The nutritional nexus: Linking niche, habitat variability and prey composition in a generalist marine predator.

Our understanding of the niche concept will remain limited while the quantity and range of different food types eaten remain a dominant proxy for niche breadth, as this does not account for the broad ecological context that governs diet. Linking nutrition, physiology and behaviour is critical to predict the extent to which a species adjusts its nutritional niche breadth at the levels of prey ("prey composition niche," defined as the range of prey compositions eaten) and diet ("realized nutritional niche" is the range of diets composed through feeding on the prey). Here, we studied adult chick-rearing Australasian gannets Morus serrator to propose an integrative approach using sea surface temperature anomalies (SSTa), geographic location and bathymetry over different years, to explore their relationship with the nutritional composition of prey and diets (i.e. prey composition and nutritional niche breadth), habitat use and foraging behaviour. We found that gannets feed on prey that varied widely in their nutritional composition (have a broad prey composition niche), and composed diets from these prey that likewise varied in composition (have a broad realized nutritional niche), suggesting generalism at two levels of macronutrient selection. Across seasons, we established "nutritional landscapes" (hereafter nutriscapes), linking the nutritional content of prey (wet mass protein-to-lipid ratio-P:L) to the most likely geographic area of capture and bathymetry. Nutriscapes varied in their P:L from 6.06 to 15.28, over time, space and bathymetry (0-150 m). During warm water events (strong positive SSTa), gannets expanded their foraging habitat, increased their foraging trip duration and consumed prey and diets with low macronutrient content (wet mass proportions of P and L). They were also constrained to the smallest prey composition and realized nutritional niche breadths. Our findings are consistent with previous suggestions that dietary generalism evolves in heterogeneous environments, and provide a framework for understanding the nutritional goals in wild marine predators and how these goals drive ecological interactions and are, in turn, ultimately shaped by environmental fluctuations.

Speciation, range contraction and extinction in the endemic New Zealand King Shag complex.

New Zealand's endemic King Shag (Leucocarbo carunculatus) has occupied only a narrow portion of the northeastern South Island for at least the past 240years. However, pre-human Holocene fossil and archaeological remains have suggested a far more widespread distribution of the three Leucocarbo species (King, Otago, Foveaux) on mainland New Zealand at the time of Polynesian settlement in the late 13th Century CE. We use modern and ancient DNA, and morphometric and osteological analyses, of modern King Shags and Holocene fossil Leucocarbo remains to assess the pre-human distribution and taxonomic status of the King Shag on mainland New Zealand, and the resultant conservation implications. Our analyses show that the King Shag was formerly widespread around southern coasts of the North Island and the northern parts of the South Island but experienced population and lineage extinctions, and range contraction, probably after Polynesian arrival. This history parallels range contractions of other New Zealand seabirds. Conservation management of the King Shag should take into account this species narrow distribution and probable reduced genetic diversity. Moreover, combined genetic, morphometric and osteological analyses of prehistoric material from mainland New Zealand suggest that the now extinct northern New Zealand Leucocarbo populations comprised a unique lineage. Although these distinctive populations were previously assigned to the King Shag (based on morphological similarities and geographic proximity to modern Leucocarbo populations), we herein describe them as a new species, the Kohatu Shag (Leucocarbo septentrionalis). The extinction of this species further highlights the dramatic impacts Polynesians and introduced predators had on New Zealand's coastal and marine biodiversity. The prehistoric presence of at least four species of Leucocarbo shag on mainland NZ further highlights its status as a biodiversity hotspot for Phalacrocoracidae.