Intra- and inter-individual variation show distinct trends as drivers of seasonal changes in the resource use of a neotropical marsupial

Abstract

Individual specialization can influence important ecological and evolutionary traits and both inter‐ and intra‐individual variation in resource use can drive niche shifts in natural populations. We evaluated the predominance of these two factors for determining seasonal differences in the trophic niche of the didelphid marsupial Gracilinanus agilis (Burmeister, 1854) in the highly seasonal Brazilian savanna. In the three sampled sites, the population of G. agilis increased its dietary niche width in the warm–wet season, when food resources are more abundant, and there were no differences between sexes and no interaction between season and sex. However, the evaluation of intra‐individual variation indicated that females reduce the number of items consumed during the warm–wet season, whereas males show no seasonal differences. Inter‐individual variation nonetheless followed the overall population pattern because both sexes increased their spread with respect to food‐item consumption in the warm–wet season. Additionally, we found positive relationships between body length and diet only in the warm–wet season, when larger animals fed more on invertebrates and less on fruits than the small ones. Our results show a previously unknown pattern for mammals, in which the trophic niche is wider during the high‐resource season as a result of inter‐individual variation along the body‐size axis. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 737–747.

Seasonal population and individual niche dynamics in a tetra fish in the Pantanal wetlands

“…, Camargo et al . ). Furthermore, our results suggest that the low scope for diet variation during the dry season may constrain the diversifying effect of intraspecific competition.…”

Availability of food resources and habitat structure shape the individual‐resource network of a Neotropical marsupial

“…These scats were analyzed in laboratory, and food categories were identified at the lowest possible taxonomic category by comparison with a reference collection of invertebrates and fruits from the study area. Details on fecal analysis can be found in other studies based on the same database that we used in the present study (Camargo et al, ; Camargo, Ribeiro, Camargo, & Vieira, ). Fecal analysis is considered an effective method for assessing the diet of Neotropical marsupials (Araújo et al, ; e.g., Pires, Martins, Araujo, & Reis, ; Camargo et al, ), despite some intrinsic limitations of the method, such as differential digestibility of food items, potential problems for the identification of food items at lower taxonomic level (e.g., family or genus), and difficulty in estimating the relative importance of each food item (Araújo et al, ).…”

“…Details on fecal analysis can be found in other studies based on the same database that we used in the present study (Camargo et al, ; Camargo, Ribeiro, Camargo, & Vieira, ). Fecal analysis is considered an effective method for assessing the diet of Neotropical marsupials (Araújo et al, ; e.g., Pires, Martins, Araujo, & Reis, ; Camargo et al, ), despite some intrinsic limitations of the method, such as differential digestibility of food items, potential problems for the identification of food items at lower taxonomic level (e.g., family or genus), and difficulty in estimating the relative importance of each food item (Araújo et al, ). Differently of other studies that estimated the number of items consumed based on small fecal remains (the number of insects consumed based on the number of leg pieces, or the number of fruits based on seed and fiber count; Anthony & Kunz, ; Mallet‐Rodrigues, ; Pires et al, ), we opted for a conservative approach of considering only the occurrence of each food category.…”

“…We found 20 distinct food items in the scats of G. agilis, represented by 10 arthropod orders (nine of insects and one of arachnid), pulp, fiber, and seeds of three plant families (represented by four species), three morphotypes of unidentified fruit fibers, and bird remains (feathers and bones) (for more details see Camargo et al, 2014aCamargo et al, , 2014b. According to Chao1 estimator of richness, we detected between 67% and 100% of the food items that could potentially be consumed by G. agilis (Supporting Information Figure S4).…”

“…Therefore, food resources availability can vary between seasons (Gouveia & Felfili, 1998;Pinheiro, Diniz, Coelho, & Bandeira, 2002;Silva, Frizzas, & Oliveira, 2011), as well as the microhabitat structure (e.g., herbaceous and canopy cover) due to the expansion and the retraction of the vegetation biomass (Schwieder et al, 2016). In this Neotropical savanna, several mammal species present betweenseason differences in both diet and space use (Camargo, Ribeiro, Camargo, & Vieira, 2014a, 2014bHannibal & Caceres, 2010;Lessa & da Costa, 2010;Ribeiro, 2011;Vieira, 2003). Therefore, the Cerrado systems provide valuable opportunities for the evaluation of how seasonal variation in resources availability and habitat structure affects patterns of within-population network structure.…”