A conceptual framework for the study of modular responses to local environmental heterogeneity within the plant crown and a review of related concepts

Plants respond to local heterogeneity in abiotic and biotic conditions by changing module-level morphology, growth, and reproductive patterns. This paper presents a conceptual framework for the study of modular responses in plant crowns, clarifies the points that should be considered for scaling up from modular responses to the consequences at the whole-plant level, characterizes the interspecific differences in modular response patterns, and discusses their ecological significance. The modular response was defined as either autonomous or interactive, depending on whether the response of a module to its local condition is independent from the conditions of other modules. For evaluation of the autonomy of the modular response, the importance of considering positional relationships and organizational levels of modules was then proposed as these internally affect the modular response pattern, and their interspecific differences were characterized using several concepts. The identification of an autonomous modular unit is essential for scaling up module-level studies to the whole plant. For understanding the ecological significance of the modular response, further interspecific comparisons and assessments of the scale and the predictability of environmental heterogeneity are required. The conceptual framework will be useful for such purposes.