Apparent resource partitioning and trophic structure of large-bodied marine predators in a relatively pristine seagrass ecosystem

Abstract

Large predators often play important roles in structuring marine communities. To understand the role that these predators play in ecosystems, it is crucial to have knowledge of their interactions and the degree to which their trophic roles are complementary or redundant among species. We used stable isotope analysis to examine the isotopic niche overlap of dolphins Tursiops cf. aduncus, large sharks (>1.5 m total length), and smaller elasmobranchs (sharks and batoids) in the relatively pristine seagrass community of Shark Bay, Australia. Dolphins and large sharks differed in their mean isotopic values for δ 13 C and δ 15 N, and each group occupied a relatively unique area in isotopic niche space. The standard ellipse areas (SEAc; based on bivariate standard deviations) of dolphins, large sharks, small sharks, and rays did not overlap. Tiger sharks Galeocerdo cuvier had the highest δ 15 N values, although the mean δ 13 C and δ 15 N values of pigeye sharks Carcharhinus amboinensis were similar. Other large sharks (e.g. sicklefin lemon sharks Negaprion acutidens and sandbar sharks Carcharhinus plumbeus) and dolphins appeared to feed at slightly lower trophic levels than tiger sharks. In this seagrass-dominated ecosystem, seagrassderived carbon appears to be more important for elasmobranchs than it is for dolphins. Habitat use patterns did not correlate well with the sources of productivity supporting diets, suggesting that habitat use patterns may not necessarily be reflective of the resource pools supporting a population and highlights the importance of detailed datasets on trophic interactions for elucidating the ecological roles of predators.

Comparative diets of sympatric batoid elasmobranchs in the Gulf of Oman

“…Partitioning of food resources has been proposed as one of the main mechanisms explaining the coexistence of closely related elasmobranchs (e.g. Heithaus et al 2013, Albo-Puigserver et al 2015, owing to differences in prey or micro-habitats (e.g. Platell et al 1998, Papastamatiou et al 2006.…”

Acoustic telemetry and network analysis reveal the space use of multiple reef predators and enhance marine protected area design

“…Predators help promote ecosystem diversity and stability by exerting strong, top-down forces that shape communities over large spatio-temporal scales [5][6][7]. Sharks, for instance, occupy high trophic levels in most marine food webs, are typically well connected trophically and can elicit strong avoidance behaviours in prey [8][9][10]. Yet most fisheries target large predators, potentially exacerbating the impacts of overfishing on ecosystem stability by selectively removing influential predators like sharks and tuna [2].…”

Sympatric elasmobranchs and fecal samples provide insight into the trophic ecology of the smalltooth sawfish

“…basal resources and trophic level; Hussey et al 2014). These techniques have revealed dietary resource partitioning among sympatric juvenile sharks in nurseries and between guild-level predator groups (Kinney et al 2011, Heithaus et al 2013). These multi-species, comparative studies can reveal the degree to which the niches of sympatric predators are unique (i.e.…”

“…Understanding how communities are structured and how resources are used within them requires knowledge of the roles members play at multiple trophic levels, including unique or redundant trophic roles among species and their life stages (Kinney et al 2011, Heithaus et al 2013. Studies that have attempted to dissect these complex, interconnected systems have shown both high degrees of interspecific difference in the diets of sympatric predator species (i.e.…”

“…Although analyzing samples collected over many years for stable isotopes introduces the potential temporal bias of resource pools, such an approach can allow for detection of robust patterns that surpass short-term and small-scale isotope variation (e.g. Layman et al 2005, Heithaus et al 2013. For complete description of stable isotope sample preparation, lab analyses, and analytical precision, see Olin et al (2013bOlin et al ( , 2014.…”