Seasonal variation of population and individual dietary niche in the avivorous bat, Ia io

The variation in niche breadth can affect how species respond to
environmental and resource changes. However, there is still no clear
understanding of how seasonal variability in food resources impacts the
variation of individual dietary diversity, thereby affecting the dynamics
of a population’s dietary niche breadth. Optimal foraging theory (OFT) and
the niche variation hypothesis (NVH) predict that when food resources are
limited, the population niche breadth will widen or narrow due to
increased within-individual dietary diversity and individual
specialization or reduced within-individual dietary diversity,
respectively. Here, we used DNA metabarcoding to examine the composition
and seasonality of diets of the avivorous bat Ia io. Furthermore, we
investigated how the dietary niches changed among seasons and how the
population niche breadth changed when the availability of insect resources
was reduced in autumn. We found that there was differentiation in dietary
niches among seasons and a low degree of overlap, and the decrease of
insect resource availability and the emergence of ecological opportunities
of nocturnal migratory birds might drive dietary niche shifts toward birds
in I. io. However, the population’s dietary niche breadth did not broaden
by increasing the within-individual dietary diversity or individual
specialization but rather became narrower by reducing dietary diversity
via predation on bird resources that served as an ecological opportunity
when insect resources were scarce in autumn. Our findings were consistent
with the predictions of OFT because birds as prey for bats provided
extremely different resources from those of insects in size and
nutritional value. Our work highlights the importance of size and quality
of prey resources along with other factors (i.e., physiological,
behavioral, and life-history traits) in dietary niche variation.