nueva página del texto (beta)
Inglés (pdf)
Articulo en XML
Traducción automática
Citado por SciELO 
Citado por Google 
Similares en
SciELO 
Similares en Google 
Permalink
The geographic range of a species is a representation of the spatial arrangement of a given taxon, which defines the biological limits for its existence: it is the basic unit of biogeography (Brown et al. 1996). However, defining a distribution area could be challenging, as this inevitably depends on occurrence records and collecting methods, a requirement that could result in underestimations of the distribution areas due to lack of sampling effort and misconceptions about the species habits. Moreover,
distribution limits dynamic boundaries that depend on resource availability and climate change (Anderson et al. 2009; Riquelme et al. 2018). This may be the case of Dromiciops gliroides (Thomas 1894, Microbiotheria), a relict marsupial that inhabits the temperate forests of Chile and Argentina in southern South America. This marsupial is considered a “living fossil” as it is the only living representative of Microbiotheria, the sister group of Australasian marsupials (Hershkovitz 1999; Mitchell et al. 2014). Several historical records of Dromiciops suggested relatively low population densities (Meserve et al. 1999; Kelt 2000), until the development of appropriate capturing methods that allowed a more frequent detection of this arboreal, nocturnal, and highly seasonal mammal (Muñoz-Pedreros et al. 2005; Fontúrbel & Jiménez 2009; Fontúrbel 2010), which makes it a cryptic species. Most of the actual knowledge about D. gliroides comes from a few well-known sites, located in a small area at the center-south of the distributional range (Martin 2010).
Here we report the southernmost records of D. gliroides, which is beyond the limits of the Valdivian rainforest ecoregion in Chile. We set eight camera-traps (Bushnell Trophy Cam) from December 2018 to April 2019 along the Palena Province (43° 24'S, 72° 05'W; 43° 25'S, 72° 12'W and 43° 00'S, 72° 28'S), southern Chile. We found 43 photographic records at Chaitén and Futaleufú (Fig. 1), extending D. gliroides distribution 100 km to the south (Fig. 2). The current distribution area of D. gliroides is based on 20 locations (Patterson et al. 2003), but in more recent reports, Martin (2010) of and (Gurovich et al. 2015) provided 69 additional occurrence locations, which fall within NatureServe's distribution map (except for one location at the north). Our study provides six new points, from which three are located southwards of the known distribution. By extending D. gliroides distribution based on this new data, it has increased 4969 km2. In sympatry with D. gliroides, we detected nocturnal activity of two rodents species (Oligoryzomys longicaudatus and Rattus spp.) along with several birds species (Pteroptochos tarnii, Scelorchilus rubecula and Campephilus magellanicus as the most frequent ones).
Figure 1 Camera trap records of Dromiciops gliroides at Chaitén and Futaleufú. / Registros de Dromiciops gliroides en cámaras trampa de Chaitén y Futaleufú.
Figure 2 Distribution map of Dromiciops gliroides, comparing the current and proposed extension areas. / Mapa de distribución de Dromiciops gliroides, comparando la distribución actual y la extensión propuesta.
We also examined D. gliroides activity patterns at the new locations (Fig. 3a), using the activity package (Rowcliffe 2019) in R 3.5.3 (R Development Core Team 2019). Activity starts at 19 h and ends at 7 h, being similar to the activity patterns previously reported for the Valdivian rainforest (Fontúrbel et al. 2014) but showing a narrower activity peak (Fig. 3b). We contrasted the activity patterns of Fontúrbel et al. (2014) against the pattern obtained here using the compareCkern function of the activity package, with 1000 permutations. We found an overlap of 82.45 ± 0.04 % between both activity patterns, but the differences were marginally significant (P = 0.053).
The ecological patterns of D. gliroides are quite consistent across the Valdivian rainforest, showing similar home ranges, body condition and population densities among sites of Argentina and Chile (Fontúrbel et al. 2012). However, we do not know how D. gliroides may respond to environmental conditions southwards of the Valdivian temperate rainforest, where there are larger daily and seasonal temperature fluctuations, lower rainfall, and colder nights that may trigger hibernation responses (Nespolo et al. 2018), narrowing their activity patterns. Also, we found differences in the forest composition. Some plant species that are typically associated with D. gliroides are less frequent or inexistent at this southernmost latitude. Such is the case of the bamboo Chusquea spp., one of the main components of D. gliroides nests and an important predictor of its presence (Rodríguez-Cabal & Branch 2011), which is considerably less frequent in the newly discovered sites than in the Valdivian ecoregion (González & Donoso 1999). Another example is the hemiparasitic mistletoe Tristerix corymbosus, which constitutes a substantial part of D. gliroides diet (Amico & Aizen 2000; Amico et al. 2009), is not present in the Chaitén-Futaleufú region. Those individuals may be feeding on the fleshy-fruited shrub Ugni molinae, which is highly abundant in these new locations (Mora & Soto-Gamboa 2011), and might be explaining its persistence below T. corymbosus' distribution. These differences may alter resource availability for D. gliroides, consequently changing its diet and metabolic requirements (Cortés et al. 2011) in ways that are yet to be explored.
Figure 3 Kernel density functions of Dromiciops gliroides activity for (a) Chaitén-Futaleufú, and (b) the comparison of the Valdivian temperate rainforest and the Chaitén-Futaleufú. / Función de densidad de kernel de la actividad de Dromiciops gliroides en: (a) Chaitén-Futaleufú, y (b) la comparación de la selva lluviosa Valdviana y Chaitén-Futaleufú.
Except for the disturbance events of volcanic eruptions of the Chaitén volcano, the overall environmental conditions of the forest area surrounding the newly found D. gliroides locations have been stable at least since the Holocene (Heusser et al. 1992; Amico et al. 2009; Swanson et al. 2013). Therefore, the presence of D. gliroides in this area may not be recent, and the lack of other reports would be a consequence of insufficient sampling efforts. We strongly encourage further assessments of this iconic species of the Chilean fauna beyond the southern limit reported here, which is highly likely. In this sense, camera traps are a powerful approach to expand our knowledge of cryptic species.
