Grazing orchids: impact of florivory on two species of Caladenia (Orchidaceae)
Renate Faast A B and José M. Facelli AA School of Earth and Environmental Sciences, The University of Adelaide, SA 5005, Australia.
B Corresponding author. Email: renate.faast@adelaide.edu.au
Australian Journal of Botany 57(4) 361-372 https://doi.org/10.1071/BT08140
Submitted: 4 August 2008 Accepted: 9 February 2009 Published: 29 July 2009
Abstract
Herbivory is considered a major threat in many of the orchid-species recovery plans in Australia. Kangaroos and rabbits are the most commonly implicated herbivores; however, no studies have attempted to confirm their role. Regular monitoring of several populations of Caladenia rigida R.S.Rogers and C. tentaculata Schldl. during 3 years in the Mount Lofty Ranges, South Australia, revealed that up to 94% of flowers and 36% of seed capsules were browsed, whereas leaf herbivory was less prevalent. Furthermore, patterns of herbivory varied markedly among sites and across years. In two seasons, predation of C. rigida flowers inside a kangaroo- and rabbit-proof exclosure was equal to or higher than outside the exclosure. Florivory within populations was influenced by proximity to the habitat edge, although the direction of this response differed among sites. Various types of mesh cages were erected around plants to elucidate the size and type of herbivores. Plants protected from florivores were almost three times more likely to produce seed than were exposed plants; however, some cage types reduced pollination. Video surveillance confirmed the role of the white-winged chough, Corcorax melanorhamphos, as a florivore. The present study is the first one to identify a herbivore unequivocally, quantify the intensity and extent of floral herbivory across a range of populations, and assess the potential cost of florivory to the direct reproductive output of orchids.
Acknowledgements
The authors thank Peter Moyle for the use of video-surveillance equipment, and David Pearce and Marlon Blencowe for field assistance. Joe Quarmby (DEHSA) and members of the Native Orchid Society of South Australia assisted with the location of orchid populations, and Jackie Crompton (Forestry SA) and Monique Blason (SA Water) facilitated site access. Thanks also go to National Parks and Wildlife rangers, Friends of Scott Creek Conservation Park, Friends of Ferguson Conservation Park, Adelaide Hills Council and private landholders in Ironbank for access to sites. Advice and editing of this manuscript provided by Jane Prider, Andy Austin, Lachlan Farrington and three anonymous reviewers is greatly appreciated. Fieldwork was conducted with permission from the Department for Environment and Heritage, South Australia, Permit No. U25018. The present research was funded by the Native Vegetation Council, South Australia, and an Australian Research Council Linkage Project (LP0560578) with the Department for Environment and Heritage SA, South Australian Museum, Foundation for Australia’s Most Endangered Species and Biocity Centre for Urban Habitats, University of Adelaide. We are grateful to Forestry SA for contributions towards video-surveillance equipment. The first author held a Faculty of Sciences Divisional Scholarship from The University of Adelaide.
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