Species In South-western Australia Research Articles

To spray or not to spray: Impact of phosphite spraying for Phytophthora cinnamomi control on Proteaceae species in southwestern Australia

AbstractPhosphite has been sprayed on threatened natural plant communities in southwestern Australia for the past 25 years to mitigate the impact of the globally widespread plant pathogen, Phytophthora cinnamomi. Of concern is that this may result in an increase in phosphorus concentrations in naturally nutrient deficient soils, causing the loss of plant species that are sensitive to increased phosphorus levels. The impact of aerial spraying phosphite on soil and Proteaceae species richness and abundance was measured at three sites within the Southeast Coastal Province of Western Australia. Healthy and diseased vegetation which had been sprayed with phosphite for 14–26 years was compared with nonsprayed healthy and diseased vegetation. Contrary to expectations, there was no evidence that spraying is doing harm to Proteaceae species at the three sites studied. Healthy‐nonsprayed and Healthy‐sprayed areas had generally similar levels of soil total P, and this was associated with similar values for Proteaceae species richness and abundance in these areas. Phosphite spraying of diseased vegetation benefited Proteaceae plant diversity and abundance by preventing the disappearance of some species. Given these results, it was recommended that phosphite spraying be continued as a management action for controlling Phytophthora cinnamomi while research into alternative solutions continues.

Role of roots in adaptation of soil-indifferent Proteaceae to calcareous soils in south-western Australia.

Very few of the >650 Proteaceae species in south-western Australia cope with the high calcium (Ca) levels in young, calcareous soils (soil indifferent); most are Ca sensitive and occur on nutrient-impoverished, acidic soils (calcifuge). We assessed possible control points for Ca transport across roots of two soil-indifferent (Hakea prostrata and Banksia prionotes) and two calcifuge (H. incrassata and B. menziesii) Proteaceae. Using quantitative X-ray microanalysis, we investigated cell-specific elemental Ca concentrations at two positions behind the apex in relation to development of apoplastic barriers in roots of plants grown in nutrient solution with low or high Ca supply. In H. prostrata, Ca accumulated in outer cortical cells at 20 mm behind the apex, but [Ca] was low in other cell types. In H. incrassata, [Ca] was low in all cells. Accumulation of Ca in roots of H. prostrata corresponded to development of apoplastic barriers in the endodermis. We found similar [Ca] profiles in roots and similar [Ca] in leaves of two contrasting Banksia species. Soil-indifferent Hakea and Banksia species show different strategies to inhabit calcareous soils: H. prostrata intercepts Ca in roots, reducing transport to shoots, whereas B. prionotes allocates Ca to specific leaf cells.

Seed traits determine species' responses to fire under varying soil heating scenarios

Abstract Many plant species in fire‐prone environments maintain persistence through fire via soil seedbanks. However, seeds stored within the soil are at risk of mortality from elevated soil temperatures during fire. Seeds may be protected from fire‐temperature impacts by burial, however, those buried too deeply may germinate but fail to emerge. Thus, successful post‐fire seed regeneration is contingent upon a trade‐off between burial depth and survival through fire. We examined the relationships between seedling emergence behaviour, seed survival and soil temperatures during fire in 13 native and four non‐native woodland species in southwestern Australia. We assessed total seedling emergence per depth, maximum seedling emergence depth and seedling emergence speed from seeds planted at eight depths (0, 1, 2, 3, 4, 5, 7, 10 cm). Soil temperatures were quantified using distributed temperature sensing in optic fibre (DTS), measured continuously between 1 and 10 cm in depth (temperatures were subsequently categorized into 1 cm increments for analysis) during five experimental fires in beds with fine fuels manipulated between 8 and 20 t/ha. Using seed survival and emergence success relative to soil temperatures, we determined vulnerability of seedling emergence relative to soil temperatures generated by combustion of fuel quantities typically observed in woodlands. Maximum depth of emergence varied between species from 2 to >10 cm, with a positive linear correlation to seed mass. Maximum soil temperatures from the two highest fuel masses exceeded seed lethal thresholds (T50—representing temperatures lethal to 50% of seeds) of at least five species. Lethal temperatures were exceeded at all potential emergence depths for all three grass species, and all four non‐native species studied. Of the remaining 10 species, temperatures did not exceed the lethal thresholds under any of the fuel mass levels tested. We found no relationship between lethal temperature thresholds and maximum emergence depth. Our data demonstrate that seeds exhibit variation in their response to soil heating and capacity to emerge from depth, with three distinct functional responses amongst our study species, which enable persistence through, and recruitment following, fire. Such variation in species attributes and fuel mass may lead to heterogeneity (within fires) or divergent trajectories (among fires) in community response under changed fire regime. A free Plain Language Summary can be found within the Supporting Information of this article.

