Diet overlap and feeding preference of Oreochromis niloticus (Linnaeus, 1758) versus two native cichlids of the upper Kabompo River, northwest of Zambia.

Evaluating the food and feeding habits of fish is fundamental in fisheries and conservation biology research. In this study, the diet of exotic Oreochromis niloticus was compared with the 2 most abundant and aquaculture preferred native cichlids of native species (Orochromis macrochir and Coptodon rendalli) in the upper Kabompo River, Zambia. We hypothesized that exotic and native cichlids would show no dietary niche overlap. We analyzed the stomach contents of 114 specimens of the fishes sampled. Fishes were grouped into 3 major feeding groups: microphages, macrophages and carnivores, and omnivores. They were also grouped into size classes of <50, 51−100, 101−150, and 151−302 mm total length (TL). O. niloticus had a larger dietary niche than two native species (71% and 22%, respectively). The dietary niche overlap between O. niloticus and native C. rendalli species in size classes <50 was significant (F (2, 45) = 0.084, p < 0.05). Dietary niche overlap between the native O. macrochir species in size class <50 mm was low (F (2, 33) = 2.13, p > 0.05), while as in size classes 51−100 mm and 101−150 mm was high (F (2, 35) = 0.27, p < 0.05) for C. rendalli. There was no clear evidence of ontogenetic diet shift of native cichlids, with the exception of O. macrochir, which showed ontogenetic diet shifts within the 51−100 mm size class. The dietary overlap results indicate interspecific competition between exotic O. niloticus and native O. macrochir, which may have major impacts on food web structure in the upper Kabompo River and may explain population decreases of some native species.

Temporal patterns in prey size between sexes in a raptor with extreme size dimorphism: testing the intersexual competition hypothesis using web-sourced photographs

In most vertebrates, males are larger than females. For raptors, sexual size dimorphism is reversed, with females being larger. Reversed sexual dimorphism (RSD) in raptors is strongly linked to diet, with species feeding on the most agile prey, for example bird-eating raptors, showing the greatest size differences between the sexes. Hypotheses for reversed sexual dimorphism (RSD) include the ‘intersexual competition’ hypothesis, which proposes that RSD evolved to enable pairs to expand their dietary niche (taking a wider range of prey sizes) during the nestling period when both sexes occupy and hunt within the same territory, and thereby reduce competition between the sexes. If intersexual competition is responsible for the evolution of RSD, we predict that sex-related differences in prey size and dietary niche breadth will be particularly pronounced during the nestling period (cf. the non-nestling period). We explore this prediction in the highly dimorphic Eurasian Sparrowhawk (Accipiter nisus), which displays the largest degree of RSD of all raptors, using web-sourced photographs to identify diet throughout the entire year. We analysed 666 photographs of sparrowhawks on their prey over time. In contrast to our predictions, sex-specific prey sizes were most similar during the nestling period compared to any other time of the year. Both males and females reduced the size of their prey during the nestling period which may be a result of the ‘ingestion rate’ hypothesis, or a strategy employed to prevent hunting-related injuries during this critical period of the year.

Trophic niche shifts and phenotypic trait evolution are largely decoupled in Australasian parrots

Background Trophic shifts from one dietary niche to another have played major roles in reshaping the evolutionary trajectories of a wide range of vertebrate groups, yet their consequences for morphological disparity and species diversity differ among groups. Methods Here, we use phylogenetic comparative methods to examine whether the evolution of nectarivory and other trophic shifts have driven predictable evolutionary pathways in Australasian psittaculid parrots in terms of ecological traits such as body size, beak shape, and dispersal capacity. Results We found no evidence for an ‘early-burst’ scenario of lineage or morphological diversification. The best-fitting models indicate that trait evolution in this group is characterized by abrupt phenotypic shifts (evolutionary jumps), with no sign of multiple phenotypic optima correlating with different trophic strategies. Thus, our results point to the existence of weak directional selection and suggest that lineages may be evolving randomly or slowly toward adaptive peaks they have not yet reached. Conclusions This study adds to a growing body of evidence indicating that the relationship between avian morphology and feeding ecology may be more complex than usually assumed and highlights the importance of adding more flexible models to the macroevolutionary toolbox.

