Study On Patterns And Impact Factors Of Changes In Dietary Niche And Adaptation Of Predation On Birds By The Great Evening Bat(Ia Io)

Food resources are the material basis for animals to survive and reproduce,and are also an important link between animals and their external environments.Dietary studies can contribute greatly to understanding predator-prey interactions and can also provide integral knowledge concerning animal community dynamics,food webs,trophic interactions,and the evolution of dietary niches.The interaction between predators and prey has always been a hot and difficult topic in the research field of ecology.Moreover,this interaction is pivotal for revealing the adaptive evolutionary traits of predators and behavioral countermeasures of prey,which has important ecological and evolutionary significance for in-depth understanding of the arms race among animals,and is also the basis for understanding the formation of animal diversity.Chiropterans(bats)occupy unique night-sky ecological niches,with a diverse ecology and diet,and are the key animal groups in the ecosystem.Bats are an ideal group for studying dietary niche changes and the interaction between predators and prey.The interaction between bats and prey is a fascinating arms race in evolution and has also become a key model for the study of co-evolution.Previous studies have focused on the interactions between bats and insects and between bats and frogs,while the relationship between bats and birds remains unclear.Bats have the most special relationship with birds.Bats are not only prey to raptors but also prey on small passerine birds,making them a research highlight.Here,we selected the great evening bat(Ia io)as the research object,integrating theories and methods of behavior,ecology,molecular biology and microbiology to systematically reveal the patterns and mechanisms of seasonal variation in the dietary niche of I.io,and further to elucidate its behavioral and sensory strategies and gut microbial adaptation to prey on birds,under the framework of the study of predator-prey interactions.We collected the feces of I.io in each season and identified the diets based on DNA metabarcoding technology.Further,we analyzed the dietary composition,seasonal differences,and utilization of bird prey by I.io.Our results showed that I.io preyed on a variety of arthropods(12 orders),dominated by Lepidoptera,and consumed 22 species of seven families from Passeriformes.The dietary composition of I.io showed clear seasonal changes,the proportion of bats that preyed on insects decreased significantly in autumn,while the proportion of bats that preyed on birds increased significantly.Most of the bird species preyed upon by I.io are migratory birds,and they preferentially selected passerine birds that weigh less than 10 g.We found that no significant positive correlation exists in body mass between I.io and bird prey,suggesting I.io is an opportunistic avivorous predator.Based on the dietary composition of I.io,the dietary diversity,niche overlap,niche breadth,and individual dietary specialization of populations,individuals,and re-captured individuals in different seasons were analyzed,and further to explore changing patterns of the dietary niche and factors affecting individual dietary specialization among seasons.The results showed that the decrease of insect resource diversity and the emergence of ecological opportunities of nocturnal migratory birds may drive dietary niche expansion towards birds of I.io.Moreover,differentiation in the dietary niches among seasons was detected.And the dietary niche breadth was the widest in summer,followed by spring,and the narrowest in autumn.Due to the differences in body size and nutritional value of bird and insect prey,the population’s dietary niche breadth did not broaden by increasing the within-individual dietary diversity,between-individual dietary diversity,or individual specialization when the diversity of food resources decreases in autumn compared to spring and summer.The findings were not support the predictions based on the optimal foraging theory and niche variation hypothesis.Additionally,the body mass of individual bats,dietary diversity,and the emergence of bird ecological opportunity affect the degree of individual dietary specialization.These results highlight the importance of size and quality of prey resources along with other factors(i.e.,physiological,behavioral,and life-history traits)in dietary niche evolution.On the basis of dietary studies,we selected two representative birds in the diet of I.io and their calls and specimens to conduct behavioral experiments on the predation and anti-predation strategies of bats and birds.Foraging strategy simulation experiments showed that I.io actively attacked the hanging bird specimens during flight in darkness.The bats emitted echolocation calls when they attacked the bird specimens,and the echolocation calls contained feeding buzzes.These results indicate that I.io can prey on birds using aerial-hawking strategy based on echolocation cues.We also found that I.io had no significant choice preference for broadcasting the calls of two representative birds(Phylloscopus inornatus and Zosterops japonicus)in their diets compared with silence,and were insensitive to sound stimuli with playback frequencies below 6 k Hz and sound intensities lower than 70 d B pe SPL via dual-choice acoustic playback and audiometric experiments based on auditory brainstem responses.Moreover,the results of the dual-choice visual presentation experiment showed that there were no significant differences in the number of choice preferences of bats on bird specimens under dim light versus those under darkness and moonlight.Taken together,our results showed that I.io uses active echolocation cues to detect and locate birds in flight in the night sky,regardless of the magnitude of the light intensity and whether the migratory birds give calls.Additionally,the experiment on the anti-predation strategy of birds against bats indicated that two species of birds(Z.japonicus and Sinosuthora webbiana)were not able to to defend against bat predation via auditory and visual cues.These results suggested that the interaction between I.io and birds may not have evolved into a co-evolutionary relationship at the sensory level.An important challenge faced by bats after preying on birds is the digestion,absorption,and metabolism of avian food.To explore how the gut microbiota of I.io adapt to the absorption and utilization of energy and nutrients in avian food,we collected individual feces of I.io in the period of preying on birds and insects by using 16 S r RNA amplicon sequencing and PICRUSt2 to predict functional profiles.The results demonstrated that seasonal dietary shifts drive the marked and specific changes in the composition and function of gut microbiomes.Moreover,increases in the relative abundance of Firmicutes and the Firmicutes-to-Bacteroidetes ratio,changes in carbohydrate and nucleotide metabolism,and a decrease in Pseudomonas were associated with higher energy demands for hunting birds and with fat storage for entering hibernation and migration.These results suggested that gut microbes play an important role in the dietary niche expansion of wild animals.In summary,our study is the first to elucidate the patterns and ecological mechanisms of seasonal changes in the dietary niche of avivorous bats,as well as the adaptive strategies of bats to prey on birds and the anti-predation strategies of birds,suggesting that the interaction between bats and birds may not have evolved into co-evolution at the sensory level.These findings are helpful to understand the ecological adaptation of carnivorous bats,especially avivorous bats,and their interaction with prey,and provide a scientific basis for in-depth understanding of the role of bats in ecosystems and their diversity conservation.