Incorporating climate change into recovery planning for threatened vertebrate species in southwestern Australia

Recovery plans are the main tool used for restoration of threatened species in Australia, and identification of key threatening processes is an important feature of them. The aim of this study was to identify how climate change can be incorporated into the recovery planning process using a case study of threatened vertebrates in a global biodiversity hotspot, southwestern Australia. Analysis of 79 recovery planning documents for threatened vertebrate species in the region found that prior to the year 2004, climate change was not included as a threatening process. Post 2004, 32 of 54 (59.3%) documents included climate change as a threatening process. Using bioclimatic modelling, 43 of these species were ranked in terms of their potential exposure to climate change, and a gradient of management intervention aimed at mitigating their exposure to climate change was proposed. This intervention gradient ranged from active management actions aimed at species potentially at risk of extinction due to climate change, through to preservation of habitat in species predicted to lose between 0 and 25% of their current population size. It was proposed that as a priority, the recovery documentation of the 20 species predicted to be most at risk and thus needing a high level of management intervention should identify climate change as a key threatening process, and that more comprehensive analyses of climate change vulnerability be undertaken for these species. Such an approach aimed at prioritising climate change mitigation in threatened species would be useful for other regions where it has been predicted that climate change could have a negative impact on biodiversity.

Future climate change scenarios differentially affect three abundant algal species in southwestern Australia

Three species of macroalgae (Ecklonia radiata, Sargassum linearifolium, and Laurencia brongniartii) were subjected to future climate change conditions, tested directly for changes in their physiology and chemical ecology, and used in feeding assays with local herbivores to identify the indirect effects of climatic stressors on subsequent levels of herbivory. Each alga had distinct physical and chemical responses to the changes in environmental conditions. In high temperature conditions, S. linearifolium exhibited high levels of bleaching and low maximum quantum yield. For E. radiata, the alga became more palatable to herbivores and the C:N ratios were either higher or lower, dependent on the treatment. Laurencia brongniartii was effected in all manipulations when compared to controls, with increases in bleaching, blade density, and C:N ratios and decreases in growth, maximum quantum yield, blade toughness, total phenolics and consumption by mesograzers. The differential responses we observed in each species have important implications for benthic communities in projected climate change conditions and we suggest that future studies target multi-species assemblage responses.

Fitness benefits of serotiny in fire- and drought-prone environments

Despite the abundance of serotinous species in southwestern Australia, demonstration of the enhancement of fitness through fire, by releasing seeds onto an optimal postfire seedbed for seedling establishment, rather than following drought death, has not been explicitly explored. In this study, we measured seed release, germination and seedling recruitment following plant death after fire and simulated drought among six serotinous species in southwestern Australia. Burning or heating the cones/fruits resulted in a marked increase in follicle opening (pyriscence) compared with plant death from drought (necriscence) among Banksia but not Hakea. We recorded higher rates of germination, lower seedling mortality and better seedling growth in the post-fire environments than in unburnt sites not burnt for at least 10 years for five species (seeds of the sixth species were non-viable). Seedling mortality among the five species of 100 % occurred in the unburnt plots over the first summer, while 28–79 % of seedlings survived in the burnt plots. Soil moisture measurements indicated much lower water availability in the unburnt sites even in spring. Our study provides strong empirical evidence that serotiny/pyriscence enhances species fitness by releasing seeds into an optimal post-fire habitat in contrast to that observed from plant/crown death due to drought. In the context of the long history of fire in southwestern Australia, the greatly enhanced fitness in response to fire rather than severe drought supports the proposition that serotiny is a specific adaptation to fire.

