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

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, the jumbo squid Dosidicus gigas, by a combined analysis of morphologic indicators of feeding capability (fin and feeding apparatuses), trophic biochemical tracers (stable isotopes and fatty acids), and stomach contents. Results showed significant variation in prey composition, isotopic values, and fatty acid profiles with size. D. gigas exhibited a shift in diet at approximately 250 mm mantle length (ML). The trophic niche of small (ML ≤ 250 mm) and large (ML > 250 mm) squid revealed low potential for resource overlap, suggesting segregation in terms of spatial and food resources of different size groups. Large individuals tend to feed deeper and on smaller prey to optimize food capture costs and energy benefits. This feeding strategy is likely related to variability in the development of feeding capacity, increasing swimming ability, and 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 can highlight subtle differentiations in diet correlated to growth in a pelagic generalist predator.

Microplastics in a pelagic squid (Dosidicus gigas) from the Eastern tropical Pacific Ocean: Characteristics, spatial variation, and preliminary risk assessment

“…D gigas is widely distributed in the eastern Pacific and its population structure is complex. Several studies have reported spatial variations of foraging strategies among population units within of D. gigas (Gong et al, 2020;Gao et al, 2022). For example, fishes were the main prey items of D. gigas collected off the coast of Chile (Pardo-Gandarillas et al, 2014) while cephalopods (including cannibalism) and fishes were the main prey items of D. gigas from the Ecuadorian waters (Rosas-Luis and Chompoy-Salazar, 2016) and the waters off Peru (Alegre et al, 2014).…”

“…Overall, these findings suggest that all sampling groups were influenced by similar level of MPs pollution. This phenomenon possibly due to MPs could be rapidly egested by D. gigas, which has a fast digestion rate (Gao et al, 2022). Until now, no evidence of MP accumulation in large predator has been documented in other studies (Chagnon et al, 2018).…”

Metabolic trade-offs associated with homeostatic adjustments in pelagic and benthic cephalopods: Comparative evaluations of NH4+/H+ transport machinery in gills

“…As an alternative, the acid-base and ammonium regulation in pelagic squid could be largely controlled by primary active transport in an energy-intensive manner since they possess higher aerobic respiration rate and more efficient NH 4 + regulation machinery than benthic crawling octopus. Due to their similar athletic hunting strategies and jet propulsion locomotion pattern, the pelagic squid may behave as a "spendthrift" for energy consumption that is not concerned with the food source (Shulman et al, 2002;Gao et al, 2022). This characteristic implies that pelagic squids are able to generate enough energy for intact physiological adjustments, such as body growth and nitrogenous waste elimination.…”