species living in each stratum presented significantly different allometric slopes. Furthermore, a preference for the canopy was significantly associated with low wing area to thoracic volume ratios and high wing aspect ratios, but not with the relative distance to the wing centroid, consistent with extended use of fast flapping flight for canopy butterflies and slow gliding for the understorey. Our results suggest that microclimate differences in vertical gradients are a key factor in generating morphological diversity in flying insects.

The importance of insects on land and in water: a tropical view.

Tropical insects are astonishingly diverse and abundant yet receive only marginal scientific attention. In natural tropical settings, insects are involved in regulating and supporting ecosystem services including seed dispersal, pollination, organic matter decomposition, nutrient cycling, herbivory, food webs and water quality, which in turn help fulfill UN Sustainable Development Goals (SDGs). Current and future global changes that affect insect diversity and distribution could disrupt key ecosystem services and impose important threats on ecosystems and human well-being. A significant increase in our knowledge of tropical insect roles in ecosystem processes is thus vital to ensure sustainable development on a rapidly changing planet.

Physical, but not chemical, antiherbivore defense expression is related to the clustered spatial distribution of tropical trees in an Amazonian forest.

The conspecific negative density dependence hypothesis states that mortality of young trees (seedlings and saplings) is higher near conspecific adults due to mechanisms such as allelopathy, intraspecific competition, and pest facilitation, explaining why in the tropics, most of plant species tend to be rare and live dispersed. However, there are some tree species that defy this expectation and grow in large clusters of conspecific juveniles and adults. We hypothesize that conspecifics living in clusters show higher and/or more variable defensive profiles than conspecifics with dispersed distributions.We evaluated our hypothesis by assessing the expression of physical leaf traits (thickness, and the resistance to punch, tear and shear) and leaf chemical defenses for six clustered and six non-clustered tree species in Yasuní National Park, Ecuadorian Amazon. We ask ourselves whether (a) clustered species have leaves with higher physical resistance to damage and more chemical defenses variability than non-clustered species; (b) saplings of clustered species may show higher physical resistance to damage and higher variation on chemical leaf defenses than their conspecific adults, and (c) saplings of non-clustered species show lower resistance to physical damage and lower variation in chemical defenses compared to conspecific adults.Overall, our study did not support any of our hypotheses. Remarkably, we found that soluble metabolites were significantly species-specific.Our study suggests that plants physical but not chemical leaf antiherbivore defenses may be a crucial strategy for explaining survivorship of clustered species. Trees in Yasuní may also fall along a suite of tolerance/escape/defense strategies based on limitations of each species physiological constraints for survival and establishment. We conclude that other mechanisms, such as those related to indirect defenses, soil nutrient exploitation efficiency, volatile organic compounds, delayed leaf-greening, and seed dispersal mechanisms, shall be evaluated to understand conspecific coexistence in this forest.

Plant herbivory responses through changes in leaf quality have no effect on subsequent leaf-litter decomposition in a neotropical rain forest tree community.

It is commonly accepted that plant responses to foliar herbivory (e.g. plant defenses) can influence subsequent leaf-litter decomposability in soil. While several studies have assessed the herbivory-decomposability relationship among different plant species, experimental tests at the intra-specific level are rare, although critical for a mechanistic understanding of how herbivores affect decomposition and its consequences at the ecosystem scale. Using 17 tree species from the Yasuní National Park, Ecuadorian Amazonia, and applying three different herbivore damage treatments, we experimentally tested whether the plant intra-specific responses to herbivory, through changes in leaf quality, affect subsequent leaf-litter decomposition in soil. We found no effects of herbivore damage on the subsequent decomposition of leaf litter within any of the species tested. Our results suggest that leaf traits affecting herbivory are different from those influencing decomposition. Herbivore damage showed much higher intra-specific than inter-specific variability, while we observed the opposite for decomposition. Our findings support the idea that interactions between consumers and their resources are controlled by different factors for the green and the brown food-webs in tropical forests, where herbivory may not necessarily generate any direct positive or negative feedbacks for nutrient cycling.