Interactions between meat ants (Iridomyrmex spadius) and bellyache bush (Jatropha gossypiifolia)
F. F. Bebawi A B C and S. D. Campbell A BA Tropical Weeds Research Centre, Queensland Department of Natural Resources and Mines, Charters Towers, Qld 4820, Australia.
B CRC for Australian Weed Management, PMB 1, Waite Campus, Glen Osmond, SA 5064, Australia.
C Corresponding author. Email: Faiz.Bebawi@nrme.qld.gov.au
Australian Journal of Experimental Agriculture 44(12) 1157-1164 https://doi.org/10.1071/EA03194
Submitted: 19 September 2003 Accepted: 10 March 2004 Published: 24 January 2005
Abstract
Understanding the dispersal of weed species is important for the development of effective control strategies. In this study, a series of experiments was conducted to clarify the role that meat ants (Iridomyrmex spadius) play in dispersing bellyache bush (Jatropha gossypiifolia), an exotic shrub currently invading the rangelands of northern Australia. The nutrient composition of food [lipids (fatty acids), fat and soluble carbohydrates] provided by bellyache bush seed components [caruncle, exotegmen and seed (without caruncle and exotegmen)] was identified. Seed components were rich in lipids, particularly palmitic, oleic, stearic, linoleic and eicosenic acids. Oleic and palmitic were most abundant in the caruncle (30% each), linoleic in the seed (61%) and palmitic in the exotegmen (36%). Over all seed components, fat concentration was relatively high (6.3%) compared with soluble carbohydrates (2.3%). The impact of feeding was then determined by comparing germination and viability of intact, non-carunculate (caruncle manually removed) and ant-discarded bellyache bush seeds. Feeding by meat ants significantly increased seed germinability, whilst having no adverse affects on viability. The quantity of seeds dispersed and the seasonal pattern of dispersal was recorded by collecting seed from the middens of randomly selected meat ant nests on a monthly basis. On average, 12 330 ± 603 seeds were retrieved from the middens of individual meat ant nests over 12 months, with highest numbers recorded between February and June (>1200 seeds/ant nest). The effect of this dispersal was determined through comparisons of plant densities within core infestations of bellyache bush, meat ant nest middens and pastures located directly adjacent to core infestations and that were being invaded primarily through localised ballistic dispersal. The density of bellyache bush plants growing from the seed reserves within middens averaged 79 plants/m2, just 18% less than that within core infestations. Seedling survival (1 year) and growth within core infestation and meat ant sites was also quantified. The middens of meat ant nests provided an environment conducive to higher seedling survival and faster growth rates than occurred within core infestations. Mutualistic interaction between bellyache bush and meat ants is likely to build local ‘infestation pressure’ that may be conducive to range extension in years of exceptionally wet seasons. Management of seed dispersal by meat ants may reduce that risk.
Acknowledgments
Special thanks are extended to The Queensland Department of Natural Resources and Mines for providing financial support, and to Dave and Pauline Chapman (Almora Station) and Charlie Truscott (Lynmore Station) for allowing us to use their property for research purposes. We also thank D. Panetta, A. Grice and A. Lindsay for reviewing the manuscript. The technical assistance of M. Madigan, R. Stevenson, C. Dennis and K. Risdale is also acknowledged.
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