Plant size: an ignored parameter in epiphyte ecophysiology?

Abstract

A central objective of many ecophysiological investigations is the establishment of mechanistic explanations for plant distributions in time and space. The important, albeit mostly ignored, question arises as to the nature of the organisms that should be used as representative in pertinent experiments. We suggest that it is essential to use a ‘demographic approach’ in physiological ecology, because physiological parameters such as photosynthetic capacity (PC, determined under non-limiting conditions with the oxygen electrode) may change considerably with plant size. A survey of ten vascular epiphyte species from Central Panama revealed an up to fivefold continuous increase in PC from small to large conspecifics. Moreover, the intraspecific variation in PC was almost always higher than the interspecific variation when comparing only large individuals. Theoretical considerations and additional evidence from other ecophysiological experiments corroborate the conclusion that size must be taken into account in the design of ecophysiological experiments with vascular epiphytes. In the past, most studies have ignored plant size, which may now lead to complications in the hitherto unambiguous interpretation of their results.