Trophic relationships among pelagic predators of the deep seas of the Madeira Islands
This thesis provides a detailed study of the diet of various procellariiformes using new molecular approaches. Dietary studies remove fundamental blocks to our understanding of the structure of food webs, and provide insights into the demographic regulation of populations and the structuring of communities. The study species were the Band-rumped Storm-petrel (Hydrobates castro), Bulwer’s petrel (Bulweria bulwerii), Cory’s shearwater (Calonectris borealis) and White-faced Storm-petrel (Pelagodroma marina). The breeding colonies of the Madeiran-archipelago are Important Bird Areas (IBA) in the North-Atlantic, but little is known about the predator-prey relationships of its seabird populations. This probably relates to difficulties associated with obtaining robust prey estimates and the need to develop new methodologies to improving the resolution of species identification. Here, new molecular approaches were developed to recover prey from faeces and stomach contents using DNA-barcoding and high-throughput sequencing (HTS). The results obtained show clear improvements to the identification of the diets of procellariiformes, considerably outperforming morphological analysis, and retrieving prey identities from non-invasive faecal remains. Such approaches further showed that sympatric small seabirds of the sub-tropical NE-Atlantic significantly segregated their resources, while showing similar prey types with the species distributed in the Pacific, indicating that these petrels maintain foraging specialization across their distribution range. Foraging efficiency in seabirds has been widely hypothesized to change according to the moon cycle. Predators either optimise foraging during moonlit nights or reduce foraging effort because less accessible prey migrate downward the water column to avoid visual predators. I tested whether prey composition and diversity differ between moon-phases. However, I found no evidence for a significant influence of the moon on the diet of Bulwer’s petrel, contradicting previous ecological assumptions. The results highlight the potential of DNA methodologies to the understanding of marine food webs and predator-prey relationships and will certainly make important contributions to marine community ecology.