Banksia Ilicifolia - Ecology

Ecology

Banksia ilicifolia has been recorded as a source of nectar for the honey possum (Tarsipes rostratus) in winter to early summer (May to December), from field studies in the Scott National Park, replaced by Adenanthos meisneri in the summer. Several honeyeater species visit and pollinate Banksia ilicifolia. The Western Spinebill (Acanthorhynchus superciliosus) in particular prefers this species over other banksias.

A field study carried out at Jandakot Airport south of Perth and published in 1988 found that birds and insects overwhelmingly preferred visiting yellow-coloured flowerheads. The species recorded include several species of honeyeater, including the Red Wattlebird (Anthochaera carunculata), Western Wattlebird (A. lunulata), Western Spinebill, Brown Honeyeater (Lichmera indistincta), New Holland Honeyeater (Phylidonyris novaehollandiae), White-cheeked Honeyeater (P. nigra), Singing Honeyeater, (Lichenostomus virescens), as well as the Twenty-eight Parrot (Barnardius zonarius semitorquatus) two species of native bee of the genus Leioproctus, a beetle of the genus Liparetrus, and ant species Iridomyrmex conifer. The yellow flowerheads are also the ones that bear the most nectar.

An analysis of the invertebrate population in the canopy of Banksia woodland found that mites and ticks (Acari), beetles (Coleoptera) and ants, bees and wasps (Hymenoptera) predominated overall, with the three orders also common on B. ilicifolia, although outnumbered by thrips (Thysanoptera). More arthropods on B. ilicifolia might be related to a higher nutrient (potassium) level in the leaves. Lower overall numbers of invertebrates on Banksia species were thought to be related to the presence of insectivorous birds.

Hand-pollination experiments on wild populations near Perth showed that Banksia ilicifolia is self-compatible, although progeny produced have less vigour and seed production is reduced. Further experiments show that seedlings of outcrossing with plants greater than 30 kilometres (19 mi) apart are more vigorous and adaptable, suggesting that plants breeding within small fragmented populations are subject to reduced vigour and genetic inbreeding.

Banksia ilicifolia regenerates after bushfire by regrowing from epicormic shoots under its bark. Follicles open and release seeds after several years. It is weakly serotinous, like eight other Banksia species, all of which tend to occur in Western Australia's southwestern corner. The other two species of the subgenus Isostylis are killed by fire and regenerate by seed.

All banksias have developed proteoid or cluster roots in response to the nutrient-poor conditions of Australian soils (particularly lacking in phosphorus). The plant develops masses of fine lateral roots which form a mat-like structure underneath the soil surface. These enable it to extract nutrients as efficiently possible out of the soil. A study of three co-occurring species in Banksia woodland in southwestern Australia—Banksia menziesii, B. attenuata and B. ilicifolia—found that all three develop fresh roots in September after winter rainfall, and that the bacteria populations associated with the root systems of B. menziesii differ from the other two, and that they also change depending on the age of the roots. Along with its shallow lateral roots, Banksia ilicifolia sinks one or more deep taproots seeking the water table. It is an obligate phreatophyte, that is, it is reliant upon accessing groundwater for its survival; it is more closely tied to the water table than the co-occurring B. menziesii and B. attenuata, and must remain in areas where the depth of the water table is less than 8 m (25 ft) below the surface. Recent falls of the water table on the Swan Coastal Plain from use of the Gnangara Mound aquifer for Perth's water supply combined with years of below average rainfall have seen the population and vigour or Banksia ilicifolia fall considerably (more so than other banksia species) since the mid 1960s.

Like many Western Australian banksias, Banksia ilicifolia has been shown to be highly sensitive to dieback from the soil-borne water mould Phytophthora cinnamomi. A study of Banksia attenuata woodland 400 km (250 mi) southeast of Perth across 16 years and following a wave of P. cinnamomi infestation showed that B. ilicifolia populations were present but significantly reduced in diseased areas. Specimens in coastal dune vegetation were reported killed by Armillaria luteobubalina, with mycelial sheaths of the fungus beneath the bark of the root collar.