Introduction

Protected natural areas include biological field stations, whose objectives are to conduct scientific research and preserve nature (^{Langholz and Lassoie 2001}). Examples of biological field stations in Mexico are Los Tuxtlas in Veracruz and Chamela in Jalisco, both managed by Universidad Nacional Autónoma de México (UNAM), as well as Piedra Herrada at Michilia, Durango, managed by Instituto de Ecología, A. C. (INECOL). In Chiapas, Natura and Ecosistemas Mexicanos, A. C., manage the Chajul and Tzendales biological field stations, dedicated to the study and conservation of the Lacandon forest. The research conducted in biological field stations is highly relevant for the knowledge and conservation of both the local species and the ecological systems they belong to. However, biological field stations involve complex issues, such as land tenure conflicts, lack of monitoring and management plans, and scarce information on the biotic resources in them (^{Smith and Ruiz-Cedillo 2009}).

Although Mexico is a country where tropical and semi-arid climates prevail, it should be noted that a large proportion of its territory is covered by temperate forests such as the pine-oak forest (^{Rzedowski 1978}). This vegetation type is home to a large number of plant and animal species, many of which are currently threatened largely due to human disturbance (^{Flores-Villela and Geréz 1994}; ^{Toledo and Ordóñez 1998}).

The San Jose Biological Field Station (EBSJ), managed by Secretariat of Environment and Natural History (SEMANH) of the State of Chiapas, was declared as such on 29 January 2015. It is the first temperate biological field station in the Chiapas Highlands dedicated to the conservation of the last wildlife refuges in the area. A number of biological studies have been carried out in this station, mainly reporting lists of bird (^{González-Ortega and Pérez-Suasnavar 2007}) and amphibian (^{Aranda-Coello et al. 2018}) species. Given the limited information on biodiversity in the Chiapas Highlands and in order to encourage research at national and international levels to advance the scientific knowledge about the region, the objective of this investigation is to communicate the importance of oak-pine forests and their associated mammalians in a highly relevant site such as EBSJ and its importance for conservation, in order to develop management and protection strategies.

Materials and Methods

Study Area. The San Jose Biological Field Station (EBSJ) is located southwest of San Cristóbal de Las Casas, a city located in the municipality of the same name in the State of Chiapas, at coordinates 16.723333 °N and -92.698333 ºW (Figure 1). It is located in a mountainous area at altitudes between 2,350 and 2,380 m, stretching across 16 hectares of oak-pine- forest (^{Aranda-Coello et al. 2018}), within the ecoregion of temperate sierras of Mexico (^{Arriaga et al. 2000}). EBSJ receives approximately 12,200 visitors from various municipalities across the Chiapas Highlands region.

Figure 1 Geographic location of mammal sampling sites (green dots) in San Jose Biological Field Station (EBSJ), San Cristobal de Las Casas, Chiapas, Mexico. Human settlements near this station are shown (red dots). 

Field Work. Rodents were monitored and recorded using 100 Sherman traps baited with oats and vanilla essence, and arranged in various linear transects covering a total area of six hectares; traps were separated from each other by 10 meters. In the case of shrews, 50 Pitfall traps were placed in the same area. For bats, three mist nets (12 x 2 m in length) were placed, which remained open for six hours every night from 18:00 hours; nets were reviewed at 20-minute intervals. Thirty samplings were carried out, with a duration of five days each, from March to November 2007, January to December 2010, April to July 2015, and January 2016. Individuals captured were identified using specialized keys (^{Álvarez-Castañeda et al. 2015}). Species of medium-sized and large mammals (cingulates, carnivores, lagomorphs and artiodactyla) were recorded through direct observation by the authors, local inhabitants (who provided the names in Tzotzil), and EBSJ staff. The common names of the species recorded were obtained from ^{Álvarez-Castañeda and Gonzalez-Ruiz (2018)}.

The records of species spotted in the study area were confirmed and extended using the databases of Global Biodiversity Information Facility (^{GBIF 2013}; http://www.gbif.org) and the Collection of Mammals at El Colegio de la Frontera Sur in San Cristóbal de Las Casas, Chiapas (ECO-SC-M). The species endemic to the state of Chiapas were identified, as well as the conservation and protection status of each species, based on the red list of the International Union for the Conservation of Nature (^{IUCN 2017}) and the Mexican Official Norm 059 (NOM-059; ^{SEMARNAT 2010}). Also, we used the taxonomy proposed by ^{Lorenzo et al. (2017)} and ^{Spradling et al. (2016)}.

