Do community-weighted mean functional traits reflect optimal strategies?

Area of Science:

• Ecology
• Trait-based ecology
• Community ecology

Background:

• Community-weighted mean (CWM) traits are often linked to environmental conditions, suggesting selection for optimal phenotypes.
• However, high interspecific trait variation within communities challenges this notion, necessitating reconciliation for predictive ecological theories.

Purpose of the Study:

• To test the "CWM-optimality" hypothesis, which posits species occurrence aligns with local CWM trait values.
• To investigate how species traits influence their distribution across environmental gradients, specifically precipitation in Puerto Rico.

Main Methods:

• Utilized geographical distribution data and three key traits (wood density, leaf mass per area, maximum height) for 173 tree species.
• Compared species occurrence patterns (as a proxy for fitness) with the functional composition of forest plots along a precipitation gradient.

Main Results:

• 70% of species supported CWM-optimality for at least one trait.
• Approximately 25% of species opposed CWM-optimality for at least one trait, enhancing local functional diversity.
• Most opposing species (85%) did so for only one trait; few opposed it in multivariate trait space.

Conclusions:

• Species traits do not always align with local CWM trait values, indicating a role for functional diversity.
• Constraints on local functional variation are stronger in multivariate trait space than for individual traits.
• Understanding trait variation is crucial for advancing functional community ecology and predictive ecological theories.