Dr R Phillips, Prof S Bearhop, Dr Yves Cherel, Dr SC Votier
No more applications being accepted
Competition Funded PhD Project (UK Students Only)
About the Project
Seabird communities are often highly diverse, including species that range in number from rare to abundant, in foraging distance from inshore to highly pelagic, and in trophic level from zooplanktivore to top predator and scavenger. Much research has focused on how these communities are maintained, including the roles of differences in timing of peak demand for prey (related to breeding phenology), foraging areas, dive depth or other aspects of feeding behaviour, and diet, which reduce competition for the same resources and lead to niche partitioning. This is complicated by other factors (intrinsic and environmental) that may operate within species and lead to spatial or temporal segregation in habitat or diet, including sex, age, breeding stage, season, year, etc., and, ultimately, individual specialisation.
Although some of these topics can be addressed using tracking or conventional diet assessment, stable isotope analyses (SIA) of predator tissues represents a potentially more powerful alternative for identifying consistent differences in diet or distribution because it avoids certain biases, and logistical difficulties of sampling birds far from land, and values reflect prey assimilated over timescales of days to months, depending on the tissue. Stable carbon and nitrogen isotope ratios in animal tissues reflect those of their prey during tissue formation; 15N to 14N ratio (d15N) increases in a stepwise manner by 3–5‰ at each trophic level, whereas 13C to 12C ratio (d13C) increases to a lesser extent with trophic level (by 0.5–1‰), but can provide spatial information, including relative reliance on inshore-versus-offshore, or benthic-versus-pelagic diet, and on latitude where a gradient exists. Difficulties arise, however, when comparing trophic level in samples from different years or regions, because of differences in the isotope baseline. Amino acid (AA) compound-specific analyses of stable isotopes (CSIA) may provide the answer, as d15N can be compared in AAs that are unchanged (source), with AAs that become enriched in 15N (trophic) in consumer tissues. Analytically, CSIA is much more complex than bulk tissue SIA, and despite the potential, the technique is currently under-utilised for a variety of reasons.
This PhD project would use SIA and CSIA of seabird tissues from Southern Ocean islands to explore; effects of age, sex and other characteristics on distribution and diet; changes within-species and across communities in distribution and trophic level associated with breeding stage and migration, accounting for variation in isotopic baselines; individual consistency; effects of fasting on d15N in source and trophic AA; implications for competition and community structure.
References
Moreno, R., Stowasser, G., McGill, R.A.R., Bearhop, S. and Phillips, R.A. Assessing the structure and temporal dynamics of seabird communities: the challenge of capturing marine ecosystem complexity. Journal of Animal Ecology 85, 199-212 (2016).
Phillips, R.A., McGill, R.A.R., Dawson, D.A. and Bearhop, S. Sexual segregation in distribution, diet and trophic level of seabirds: insights from stable isotope analysis. Marine Biology 158, 2199-2208 (2011).
Lorrain, A. et al., Nitrogen and carbon isotope values of individual amino acids: a tool to study foraging ecology of penguins in the Southern Ocean. Marine Ecology Progress Series 391, 293-306 (2009).
S. C. Votier et al., Individual responses of seabirds to commercial fisheries revealed using GPS tracking, stable isotopes and vessel monitoring systems. Journal of Applied Ecology 47, 487-497 (2010)