Bird pollinators, seed storage and cockatoo granivores explain large woody fruits as best seed defense in Hakea

摘要

Nutrient-impoverished soils with severe summer drought and frequent fire typify many Mediterranean type regions of the world. Such conditions limit seed production and restrict opportunities for seedling recruitment making protection from granivores paramount. Our focus was on Hakea, a genus of shrubs widespread in southwestern Australia, whose nutritious seeds are targeted by strong-billed cockatoos. We assessed 56 Hakea species for cockatoo damage in 150 populations spread over 900 km in relation to traits expected to deter avian granivory: dense spiny foliage; large, woody fruits; fruit crypsis via leaf mimicry and shielding; low seed stores; and fruit clustering. We tested hypothesises centred on optimal seed defenses in relation to (a) pollination syndrome (bird vs insect), (b) fire regeneration strategy (killed vs resprouting) and (c) on-plant seed storage (transient vs prolonged).