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

Abstract

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.

Sex and occupation time influence niche space of a recovering keystone predator

“…Previous research suggests that most critical macro-and micronutrients are well represented in sea otter diets and that energy is the primary resource driving sea otter prey selection (Oftedal et al, 2007). However, variability in macronutrient composition among prey species can be an important driver of diet choice and niche space (Machovsky-Capuska et al, 2018;Machovsky-Capuska, Senior, Simpson et al, 2016;Mayntz, Raubenheimer, Salomon, Toft, & Simpson, 2005;Raubenheimer, Simpson, & Mayntz, 2009;Tait, Raubenheimer, Stockin, Merriman, & Machovsky-Capuska, 2014). Accordingly, including data on the macronutrient content of prey may enhance our characterization of niche space, but quantifying macronutrient profiles for the diverse suite of prey that sea otters consumed was beyond the scope of this study.…”

“…The multidimensional niche space of a species (Hutchinson, ) can be examined by mapping a species’ biotic and abiotic requirements and then used to predict what interactions a species may have within a larger community (Holt, ). Recently, nutrition, physiology, and behaviour have also been used to better characterize niche breadth and predict a species’ trophic interactions (Machovsky‐Capuska et al, ). Although once viewed as static, niche space is no longer seen as a fixed property, but one that can change as a function of intraspecific variation (Baudrot, Perasso, Fritsch, Giraudoux, & Raoul, ; Ingram, Costa‐Pereira, & Araujo, ; Lafferty, Belant, & Phillips, ; Newsome et al, ).…”

“…The multidimensional niche space of a species (Hutchinson, 1957) can be examined by mapping a species' biotic and abiotic requirements and then used to predict what interactions a species may have within a larger community (Holt, 2009). Recently, nutrition, physiology, and behaviour have also been used to better characterize niche breadth and predict a species' trophic interactions (Machovsky-Capuska et al, 2018).…”

Biologging Special Feature

“…Daily energy needs of animals are mostly achieved by the metabolization of macromolecules (protein, lipid and carbohydrates) obtained from foods (Nagy, Girard, & Brown, 1999). Environmental fluctuations influence the nutritional composition and energy contents of foods shaping the foraging behaviour and habitat use of wild animals (Machovsky-Capuska et al, 2018). Under these circumstances, fieldbased research has the challenge to overcome complex logistical constraints to collect reliable data on nutritional and energy requirements in free-ranging animals (Machovsky-Capuska et al, 2016).…”

Predicting Which Species Succeed in Climate-Forced Polar Seas

“…For example, temperature and other environmental factors are known to influence the nutritional quality of prey as well as the nutritional requirements of predators. Incorporating nutritional ecology into assessments of climate change effects (Rosenblatt and Schmitz, 2016;Machovsky-Capuska et al, 2018) is just one of the improvements that will become possible as data availability increases. Our knowledge of the importance of factors that are likely to mitigate or even feedback against climate change, can be incorporated in more complex assessments.…”