Predicting trait‐environment relationships for venation networks along an Andes‐Amazon elevation gradient

Abstract

Understanding functional trait-environment relationships (TERs) may improve predictions of community assembly. However, many empirical TERs have been weak or lacking conceptual foundation. TERs based on leaf venation networks may better link individuals and communities via hydraulic constraints. We report measurements of vein density, vein radius, and leaf thickness for more than 100 dominant species occurring in ten forest communities spanning a 3,300 m Andes-Amazon elevation gradient in Peru. We use these data to measure the strength of TERs at community scale and to determine whether observed TERs are similar to those predicted by physiological theory. We found strong support for TERs between all traits and temperature, as well weaker support for a predicted TER between maximum abundance-weighted leaf transpiration rate and maximum potential evapotranspiration. These results provide one approach for developing a more mechanistic trait-based community assembly theory.

Structural and defensive roles of angiosperm leaf venation network reticulation across an Andes–Amazon elevation gradient

“…These images and tracing methods are fully described in Blonder et al. (). This large image extent was necessary to robustly estimate reticulation traits, and therefore, necessarily included a small number of non‐minor veins.…”

“…We used these values to rescale vein density and loopiness values (with units per mm or per mm 2 respectively) by a factor of √(1 − S) or (1 − S), following Blonder et al. ().…”

“…Empirical studies have shown that minor venation patterns reflect hydraulic functioning across environments (Blonder & Enquist, ; Blonder et al., ; Sack & Scoffoni, ). Higher vein density may occur in with warmer and drier abiotic conditions (Sack & Scoffoni, ).…”

“…Sites with higher potential evapotranspiration or temperatures should select for species that achieve high carbon assimilation rates by transpiring either a high amount of water when water is temporarily abundant or that use the same amount of water more efficiently when water is not (Blonder, Violle, Bentley, & Enquist, ). Thus, higher vein density or water use efficiency should be associated with warmer environments (Blonder et al., , , ; Sack & Scoffoni, ; Uhl & Mosbrugger, ). As many scale‐dependent reticulation metrics are necessarily correlated based on geometrical scaling considerations (Blonder, Violle, & Enquist, ; Carins Murphy, Jordan, & Brodribb, ; Sack et al., ), warmer and less wet environments are expected to also have higher reticulation due to their direct impacts on vein density.…”

“…We explore several scale‐dependent and scale‐independent metrics for characterizing reticulation (Table ) and then determine whether the above hypotheses are related to different functional traits or abiotic variables. Empirical data come from the dominant tree species occurring along a 3,300 m humid tropical forest elevation gradient in western Amazonia and the Andes (Blonder et al., ).…”