The generality of cryptic dietary niche differences in diverse large-herbivore assemblages

Abstract

Ecological niche differences are necessary for stable species coexistence but are often difficult to discern. Models of dietary niche differentiation in large mammalian herbivores invoke the quality, quantity, and spatiotemporal distribution of plant tissues and growth forms but are agnostic toward food plant species identity. Empirical support for these models is variable, suggesting that additional mechanisms of resource partitioning may be important in sustaining large-herbivore diversity in African savannas. We used DNA metabarcoding to conduct a taxonomically explicit analysis of large-herbivore diets across southeastern Africa, analyzing ∼4,000 fecal samples of 30 species from 10 sites in seven countries over 6 y. We detected 893 food plant taxa from 124 families, but just two families—grasses and legumes—accounted for the majority of herbivore diets. Nonetheless, herbivore species almost invariably partitioned food plant taxa; diet composition differed significantly in 97% of pairwise comparisons between sympatric species, and dissimilarity was pronounced even between the strictest grazers (grass eaters), strictest browsers (nongrass eaters), and closest relatives at each site. Niche differentiation was weakest in an ecosystem recovering from catastrophic defaunation, indicating that food plant partitioning is driven by species interactions, and was stronger at low rainfall, as expected if interspecific competition is a predominant driver. Diets differed more between browsers than grazers, which predictably shaped community organization: Grazer-dominated trophic networks had higher nestedness and lower modularity. That dietary differentiation is structured along taxonomic lines complements prior work on how herbivores partition plant parts and patches and suggests that common mechanisms govern herbivore coexistence and community assembly in savannas.

Mechanisms of individual variation in large herbivore diets: Roles of spatial heterogeneity and state‐dependent foraging

“…They are solitary but not aggressively antisocial, such that home ranges overlap and individuals often forage in close proximity (Estes, 1991). As strict browsers, bushbuck feed almost exclusively on trees, shrubs, and forbs to the exclusion of grasses (Daskin et al, 2022;Kartzinel & Pringle, 2020;Pansu et al, 2019bPansu et al, , 2022Potter et al, 2022). Bushbuck also use woody plants for concealment and are considered "dependent on thick cover" for predator avoidance (Kingdon, 1997, p. 352).…”

A bioenergetic framework for aboveground terrestrial food webs

“…Herbivores exhibit species-specific behaviors designed to optimize " !" within particular communities and habitats [47], the result of unique evolutionary trajectories driven by local fitness gradients [48].…”

“…Herbivores adaptively forage in a multi-scale manner [49] by first searching the landscape for a promising foraging habitat, and then locating particular plant individuals using multiple sensory modalities [50], after which a decision to eat them or keep searching is made [48]. Insects use a diverse array of cues to find their hosts, including habitat context and plant odor and color, after which many sense tissue quality and make feeding decisions using specialized chemoreceptors [49,51].…”

Picky eating as a means for coexistence

“…Pansu et al. ( 11 ) offer a complementary perspective that bridges the gap from the small scale of nutrient partitioning to the broad scale of partitioning time and space: partitioning plant species. They postulate that divergent use of plant species underlies observed niche differences and can promote stable coexistence, and therefore structures trophic networks.…”

“…Using an impressive dataset of fecal samples collected from 30 herbivore species across 10 savanna sites, Pansu et al. ( 11 ) used DNA metabarcoding to identify plant taxa within the diets of herbivores. They detected 893 plant taxa from 124 families, but the median population’s diet comprised only 31 taxa.…”