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Among South American small mammals, rodents and marsupials represent two groups where competition for resources and spatial use might be intense. In order to explore the ecological differences between these clades, we collected morphological data and isotope ratios (δ13C and δ15N) from live-trapped specimens of Didelphidae and Sigmodontinae in four different Brazilian biomes: Atlantic Forest, Cerrado, Pampa and Pantanal. The specimens included in this study were collected and measured on field expeditions to central and southern regions of Brazil. The morphological measurements used here were body, foot and tail length. Tail and foot ratios were obtained by dividing these measurements by the specimen body length. The preserved skin of the specimens used in this study are available for consultation in the mammal collection of the Universidade Federal de Santa Maria (UFSM), where hair samples were collected directly from the skin. Our results show that marsupials generally show higher δ15N than rodents, while δ13C values are similar for both groups. Substantial differences in isotope ratios occur between biomes. Rodents exhibit higher δ13C values when in more open environments like Cerrado, Pampa and Pantanal supporting the consumption of C4 plants, while marsupials rely on C3 plants only. All specimens from the Pampa biome have the highest δ13C, while an increase in δ15N is detected in marsupials only. Since the Pampa has less fruit offer, marsupials tend to increase their consumption of animal protein, while rodents start consuming also C4 plants to supplement their diet. Interestingly, we also found some degree of correlation between stable isotopes and morphological traits. In rodents, tail ratio (an indicator of arboreality) negatively correlates with δ13C confirming that more terrestrial species [=relatively short tail, typical of open biomes] incorporate C4 plants into their diets. For marsupials, species with larger feet in relation to their body length showed the highest δ15N, in relation to animal consumption due to their cursorial lifestyle. These results suggest that combining isotopic signatures and morphological data improves the identification of differences in ecological niches between competing groups of small mammals.


coexistence, feeding ecology, locomotion habitat, trophic levels


Stable isotope analyses were funded by Natural Environment Research Council (EK309-10/18 East Kilbride LSMSF) to MC. JB and TFB were financed by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brazil (CAPES), Finance Code 001. JB was additionally funded by CAPES sandwich PhD program/Process number 88881.189949/2018-01. GM is a post-doc fellow financed by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brazil (CAPES).NC has a research fellowship in Ecology (Process number 313.191/2018-2), granted by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).




Jamile Bubadué, Nilton Cáceres, Thaís Battistella, Geruza Melo, Jonas Sponchiado, Jason Newton, Carlo Meloro