HOLOCENE DISTRIBUTION OF OCTODONTID RODENTSRevista Chilena de Historia Natural383 76: 383-389, 2003 76: ¿¿-??, 2003 Holocene distribution of Octodontid in central Chile

Distribución holocénica de roedores octodóntidos en Chile central

BÁRBARA SAAVEDRA & JAVIER A. SIMONETTI

Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile; e-mail: [email protected]

ABSTRACT

We describe the Holocene distribution of the Octodontids Aconaemys fuscus, bridgesi, O. degus, O. lunatus, O. pacificus and Spalacopus cyanus from Central Chile. We compared ancient and present day ranges. The Holocene pattern was inferred from zooarchaeological records. Octodon degus, O. lunatus, O. bridgesi, and Aconaemys fuscus showed a reduction in their geographic range. Although specific mechanisms remain to be tested, human disturbance seems to be the distal factor that explains the reduction of ranges for some taxa.

Key words: , Holocene, central Chile, zooarchaeology.

RESUMEN

Describimos la distribución holocénica de los roedores octodóntidos Aconaemys fuscus, Octodon bridgesi, O. degus, O. lunatus, O. pacificus y Spalacopus cyanus en Chile central, y la comparamos con su distribución actual. El patrón de distribución holocénico se infirió de registros zooarqueológicos. Octodon degus, O. lunatus, O. bridgesi y Aconaemys fuscus muestran una reducción en su rango geográfico. A pesar de que los mecanismos específicos que explican este patrón permanecen sin ser resueltos, la perturbación humana parece ser el factor distal que explicaría la reducción en el rango de distribución para algunas de estas especies.

Palabras clave: Octodontidae, Holoceno, Chile central, zooarqueología.

INTRODUCTION unresolved, a fact reflected in the wealth of new records of these taxa (e.g., Hutterer 1994, Octodontids represent a conspicuous group Podestá et al. 2000, Díaz et al. 2002). The among Chilean rodents (Contreras et al. 1987, state of knowledge is even worse for Gallardo & Kirsch 2001). As a result of a long paleoecology, where scarce knowledge of past evolutionary history in southern South distribution and abundance of Octodontids America, this taxon gathers 11 endemic exists (Simonetti 2000). species, six of which occupy central Chile, all Human activities might indeed have herbivores: Aconaemys fuscus, Octodon affected population’s persistence of several bridgesi, O. degus, O. lunatus, O. pacificus and Octodontid species, determining local Spalacopus cyanus. These taxa are currently extinction in late Holocene and historical distributed from 27¼ to 38¼ S, mostly in the times. Octodon bridgesi for example, Mediterranean region of Chile (Contreras et al. disappeared from Andean range in central 1987). Octodontids use different habitats, like Chile due to habitat clearance for horticultural O. lunatus and O. bridgesi that inhabit dense development (Simonetti 1989a). It also went vegetation, or O. degus that prefer more open extinct in the coastal range due to local shrublands (Contreras et al. 1987, Simonetti intensification of agriculture in areas 1989a, Muñoz-Pedreros 2000). Despite being a previously unused by local farmers (Simonetti comparatively well known group, several & Saavedra 1998). The current absence of O. aspects of their ecology and distribution remain bridgesi in north-central Chile was then 384 SAAVEDRA ET AL. achieved only recently, as a result of local extinction driven by human activities. Changes in geographic distribution have been also reported for other Octodontids. Aconaemys fuscus, currently confined to the southern Andes, ca. 1,000 years ago inhabited areas close to Santiago, more than 100 km north of its current distribution (Simonetti & Saavedra 1994). On the same vein, O. lunatus and O. degus, currently restricted to central Chile, were found at least 50 km south of their current distribution in archaeological sites dated 1,000 years old (Saavedra et al. 1991). Evidence suggests that present-day distribution for Octodontids was achieved recently. As new information is available, here we describe the Holocene distribution of Octodontid in central Chile, based on published and new zooarchaeological records, aiming to illustrate their geographic range dynamics.

