FRUIT-SEED RELATIONS IN HAKEA - SEROTINOUS SPECIES INVEST MORE DRY-MATTER IN PREDISPERSAL SEED PROTECTION

The ability to maintain a canopy stored seedbank (serotiny) is charact eristic of many woody genera inhabiting fire-prone environments. The r elationship between level of serotiny for 94 Hakea (Proteaceae) specie s in southwestern Australia and follicle mass, density, three wall thi cknesses and seed mass was investigated. Two species were nonserotinou s (fruits open at maturity), 12 were weakly serotinous (majority of fr uits open at maturity), 9 were moderately serotinous (fruits open with in five years of maturity) and 71 were strongly serotinous (fruits sti ll closed at least five years after reaching maturity). A positive rel ationship existed between the level of serotiny and follicle morpholog y. Strongly serotinous species were more likely to have heavier, woodi er and thicker-walled follicles than non-and weakly serotinous species . Moderately/strongly serotinous species invested more energy (six tim es higher follicle:seed mass ratio) than non weakly serotinous species , consistent with increased protection of the seeds from granivores, p athogens, desiccation and/or heat. Recent work has shown that thicker fruit walls (strongly serotinous species) provide better insulation to seeds from heat, although the need to survive fire is just as critica l for thin-walled, weakly serotinous species. Greater protection from granivores may provide a better explanation for the adaptive significa nce of dense, thick-walled serotinous follicles, as the opportunities for predispersal granivore damage are low among weakly serotinous spec ies.