Abstract
Hette‐Tronquart (2019, Ecol. Lett.) raises three concerns about our interpretation of stable isotope data in Sheppard et al. (2018, Ecol. Lett., 21, 665). We feel that these concerns are based on comparisons that are unreasonable or ignore the ecological context from which the data were collected. Stable isotope ratios provide a quantitative indication of, rather than being exactly equivalent to, trophic niche.
Highlights
Hette-Tronquart (2019) raises three concerns about our study demonstrating that increased intragroup competition predicts higher individual foraging specialisation in banded mongooses Mungos mungo (Sheppard et al 2018)
The multiple stable isotope values used to create our relative individual niche index (RINI) measure ‘the variability of diet over the sampling period’ and so we may not be able to differentiate between feeding strategies that vary over shorter or longer timescales than the sampling period
Hette-Tronquart suggests that the variation we observed in mongoose stable isotope ratios may be due to temporal changes in prey isotope values (‘isotopic baseline’) rather than variation in individual diet (Yeakel et al 2016)
Summary
Hette-Tronquart (2019) raises three concerns about our study demonstrating that increased intragroup competition predicts higher individual foraging specialisation in banded mongooses Mungos mungo (Sheppard et al 2018). The multiple stable isotope values used to create our relative individual niche index (RINI) measure ‘the variability of diet over the sampling period’ and so we may not be able to differentiate between feeding strategies that vary over shorter or longer timescales than the sampling period. Hette-Tronquart suggests that the variation we observed in mongoose stable isotope ratios may be due to temporal changes in prey isotope values (‘isotopic baseline’) rather than variation in individual diet (Yeakel et al 2016) As he points out, there is no reason to expect the isotopic baseline to vary systematically with mongoose group size (our measure of intragroup competition). The RINI would support assessment of niche variation over shorter timescales (e.g. days) if the measures were based on tissue samples synthesised over shorter periods
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