Fine-scale intraspecific niche partitioning in a highly mobile, marine megafauna species: implications for ecology and conservation

Abstract

A species may partition its realized ecological niche along bionomic and scenopoetic axes due to intraspecific competition for limited resources. How partitioning manifests depends on resource needs and availability by and for the partitioning groups. Here we demonstrate the utility of analysing short- and long-term stable carbon and nitrogen isotope ratios from imperiled marine megafauna to characterize realized niche partitioning in these species. We captured 113 loggerhead sea turtles ( Caretta caretta ) at a high-use area in the eastern Big Bend, Florida, between 2016 and 2022, comprising 53 subadults, 10 adult males and 50 adult females. We calculated trophic niche metrics using established and novel methods, and constructed Bayesian ellipses and hulls, to characterize loggerhead isotopic niches. These analyses indicated that loggerheads partition their realized ecological niche by lifestage, potentially along both bionomic (e.g. trophic) and/or scenopoetic (e.g. habitat, latitude or longitude) axes, and display different characteristics of resource use within their niches. Analysis of stable isotopes from tissues with different turnover rates enabled this first characterization of intraspecific niche partitioning between and within neritic lifestages in loggerhead turtles, which has direct implications for ongoing research and conservation efforts for this and other imperiled marine species.

Isotopic niche overlap among foraging marine turtle species in the Gulf of Mexico

“…This ontogenetic shift could be a major source of the observed isotopic variation contributing to the wider isotopic niche of green turtles (Figure S1). It is possible that within the juvenile green turtle population, there may be size‐related differences in resource use, as has been found in the loggerhead (Silver‐Gorges et al., 2023) and Kemp's ridley (Weber et al., 2023) turtle populations within the Crystal River foraging site. Although turtle size‐partitioning was beyond the scope of this study, we plotted SIA values against marine turtle size (Figure S2).…”

“…It is possible that within the juvenile green turtle population, there may be size-related differences in resource use, as has been found in the loggerhead (Silver-Gorges et al, 2023) and Kemp's ridley (Weber et al, 2023) turtle populations within the Crystal River foraging site.…”