Absence of nectar resource partitioning in a community of parasitoid wasps

Parasitoid wasps occur in diverse communities, with the adults of most species sourcing carbohydrates from nectar or honeydew. However, the role of niche partitioning of nectar resources in maintaining diverse communities of parasitoid Hymenoptera is poorly known. To elucidate patterns of nectar resource use and test whether species partition resources, we investigated pollen loads in a community of parasitoid thynnine wasps in the biodiversity hotspot of southwestern Australia. In total, 304 thynnine wasps from 28 species were captured. Eighteen of these species are undescribed, highlighting the high diversity of unrecognized species in southwestern Australia. Pollen loads were detected on 111 individuals representing 19 species. Six pollen types were identified. All species that carried pollen primarily visited two tree species, Agonis flexuosa and Eucalyptus marginata, in the Myrtaceae. The other four pollen types were only recorded from single wasps. There was no evidence of nectar-resource partitioning. This may be due to these Myrtaceae producing abundant, open-faced flowers. Wasp species that were not recorded carrying pollen may utilise other carbohydrate sources, such as homopoteran honeydew. Niche partitioning is predicted to occur during the parasitoid larval phase of the life cycle. This study highlights the importance of nectariferous Myrtaceae in supporting diverse wasp communities. Further, two species of nectar-foraging wasps collected here are involved in the pollination of rare orchid species. Hence, conservation and management of habitats that support floriferous Myrtaceae are important for both the maintenance of diverse wasp communities, and the plants they pollinate.

Shallow environmental gradients put inland species at risk: Insights and implications from predicting future distributions ofEucalyptusspecies in South Western Australia

As climate changes, tree decline in Mediterranean-type ecosystems is increasing worldwide, often due to decreased effective precipitation and increased drought and heat stress, and has recently been observed in coastal species of the iconic Eucalyptus (Myrtaceae) genus in the biodiversity hotspot of south-west Western Australia. To investigate how this drought-related decline is likely to continue in the future, we used species distribution modelling techniques to generate broad-scale predictions of future distribution patterns under three distinct projected climate change scenarios. In a moderate climate change scenario, suitable habitat for all species was predicted to decrease by, on average, 73% by the year 2100, with most receding into southern areas of their current distribution. Although the most severe Eucalyptus declines in south-west Western Australia have been observed in near-coastal regions, our predictions suggest that inland species are at greater risk from climate change, with six inland species predicted to lose 95% of their suitable habitat in a moderate change scenario. This is due to the shallow environmental gradients of inland regions causing larger spatial shifts of environmental envelopes, which is likely to be relevant in many regions of the world. The knowledge gained suggests that future research and conservation efforts in south-west Western Australia and elsewhere should avoid focussing disproportionately on coastal regions for reasons of convenience and proximity to population centres, and properly address the inland region where the biggest future impacts may occur.

A climate change context for the decline of a foundation tree species in south-western Australia: insights from phylogeography and species distribution modelling.

A worldwide increase in tree decline and mortality has been linked to climate change and, where these represent foundation species, this can have important implications for ecosystem functions. This study tests a combined approach of phylogeographic analysis and species distribution modelling to provide a climate change context for an observed decline in crown health and an increase in mortality in Eucalyptus wandoo, an endemic tree of south-western Australia. Phylogeographic analyses were undertaken using restriction fragment length polymorphism analysis of chloroplast DNA in 26 populations across the species distribution. Parsimony analysis of haplotype relationships was conducted, a haplotype network was prepared, and haplotype and nucleotide diversity were calculated. Species distribution modelling was undertaken using Maxent models based on extant species occurrences and projected to climate models of the last glacial maximum (LGM). A structured pattern of diversity was identified, with the presence of two groups that followed a climatic gradient from mesic to semi-arid regions. Most populations were represented by a single haplotype, but many haplotypes were shared among populations, with some having widespread distributions. A putative refugial area with high haplotype diversity was identified at the centre of the species distribution. Species distribution modelling showed high climatic suitability at the LGM and high climatic stability in the central region where higher genetic diversity was found, and low suitability elsewhere, consistent with a pattern of range contraction. Combination of phylogeography and paleo-distribution modelling can provide an evolutionary context for climate-driven tree decline, as both can be used to cross-validate evidence for refugia and contraction under harsh climatic conditions. This approach identified a central refugial area in the test species E. wandoo, with more recent expansion into peripheral areas from where it had contracted at the LGM. This signature of contraction from lower rainfall areas is consistent with current observations of decline on the semi-arid margin of the range, and indicates low capacity to tolerate forecast climatic change. Identification of a paleo-historical context for current tree decline enables conservation interventions to focus on maintaining genetic diversity, which provides the evolutionary potential for adaptation to climate change.

