Relationships between physical and chemical attributes of congeneric seedlings: how important is seedling defence?

1. While herbivory is considered a major selective force operating in mature vegetation, much less is known about how herbivores affect the expression of defence at the seedling stage. In this study we quantified several chemical and physical properties, usually considered to affect seedling palatability, of 14 Western Australian Hakea species. We also determined whether seedling defences were related to other plant life-history attributes. 2. Of all of the attributes measured, chemical defence (phenolic content of shoots) exhibited the most significant correlations with other traits (six of a possible eight). We also detected an apparent trade-off between chemical (phenolics) and physical (spinescence) defence. 3. Seed mass, relative growth rate and specific leaf area are traits commonly held to have the most predictive power in simplifying our understanding of plant ecological and evolutionary processes across species boundaries. Within this genus, however, these attributes were poorly correlated with other traits. 4. We conclude that more extensive studies of seedling defence attributes are needed for a fuller understanding of what governs the evolution of plant life-history traits.