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Dietary shifts and niche partitioning throughout ontogeny avoid intraspecific competition in a pelagic generalist predator

Xiaodi Gao, Yi Gong, Xinjun Chen, Yunkai Li*

*Corresponding author:

ABSTRACT: Patterns of feeding strategy change throughout ontogeny according to size-specific abilities and requirements. Characterizing the extent and potential repeated occurrence of dietary differences within the population can improve understanding of the intraspecific predation regime and population dynamics. Here, we investigated size-related feeding habits and trophic niche partitioning of an iconic pelagic generalist predator, jumbo squid Dosidicus gigas, by a combined analysis of morphologic indicators of feeding capability (fin and feeding apparatuses), trophic biochemical tracers (stable isotope and fatty acid), and stomach content. Results showed significant variations in prey composition, isotopic values, and fatty acid profiles with size. D. gigas exhibited a shift in diets at approximately 250 mm mantle length (ML). The trophic niche of small (ML ≤ 250 mm) and large (ML > 250 mm) squid revealed the low potential for resource overlap, suggesting the segregation in terms of spatial and food resources of the different size groups. Large individuals tend to feed on deeper and smaller prey to optimize food capture costs and energy benefits. This feeding strategy is likely related to the variability in the development of the feeding capacity, increasing swimming ability, and the metabolic demand as squid grow and may reduce intraspecific competition to improve survival. These results highlight the dietary flexibility of D. gigas and demonstrate that niche differentiation acts as a major factor in a cohort, which may have important implications for their population dynamics and management. In addition, this study demonstrates that using multiple diet tracers together could provide subtle differentiation in the diet along growth for a pelagic generalist predator.