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

Abstract

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.

Disentangling the effects of environment and ontogeny on tree functional dimensions for congeneric species in tropical forests

“…As predicted, variation in morphological and chemical traits is mainly driven by habitat and developmental stage. In line with previous work in tropical forests, forest habitat appears as an important driver of leaf chemical traits (Kraft et al, 2008;Katabuchi et al, 2012;Fortunel et al, 2014), whereas developmental stage mostly impacts morphological traits (Kitajima et al, 2013;Cobo-Quinche et al, 2019). Interestingly, variation in physiological, morphological, and chemical traits with developmental stage is overall independent of habitats, which suggests that ontogenetic trajectories are primarily shaped by inherent developmental constraints within species.…”

Forest stratification shapes allometry and flight morphology of tropical butterflies

“…The use of trait-based approaches to explore species responses to their biotic and abiotic environment are central to our understanding of the structure of natural assemblages [95], proving effective in tropical rainforests (e.g. [96,97]). Here, we report a consistent pattern of habitat specialization linked to the evolution of flight traits.…”

Top-down and bottom-up controls on an herbivore on a native and introduced plant in a tropical agricultural landscape

“…Specific leaf area (SLA) was evaluated on 45 mm diameter leaf discs, avoiding the midvein, recording fresh and dry mass with the portable balance to calculate water content. Leaf toughness was evaluated as the force to fracture the leaf lamina using a penetrometer (Cobo-Quinche et al, 2019). Trichome density, water content and SLA were also measured on open habitat S. myriacanthum.…”