Intragroup competition predicts individual foraging specialisation in a group-living mammal.

Catherine E Sheppard,Michael A Cant,Faye J Thompson,Richard Inger,Sam Barker,Harry H Marshall,Robbie A Mcdonald,Andrew L Jackson,Emma I K Vitikainen,Andrew Bourke

doi:10.1111/ele.12933

Catherine E Sheppard, Michael A Cant + Show 8 more

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https://doi.org/10.1111/ele.12933

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Abstract

Individual foraging specialisation has important ecological implications, but its causes in group‐living species are unclear. One of the major consequences of group living is increased intragroup competition for resources. Foraging theory predicts that with increased competition, individuals should add new prey items to their diet, widening their foraging niche (‘optimal foraging hypothesis’). However, classic competition theory suggests the opposite: that increased competition leads to niche partitioning and greater individual foraging specialisation (‘niche partitioning hypothesis’). We tested these opposing predictions in wild, group‐living banded mongooses (Mungos mungo), using stable isotope analysis of banded mongoose whiskers to quantify individual and group foraging niche. Individual foraging niche size declined with increasing group size, despite all groups having a similar overall niche size. Our findings support the prediction that competition promotes niche partitioning within social groups and suggest that individual foraging specialisation may play an important role in the formation of stable social groupings.

Highlights

Within animal populations there is often remarkable heterogeneity in foraging behaviour
Banded mongooses in larger groups gained less weight day-today (LMM: b Æ SE = À 0.46 Æ 0.054, v21 = 70.47, P < 0.001; Fig. 2a) and overall were in poorer condition (b Æ SE = À 2.92 Æ 0.19, v21 = 227.57, P < 0.001; Table 1; Fig. 2b)
We found that individual banded mongooses in larger groups had smaller relative isotopic niches (RINIs), despite larger groups occupying similar sized niches to smaller groups

Summary

Introduction

Within animal populations there is often remarkable heterogeneity in foraging behaviour (birds: Harris et al 2014; sharks: Matich et al 2011; mammals: Newsome et al 2009; Robertson et al 2014, 2015) This intraspecific variation in foraging niche can often be attributed to differences in sex (Bearhop et al 2006; Stauss et al 2012), age (Newland et al 2009) or morphology (Pegg et al 2015). Foraging specialisation in these species merits particular consideration as social group characteristics are likely to have a greater impact on individual ecological and evolutionary processes, such as individual specialisation, than the characteristics of the whole population, made up of multiple social groups (Chepko-Sade & Halpin 1987; Johnstone & Cant 2010)

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