Plant Interactions Alter the Predictions of Metabolic Scaling Theory

Abstract

Metabolic scaling theory (MST) is an attempt to link physiological processes of individual organisms with macroecology. It predicts a power law relationship with an exponent of −4/3 between mean individual biomass and density during density-dependent mortality (self-thinning). Empirical tests have produced variable results, and the validity of MST is intensely debated. MST focuses on organisms’ internal physiological mechanisms but we hypothesize that ecological interactions can be more important in determining plant mass-density relationships induced by density. We employ an individual-based model of plant stand development that includes three elements: a model of individual plant growth based on MST, different modes of local competition (size-symmetric vs. -asymmetric), and different resource levels. Our model is consistent with the observed variation in the slopes of self-thinning trajectories. Slopes were significantly shallower than −4/3 if competition was size-symmetric. We conclude that when the size of survivors is influenced by strong ecological interactions, these can override predictions of MST, whereas when surviving plants are less affected by interactions, individual-level metabolic processes can scale up to the population level. MST, like thermodynamics or biomechanics, sets limits within which organisms can live and function, but there may be stronger limits determined by ecological interactions. In such cases MST will not be predictive.

General allometric scaling of net primary production agrees with plant adaptive strategy theory and has tipping points

“…; Lin et al . ). Specifically with regard to NPP, larger plants are predicted to competitively reduce NPP of smaller plants and thus constrain MTE‐based NPP scaling (Kerkhoff & Enquist ; Coomes & Allen ; Coomes, Lines & Allen ; Lin et al .…”

“…,b), even if coefficients have been predicted to shift due to other factors (e.g., Kerkhoff & Enquist ; Coomes, Lines & Allen ; Lin et al . ; Michaletz et al . ; Hatton et al .…”

“…Instead, separate NPP scaling models exist for separate systems (e.g., forest stands, grasslands), all using power laws but reporting model coefficients unique to each data set (Kerkhoff & Enquist ; Coomes, Lines & Allen ; Lin et al . ; Michaletz et al . ; Hatton et al .…”

The use of Eucalyptus in agroforestry systems of southern Rwanda : to integrate of segregate

“…Variation in plant size creates size asymmetric interactions where larger individuals (trees) may pre-empt resources by acquiring them while they are unavailable to smaller individuals (annual crops) (Weiner and Damgaard, 2006). These interactions are among the strongest drivers of dynamics in tree-crop systems because they set the limits within which organisms can live and function (Lin et al, 2013).…”

Influence of shade tolerance and development stage on the allometry of ten temperate tree species

“…Previous studies have proposed inclusion of the notion of limiting resources in the MST by considering the allometry between individual mass and density of trees growing under the self-thinning law (Lin et al 2012(Lin et al , 2013. They achieved this by adding two terms representing abiotic stress (e.g.…”