Evolution of degrees of carnivory and dietary specialization across Mammalia and their effects on speciation

Abstract

Conflation between omnivory and dietary generalism limits ecological and evolutionary analyses of diet, including estimating contributions to speciation and diversification. Additionally, categorizing species into qualitative dietary classes leads to information loss in these analyses. Here, we constructed two continuous variables — degree of carnivory (i.e., the position along the continuum from complete herbivory to complete carnivory) and degree of dietary specialization (i.e., the number and variety of food resources utilized) — to elucidate their histories across Mammalia, and to tease out their independent contributions to mammalian speciation. We observed that degree of carnivory significantly affected speciation rate across Mammalia, whereas dietary specialization did not. We further considered phylogenetic scale in diet-dependent speciation and saw that degree of carnivory significantly affected speciation in ungulates, carnivorans, bats, eulipotyphlans, and marsupials, while the effect of dietary specialization was only significant in carnivorans. Across Mammalia, omnivores had the lowest speciation rates. Our analyses using two different categorical diet variables led to contrasting signals of diet-dependent diversification, and subsequently different conclusions regarding diet's macroevolutionary role. We argue that treating variables such as diet as continuous instead of categorical reduces information loss and avoids the problem of contrasting macroevolutionary signals caused by differential discretization of biologically continuous traits.

Prey size reflected in tooth wear: a comparison of two wolf populations from Sweden and Alaska

“…Within the mammalian order Carnivora (canids, felids, hyenids, mustelids, ursids and pinnipeds), various dietary classification systems are employed to describe carnivory. These systems include different cut-offs, sub-categories with or without invertebrates; for a comprehensive review, see Pollard and Puckett [11]. In this context, the term 'carnivore' is used to reflect the percentage of prey species in the diet of Canis lupus, as reported by Ballard et al [12], Olsson et al [13] and Müller [14].…”

Convergent relaxation of molecular constraint in mammalian herbivores highlights the roles of liver and kidney functions in carnivory

“…To date, comparative genomic studies that sampled broadly within mammals have used coarse dietary classification systems, such as herbivore, carnivore, and omnivore (10)(11)(12). This results in a loss of important dietary information, as species grouped together differ in the proportions of plant and animal matter consumed and may show divergent adaptations (13)(14)(15)(16). Thus, the power of comparative genomic studies that investigate the molecular mechanisms of dietary adaptation may be reduced.…”