MATERIAL AND METHODS

Holocene distribution was inferred for the six octodontid species that currently inhabit central Chile: Octodon bridgesi, O. degus, O. lunatus, O. pacificus, Aconaemys fuscus and Spalacopus cyanus. Distribution was inferred based on zooarchaeological composition of 12 new, and seven published archaeological sites (Saavedra et al. 1991, 2003, Simonetti 1994, Simonetti & Saavedra 1994, 1998). All sites were excavated using regular archaeological methods, and analysis was made based on usual identification keys (e.g., Reise 1973, Pearson 1995), as well as comparison with voucher specimens deposited in museums and collections. Sites were arranged in seven areas, from Huentelauquén in the north, to Isla Mocha in the south (Fig. 1). When more than one site was analyzed in an area, all were located within a range of 5 km for the area. For each site, we recorded Octodontid composition. Due to the scarcity of zooarchaeological records, we also included information regarding other caviomorphs found in new sites, although those data were not analyzed here. New zooarchaeological information was Fig. 1: Geographic localization of archaeologi- recovered from: (A) Huentelauquén (31º38’ S, cal areas included in this analysis. Letters are: 71º33’ W, Fig. 1). Here we report the (a) Huentelauquén, (b) La Granja, (c) Chanco, zooarchaeological content of site “04. Mi. Hue. (d) Cordón de Chacabuco, (e) El Manzano, 2”. This is an Early Holocene site dated 9,110 - (f) Quivolgo, and (g) Isla Mocha. 8,800 years BP (Weisner et al. 2000), where 2,962 bone remains were retrieved. From these, Localización geográfica de áreas arqueológicas incluidas 752 (25.4%) were small that we en este análisis. Las letras son: (a) Huentelauquén, (b) La classified as the following taxa: Abrocoma Granja, (c) Chanco, (d) Cordón de Chacabuco, (e) El Man- bennetti, Lagidium viscacia, Octodon degus, O. zano, (f) Quivolgo e (g) Isla Mocha. HOLOCENE DISTRIBUTION OF OCTODONTID RODENTS 385 lunatus, and Spalacopus cyanus; (B) La Granja Length of human occupation varied among (34º24’ S, 71º11’ W), located 100 km south of sites, ranging from 7,400 years (e.g., El Santiago (Fig. 1). Bone material was recovered Manzano 1), to less than 300 years (e.g., La from three archaeological sites: “La Granja 1”, Granja and Isla Mocha sites). To pursue our “La Granja 2”, and “La Granja 3”, excavated analysis, only presence/absence of a taxon was during 1993-1995 (Planella & Tagle 1998). considered, ignoring changes in abundance These sites dated in 1,400Ð975 years BP. A (Reitz & Wing 1999). total of 5,249 bone specimens were recovered, comprising 1,928 rodents (36.7%), of the species A. bennetti, A. fuscus, Myocastor RESULTS coypus, O. degus, and S. cyanus; and (C) Chanco (35º43’ S, 72º29’ W) is a coastal area Six Octodontids were recorded during the in the southern margin of the Mediterranean Holocene in central Chile. Although the same zone (Fig. 1). Three sites were analyzed: species are observed today in the area, “Punta La Gaviota”, “Cerro Las Conchas”, and significant reductions in geographic range were “Conchal Valenzuela”, dated in 5,685-500 detected for four of these taxa. Octodon degus, years BP (Gaete et al. 1992, Gaete & Sánchez currently the most abundant Chilean 1993, Sánchez & Gaete 1993). A total of 474 caviomorph, showed an extended latitudinal bone specimens contained 128 (27%) rodents. range in ancient time (Fig. 2). Until 1,000 years The species found here were: A. bennetti, A. BP, its southern limit was found in Quivolgo, fuscus, and M. coypus. extending its current distribution ca. 50 km Among published zooarchaeological records south. Octodon lunatus was also found in this we included: (D) Cordón de Chacabuco, site, ca. 155 km south of its present located 70 km north of Santiago (32º59’ S, distribution, representing a change of at least 70º42’ W, Fig. 1). Here, five archaeological two degrees south during Holocene (Fig. 2). sites were excavated: “Las Chilcas 1”, “Las Octodon lunatus was present in Quivolgo at Chilcas 2”, “Piedra El Indio”, “El Carrizo”, and least until ca. 1,000 years BP (Saavedra et al. “La Nogalada” (Hermosilla & Saavedra 2000), 1991). This species is now restricted to the dated 2,830 to 160 years BP. Octodontids coastal range of central Chile from Fray Jorge included A. fuscus, O. bridgesi, O. degus, O. (30º39’ S, 71º40’ W) to Quilpué (33º03’ S, lunatus, and S. cyanus; (E) El Manzano (33º16’ 71º26’ W), and in the Andes close to Santiago S, 70º37’ W), located in the Andean range (33º46’ S, 70º27’ W, Fig. 2). During most the close to Santiago (Fig. 1), where two Holocene, O. bridgesi reached up to 33¼ S, and archaeological sites (“La Batea 1” and “El was recorded in El Manzano, Las Chilcas and Manzano 1”) were excavated (Simonetti 1989a, La Granja (Fig. 2). Currently, O. bridgesi is 1994, Saavedra et al. 1991, Simonetti & restricted to the southern portion of central Saavedra 1994). These sites have a chronology Chile, depicting a reduction of 100 km in their from 8,900 up to ca. 500 years BP. Octodontids northern range. Finally, the presence of O. recorded were A. fuscus, O. bridgesi, O. degus, pacificus in all archaeological sites analyzed in O. lunatus, and S. cyanus; (F) Quivolgo (35º19’ Isla Mocha, indicates its presence in the island S, 71º24’ W), a coastal location at the mouth of during Holocene. Maule River, where the site “07Co24” was Changes in distribution also modified excavated (Saavedra et al. 1991, Simonetti sympatry patterns among Octodontid species. 1994, Fig. 1). Here five Octodontids were Octodon degus and O. bridgesi overlapped recognized: A. fuscus, O. bridgesi, O. degus, O. during the Holocene. Co-occurrence was lunatus, and S. cyanus; (G) Isla Mocha, is the observed in six out of 19 archaeological sites. single off-continental area analyzed (38º22’ S, Octodon lunatus and O. bridgesi also co- 73º3’ W, Fig. 1). Four sites were excavated: occurred during the Holocene, and were found “P5-1”, “P22-1”, “P25-1”, and “P31-1”. together in six sites. The archaeological Octodon pacificus was the only Octodontid coexistence of the three continental Octodon found in these remains (Quiroz & Sánchez species was acknowledged for the first time in 1993, Saavedra et al. 2003). Quivolgo (Saavedra et al. 1991). Currently, O. Zooarchaeological remains covered almost degus and O. bridgesi, as well as O. lunatus all the Holocene, including sites from early and O. bridgesi are allopatric species Holocene (e.g., Huentelauquén: ca. 9,000-8,000 (Contreras et al. 1987). years BP), to late Holocene (e.g., La Granja 1: Aconaemys fuscus also showed a ca. 1,200-500 AD), as well as recent historical significant range reduction in their northern times (e.g., Piedra El Indio: ca. 500 years BP). distribution during Holocene. During early 386 SAAVEDRA ET AL.

