Abstract
Dietary variation within species has important ecological and evolutionary implications. While theoreticians have debated the consequences of trait variance (including dietary specialization), empirical studies have yet to examine intraspecific dietary variability across the globe and through time. Here, we use new and published serial sampled δ13Cenamel values of herbivorous mammals from the Miocene to the present (318 individuals summarized, 4134 samples) to examine how dietary strategy (i.e. browser, mixed-feeder, grazer) affects individual isotopic variation. We find that almost all herbivores, regardless of dietary strategy, are composed of individual specialists. For example, Cormohipparion emsliei (Equidae) from the Pliocene of Florida (approx. 5 Ma) exhibits a δ13Cenamel range of 13.4‰, but all individuals sampled have δ13Cenamel ranges of less than or equal to 2‰ (mean = 1.1‰). Most notably, this pattern holds globally and through time, with almost all herbivorous mammal individuals exhibiting narrow δ13Cenamel ranges (less than or equal to 3‰), demonstrating that individuals are specialized and less representative of their overall species' dietary breadth. Individual specialization probably reduces intraspecific competition, increases carrying capacities, and may have stabilizing effects on species and communities over time. Individual specialization among species with both narrow and broad dietary niches is common over space and time—a phenomenon not previously well recognized or documented empirically.
Highlights
Food selection is a critical component of life at the individual, population and species level, and is one of the crucial aspects that defines the ecological niche of an organism
The dietary niche of an animal is often inferred as broad or narrow based on the breadth of food items consumed
When diet is examined directly or inferred via proxies such as stable isotopes, generalist populations/species are often found to be composed of individual specialists—though only a handful of species have been examined [8,9,10,11,12]
Summary
Food selection is a critical component of life at the individual, population and species level, and is one of the crucial aspects that defines the ecological niche of an organism. When diet is examined directly or inferred via proxies such as stable isotopes, generalist populations/species are often found to be composed of individual specialists—though only a handful of species have been examined [8,9,10,11,12] The reason for this phenomenon is not entirely clear, but for carnivores it is likely to be related to tradeoffs between specializing on one versus many prey species, with selection acting against individual generalists [7]. Food selection in herbivores results from the complex interplay between vegetation characteristics and herbivore anatomy, physiology and behaviour, a series of ecological and evolutionary interactions that occur at the species, population and individual levels [14]. Understanding how herbivores choose and consume vegetation at the individual, population, and species levels is fundamental for effective environmental conservation and management [29]
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