Organic contaminants as an ecological tool to explore niche partitioning: a case study using three pelagic shark species

Kady Lyons,David Gillett,Antonella Preti,Dovi Kacev,Heidi Dewar

doi:10.1038/s41598-019-48521-6

Abstract

Chemical contaminant profiles are linked to an animal’s niche, providing a potential tool by which to assess resource partitioning in pelagic species. As proof of concept, we examined contaminant signatures in three species of sharks (Isurus oxyrinchus, Prionace glauca, and Alopias vulpinus) known to overlap in both space and time. Since these sharks comprise a predatory guild within the Southern California Bight (SCB), we predicted that species may partition spatial and dietary resources to limit the extent of competitive exclusion. Indeed, species were distinguishable by both total contaminant loads and their contaminant fingerprint, as random forest analysis found that species could be correctly classified 96% of the time. Our results demonstrate the utility of chemical analyses for ecological studies, and how contaminant tracers can be used in combination with traditional methods to elucidate how species may undergo niche partitioning to reduce competition for overlapping resources within predatory guilds.

Highlights

Interspecific resource competition is one of the primary biotic drivers modifying species’ fundamental niches towards their realized niches within a community[1,2,3]
A subset of these archived samples was analyzed for organic contaminants in individuals selected to represent a range of sizes and sexes for I. oxyrinchus, P. glauca, and A. vulpinus sampled from the years 2011–2013
Ion peaks were identified using gas chromatography mass spectrometry (GCMS) software for 54 polychlorinated biphenyls (PCBs) congeners, DDT and its metabolites (4,4′-DDT, 4,4′-DDE, 4,4′-DDD, 2,4′-DDT, 2,4′-DDE, 2,4′-DDD; sum = tDDXs), and non-DDT chlorinated pesticides (24 compounds screened; sum = tPEST); total concentrations were expressed as the sum of all contaminant groups

Summary

Introduction

Interspecific resource competition is one of the primary biotic drivers modifying species’ fundamental niches towards their realized niches within a community[1,2,3]. Niche partitioning is evaluated using tagging and/or gut content studies, where separation of species’ trophic or spatial resources can be identified through their movements[12,13] or prey composition[14,15,16] These methods are, logistically challenging in marine environments where organisms spend the majority of their time underwater and can be difficult to observe (tagging) or are dependent on capture directly after a meal (gut contents). Organic contaminants can offer some degree of spatial resolution as different areas have unique chemical signatures based on the history of direct contaminant release or atmospheric deposition[29] These contaminant signatures are incorporated into local biota, which will generally reflect the environment, assuming a majority of contaminants from the diet are absorbed and metabolism by the predator is limited so as to not alter these contaminant signatures. We aimed to demonstrate the applicability of organic contaminants as a tool to examine the degree of niche partitioning among three species of sympatric sharks within the same predatory guild using contaminant information collected previously[33]

Objectives

Methods

Results

Conclusion