Results

A total of 23 species were recorded, comprising 8 orders and 13 families (Table 1). The orders with the highest number of species were Rodentia (7), Chiroptera (5), and Carnivora (4). Of the total number of species, two are endemic to Chiapas: the Chiapan deer mouse, Peromyscus zarhynchus, and the Guatemalan broad-clawed shrew, Cryptotis griseoventris. With regard to the conservation status, both endemic species are listed by the ^{IUCN (2017)}: Cryptotis griseoventris as endangered, and P. zarhynchus as vulnerable. In NOM-059 (^{SEMARNAT 2010}), Reithrodontomys microdon is listed as threatened and P. zarhynchus is listed as subject to special protection.

Discussion

The Chiapas Highlands, where EBSJ is located, is the subprovince of Chiapas with the greatest amount of non-endemic (n = 157) and endemic (n = 3) mammal species (^{Lorenzo et al. 2017}); therefore, it constitutes an important biodiversity sanctuary in the region (^{March and Flamenco 1996}). The total number of records obtained in EBSJ represents 57.5% of the species reported for the municipality of San Cristóbal de Las Casas (n = 40 spp.) and 10.9% of those for the state of Chiapas (n = 211 spp.), which illustrates the importance of EBSJ in terms of species diversity and richness (^{Lorenzo et al. 2017}; ^{Porter et al. 2017}). In particular, the oak-pine forests located in this station are important from the mammal ecology perspective (^{Horváth and Sarmiento-Aguilar 2001}; ^{García-Méndez et al. 2014}), since they offer plentiful resources including food, shelter and breeding sites. The mammal species favored by this type of habitat in EBSJ include those with restricted and fragmented distribution due to extensive deforestation in other areas within their distribution range, such as C. griseoventris, a species with only 11 known individuals since it was first collected by F. L. Burnet in 1956 (^{Guevara et al. 2014a}), P. zarhynchus and R. microdon (^{IUCN 2017}; ^{Guevara et al. 2014b}; ^{Lorenzo et al. 2017}). The mammals listed in the risk category by NOM-059 require immediate actions for conservation, such as the development of a management program to preserve both the habitat and the species living in it, and the creation of a regional network for the elaboration of strategies aiming at the protection of their habitat. Currently, there are few areas in the Chiapas Highlands region covered by oak-pine forests in a good state of conservation, which are limited to small scattered patches (^{Horváth and Sarmiento-Aguilar 2001}).

On the other hand, the loss and fragmentation of natural ecosystems in Chiapas facilitate the movement of opportunistic mammal species (e. g., rodents, domestic cats and dogs) that, in addition to competing for the same space and food resources with native mammals, are predators of native fauna and potential carriers of diseases, both for wildlife and humans (^{Naranjo et al. 2016}). The above indicates that these are potential threats in EBSJ, since these opportunistic animals have been observed given their proximity to Tzotzil communities, such as Nachig, San Felipe, Zacualpa and Navenchauc.

Therefore, we believe that the creation of natural spaces is a key tool for conducting research on the local flora and fauna, and also to understand the responses of wild mammal populations to the impacts and threats currently affecting forests in the Chiapas Highlands. Thus, biological and ecological studies should be encouraged in oak-pine forests in the region, including regular evaluations of the fauna; particularly in EBSJ, it is essential to conduct short-, medium- and long-term monitoring of mammals to determine the state of their populations. Specialized sampling with aerial and camera traps will allow to elaborate a more comprehensive list of those species that are potential inhabitants in the area but are rarely captured at ground level (e. g., the rodents Habromys lophurus, Nyctomys sumichrasti and Glaucomys volans). Furthermore, the influence of nearby human settlements on forest structure and composition and on mammal populations should be assessed, including the introduction of exotic species (i.e., dogs, cats, rats and mice), as well as an assessment of the convenience of creating biological corridors connecting with other protected natural areas, and the development of programs in partnership between municipal governments and society to implement urgent actions for management and conservation of the local habitats, plants and animals. EBSJ currently conducts environmental education campaigns in schools within the region as well as in the field station itself, where we use P. zarhynchus as a symbol of conservation of the area, and undertake research projects on the ecology and distribution of the red-lipped arboreal aligator lizard (Abronia lythrochila, Reptilia: Squamata) and the unspotted saw-whet owl (Aegolius ridgwayi, Birds: Strigiformes).

The conservation and proper management of the oak-pine forest in EBSJ are appropriate strategies to promote the survival of most mammal species (^{Naranjo et al. 2016}; ^{Lorenzo et al. 2017}). For this reason, this note sets the grounds for developing scientific knowledge and continue with the biological studies, as EBSJ is home to species of great ecological and conservation importance.