Temporal shifts in nitrogen stable isotopic profiles of tropical bats revealed by multi-tissue analyses

Abstract

Seasonal variation in temperature and precipitation affects food availability for organisms. Tropical bats are trophically diverse, representing many feeding guilds, and can represent about half of mammalian diversity in tropical areas. Stable isotope analysis of nitrogen ( δ ¹⁵ N) in animal tissues permits inference on phenology of diet and trophic level through repeated sampling of a single tissue over time or by simultaneous sampling of multiple tissues that vary in isotopic turnover rate. The goal of our study was to use multi-tissue stable isotope analysis to investigate the phenology of diet (i.e., trophic-level switching) in bats. We sampled tissues of museum specimens from five tropical bat species representing different trophic guilds (insectivores, frugivores) and movement capacities (wide-ranging, narrow-ranging). We measured δ ¹⁵ N in three metabolically latent (hair, skin, bone) and four active (heart, kidney, spleen, liver) tissues and generated mathematical model predictions of expected δ ¹⁵ N values of these tissues based on their foraging guild. Specifically, we predicted that species with more sedentary movement patterns (i.e., narrow-ranging species) would have high among-tissue variation in δ ¹⁵ N and species that move further and more often (i.e., wide-ranging) would have less δ ¹⁵ N variation among tissues. Our results supported our predictions and suggest that the phenology of diet is detectable by multi-tissue isotope analysis using δ ¹⁵ N.