Dietary specialization depending on ecological context and sexual differences in Asiatic black bears

Temporal and individual variation in the feeding habits of Asiatic black bears (Ursus thibetanus)

Foraging plays a vital role in the survival of wildlife, and shifts in food availability can impact species fitness and survival. Ursids are known to consume a wide variety of foods and are known to be opportunistic omnivores. Consequently, seasonal shifts in diet, which correspond to temporal and spatial shifts in the availability of food resources, have long captivated researchers studying the foraging behavior of Ursidae. Nevertheless, comprehensive dietary studies encompassing both the population and individual levels remain scarce. In this study, we investigated the dietary patterns of Asiatic black bears (Ursus thibetanus) at both the population and individual levels, using data collected through GPS collars and field surveys of individual bear scat samples in Nagano Prefecture, Japan, from 2016 to 2020. From early April to late June, bears mainly foraged on green vegetation. During this period, male and large-bodied female bears showed a strong preference for green vegetation. Small-bodied female bears also ate mostly green vegetation but tended to consume more fruit than other bears towards the end of this period. From June to October, bears' diets included a substantial amount of fruit, with notable peaks in fruit consumption in late June and early September. During the summer months, female bears often incorporated social insects into their diet compared to the population-level trend. In mid-September, the consumption of seeds from the Fagaceae family surged, becoming the primary dietary component during this period. This trend was consistently observed across the population. These findings underscore the importance conducting in-depth dietary analyses that take into account individual characteristics such as sex, age, and body weight.

Evolutionary transitions in diet influence the exceptional diversification of a lizard adaptive radiation

Background

Diet is a key component of a species ecological niche and plays critical roles in guiding the trajectories of evolutionary change. Previous studies suggest that dietary evolution can influence the rates and patterns of species diversification, with omnivorous (animal and plant, ‘generalist’) diets slowing down diversification compared to more restricted (‘specialist’) herbivorous and carnivorous diets. This hypothesis, here termed the “dietary macroevolutionary sink” hypothesis (DMS), predicts that transitions to omnivorous diets occur at higher rates than into any specialist diet, and omnivores are expected to have the lowest diversification rates, causing an evolutionary sink into a single type of diet. However, evidence for the DMS hypothesis remains conflicting. Here, we present the first test of the DMS hypothesis in a lineage of ectothermic tetrapods—the prolific Liolaemidae lizard radiation from South America.

Results

Ancestral reconstructions suggest that the stem ancestor was probably insectivorous. The best supported trait model is a diet-dependent speciation rate, with independent extinction rates. Herbivory has the highest net diversification rate, omnivory ranks second, and insectivory has the lowest. The extinction rate is the same for all three diet types and is much lower than the speciation rates. The highest transition rate was from omnivory to insectivory, and the lowest transition rates were between insectivory and herbivory.

Conclusions

Our findings challenge the core prediction of the DMS hypothesis that generalist diets represent an ‘evolutionary sink’. Interestingly, liolaemid lizards have rapidly and successfully proliferated across some of the world’s coldest climates (at high elevations and latitudes), where species have evolved mixed arthropod-plant (omnivore) or predominantly herbivore diets. This longstanding observation is consistent with the higher net diversification rates found in both herbivory and omnivory. Collectively, just like the evolution of viviparity has been regarded as a ‘key adaptation’ during the liolaemid radiation across cold climates, our findings suggest that transitions from insectivory to herbivory (bridged by omnivory) are likely to have played a role as an additional key adaptation underlying the exceptional diversification of these reptiles across extreme climates.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-022-02028-3.

Activity pattern study of Asiatic black bear (Ursus thibetanus) in the Qinling Mountains, China, by using infrared camera traps

The study of activity patterns is important for understanding the capacity of animals for adapting their behavior based on their habitat conditions. Among bears, daily activity patterns are considered to be strongly influenced by regional climate conditions. We monitored the activity patterns (active vs. inactive) of the Asiatic black bear (Ursus thibetanus) using infrared camera traps (from May 2013 to November 2016) in the Qinling Mountains, China. We used 125 photos, with 19,132 camera days from 55 camera locations. Based on relative independent capture (RIC), bears were found to be intensively active during June (5.86 ± 1.05 SE), July (8.45 ± 2.74), September (14.83 ± 6.13), and October (8.70 ± 3.43), with activity levels gradually decreasing beyond October. After this decline, activities eventually come to a halt when the bears enter in hibernation. We found that their hibernation period was shorter in the Qinling bears, with only 3 months of denning from January to March. Based on their daily patterns, bears were predominantly active during the daytime both in spring (70.83 ± 35.41%) and summer (52.09 ± 28.89%), but more active at twilight during autumn (51.12 ± 42.88%). We assumed that food preferences and food availability (due to warmer regional climatic conditions) might be responsible for such deviations in daily and monthly activity patterns.