The “all-purpose” trophic strategy of Dromiciops
The common name “monito del monte” refers to the arboreal habits of this marsupial, which includes opposable thumbs and a prehensile tail, resembling a small primate. They move relatively long distances (home range: 1.6 ± 0.6 ha) (Fontúrbel et al., 2012), across the canopy, reaching 30 meters of height (Godoy-Güinao et al., 2018), and speeds of 1 m/s (3.7 km/h, see Mejías et al., 2021), which for a 20–30 g mammal is extremely fast (e.g., Djawdan & Garland, 1988). Their agility in forest canopies permits these animals to forage efficiently on a variety of food items, for which qualitative descriptions exist, based on faecal analysis and laboratory preference trials (Amico, Rodríguez-Cabal, & Aizen, 2009; Celis-Diez et al., 2012; Cortés, Franco, Sabat, Quijano, & Nespolo, 2011; di Virgilio et al., 2014; Meserve et al., 1988; Quijano, 2008). These studies have shown that D. gliroides does not appear to be selective (contrarily to other mammals, which select food items with specific nutrient composition, see Torres-Contreras & Bozinovic, 1997; Woods, 2009), but rather opportunistic (i.e., dietary composition follows environmental availability, see Bozinovic, Muñoz, Naya, & Cruz-Neto, 2007; Cortés et al., 2011; Quijano, 2008). However,Dromiciops cannot fulfil its nutritional requirements only from fruits or insects. Contrarily, it needs a mixed diet of fruits and insects to maintain a healthy body condition and a proper energy balance (Cortés et al., 2011). It is well established that differences in the digestive physiology of vertebrates reflect the historic levels of specific substrates of the natural diets, linking digestive enzyme activity, dietary flexibility, and digestive plasticity in an evolutionary context (Ramirez-Otarola, Narvaez, & Sabat, 2011; Sabat, Lagos, & Bozinovic, 1999; Sabat, Novoa, Bozinovic, & del Rio, 1998). Therefore, the digestive physiology of D. gliroides supports the hypothesis that digestive capabilities are a necessary—but not an essential—component for explaining dietary selection (Bozinovic & Martínez del Río, 1996; Cortés et al., 2011; Silva, Jaksic, & Bozinovic, 2004; Veloso & Bozinovic, 2000).
Fruit availability represents a strong driver of Dromiciopsdietary habits. They select individual fruits according to their size and colour, exerting important selective forces on plant populations (Fontúrbel & Medel, 2017), performing long foraging trips to disturbed forest stands to consume fleshy fruits (Amico, Rodríguez-Cabal, & Aizen, 2011; di Virgilio et al., 2014; Mora & Soto-Gamboa, 2011; Salazar & Fontúrbel, 2016). In fact, Dromiciops consumes fruits from at least 16 species of shrubs, trees, vines, and particularly from the hemiparasite mistletoe Tristerix corymbosus (see Table 1 in Amico et al., 2009). Then, considering the assorted nutrient content onDromiciops ’ diet, an interesting set of questions arises, such as how these requirements vary among individuals at different ontogenetic stages (Maldonado et al., 2016), or if they exhibit ontogenetic trophic niche shifts as a logic outcome (Araujo, Bolnick, & Layman, 2011; Schoener, 1971). Furthermore, considering that male and female marsupials invest energy differently during the reproductive period, ecological sexual dimorphism in diet selection could be expected (Araujo et al., 2011; Schoener, 1971). This is an interesting avenue that can be explored, for instance, using the most recent technologies in stable isotope analysis (Maldonado, Bozinovic, Newsome, & Sabat, 2017).