Dietary Similarity of Friends and Lovers: Vegetarianism, Omnivorism, and Personal Relationships

In a series of studies conducted in the USA and Poland, we found that vegetarianism can serve as a basis for the formation of personal relationships. Consistent with research on the similarity-attraction effect, we found that vegetarians were more likely than omnivores to have friends and lovers who were vegetarians. In study 1, vegetarians reported that their diets were a more important part of their identities than omnivores did. In studies 2, 3, and 4, we found that vegetarians were three to six times more likely to have vegetarian friends than omnivores were. In study 4 we found that vegetarians were twelve times more likely to have romantic partners who were vegetarians than omnivores were. These results suggest that following a vegetarian or an omnivorous diet is an important influence on an individual’s choice of relational partners, possibly because dietary choice is part of an individual’s social identity.

Inter- and intra-individual variation in the diet of Australasian gannets Morus serrator

Animal diets often vary according to age, sex, experience and/or individual preferences, which, when maintained over time, can lead to behavioural consistency and individual specialisations within populations. In addition, behavioural and dietary similarity within breeding pairs confers reproductive benefits in some species. We investigated inter- and intra-individual variation in diet in Australasian gannets Morus serrator through analysis of voluntary regurgitations, blood plasma stable isotopes and reconstructed diets. Samples were collected from nesting adults (mostly partners) over 4 breeding seasons (2012-2015) at 2 colonies (Point Danger, PD; and Pope’s Eye, PE), 215 km apart and with divergent oceanographic conditions. Inter-individual variation in δ13C and δ15N values and reconstructed diets was associated with colony, year, breeding stage and sex. The diet of PD individuals was dominated by pelagic schooling prey species, whereas PE birds consumed a substantial amount of benthic/inshore species. Correspondingly, the proportional similarity in diet of individuals was greater at PD, where individuals foraged within a relatively uniform environment, than at PE, where birds had access to a greater diversity of foraging habitats. Intra-individual variation in isotopic values indicated that trophic consistency was higher over medium timescales (between breeding stages within breeding seasons) than longer timescales (between breeding seasons), in accordance with recently documented temporal patterns of behavioural consistency. Lastly, nest partners consumed prey of similar trophic level (δ15N values), although a high degree of similarity did not confer a reproductive advantage to nest partners, and the mechanisms for such similarity are unknown.

Hominoid dietary evolution

During the later Palaeocene and early Miocene, catarrhine primates and the evolving hominoids had adaptations for frugivorous diets, with the emphasis on soft foods. Early in the middle Miocene the hominoids underwent a major shift, both in morphology and in habitat, with the morphology characterized by thickened enamel on the molars, enlarged incisors and massive jaws. The diet indicated by this morphology is interpreted as still mainly frugivorous but with changed emphasis, possibly towards harder objects. The thick-enamelled hominoids are found associated with more open forest habitats, and the distribution of food resources in equivalent habitats today is discontinuous both in time and in space, leading to evolutionary pressures particularly affecting locomotion, brain size and social behaviour. The earliest known hominid fossils differed little in dental and mandibular morphology from the middle Miocene apes, and the implied dietary similarity, together with ape-like patterns of dental development and retained arboreal adaptations of the postcrania, suggests little change in the foraging strategies of the earliest hominids compared with their ape ancestors and further suggests similarity in evolutionary grade. This similarity may have extended to other aspects of behaviour, for example to patterns of tool making and use, which may have been similar in the common ancestor of apes and humans to the pattern shared by the earliest australopithecines and chimpanzees.

Food resource allocation in larval newt guilds (genus Triturus)

Changes in the natural diet by different developmental stages of larval Triturus vulgaris, T. vittatus, T montandoni, T. alpestris, T. cristatus and T. karelini and the dynamics of resource allocation in their guilds are discussed. Larval feeding is subdivided into three periods: endogenous, mixed and exogenous. The main trends in age-specific changes of food composition and electivity are similar in the different species. Against a background of general dietary similarity, however, there are interspecific differences in the mode of resource utilization. These are not related to competition for food but correlate with stable interspecific differences in morphology, behaviour and spatial distribution of larvae. The ontogenetic dynamics of food resource allocation are similar in guilds of similar ecological and morphological structure.