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Background <p>Individuals within populations may have distinct ecological niches, leading to a partitioned population niche structure. Such structure occurs because of both extrinsic and intrinsic factors. Body mass is suggested to limit between-individual diet niche variation within large-bodied mammalian herbivore populations, as their high intake requirements and associated search costs restricts opportunity for individuals to specialise. This study used stable isotope analysis to investigate niche structure within populations of mammalian herbivores to determine if (1) body mass correlates with the degree of niche structure and if (2) environmental conditions mediate this relationship. Stable carbon and nitrogen isotope compositions of faecal material of 16 herbivore species ranging in body mass (~ 10 to ~ 1420&#xa0;kg) and geographical location were analysed. For each population, isotopic niche width (ellipse areas) and dispersion patterns (variance in geometric distance between individuals) in isotopic bi-space were quantified as proxies for population niche structure. Linear mixed models were used to test the effect of body mass, and local rainfall and reserve area (proxy for ecological conditions) on these indices of structure.</p> Results <p>Isotopic niche widths and dispersion metrics varied between species both within and between reserves, but the directionality of differences was not consistent, with some populations having broader niche widths and/or higher levels of dispersion than others, even within the same species. Although species differed in the degree of niche structuring within their respective populations, there was no effect of interspecific differences in body mass. The degree of dispersion (and thus between individual isotopic niche differences) is also not a function of ecological opportunity, but increased area might allow populations to expand their isotopic niche widths.</p> Conclusions <p>These findings suggest that niche variation and dispersion patterns in herbivore populations is limited by factors other than body size and intake requirement, despite the well-established role of body mass in shaping diet, as well as many other behavioural, ecological, and life history traits.</p>

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Within-population isotopic niche variation of mammalian herbivores over a body mass and habitat gradient

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月3日

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  • Runè van der Merwe,
  • Chanel Lewis,
  • Daryl Codron

摘要

Background

Individuals within populations may have distinct ecological niches, leading to a partitioned population niche structure. Such structure occurs because of both extrinsic and intrinsic factors. Body mass is suggested to limit between-individual diet niche variation within large-bodied mammalian herbivore populations, as their high intake requirements and associated search costs restricts opportunity for individuals to specialise. This study used stable isotope analysis to investigate niche structure within populations of mammalian herbivores to determine if (1) body mass correlates with the degree of niche structure and if (2) environmental conditions mediate this relationship. Stable carbon and nitrogen isotope compositions of faecal material of 16 herbivore species ranging in body mass (~ 10 to ~ 1420 kg) and geographical location were analysed. For each population, isotopic niche width (ellipse areas) and dispersion patterns (variance in geometric distance between individuals) in isotopic bi-space were quantified as proxies for population niche structure. Linear mixed models were used to test the effect of body mass, and local rainfall and reserve area (proxy for ecological conditions) on these indices of structure.

Results

Isotopic niche widths and dispersion metrics varied between species both within and between reserves, but the directionality of differences was not consistent, with some populations having broader niche widths and/or higher levels of dispersion than others, even within the same species. Although species differed in the degree of niche structuring within their respective populations, there was no effect of interspecific differences in body mass. The degree of dispersion (and thus between individual isotopic niche differences) is also not a function of ecological opportunity, but increased area might allow populations to expand their isotopic niche widths.

Conclusions

These findings suggest that niche variation and dispersion patterns in herbivore populations is limited by factors other than body size and intake requirement, despite the well-established role of body mass in shaping diet, as well as many other behavioural, ecological, and life history traits.