Within-Population Isotopic Niche Variability in Savanna Mammals: Disparity between Carnivores and Herbivores

Abstract

Large mammal ecosystems have relatively simple food webs, usually comprising three-and sometimes only two-trophic links. Since many syntopic species from the same trophic level therefore share resources, dietary niche partitioning features prominently within these systems. In African and other subtropical savannas, stable carbon isotopes readily distinguish between herbivore species for which foliage and other parts of dicot plants (13 C-depleted C 3 vegetation) are the primary resource (browsers) and those for which grasses (13 C-enriched C 4 vegetation) are staples (grazers). Similarly, carbon isotopes distinguish between carnivore diets that may be richer in either browser, grazer, or intermediate-feeding prey. Here, we investigate levels of carbon and nitrogen isotopic niche variation and niche partitioning within populations (or species) of carnivores and herbivores from South African savannas. We emphasize predictable differences in within-population trends across trophic levels: we expect that herbivore populations, which require more foraging effort due to higher intake requirements, are far less likely to display within-population resource partitioning than carnivore populations. Our results reveal generally narrower isotopic niche breadths in herbivore than carnivore populations, but more importantly we find lower levels of isotopic differentiation across individuals within herbivore species. While these results offer some support for our general hypothesis, the current paucity of isotopic data for African carnivores limits our ability to test the complete set of predictions arising from our hypothesis. Nevertheless, given the different ecological and ecophysiological constraints to foraging behavior within each trophic level, comparisons across carnivores, and herbivores, which are possible within such simplified foodwebs, make these systems ideal for developing a process-based understanding of conditions underlying the evolution of intra-specific, individual-level separation of ecological niches.

Predator size and prey size–gut capacity ratios determine kill frequency and carcass production in terrestrial carnivorous mammals

“…Thus, a functional dichotomy seems to exist in carnivores, but ecologic rather than physiologic factors seem to determine whether a carnivore is a 'small prey-feeder' or a 'large prey-feeder'. This functional dichotomy may well occur within species where different individuals are specialized on different prey (Codron et al 2016), within individuals over ontogeny (Elbroch et al 2017), or in individuals between hunting events (Lumetsberger et al 2017). Observations deviating from the general pattern, such as a population of wild cats living on rabbits rather than small rodents (Malo et al 2004), or a population of wild dogs living mainly on very small ungulates (Woodroffe et al 2007), indicate that the underlying cause for the dichotomy must be sought in ecological circumstances rather than fixed physiological and behavioural adaptations.…”

Trophic ecology of large herbivores in a reassembling African ecosystem

“…Less is known about the degree and determinants of intraspecific variation in LMH diet composition. Within populations of apparently generalist consumers, individuals can be relatively specialized, utilizing narrow and distinct subsets of the population‐level diet (Bolnick et al, ; Bolnick, Svanbäck, Araújo, & Persson, ; Codron, Codron, Sponheimer, & Clauss, ; Maldonado, Bozinovic, Newsome, & Sabat, ). Together, the extent of among‐individual differentiation and the breadth of individual diets shape the population niche (Roughgarden, ; Van Valen, ).…”

Multifaceted disparity approach reveals dinosaur herbivory flourished before the end-Cretaceous mass extinction

“…Herbivorous dinosaurs are of particular interest, as they were hugely abundant and positioned at the bottom of the vertebrate food chain, and therefore changes in their diversity and ecology had the potential to create cascading effects through the ecosystem (Pringle et al 2007;Vila et al 2016). Moreover, herbivores are expected to encompass more species with dietary specializations than carnivores (Bernays and Graham 1988;Codron et al 2016), so herbivorous dinosaurs should have been particularly sensitive to environmental perturbations (Davies et al 2004;Clavel et al 2011). Several studies have investigated dinosaur disparity leading up to the K-Pg extinction, three of which exclusively focused on ecomorphology (Larson et al 2016;Strickson et al 2016;MacLaren et al 2017).…”