Burrow building in seabird colonies: a soil-forming process in island ecosystems |
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Authors: | Wesley J Bancroft Mark J Garkaklis J Dale Roberts |
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Institution: | aSchool of Animal Biology, M092, University of Western Australia, Crawley, WA 6009, Australia;bWestern Australian Department of Conservation and Land Management, Swan Region, PO Box 1167, Bentley Delivery Centre, Bentley, WA 6983, Australia;cSchool of Biological Sciences and Biotechnology, Murdoch University, Murdoch, WA 6150, Australia |
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Abstract: | Soil modification via biopedturbation by burrow-building seabirds was examined in a Mediterranean, island ecosystem. Physical and chemical soil properties were compared between a colony of Wedge-tailed Shearwaters (Puffinus pacificus) and adjacent heath across a 14-month period. When compared to heath soil, the biopedturbated soil was 28% drier (6.04±5.40 vol%), had increased bulk density (by 29% to 1.30±0.11 g cm−3, 51% porosity), wetting capacity (by 83% to 0.55±0.83 molarity of ethanol droplet), hydraulic conductivity (by 266% to 398.91±252.04 mm h−1), and a greater range in soil surface temperature (31.7±6.2 °C diurnally to 18.3±3.2 °C nocturnally). Soil penetration resistance was reduced by 26% at a depth of 0–100 mm (326.5±122.4 kPa) and by 55% at 500–600 mm (1116.8±465.0 kPa). Colony soil also had increased levels of nitrate (by 470%), phosphorous (118%), ammonium (102%), sulphur (69%), and potassium (34%), decreased levels of iron (by 50%) and organic carbon (61%), was more alkaline, and had a 78% greater conductivity. Shearwaters deposited guano at a rate of 234.4 kg ha−1 yr−1 (dry mass). Chemical analysis of guano equated this to 50.9, 5.7, 5.5, and 3.6 kg ha−1 yr−1 of nitrogen, potassium, sulphur, and phosphorous, respectively. Experimentally constructed burrows demonstrated that digging alone can alter physical and chemical soil factors, but that changes in the nutrient profile of colony soils are predominantly guano-driven. We argue that the physical impact of seabirds on soil should not be overlooked as a soil-forming and ecosystem-shaping factor in island ecosystems, and that biopedturbation can exert major bottom-up influences on insular plant and animal communities. |
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Keywords: | Biopedturbation Ecosystem engineering Physical soil properties Seabird Soil nutrients |
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