Differences in Protea Traits Add up to Explain Differences in Fitness

Global plant trait datasets commonly identify trait relationships that are interpreted to reflect fundamental trade-offs associated with plant strategies, but often these trait relationships are not identified when evaluating them at smaller taxonomic and spatial scales. Kristen Nolting and colleagues evaluated trait relationships measured on individual plants for five widespread Protea species in South Africa to determine whether broad scale patterns of structural trait (e.g. leaf area) and physiological trait (e.g. photosynthetic rates) relationships can be detected within natural populations, and if these traits are themselves related to plant fitness.

The team evaluated the variance structure (i.e. the proportional intraspecific trait variation relative to among species variation) for nine structural traits and the six physiological traits measured in wild populations. They used a multivariate path model to evaluate the relationships between structural traits and physiological traits, and the relationship between these traits and plant size and reproductive effort.

“Although much work in plant ecology over the past decade has focused on analysis of functional traits, relatively few have examined the association between those traits and indicators of physiological performance or fitness, and even fewer have examined those associations at the level of individuals,”write Nolting and colleagues. “Here we demonstrate in five species of Protea from the western Cape region of South Africa that individual differences in structural traits are associated with individual differences in physiological performance, and that both are associated with individual differences in overall plant size and reproductive effort.”

“In addition, we show that in spite of substantial structural trait differences among species, differences in physiological traits among species are relatively modest. Finally, we show that a substantial fraction of the differences in physiological traits among individuals can be accounted for by multivariate differences in structural traits even when associations of individual traits with physiological trait measures are weak or uncertain.”