Interspecific Competition and Vertical Niche Partitioning in Fiji’s Forest Birds

Abstract

Charles Darwin proposed his ‘principle of divergence’ to account for changes in traits that could promote speciation and coexistence of diverse forms through occupation of different niches to reduce interspecific competition. We explore interspecific foraging behaviour overlap in Fiji’s forest birds, and address two main questions: (1) Is there vertical stratification of foraging behavior? and (2) Is there evidence of interspecific competition driving the differences in foraging behaviour? We explore these questions across three foraging guilds, nectarivores (three species), insectivores (two species), and omnivores (two species), and find vertical portioning of foraging in each group. To investigate the effect of interspecific competition, we compared foraging heights of the Orange-breasted Myzomela (Myzomela jugularis) honeyeater on Viti Levu Island (where it coexists with two other honeyeater species) and Leleuvia Island (no other honeyeater species). On the main island Viti Levu, we found evidence for vertical niche partitioning within each foraging guild. On Leleuvia, with the ‘one-species only foraging guild’, Orange-breasted Myzomela occupied broader vertical foraging niche than on Viti Levu with two other competitor honeyeater species. This result supports the idea that vertical foraging height can be shaped by interspecific competition. The findings of this study support Darwin’s principle of divergence in Fiji’s forest birds for every foraging guild measured and adds to our understanding of the significance of interspecific competition and niche divergence for patterns of ecological speciation on islands.

A Comparison of Fijian Honeyeaters Abundance and Foraging Behaviour at USP Laucala Campus and Colo-I-Suva Forest Reserve

“…Figure 1 Km 2 of native land that was leased and gazetted for conservation purposes to counteract aggressive logging practices. Approximately, 25% of the reserve (92 hectares) is declared as the Colo-i-Suva forest park, now recognized as a conservation and eco-touristic site (Naikatini et al, 2022). Most of the trees colonizing the area are introduced mahogany (Swietenia macrophylla), however native tree species have regenerated overtime (Naikatini et al, 2022).…”

“…Three sympatric species of honeyeater viz Orange-breasted myzomela (Myzomela jugularis), Kikau wattled honeyeater (Foulehaio procerior) and Giant honeyeater (Gymnomyza brunneirostris) were surveyed from the proposed sites. Field surveys were conducted for 3 weeks between the month of August and September as Fijian birds are more readily observed during their breeding season (June to September) (Naikatini et al, 2022). In each site, three replicates were conducted for higher precision of results.…”

“…A total of three endemic, nectarivore honeyeater species were recorded in this study, namely Kikau wattled honeyeater (Foulehaio procerior), Orange-breasted myzomela (Myzomela jugularis) and Giant honeyeater (Gymnomyza brunneirostris). The Orange-breasted myzomela and Wattled honeyeater are more widespread, inhabiting almost all terrestrial habitats in Fiji (Naikatini et al, 2022). Conversely, Giant honeyeater are more reserved and cryptic in nature, thus are confined to intact mature primary forests (Naikatini et al, 2022).…”

“…Fiji's avifauna are diverse and hold significant cultural value (Watling, 2013). About 34 of the known 66 land bird species characterized in Fiji are endemic, with majority residing in the forest (Reid et al, 2019), but knowledge regarding their ecology and behaviour remains rare (Naikatini et al, 2022). It has been documented that more than 60 % of Fiji's native forest was deforested, creating a mosaic of primary and secondary forest (Olson et al, 2010).…”

Birds in Temperate and Tropical Forests: Introduction to the Special Issue

“…The last article describes the foraging behavior of selected bird species in Fiji's forest in detail [6]. Since forest bird communities are often very complex, the feeding behavior of particular species should be optimized according to the feeding tactics of other species due to their competitive relationships.…”