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From molecules to bird communities: A mistletoe story

Napier, Kathryn (2013) From molecules to bird communities: A mistletoe story. PhD thesis, Murdoch University.

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Worldwide, mistletoes act as a keystone resource, providing food (nectar, fruit and foliage) and structural (nesting sites) resources to hundreds of fauna species. 75 species of ‘showy’ Loranthaceae mistletoes are native to Australia, and are found in wooded habitats throughout the mainland. The mistletoebird (Dicaeum hirundinaceum) is considered the primary disperser of mistletoe fruit in south-west Western Australia (WA). Other ‘generalist’ species, including several honeyeater species and the silvereye (Zosterops lateralis), also regularly consume and disperse mistletoe fruits.

This thesis takes a broad, eco-physiological approach to investigate the interactions between two Australian loranthaceous mistletoes species (Amyema miquelii and A. preissii), their host plants and their avian consumers. This was achieved through a combination of intensive field surveys and sampling at five sites where mistletoe was extremely abundant, and laboratory experiments assessing various aspects of avian digestive physiology of three frugivorous bird species; the mistletoebird (specialised frugivore), silvereye (generalist frugivore) and singing honeyeater (Lichenostomus virescens; generalist nectarivore).

A stable isotope approach was used to investigate the parasitic relationship between A. miquelii and A. preissii and their eucalypt or acacia hosts (respectively). Results demonstrate that these mistletoes regulate their water use in relation to the supply of nitrogen available from the host.

Next, the importance of mistletoe to bird communities in south-west WA was investigated through surveys and the use of stable isotopes. The presence of fruiting (but not flowering) mistletoe was associated with significant changes in bird community structure. Mistletoebirds were more likely to be recorded during months when ripe mistletoe fruit was present, and overall bird species richness was higher for these survey months. The contribution of mistletoe fruit to the diet of mistletoebirds ranged from 33% to 55%, demonstrating that despite mistletoe fruit being low in nitrogen, it is an important source of nutrients. Fruiting mistletoes therefore provide important food resources to bird communities in south-west WA.

Various aspects of avian digestive physiology were compared for three species that include mistletoe fruit in varying degrees to their diet. Mistletoebirds, silvereyes and singing honeyeaters demonstrated similar patterns of sugar preferences with similarly high (>97.5%) apparent assimilation efficiencies (AE*) for sucrose, glucose and fructose and lower AE* for the pentose monosaccharide xylose (56-78%), yet demonstrated differences in their absorption of dietary sugars. Mistletoebirds, in contrast to the other two species, did not vary bioavailability (f) with diet concentration, and appear to absorb xylose through both mediated and paracellular mechanisms. This may be a result of the short, specialised intestinal tract of mistletoebirds, which facilitates faster transit rates of mistletoe fruit compared to silvereyes and honeyeaters.

This thesis presents new insight into the parasitic relationship between mistletoes and hosts, and the relationship between mistletoes and its avian consumers. Mistletoebirds differ from other opportunistic mistletoe feeders in their ability to process large numbers of mistletoe fruit quickly, while obtaining sufficient nutrients such as nitrogen and carbohydrates from these fruits.

Publication Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary and Life Sciences
Supervisor: Fleming, Trish, McWhorter, Todd and Martínez del Rio, Carlos
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