Some carnivores are known to survive well in urban habitats, yet the underlying behavioral tactics are poorly understood. One likely explanation for the success in urban habitats might be that carnivores are generalist consumers. However, urban populations of carnivores could as well consist of specialist feeders. Here, we compared the isotopic specialization of red foxes in urban and rural environments, using both a population and an individual level perspective. We measured stable isotope ratios in increments of red fox whiskers and potential food sources. Our results reveal that red foxes have a broad isotopic dietary niche and a large variation in resource use. Despite this large variation, we found significant differences between the variance of the urban and rural population for δ¹³C as well as δ¹⁵N values, suggesting a habitat‐specific foraging behavior. Although urban regions are more heterogeneous regarding land cover (based on the Shannon index) than rural regions, the dietary range of urban foxes was smaller compared with that of rural conspecifics. Moreover, the higher δ¹³C values and lower δ¹⁵N values of urban foxes suggest a relatively high input of anthropogenic food sources. The diet of most individuals remained largely constant over a longer period. The low intraindividual variability of urban and rural red foxes suggests a relatively constant proportion of food items consumed by individuals. Urban and rural foxes utilized a small proportion of the potentially available isotopic dietary niche as indicated by the low within‐individual variation compared to the between‐individual variation. We conclude that generalist fox populations consist of individual food specialists in urban and rural populations at least over those periods covered by our study.

Plains viscachas (Lagostomus maximus) are large South American, fossorial rodents susceptible to diabetic cataracts. Various aspects of their digestive physiology were studied in three different experiments with nine male and seven female adult animals and six different diets (total n of feeding trials = 35). Viscachas achieved mean retention times of 23–31 hr, which is of a magnitude also recorded in horses; these did not differ for solute or small particle (<2 mm) markers. Secondary marker excretion peaks indicated coprophagy, and were rarer on high‐protein as compared to grass hay‐only diets. Mean resting metabolic rate was, at 229 kJ/kg^0.75/day, lower than expected for a mammal of this size. Digestible energy requirement for maintenance was 445 kJ/kg^0.75/day. At 1.6–2.7 L/day, viscachas produced more methane than expected for a hindgut fermenter of their size. On diets that included concentrate feeds, viscachas excreted glucose in their urine, corroborating reports on the susceptibility of this species for diabetes when kept on energy‐dense food. Viscachas had a similar apparent digestibility of protein, lipids, and macrominerals as other rodents, rabbits, or domestic horses. This suggests that whether or not a species practices coprophagy does not have a major influence on these measures. Viscachas resemble other hindgut fermenters in their high apparent calcium digestibility. With respect to a digestibility‐reducing effect of dietary fiber, viscachas differed from rabbits and guinea pigs but were similar to horses, suggesting that small body size needs not necessarily be linked to lower digestive efficiency on high‐fiber diets. Zoo Biol. 34:345–359, 2015. © 2015 Wiley Periodicals Inc.

The inactivation of ancestral protein‐coding genes (gene loss) can be associated with phenotypic modifications. Within placental mammals, repeated losses of PNLIPRP1 (gene inhibiting fat digestion) occurred preferentially in strictly herbivorous species, whereas repeated NR1I3 losses (gene involved in detoxification) occurred preferentially in strictly carnivorous species. It was hypothesized that lower fat contents of herbivorous diets and lower toxin contents of carnivorous diets cause relaxed selection pressure on these genes, resulting in the accumulation of mutations and ultimately to convergent gene losses. However, because herbivorous and carnivorous diets differ vastly in their composition, a fine‐grained analysis is required for hypothesis testing. We generated a trait matrix recording diet and semi‐quantitative estimates of fat and toxin consumption for 52 placental species. By including data from 31 fossil taxa, we reconstructed the ancestral diets in major lineages (grundplan reconstruction). We found support that PNLIPRP1 loss is primarily associated with low levels of fat intake and not simply with herbivory/carnivory. In particular, PNLIPRP1 loss also occurred in carnivorous lineages feeding on a fat‐poor diet, suggesting that the loss of this gene may be beneficial for occupying ecological niches characterized by fat‐poor food resources. Similarly, we demonstrated that carnivorous species are indeed less exposed to diet‐related toxins, suggesting that the loss of NR1I3 and related genes (NR1I2 and UGT1A6) resulted from relaxed selection pressure. This study illustrates the need of detailed phenotype studies to obtain a deeper understanding of factors underlying gene losses and to progress in understanding genomic causes of phenotypic variation in mammals.

Patch use can illustrate the contributions that forage quality and foraging risk make in shaping foraging decisions made under the risk of being killed. We aimed to determine whether forage selection by European bison Bison bonasus was state-dependent in being shaped by risk (wolf predation or human poaching/culling avoidance) or nutrient quality at two time periods—early winter (when resources are abundant) and at the end of winter (when resources are scarce)—in Białowieża Primeval Forest (Poland). We used a giving-up density framework using the proportional consumption of hay provided by humans to measure the perceptions of risk in European bison. European bison resource selection was primarily driven by minimising the distance they travel over open ground in early winter (i.e. avoiding humans), however by the end of winter, when resources are scarce, bison selected haystacks for their nutrient quality (low fibre, high Mg and energy). This study illustrates how resource selection varies according to the condition of animals (i.e. state-dependency affects the marginal value theorem). It also indicates conservation managers using hay quality may actively manage human–bison conflicts in trouble spots and that bison are currently free from top-down limitation in Białowieża as they do not perceive wolves as threatening enough to alter their foraging behaviour.

1. Studying species interactions and niche segregation under human pressure provides important insights into species adaptation, community functioning and ecosystem stability. Due to their high plasticity in behaviour and diet, urban mesocarnivores are ideal species for studying community assembly in novel communities. 2. We analysed the spatial and temporal species interactions of an urban mesocarnivore community composed of the red fox (Vulpes vulpes) and the marten (Martes sp.) as native species, the raccoon (Procyon lotor) as invasive species, and the cat (Felis catus) as a domestic species in combination with human disturbance modulated by the SARS-CoV-2 lockdown effect that happened while the study was conducted. 3. We analysed camera-trap data and applied a joint species distribution model to understand not only the environmental variables influencing the detection of mesocarnivores and their use intensity of environmental features but also the species’ co-occurrences while accounting for environmental variables. We then assessed whether they displayed temporal niche partitioning based on activity analyses, and finally analysed at a smaller temporal scale the time of delay after the detection of another focal species. 4. We found that species were more often detected and displayed a higher use intensity in gardens during the SARS-CoV-2 lockdown period, while showing a shorter temporal delay during the same period, meaning a high human-induced spatio-temporal overlap. All three wild species spatially co-occurred within the urban area, with a positive response of raccoons to cats in detection and use intensity, whereas foxes showed a negative trend towards cats. When assessing the temporal partitioning, we found that all wild species showed overlapping nocturnal activities. All species displayed temporal segregation based on temporal delay. According to the temporal delay analyses, cats were the species avoided the most by all wild species. To conclude, we found that although the wild species were positively associated in space, the avoidance occurred at a smaller temporal scale, and human pressure in addition led to high spatio-temporal overlap. 5. Our study sheds light to the complex patterns underlying the interactions in a mesocarnivore community both spatially and temporally, and the exacerbated effect of human pressure on community dynamics.