INTRODUCTION

Formicids play an important role in the environment not only as plant and sap feeders, but also because they are zoophagous and detritivorous, necrophagous and coprophagous (^{Ipinza-Regla, 1971}). The 62 species of Formicidae in Chile represent a poor myrmecological fauna compared to that of South America (^{Snelling and Hunt, 1975}). The flora in Río Clarillo Reserve has been studied by ^{Espinoza (1981}), ^{Gajardo (1994}), and ^{Niemeyer et al. (2002}). In general, the insect fauna in the reserve is better known than that of other protected areas in the central zone of Chile, particularly the soil micro arthropods (^{Covarrubias, 1991}), epigeous insects (^{Solervicens et al., 1991}), coleopterans associated to the foliage of shrubs (Solervicens and Estrada, 1996), tabanid and tachinid flies (^{González, 1992}), plant feeding hemipterans (Niemeyer et al., 2002), and wasps Vespula germanica (F.) and Polistes buyssonii (Brèthes) (CONAF, 1996).

In Chile, there are ten introduced and 34 endemic ant species (^{Snelling and Hunt, 1975}). Some studies conducted in Río Clarillo Reserve (e.g., ^{Covarrubias, 1991}; ^{Solervicens et al., 1991}; ^{González, 1992}; ^{Niemeyer et al., 2002}; Solervicens and Estrada, 2002; Estrada and Solervicens, 2004; ^{Jara, 2008}) have determined a total of 18 species.

The spatial distribution of the nests of formicids is related to availability of food, nest areas, and the intra- and inter-specific competition between different species of formicids with the same diet (^{Bernstein and Goebel, 1979}; ^{Levings and Franks, 1982}; ^{Hõlldobler and Wilson, 1990}; ^{Ipinza-Regla et al., 2010}; 2013). The availability of substrates for building nests and the physicochemical characteristics of the soil are also important factors (^{Petal, 1978}; ^{Torres, 1984}, ^{Johnson, 1992}).

It is evident that the distribution of ants is affected by the presence of people. Therefore, this work aimed at studying the distribution of different species of ants coexisting in an area with endemic and introduced flora in Río Clarillo National Reserve in the Andean foothills southeast of Santiago, Metropolitan Region, Chile. The characteristics, frequency, and spatial distribution of the species were determined in two different areas that differed in human presence.

MATERIALS AND METHODS

As formicids use their nests as working centers around which all members of the colony conduct their activities. Herein the minimum area method was used to determine the area where a large amount of species was found. The minimum area method is used in plant studies to determine the area where all species that represent a community are present (^{Ipinza-Regla et al., 1983}). This method may also be used to analyze the nests of ants, which are fixed structures that can be counted. The selected area is divided in quadrants of a certain size, and species of ants are identified. The search finishes when no more new species appear during sampling so that the minimum area is then established (Ipinza-Regla et al., 1983; 1987). In this study, no new ant species appeared when revising 3 quadrant lines (Table 1).

The area with human presence in the study was a picnic site near a trail in El Maitén - La Roca (33^e43'34,3" S, 70^e28'47,8" W), at 901 m altitude, with a 1.71 ± 0.75 plant cover index (1 = scarce; 2 = medium; 3 = high; 4 = soil fully covered), including quillay (Quillaja saponaria Molina) and espino [Acacia caven (Molina)], a 1.27 ± 0.60 stone cover index, and 2.27 ± 1.03 plant remains. The area with less human intervention was located at 33^e43'50,8" S; 70^e28'78" W, at 930 m altitude, and had a 1.32 ± 0.56 plant cover index, including quillay, litre [Lithraea caustica (Molina) Hook et Arn.], peumo [Cryptocarya alba (Molina) Looser], and espino, a

2.06 ± 0.79 stone cover index, and 3.29 ± 0.94 plant remains (^{Jara, 2008}).

Each quadrant in Table 1 was examined to record the total number of ant nests from November 2006 through February 2007. Ants were searched for by looking under each stone or on branches, and vegetation in general. Once a nest was found, 15 ants were collected at the entrance of each nest using twigs or a brush and were kept in hermetic glass vials, together with material from where they were obtained (soil, dead plant material, trunks, etc.). Species were then identified by comparison with specimens stored in the Zoology and Ethology Laboratory, College of Agroforestry Sciences, Universidad Mayor, Santiago, and by using the taxonomic keys for Chilean formicids by ^{Snelling and Hunt (1975}). The nests in the vials were fed with honey, apple puree, ham pieces, and water in humid cotton.