Species distribution and crown decline are associated with contrasting water relations in four common sympatric eucalypt species in southwestern Australia

Drought-associated vegetation declines are increasingly observed worldwide. We investigated whether differences in water relations can potentially explain the distribution and vulnerability to drought-induced decline of four common tree species in Mediterranean southwestern Australia. We compared seasonal and daily water relations of four eucalypt species (i.e. C. calophylla, E. accedens, E. marginata, E. wandoo) when co-occurring as well as on nearby typical sites for each species. When co-occurring, species generally inhabiting drier regions (i.e. E. accedens, E. wandoo) had lower summer leaf water potentials, osmotic potential, and vulnerability to cavitation and higher stomatal conductance and relative sapflow velocity. Both wetter zone species (e.g. C. calophylla and E. marginata) had remarkably high vulnerabilities to cavitation for Mediterranean woody species but showed greatly improved leaf water status on nearby sites where they dominate. Using local soil moisture retention curves of saprolitic clay layers underlying southwestern Australia we show the large disadvantage that the wetter zone species have in terms of accessing tightly bound water in these layers. Our work shows that species distribution and local dominance of four dominant overstorey species in southwestern Australia is largely a function of plant water relations interacting with local soil profiles. The observed differences in water relations amongst species are consistent with some of the declines that have been observed in recent decades.

Proteaceae from severely phosphorus‐impoverished soils extensively replace phospholipids with galactolipids and sulfolipids during leaf development to achieve a high photosynthetic phosphorus‐use‐efficiency

Proteaceae species in south-western Australia occur on severely phosphorus (P)-impoverished soils. They have very low leaf P concentrations, but relatively fast rates of photosynthesis, thus exhibiting extremely high photosynthetic phosphorus-use-efficiency (PPUE). Although the mechanisms underpinning their high PPUE remain unknown, one possibility is that these species may be able to replace phospholipids with nonphospholipids during leaf development, without compromising photosynthesis. For six Proteaceae species, we measured soil and leaf P concentrations and rates of photosynthesis of both young expanding and mature leaves. We also assessed the investment in galactolipids, sulfolipids and phospholipids in young and mature leaves, and compared these results with those on Arabidopsis thaliana, grown under both P-sufficient and P-deficient conditions. In all Proteaceae species, phospholipid levels strongly decreased during leaf development, whereas those of galactolipids and sulfolipids strongly increased. Photosynthetic rates increased from young to mature leaves. This shows that these species extensively replace phospholipids with nonphospholipids during leaf development, without compromising photosynthesis. A considerably less pronounced shift was observed in A. thaliana. Our results clearly show that a low investment in phospholipids, relative to nonphospholipids, offers a partial explanation for a high photosynthetic rate per unit leaf P in Proteaceae adapted to P-impoverished soils.

Population Size Effects on Progeny Performance in Banksia ilicifolia R. Br. (Proteaceae)

A reduction in population size due to land clearing and habitat fragmentation may have negative effects on plant fitness. A relationship between population size and progeny performance for four small (n 100 plants) populations of Banksia ilicifolia, a widespread but naturally fragmented species in south-western Australia, was assessed. Seeds collected from the field were germinated and a comparative growth study conducted in a greenhouse. After six months, the survival rate of seedlings from larger populations was double (36%) that of smaller populations, while germination rates and other measures of growth performance were independent of population size. The conservation and management implications of reduced fitness associated with small population size in B. ilicifolia are discussed.

A hypothesis to explain why the south-western subspecies of the Crested Shrike-tit (Falcunculus frontatus leucogaster) is rare and declining

The south-western subspecies of the Crested Shrike-tit (Falcunculus frontatus leucogaster) is uncommon and declining in abundance. Moreover, populations fail to persist in even large remnants of native vegetation within agricultural areas. Reasons for the scarcity of Shrike-tits in south-western Australia, their decline, and their failure to survive in fragmented habitats are unclear, but are possibly related to the scarcity of persistent decorticating bark on south-western Australian eucalypts relative to eucalypts in habitats where the species is abundant in eastern Australia. At two widely separated areas of eucalypt forest and woodland in eastern Australia, where Shrike-tits have been studied and appear relatively abundant, they take most of their prey from bark, particularly loose and decorticating bark. By contrast, in woodlands of south-western Australia, most prey appears to be obtained by foliage gleaning. I suggest that bark substrates provide a richer food resource for Shrike-tits than foliage, and that Shrike-tits in south-western Australia must forage over much larger areas to obtain adequate food than those that have been studied in the east. Other studies have shown that canopy arthropods are less abundant on eucalypts in south-western than in eastern Australia. Thus, as a result of both differences in foraging substrate availability and lower arthropod abundances, Shrike-tit population densities are lower in south-western Australia than much of eastern Australia. Low population densities and the need for large home-ranges typify organisms sensitive to habitat fragmentation. It is therefore hypothesised that both low numbers and a failure to persist in habitat fragments by Shrike-tits in southwestern Australia are a consequence of the limited abundance of suitable bark substrates for foraging, a reliance on foliage gleaning, and lower arthropod abundances. Conservation of this species in south-western Australia therefore requires protection of large contiguous areas of eucalypt woodlands and forests.

