Cryptic polymorphic Proteaceae seeds reduce detection by visually-cued predators on post-fire soils

Abstract

Plant species with large seeds are susceptible to high levels of seed predation. Seeds of serotinous Proteaceae plants display what appears to be background matching, with polymorphic colours or ornamented surfaces reducing their detectability on certain soil types. We investigated whether seed crypsis (background matching) in Proteaceae seeds can reduce seed predation by visually-cued bird granivores using field observations, seed removal trials and spectrophotometry data. We found no difference in seed predation of winged seeds on different substrates by a diurnal rodent granivore. We therefore ruled out rodent granivores as selective agents driving visual seed crypsis in Cape Proteaceae. Light seeds of most polymorphic Leucadendron seeds showed background matching with their native soils, with granivorous birds predicted to have difficulty distinguishing them apart. Monomorphic Protea seeds with hairs generally do not background match with no reduction in detectability from visually cued predators. This is the first widescale documentation of seed colours and first description of crypsis in the seeds of Cape plants. We suggest that seed colour polymorphisms are adaptations to substrate-specific seed predation biases, with visually-cued bird granivores the likely selective agent driving the visual crypsis of Cape fynbos seeds.