Seasonal isotopic niche of a rodent: High between-individual variation but no changes in individual niche width during the rich-resource period

The dynamics of trophic niche width in animals at both population- and
individual-level is potentially influenced by temporal variation of food
resources, by between-individual differences in food-resource rank
preferences, and also by competition. Using stable isotope of carbon and
nitrogen (δ13C and δ15N) of fecal samples, we investigated the trophic
niche dynamics and individual variation in food-resource use by the
arboreal rat Rhipidomys macrurus, in the highly seasonal Brazilian savanna
(Cerrado). We tested the hypothesis that dietary niche expansion during
the rich-resource period (wet season) occurs via individual specialization
and consequently lower individual niche overlap in contrast with niche
retraction during the low-resource period (dry season) via increase in
niche overlap and expansion of individual niches. The results indicated
that R. macrurus is primarily frugivorous and presents a wider isotopic
niche in the rich-resource period in comparison to the low-resource
period. The increase in niche width was achieved by individual
specialization (decrease in niche overlap), as expected. During the
low-resource period, however, individual niche widths were not wider than
during the rich-resource period. Additionally, individual body condition
was lower in the wet season than in the dry season, suggesting higher
competition in this period. We conclude that an increase in the population
niche may involve only between-individual variation and not necessarily
requiring changes in individual niche width. We propose that the
combination of ecological opportunity (high resource diversity) in
addition to a greater competition in the warm-wet season leads to
expansion of the population trophic niche width via individual
specialization.