Mortality of the demersal West Australian dhufish, Glaucosoma hebraicum (Richardson 1845) following catch and release: The influence of capture depth, venting and hook type

Cages were used to investigate the mortality after catch and release angling of the demersal reef fish Glaucosoma hebraicum (Family Glaucosomatidae), a recreationally and commercially important species in southwestern Australia. The effects of capture depth, venting the swim bladder, two types of hooks and anatomical hooking location, on mortality of G. hebraicum were examined by simulating actual catch and release fishing by recreational anglers. Additional factors (length of fish, duration of caging and the ability of released fish to swim) were included in a logistic regression. Only depth ( p < 0.01), duration of caging ( p = 0.01) and hook location ( p = 0.01) were significant factors in predicting whether or not a fish died after release. Mortality of G. hebraicum increased with depth of capture from 21% at 0–14 m to 86% at 45–59 m. Timing of mortality within the experiment (duration of caging) varied with depth due to the severity of barotrauma. Overall, 51% of all G. hebraicum caught in the experiment died. Most deaths (38.4% mortality of the total catch) were attributed to barotrauma while the remainder (13.2%) was caused by damage by hooks. The high post-release mortality of G. hebraicum at any given depth compared to other demersal species is best explained by their susceptibility to barotrauma. This additional source of mortality must be considered when setting sustainable catch levels for controls on exploitation rates. Traditional management strategies that assume the survival of undersize or excess fish that are returned to the water are not appropriate for G. hebraicum, particularly in deeper waters. Alternative management options must be developed to protect this slow growing, long-lived species.

Does transported seagrass provide an important trophic link in unvegetated, nearshore areas?

The contribution of detritus from seagrass and other primary producers to faunal production in unvegetated nearshore areas was examined primarily using stable isotopes. Fish, macroinvertebrates, meiofauna and primary producers (seagrasses, macroalgae, seston and benthic microalgae) were sampled from sites in south-western Australia. All samples were analysed for δ 13C and δ 15N values and fish gut contents were determined. δ 13C values for seagrasses in the region were high compared to other macrophytes, ranging from 49.9 to −8.2‰ compared to −19.8 to −12.6‰ for macroalgae. The δ 15N values ranged between 4.0 and 7.7‰ for the red, brown and green algae, and between 3.2 and 5.9‰ for seagrasses. Seston and benthic microalgae samples had a mean δ 13C value of −12.8 and −14.0‰, respectively, and their δ 15N values were comparable to the macroalgae. All invertebrate fauna had mean δ 13C values considerably lower than seagrasses. However, individual samples harpacticoid copepods and polychaetes had a value as high as −11.7‰. δ 15N values for consumers were higher than those of the primary producers, except for copepods and amphipods. The δ 13C values for fish had a relatively small range, between −16.6 and −13.1‰, and the δ 15N values of fish were elevated compared to the invertebrates and primary producers, ranging mostly between 10.0 and 12.6‰. Mixing model analysis based on δ 13C values indicated that seagrass ranked low as a likely carbon source for all invertebrates other than harpacticoid copepods at a single site and some samples of polychaetes. The δ 13C values for fish were similar to those of a combination of harpacticoid and calanoid copepods, amphipods and polychaetes. The consumption of harpacticoid copepods by some fish species indicates that Amphibolis and Posidonia species in south-western Australia can contribute to the food web of unvegetated nearshore areas as detritus, but brown algae is likely to make a greater contribution. At least for the time of year that was sampled, the flow of detrital seagrass material into the foodweb may be mediated by specific detrivores, in this case harpactacoid copepods, rather than by all detritivores.

Larvae of Contracaecum sp. among inshore fish species of southwestern Australia.