The ants and nests identified in the quadrants were analyzed considering plants, stones, and plant remains indexes using a Fisher test. The following determinations were made: total nests per quadrant, percentage of quadrants with nest entrances of each species, i.e. percentage of nests in the total quadrants, and the number of nests in relation with the total number of entrances of each species, which indicates the number of nest entrances for the area occupied.

Table 1 Diagram of the minimum area method. Each quadrant represents a 1 m² area. The light grey area are the quadrants where the study began (36 m²), while the dark gray quadrants are the three lines where no new ant species were found, at which point the study ended. 

RESULTS AND DISCUSSION

The formicids Brachymyrmex giardii (Emery), Nothidris bicolor (Snelling), and Camponotus chilensis (Spinola) were found in the study. The results of nests found in the area with human presence (picnic site) and in that with less human intervention are presented in Table 2.

The area with human presence had a total of 34 nest entrances: 32 of them with B. giardii (94%), 1 with N. bicolor, and 1 with C. chilensis (3% each).

A number of 39 nests were found in the area with less human intervention: 37 with B. giardii (95%), 2 with N. bicolor (5%), and none with C. chilensis.

The nest totals, frequency, density, and abundance of the three formicid species in the areas with human presence (a) and less human intervention (b) are presented in Table 3.

In both areas, the predominant species was B. giardii, which was found in 16.32 and 18.00% of the quadrants in the areas with human presence and less human intervention, respectively, occupying > 90% of the study area (Table 3). The nests of this species are large and may have several entrances (polycaly) (^{Ipinza-Regla et al., 2005}); some entrances may belong to the same nest. To verify this hypothesis, chromatograph studies of the epicuticle of the ants can be conducted. According to a Fisher test (p = 0.027) a significant effect was found between species abundance in both areas, with a confidence interval of 0.6714 to 236.23.

Table 2 Distribution of nests of three formicid species in the areas with human presence (a) and less human intervention (b) in the study. 

Table 3 Nest entrances, frequency, density, and abundance of B. giardii, N. bicolor, and C. chilensis in the areas with human presence (a) and less human intervention (b) in the study. 

The results of this study are similar to those reported by ^{Vidal (2000}) in El Ingenio, Cajón del Maipo, Región Metropolitana, Chile, who found three species, B. giardii, C. morosus (Smith), and Solenopsis gayi Spinola, with dominance of B. giardii since nests were found in 83% of the quadrants. ^{Solervicens et al. (1991}) also found three ant species: C. morosus, Pogonomyrmex odoratus Kusnezov, and Pseudomyrmex lynceus (Spinola).

^{Estrada and Solervicens (2004}) found 18 formicid species in the Río Clarillo Reserve using Barber traps for nests on the surface of the soil and collecting by shaking branches over an umbrella. These 18 formicid species correspond to 29% of the 62 species described in Chile. The greater number of species obtained in that study is explained by the sampling of individuals foraging rather than by the number of nests. In our work, the three species found are equivalent to 4.8% of the formicid species described in Chile.

^{Ribeiro de Castro et al. (2016}) have indicated that quantifying and understanding the main drivers of biodiversity responses to human disturbances are key issues to foster effective conservation plans and management systems. In their study, irrespective of forest disturbance ant species richness was almost twice as high in forests when compared to areas in production. In contrast, ant species composition presented continuous variations from primary forest to intensive agriculture, following a gradient of aboveground biomass.

The management objectives of Río Clarillo Reserve to preserve and protect the soil and wild fauna and flora have not been fully accomplished. In fact, as some areas are used for recreation, only a few areas are not affected by anthropomorphic pressure. This affected the study because it was difficult to find an area which was totally free of human intervention in order to differentiate the distribution of formicids from an area with people activity. In fact, the presence of people was frequent in trails and buildings as well as the presence of introduced animals. However, the anthropomorphic effect in the environment did not affect the distribution of the formicid species found in this study; nests of three species were found in the area with human presence, while only two were found in the area with less human intervention. This result was not expected, because it was thought that fewer species would occur in the intervened area. However, this result may be explained by the feeding of formicids, which use the food left in the garbage by visitors to the reserve. Further study is required to determine if there are different nests or several entrances to the same nest of an ant species (policaly). This was not included in this study because we tried to manipulate the area as little as possible.

CONCLUSIONS

Three formicid species were found in Río Clarillo National Reserve in central Chile: Brachymyrmex giardii, Camponotus chilensis, and Nothidris bicolor. Their distribution was aggregated and was not affected by human presence. The minimum area method used in this study may not be the most adequate to determine the diversity of formicid species, but it proved useful herein in determining nest distribution.