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Understanding the mechanisms that promote the coexistence of hundreds of species over small areas in tropical forest remains a challenge. Many tropical tree species are presumed to be functionally equivalent shade-tolerant species that differ in performance trade-offs between survival in shade and the ability to quickly grow in sunlight. Variation in plant functional traits related to resource acquisition is thought to predict variation in performance among species, perhaps explaining community assembly across habitats with gradients in resource availability. Many studies have found low predictive power, however, when linking trait measurements to species demographic rates. Seedlings face different challenges recruiting on the forest floor and may exhibit different traits and/or performance trade-offs than older individuals face in the eventual adult niche. Seed mass is the typical proxy for seedling success, but species also differ in cotyledon strategy (reserve vs photosynthetic) or other seedling traits. These can cause species with the same average seed mass to have divergent performance in the same habitat. We combined long-term studies of seedling dynamics with functional trait data collected at a standard developmental stage in three diverse neotropical forests to ask whether variation in coordinated suites of traits predicts variation among species in demographic performance. Across hundreds of species in Ecuador, Panama, and Puerto Rico, we found seedlings displayed correlated suites of leaf, stem, and root traits, which strongly correlated with seed mass and cotyledon strategy. Variation among species in seedling functional traits, seed mass, and cotyledon strategy were strong predictors of trade-offs in seedling growth and survival. Our findings highlight the importance of cotyledon strategy in addition to seed mass as a key component of seed and seedling biology. These results also underscore the importance of matching the ontogenetic stage of the trait measurement to the stage of demographic dynamics. Synthesis: With strikingly consistent patterns across three tropical forests, we find strong evidence for the promise of functional traits to provide mechanistic links between seedling form and demographic performance.
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The functional underpinnings of tropical forest dynamics—Functional traits, groups, and unmeasured diversity
Abstract The structure and dynamics of forest ecosystems are the outcome of differential performance playing out at the individual level. Interactions between the traits of an organism and its environment determine performance. Thus, our ability to understand and, ultimately, model forest dynamics critically relies on knowledge regarding the functional biology of the organisms. In tropical forests, this is a daunting challenge due to the diversity of the systems. This has driven ecologists to focus on identifying a handful of fundamentally important trade‐offs and a few traits that may indicate where a species falls along that trade‐off axis. In other cases, some ecologists have argued that species can be roughly binned into a handful of functional groups or guilds that capture most of the information needed to generate realistic models of forest dynamics. Here, we discuss the functional biology of tropical forest dynamics. We identify a series of key trade‐offs that should underpin forest dynamics and the traits ecologists have attempted to link to these trade‐offs. We then explore how far we can get by using functional groups or guilds to model tropical forest dynamics, the conceptual frameworks used for promoting such approaches, and what this modeling framework does not capture. We then use this to identify key gaps that should motivate the future of tropical tree functional ecology.
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- Award ID(s):
- 2124466
- PAR ID:
- 10579578
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Biotropica
- Volume:
- 57
- Issue:
- 1
- ISSN:
- 0006-3606
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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