in many ways, as exciting as those facing physiological ecology in the 1960's and 1970's.
(3) Analysing the impact of a trait on whole-plant carbon gain is an important, if
not essential, step toward understanding its adaptive value, but such studies alone are
inadequate to demonstrate that such a value exists and is biologically relevant. Only
appropriately controlled studies of competition between plants with different expressions
of a trait, conducted under natural conditions, can demonstrate that such variants have
adaptive significance. Natural within-population variation in traits that affect adaptation
to irradiance level has been little studied, and the implications of such variation
for whole-plant carbon gain under different conditions have been largely ignored.
Ultimately, to demonstrate adaptation to irradiance level more rigorously, we must
relate within-population variation to differences in whole-plant carbon gain, growth and
reproductive success under different irradiance levels.