Methods for detecting and quantifying individual specialisation in movement and foraging strategies of marine predators

Abstract

There is increasing realisation that individuals in many animal populations differ substantially in resource, space or habitat use. Differences that cannot be attributed to any a priori way of classifying individuals (i.e. age, sex and other group effects) are often termed 'individual specialisation'. The aim of this paper is to assess the most common approaches for detecting and quantifying individual specialisation and consistencies in foraging behaviour, movement patterns and diet of marine predators using 3 types of data: conventional diet data, stable isotope ratios and tracking data. Methods using conventional diet data rely on a comparison between the proportions of each dietary source in the total diet and in the diet of individuals, or analyses of the statistical distribution of a prey metric (e.g. size); the latter often involves comparing ratios of individual and population variance. Approaches frequently used to analyse stable isotope or tracking data reduced to 1 dimension (trip characteristics, e.g. maximum trip distance or latitude/longitude at certain landmarks) include correlation tests and repeatability analysis. Finally, various spatial analyses are applied to other types of tracking data (e.g. distances between centroids of distributions or migratory routes, or overlap between distributions), and methods exist to compare habitat use. We discuss the advantages and disadvantages of these approaches, issues arising from other effects unrelated to individual specialisation per se (in particular those related to temporal scale) and potential solutions.

Intra-specific Niche Partitioning in Antarctic Fur Seals, Arctocephalus gazella

“…S2), added to the estimated TDF for Antarctic fur seal whiskers (2.06‰ ± 1.79 for δ 13 C). The variation in δ 13 C values along each whisker suggested all 20 females and only six males foraged north of the Polar Front at any point during their lives (as their maximum δ 13 C values exceeded −18.92‰) ( Supplementary Tables S3 and S4). Stable isotope bi-plots ( Fig.…”

“…The ratios of carbon and nitrogen isotopes in these gases were measured on a Thermo-Fisher-Scientific (Bremen, Germany) Delta XP Plus Isotope-Ratio Mass Spectrometer. The internal reference materials (mean ± SD) were GEL (gelatin solution, δ 13 C= −20.09 ± 0.19‰, δ 15 N= 5.59 ± 0.12‰), ALAGEL (alanine-gelatine solution spiked with 13 www.nature.com/scientificreports www.nature.com/scientificreports/ where X is 15 N or 13 C and R is the corresponding ratio ( 15 N/ 14 N) or ( 13 C/ 12 C). Stable isotope ratios were reported as δ 13 C values for carbon and δ 15 N values for nitrogen.…”

Short‐term prey field lability constrains individual specialisation in resource selection and foraging site fidelity in a marine predator

“…; Carneiro et al . ). We tested the added value of using random coefficients based on the Akaike information criterion (AIC).…”

“…Random intercepts corrected for differences in sample size between foraging trips and individuals (Gillies et al 2006). We added random coefficients (one slope per individual and per trip) to assess differences in resource selection between individuals and trips (conditional estimates) in addition to estimate population-level responses (marginal estimate; Gillies et al 2006;Hebblewhite & Merrill 2008;Leclerc et al 2016;Carneiro et al 2017). We tested the added value of using random coefficients based on the Akaike information criterion (AIC).…”

Quantifying individual specialization using tracking data: a case study on two species of albatrosses

“…generalist individuals), there is often some specialisation at the individual level (Bolnick et al 2003 ). Accordingly, there is a growing awareness of the importance of considering intra-specific variation in niches, and in the development of appropriate methodology (Bolnick et al 2011 ; Carneiro et al 2017 ; Phillips et al 2017 ).…”