Ontogenetic shifts in trait‐mediated mechanisms of plant community assembly

Abstract

Abstract. Identifying the processes that maintain highly diverse plant communities remains a central goal in ecology. Species variation in growth and survival rates across ontogeny, represented by tree size classes and life history stage-specific niche partitioning, are potentially important mechanisms for promoting forest diversity. However, the role of ontogeny in mediating competitive dynamics and promoting functional diversity is not well understood, particular in high-diversity systems such as tropical forests. The interaction between interspecific functional trait variation and ontogenetic shifts in competitive dynamics may yield insights into the ecophysiological mechanisms promoting community diversity. We investigated how functional trait (seed size, maximum height, SLA, leaf N, and wood density) associations with growth, survival, and response to competing neighbors differ among seedlings and two size classes of trees in a subtropical rain forest in Puerto Rico. We used a hierarchical Bayes model of diameter growth and survival to infer trait relationships with ontogenetic change in competitive dynamics. Traits were more strongly associated with average growth and survival than with neighborhood interactions, and were highly consistent across ontogeny for most traits. The associations between trait values and tree responses to crowding by neighbors showed significant shifts as trees grew. Large trees exhibited greater growth as the difference in species trait values among neighbors increased, suggesting traitassociated niche partitioning was important for the largest size class. Our results identify potential axes of niche partitioning and performance-equalizing functional trade-offs across ontogeny, promoting species coexistence in this diverse forest community.

Topography and neighborhood crowding can interact to shape species growth and distribution in a diverse Amazonian forest

“…The fact that traits did not appear to consistently mediate species response to neighborhood crowding is consistent with previous work in a subtropical forest (Lasky et al. ) but contradicts recent work in a secondary tropical forest (Uriarte et al. ) and in forests globally (Kunstler et al.…”

“…Similar positive effects were detected on the survival of tropical seedlings in Puerto Rico (Lasky et al. ). Such findings could be due to positive interactions between plant species or to more favorable environmental conditions that surpassed any negative crowding effects.…”

“…Future studies would need to combine demographic data across ontogenetic stages (Lasky et al. ), from seedlings to adult trees, to better evaluate the role of multiple mechanisms in shaping species dynamics and coexistence in highly diverse tropical rainforests.…”

Accelerated development in Johnsongrass seedlings (Sorghum halepense) suppresses the growth of native grasses through size-asymmetric competition

“…Ontogenetic shifts between small juvenile stages and large adult stages are important niche components [40–42]. Species differences in growth patterns during early seedling development may be particularly pertinent in invasion ecology under the scenario we outlined here.…”

Interspecific Functional Convergence and Divergence and Intraspecific Negative Density Dependence Underlie the Seed-to-Seedling Transition in Tropical Trees

“…Maximum height was measured to represent the adult light niche of species. It was included in this study of seedlings, as it is linked to growth rates across life stages (Iida et al 2014;Lasky et al 2015). Seed mass was measured, as it represents where a species is located on an axis between producing few well-provisioned offspring and producing many poorly provisioned offspring, where provisioning is expected to be strongly related to success along resource availability gradients.…”