Artificial selection for predatory behavior results in dietary niche differentiation in an omnivorous mammal

The diet of an individual is a result of the availability of dietary items and the individual's foraging skills and preferences. Behavioral differences may thus influence diet variation, but the evolvability of diet choice through behavioral evolution has not been studied. We used experimental evolution combined with a field enclosure experiment to test whether behavioral selection leads to dietary divergence. We analysed the individual dietary niche via stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) in the hair of an omnivorous mammal, bank vole, from 4 lines selected for predatory behavior and 4 unselected control lines. Predatory voles had higher hair δ15N values than control voles, supporting our hypothesis that predatory voles would consume a higher trophic level diet (more animal vs. plant foods). This difference was significant in the early but not the late summer season. The δ13C values also indicated a seasonal change in the consumed plant matter and a difference in food sources among selection lines in the early summer. These results imply that environmental factors interact with evolved behavioral tendencies to determine dietary niche heterogeneity. Behavioral selection thus has potential to contribute to the evolution of diet choice and ultimately the species' ecological niche breadth.

Dietary niche breadth of endemic and introduced anurans (Amphibia: Anura) in Lombok, Lesser Sunda Islands– Indonesia

Anurans are important organisms as components of faunal community structure in ecosystems because of their roles as secondary and tertiary consumers in food webs. Anurans are opportunistic organisms that will consume any resources in their habitat. In this study, we dissected thirty-nine specimens of anurans from Museum Universitas Mataram (MUM) reference collection, it consists by three endemic (Ingerophrynus biporcatus, Limnonectes dammarmani and L. kadarsani) and one introduced species (Duttaphrynus melanostictus) of anurans. These reference collections were collected by authors during herpetofauna survey at Pusuk Forest, western Lombok in 2018. Based on stomach content analysis, both endemic and introduced anurans are generalist arthropod predators where hymenoptera, coleoptera, orthoptera and chilopoda are the most important food. In this study, we found positive correlations between body size and dietary niche breadth in which each anuran species has a high overlap of dietary niches. Anurans with large body size have a variety of prey than the small one.

The role of the gut microbiota in the dietary niche expansion of fishing bats

Background Due to its central role in animal nutrition, the gut microbiota is likely a relevant factor shaping dietary niche shifts. We analysed both the impact and contribution of the gut microbiota to the dietary niche expansion of the only four bat species that have incorporated fish into their primarily arthropodophage diet. Results We first compared the taxonomic and functional features of the gut microbiota of the four piscivorous bats to that of 11 strictly arthropodophagous species using 16S rRNA targeted amplicon sequencing. Second, we increased the resolution of our analyses for one of the piscivorous bat species, namely Myotis capaccinii, and analysed multiple populations combining targeted approaches with shotgun sequencing. To better understand the origin of gut microorganisms, we also analysed the gut microbiota of their fish prey (Gambusia holbrooki). Our analyses showed that piscivorous bats carry a characteristic gut microbiota that differs from that of their strict arthropodophagous counterparts, in which the most relevant bacteria have been directly acquired from their fish prey. This characteristic microbiota exhibits enrichment of genes involved in vitamin biosynthesis, as well as complex carbohydrate and lipid metabolism, likely providing their hosts with an enhanced capacity to metabolise the glycosphingolipids and long-chain fatty acids that are particularly abundant in fish. Conclusions Our results depict the gut microbiota as a relevant element in facilitating the dietary transition from arthropodophagy to piscivory.

Rapid increase in snake dietary diversity and complexity following the end-Cretaceous mass extinction

The Cenozoic marked a period of dramatic ecological opportunity in Earth history due to the extinction of non-avian dinosaurs as well as to long-term physiographic changes that created new biogeographic theaters and new habitats. Snakes underwent massive ecological diversification during this period, repeatedly evolving novel dietary adaptations and prey preferences. The evolutionary tempo and mode of these trophic ecological changes remain virtually unknown, especially compared with co-radiating lineages of birds and mammals that are simultaneously predators and prey of snakes. Here, we assemble a dataset on snake diets (34,060 observations on the diets of 882 species) to investigate the history and dynamics of the multidimensional trophic niche during the global radiation of snakes. Our results show that per-lineage dietary niche breadths remained remarkably constant even as snakes diversified to occupy disparate outposts of dietary ecospace. Rapid increases in dietary diversity and complexity occurred in the early Cenozoic, and the overall rate of ecospace expansion has slowed through time, suggesting a potential response to ecological opportunity in the wake of the end-Cretaceous mass extinction. Explosive bursts of trophic innovation followed colonization of the Nearctic and Neotropical realms by a group of snakes that today comprises a majority of living snake diversity. Our results indicate that repeated transformational shifts in dietary ecology are important drivers of adaptive radiation in snakes and provide a framework for analyzing and visualizing the evolution of complex ecological phenotypes on phylogenetic trees.