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Niche breadths of island and mainland populations of the Singing Honeyeater Lichenostomus virescens

Adriano, Sarah (1995) Niche breadths of island and mainland populations of the Singing Honeyeater Lichenostomus virescens. Honours thesis, Murdoch University.

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Abstract

Foraging niche breadths of Singing Honeyeaters (Lichenostomus virescens) at two island sites - Rottnest Island and Garden Island, and two mainland sites - Swanbourne and Kellerberrin in south..-western Western Australia, were studied. The hypothesis that the island populations with larger Singing Honeyeaters (20% by weight), have a broader foraging niche than those on the mainland was tested by (i) analysis of foraging behaviour at each site, (ii) analysis of insect diet at each site, (iii) integration of these results to compare the foraging breadths of island and mainland populations.

Replicated sites were matched on the basis of vegetation structure, which was analysed by levy pole count and plant species abundance. Except for the density of the lower height categories on Garden Island, the vegetation was successfully matched at all sites.

Field trips from mid-spring (October) to early summer (December) recorded the foraging behaviour of the Singing Honeyeater under four categories-foraging plant, foraging height, foraging substrate and foraging behaviour. Results were summarised as the Shannon-Wiener test of niche breadth and also as J (evenness) values, giving an idea of how generalised each population is in relation to each dimension of foraging behaviour.

These results showed that the island populations did have a broader foraging niche than the mainland populations which have a more specialised foraging niche breadth. (The Rottnest Island birds were also more generalised than the Garden Island birds).

Foraging breadth was also determined through the analysis of droppings from Singing Honeyeater populations at Rottnest Island, and Kellerberrin (collected in the 1980's and 1990's) and Shark Bay (collected in spring 1994). Invertebrates from 10 different taxa were identified as well as a large proportion of fruit and seeds. These results showed that the island populations actually have a much narrower diet than those on the mainland, indicating a narrow foraging niche breadth. The contradiction in results may be due to several factors:

i) the timing of dropping collection and the non-sequential recording of foraging observations at each study site;
ii) the paucity of invertebrate taxa or abundance on Rottnest Island.

However, the integration of foraging behaviour and diet analysis results is comparable. For example, the Singing Honeyeaters at Rottnest Island provided droppings with a high proportion of ant and wasp remains, and their behaviour included a large proportion of sallying and gleaning from the ground.

Prey sizes determined from invertebrate remains concluded that the size of the bird has no relation to the size of prey taken. Kellerberrin birds took the largest prey, while Shark Bay and Rottnest Island populations took considerably smaller prey.

Overall, it can be concluded that the island populations of Singing Honeyeater do have a broader foraging niche. Further research, such as the manipulative removal or addition of a competitive species to a mainland or island population respectively, is necessary to determine whether competition is the influencing factor on niche breadth. However, ethical considerations and a year­long study to determine seasonal interactions is essential prior to manipulative experimentation.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Biological and Environmental Sciences
Supervisor(s): Calver, Michael
URI: http://researchrepository.murdoch.edu.au/id/eprint/60392
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