Inherent conflicts between reaction norm slope and plasticity indices
when comparing phenotypic plasticity between species: a theoretical
framework and empirical test
Abstract
Quantifying the magnitude of phenotypic plasticity to compare among
species, populations, cultivars, or genotypes is important for revealing
the ecological and evolutionary significance of plastic responses to
various abiotic and biotic factors. Commonly used plasticity estimators
have occasionally been found to generate different species’ plasticity
rankings. However, we do not know how frequent this incongruence is or
the factors that influence the occurrence thereof; nor do we know which
plasticity estimator is more reliable. We first addressed these problems
using a theoretical framework, revealing inherent conflicts between the
reaction norm slope and plasticity indices, and the conditions affecting
these conflicts. We then empirically tested the effects of the
estimators on interspecific plasticity differences by reanalyzing 1248
sets of relevant data, confirming the predictions derived from our
theoretical framework. Finally, we show through theoretical analyses
that the reaction norm slope is more reliable than plasticity indices
for interspecific comparisons.