Jamie Males & Howard Griffiths
The bromeliads are one of the world’s most diverse plant families, with species occurring in an extremely broad range of habitats across the tropical and subtropical Americas. The colonisation of new habitat types by different bromeliad lineages is known to have involved transitions in growth form (functional type), including switches to life in the canopy and modifications to the photosynthetic pathway on more than one occasion. However, exactly which traits are important in determining the habitat preferences and bioclimatic distributions of species of different functional type has remained rather poorly studied. In particular, despite many isolated studies of drought responses in individual species, there has been no comprehensive analysis of the components of drought resistance in bromeliad species.
We devised a set of hypotheses as to how four easily quantifiable leaf traits might show evolutionary coordination across the bromeliads, and how they might interact to determine ecophysiological tolerances and bioclimatic distributions. We then quantified these traits in an unprecedentedly wide range of species, representing 10% of the entire family. Analysis of the data provided extensive support for the hypotheses that these traits would be intercorrelated and that they would also be linked with bioclimatic distributions. Species from more arid and seasonal environments tended to invest more in drought resistance, including both avoidance and tolerance mechanisms. Functional types clearly diverged in drought resistance trait values, which could explain the unique ecological strategies associated with each.
This study shows reveals how individual structural and biochemical leaf traits can interact to mediate ecophysiological differentiation, which could be a key mode for the evolution of ecological diversity and species diversity within and between plant lineages.
Image caption: Vriesea glutinosa Lindl., a tank-forming bromeliad native to montane forest in Trinidad and Venezuela. © Jamie Males.