DOI: 10.5061/dryad.d51c5b05m
title: Incubation mound-building by the Australian megapode (Malleefowl, Leipoa ocellata) creates novel, resource-rich patches in a semi-arid woodland

description:  Desert ecosystems are characterised by a patchy distribution of
 resources. Nutrient sinks associated with landscape modulators (trees)
 differ markedly from the resource-poor interpatch matrix. Fauna can also
 act as landscape modulators, modifying patch dynamics by redistributing
 resources via 'ecosystem engineering’. In semi-arid woodlands,
 malleefowl (Leipoa ocellata: Megapodiidae) reconfigure surface
 characteristics by scavenging leaf litter to construct large incubation
 mounds. The extent to which this movement of resources creates a novel
 patch and alters extant patches is largely unknown. Ecosystem engineering
 effects by megapodes have been little studied, but are potentially great,
 particularly in drylands, where mammalian engineers are known to enhance
 ecosystem function and drive restoration. We measured vegetation, ground
 cover, and soil chemistry at malleefowl mounds and four extant microsites
 (trees and open areas close to, and far from, mounds) and predicted that:
 1) malleefowl mounds would represent enriched, yet novel, microsites; 2)
 the characteristics of tree and open patches close to the mounds would
 differ from those away from the mounds, because of the diminishing
 intensity of disturbance; and 3) effects at tree and open patches close to
 the mound would be shorter-term, compared to the more substantial
 high-resource patch formation occurring at the mound, but we expected all
 effects would diminish with time since malleefowl activity. We found that:
 1) malleefowl mounds were novel microsites with soil chemistry more
 similar to tree-modulated patches, and groundcover and vegetation
 variables more similar to the open, interpatch matrix; 2) effects extended
 to tree and open patches near the mound, but most effects were short
 lived; and 3) some novel mound attributes (e.g., soil pH, phosphorus,
 nitrogen, carbon) were greater at mounds, irrespective of their age, while
 less plant cover and richness on young mounds dissipated with age.
 Synthesis: Mound-building megapodes can modulate the distribution of
 locally derived resources and create a novel microsite. Engineering
 effects can enhance spatial heterogeneity and ecosystem function over
 broad spatial and temporal scales, and may assist with ecological
 restoration, particularly in depauperate, arid systems.
description: <strong><em>Study
 system</em></strong> <em>
 </em> The study was conducted on Calperum Station
 in the Murray mallee region, near Renmark, South Australia (-33.659°,
 140.563°). Calperum was formerly a pastoral property, but livestock were
 removed in 1994. The area is on the boundary between arid and semi-arid,
 rainfall is highly variable and averages 256 mm. The landscape is
 characterised by a broad sand sheet (the Woorinen Formation; Lawrence et
 al. 1988), upon which are superimposed low west-east trending sand dunes
 dominated by mallee (<em>Eucalyptus </em>spp.) woodlands and
 shrublands communities. The soils are dominated by calcareous earths
 (Isbell 2021), with abundant carbonate in the profile and therefore high
 pH levels (Hutton and Dixon 1981). Slopes are generally level to slightly
 undulating (&lt; 2%). The dominant overstorey tree
 species are <em>Eucalyptus socialis</em>, <em>E.
 oleosa</em>, <em>E. dumosa</em> and <em>E.
 gracilis</em>. Understorey ranges from sparse Zygophyllum spp. forbs
 to extensive areas of spinifex (<em>Triodia scariosa</em>) and
 native shrubs (Senna <em>artemisiodes </em>ssp.,
 <em>Eremophila scoparia</em> and <em>Beyeria
 opaca</em>). Mallee trees are the dominant biotic patch type in
 these woodlands and function as resource modulators (Travers and Eldridge
 2012). Trees accumulate considerable litter beneath their canopies,
 providing important habitat for a range of invertebrates (Noble et al.
 1996). The accumulated litter layer around the trees acts as ground fuel
 and facilitates frequent fires in mallee landscapes (Haslem et al. 2011).
 The density of mallee trees varies markedly, and projected foliage cover
 of trees and their understorey litter vary with time since last fire.
 Typically, cover increases rapidly up to about 30% and stabilises about 30
 years after fire (Haslem et al. 2011).
 <em><strong>Malleefowl mound
 selection</strong></em> Malleefowl mounds
 have been monitored annually at Calperum since 2012 within three adjacent
 2 km x 2 km grids (National Malleefowl Monitoring Grids; National
 Malleefowl Recovery Team, 2016). All mounds within each grid are visited
 during the breeding season and recorded as active or inactive. Calperum is
 at the arid end of the range of malleefowl (Jones and Goth 2008). The
 average density of active and inactive malleefowl mounds at Calperum is
 approximately five mounds per km<sup>2</sup> (Heather Neilly,
 unpublished data, 2018). In August 2018, when malleefowl were preparing
 their mounds, we selected 12 mounds for study across the three monitoring
 grids. Four mounds were identified as active within the past 3 years, and
 four mounds active 3-6 years previously. An additional four mounds older
 than 6 years were selected, randomly, from a larger pool of mounds known
 to be more than 6 years old. To sub-sample mounds older than 6 years, any
 mound with an average rim height of &lt; 10 cm was excluded from
 selection. Mounds of this height are classified as ‘long unused’ and ‘very
 degraded’ and generally have no history of ever being active during the
 time they have been monitored (National Malleefowl Recovery Team
 2016). <em><strong>Microsites, and plant
 and soil measurements</strong></em> At each
 of the 12 mound locations we selected five microsites (Appendix S1, Fig.
 1) to test the effects of mounds on biotic and abiotic attributes within
 the vicinity of the mounds. These microsites were: 1) the mound (Fig. 2a),
 2) a <em>Eucalyptus </em>tree closest and within 15 m of the
 mound (hereafter ‘Tree near’), 3) an open area adjacent to the nearest
 tree and within 15 m of the mound (‘Open near’), 4) a <em>Eucalyptus
 </em>tree 50 m from the mound (‘Tree far’), and 5) an open area
 adjacent to the distant tree (‘Open far’). All measurements were taken
 from within a 5 m by 5 m quadrat centred upon each microsite. The tree and
 open microsites near the mound represent the zones of potential malleefowl
 leaf-raking activity, which has been known to extend to 15 m beyond the
 mound (Priddel and Wheeler 2003). The distant open and tree microsites
 would be expected to be outside the zone of malleefowl
 activity.   Within each quadrat we assessed
 groundstorey plant cover (visual estimate from single observer), abundance
 (number of individuals) and species richness (number of species), and the
 cover of litter, biocrusts (soil lichens and bryophytes) and bare soil.
 Ten samples of the surface 10 cm of the soil were collected, mixed, and a
 subsample taken for chemical analyses after air drying and sieving
 (&lt; 2 mm). Soils were analysed for total organic carbon (C; using
 H<sub>2</sub>SO<sub>4</sub> added to soil wetted
 by dichromate solution
 Cr<sub>2</sub>O<sub>7</sub><sup>2-</sup>), available nitrogen (NO<sub>3</sub>, using 2M KCl extraction, N), available phosphorus (P; Colwell, 1:100 soil:extract) and pH (1:5 soil:water extract).