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Type: Theses
Title: Insects, orchids and fire: the effects of fire on orchid pollinators in eucalypt woodlands of South Australia
Author: Marquart, Anita Evelyn
Issue Date: 2017
School/Discipline: School of Biological Sciences
Abstract: Populations of orchids are declining throughout Australia, mainly because of habitat destruction and the effects of habitat fragmentation (Coates et al., 2002). In addition the loss of pollinators due to fire events may have an important impact on orchid populations. Given that orchids are frequently pollen limited they may be particularly sensitive and responsive to changes in pollinator communities (Ashman et al. 2004; Burd 1994; Faast et al. 2011). The loss of certain pollinators could have devastating consequences and lead to decline or even extinction for those orchids that are specialists in their pollination strategy and rely on a single species of insect pollinator. This study assessed the response of three families of orchid pollinating insects and their habitat to prescribed burns and wildfires in eucalypt woodlands in southern Australia. Insects and selected habitat characteristics were surveyed over three years during spring at four different locations, and before and after fire events using a “Before-After, Control-Impact” approach. Fire induced changes of selected insect habitat characteristics including plant composition, floral abundance and nesting resources were investigated. Both prescribed burns and wildfires reduced floral abundance, altered the structure of vegetation and increased the amount of bare ground. Unlike earlier studies (Carrington, 1999; Hubbert et al., 2006), prescribed burning was shown to not reduce litter depth or the abundance of logs and standing litter. An increase in logs after prescribed spring burning, due to limb or tree mortality and fall was also documented. As expected, the impacts of a wildfire were more severe, as it significantly decreased litter depth and the abundance of logs, due to the high intensity of the wildfire resulting in destruction of more biomass. Potential orchid pollinators were identified using DNA barcoding methods combined with morphological identification. Results show that even just five month after a fire there was no severe effect on the abundance of members of the three most common orchid pollinator families (Apidae s.l., Syrphidae, Tiphiidae). Hoverflies (Syrphidae) were not affected by the fire regimes, but abundance differed among the years of sampling. Native bee (Apidea s.l.) abundance showed only a marginal decline in the second year after prescribed burning. Some bee species, especially ground nesters, showed a positive response to fire, which is most likely associated with fire induced habitat changes such as the increased availability of bare ground. No effects of fire on the abundance of tiphiid wasps could be found. Thiphiid wasps are from great importance for some sexual deceptive orchids, which rely on specific wasp species for pollination. Although prescribed burning and wildfires affected insect habitat differently, pollinator responses to both fire regimes did not differ. The fire-induced decline in floral resources did not affect pollinator communities in the first year following fire, but the availability of nesting sites seems to influence the responses of certain insect species. The results suggest that pollination success of orchids in South Australia is unlikely to be negatively impacted by both prescribed burns or wildfires, as orchid pollinators were still abundant and diverse in fire prone habitats.
Advisor: Facelli, Jose Maria
Austin, Andrew Donald
Faast, Renate
Dissertation Note: Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Biological Sciences, 2018
Keywords: Research by publication
prescribed burning
insect habitat
eucalypt woodland
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at:
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