Banksia Oligantha - Ecology

Ecology

Little has been published on the ecology of B. oligantha. Its lifespan is probably around 10 to 30 years.

Six species of honeyeater have been observed feeding at its flowers, as have insects including honeybees, ants, butterflies, beetles and native bees. Both birds and insects function as pollinators, but honeybees are probably not very effective: in one study only about 4% of honeybees collected pollen, and they tended to move from inflorescence to inflorescence on the same plant, rather than moving between plants.

Assessments of the mating system of this species have found that outcrossing rates vary between populations, with populations in disturbed environments tending to be more inbred than populations in relatively intact bushland. This has been attributed to a range of causes. Firstly, the higher density of disturbed populations leads to greater rates of mating between neighbouring plants, resulting in more genetic structure and thus more effective selfing. Secondly, disturbed populations usually lack an understorey, and so cannot support a resident population of honeyeaters; instead, they rely upon sporadic visits for pollination. The greatly reduced pollination rates means fewer outcrossing fertilisations on average, leading to less selection against inbred fertilisations.

Like many plants in south-west Western Australia, B. oligantha is adapted to an environment in which bushfire events are relatively frequent. Most Banksia species can be placed in one of two broad groups according to their response to fire: reseeders are killed by fire, but fire also triggers the release of their canopy seed bank, thus promoting recruitment of the next generation; resprouters survive fire, resprouting from a lignotuber or, more rarely, epicormic buds protected by thick bark. B. oligantha is a reseeder; it has thin bark, and lacks a lignotuber, so it is killed by fire. However the species is weakly serotinous: fire triggers seed release, yet seed release still occurs in the absence of fire.

Seed germination rates are quite high. One study found germination rates better than 77% in most batches tested. Seed is likely to remain viable for a long time, as seed of the closely related B. cuneata remains viable for around ten years.