Larval nematode infections were investigated in 236 fish from 17 estuarine and near-shore species in southwestern Australia. Larvae of the genus Contracaecum were found in 4 species of fish (Acanthopagrus butcheri, Sillaginodes punctata, Mugil cephalus and Aldrichetta forsteri). The prevalence and intensity of infection was highest in the 2 species of mullet: 81% infected and 9.8 +/- 1.5 larvae fish(-1) for M. cephalus; 100% and 12.7 +/- 3.7 larvae fish(-1) for A. forsteri. There was no evidence of post-mortem migration of worms from the visceral organs to the musculature of the fish.

Fruit‐seed relations in Hakea: serotinous species invest more dry matter in predispersal seed protection

Abstract The ability to maintain a canopy stored seedbank (serotiny) is characteristic of many woody genera inhabiting fire‐prone environments. The relationship between level of serotiny for 94 Hakea (Proteaceae) species in southwestern Australia and follicle mass, density, three wall thicknesses and seed mass was investigated. Two species were non‐serotinous (fruits open at maturity), 12 were weakly serotinous (majority of fruits open at maturity), 9 were moderately serotinous (fruits open within five years of maturity) and 71 were strongly serotinous (fruits still closed at least five years after reaching maturity). A positive relationship existed between the level of serotiny and follicle morphology. Strongly serotinous species were more likely to have heavier, woodier and thicker‐walled follicles than non‐ and weakly serotinous species. Moderately/strongly serotinous species invested more energy (six times higher follicle:seed mass ratio) than non weakly serotinous species, consistent with increased protection of the seeds from granivores, pathogens, 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 critical for thin‐walled, weakly serotinous species. Greater protection from granivores may provide a better explanation for the adaptive significance of dense, thick‐walled serotinous follicles, as the opportunities for predispersal granivore damage are low among weakly serotinous species.

Biogeography of Banksia in southwestern Australia

Comprehensive new data bases on the taxonomy, distribution, ecology and climate of Banksia (Proteaceae) were used to study the biogeography of the sixty endemic species in southwestern Australia. They occur at the wettest coastal tip, with up to 1.5 m rainfall p.a., 1500 km along the north coast, 1000 km along the south coast and up to 450 km inland to the desert margin, with as low as 0.2 m rainfall p.a. The largest areas (sum of 30´ lat.×30´ long. grid cells) containing banksias were under much more arid climates than those with highest species density. Species density was usually lowest at the climatic extremes. Two nodes of species richness and ten floristic groups, each with a characteristic climate, landscape, vegetation and soil types and suite of indicator and endemic species, were recognized. A case is made for resurrecting the Lesueur (northern node) and Stirling (west portion of the southern node) phytogeographic districts, together with separating the West (east portion of the southern node) from the East Eyre district. These species‐rich areas coincide with nutrient impoverished sands and laterite associated with dissected uplands having low, highly sclerophyllous vegetation. The distribution of strongly serotinous species and those with persistent florets is consistent with greater reliance on fire for creating suitable recruitment conditions with increasing aridity. The distribution of needle‐leaved species is only partly explained by their superior drought tolerance. A preliminary transplant trial with two Banksia species showed that their distribution was only partly restricted by their current climatic profile.

Errata: Coexistence of Banksia Species in Southwestern Australia: The Role of Regional and Local Processes

Errata: Coexistence of Banksia Species in Southwestern Australia: The Role of Regional and Local Processes

Coexistence of Banksia species in southwestern Australia: the role of regional and local processes

Abstract. 60 of the 75 Banksia species are confined to southwestern Australia where five or six species often coexist. We explored the role of regional species richness, niche differentiation, and habitat specialization in structuring banksia assemblages. The diversity of growth forms and categories of seed production and response to fire were assessed in actual assemblages at 40 sites throughout southwestern Australia. Diversity indices at each site were compared with those from null communities assembled on the basis of the abundance and sociability of taxa in regional species pools. The relationship between local and regional species richness suggests that processes at the scale of 100‐m2 quadrats limit local richness and therefore coexistence. However, there was no consistent evidence that taxa are differentiated by growth form or regeneration strategy. No particular biological profile makes a banksia adept at coexisting with a wide range of other taxa. Habitat specialization is an important factor contributing to lower local richness than would be predicted from niche differentiation of taxa in regional pools. There is recent empirical evidence of several mechanisms whereby the number of coexisting banksias is increased beyond the limits suggested by simple niche theories. Variability in the fire regime also provides a mechanism for maintaining local species richness because different fires favour recruitment of different taxa.