Holocene, A. fuscus occupied Andean areas Spalacopus cyanus did not show modification close to Santiago, along with coastal sectors in its distribution range when comparing ancient of the Maule River (Fig. 2). This species was and present day distribution (Fig. 3). During also found in Tagua-Tagua records (34º30’ S, Holocene, S. cyanus was distributed from 71º10’ W), dated ca. 10.000 years BP Huentelauquén to Quivolgo along the coast, and (Simonetti 1989b). Currently, A. fuscus is in the Andean portion near Santiago. The same mostly confined to southern Andes from distribution is observed today for the species (Fig. Curicó to Temuco (38º44’ S, 72º35’ W), 3). Stratigraphical co-occurrence of A. fuscus and reaching the coast near Concepción. Our S. cyanus was observed in six out of 19 sites. No findings imply a reduction of ca. 120 km in coexistence is observed today for these species its northern limit. (Contreras et al. 1987).

Fig. 2: Holocene and present distribution of Octodon bridgesi, O. degus, O. lunatus, and O. pacifi- cus in central Chile, inferred from zooarchaeological and literature survey, respectively. Distribución Holocénica y Presente de Octodon bridgesi, O. degus, O. lunatus y O. pacificus en Chile central, inferidas a partir del análisis zooarqueológico y de revisión de literatura, respectivamente. HOLOCENE DISTRIBUTION OF OCTODONTID RODENTS 387

Fig. 3: Holocene and present distribution of Aconaemys fuscus and Spalacopus cyanus in central Chile inferred from zooarchaeological and literature survey, respectively. Distribución Holocénica y Presente de Aconaemys fuscus y Spalacopus cyanus en Chile central, inferidas a partir del análisis zooarqueológico y de revisión de literatura, respectivamente.

DISCUSSION wheat production, triggering the local extinction of this taxon (Simonetti & Saavedra 1998). Four out of six Octodontid species showed Local extinction in the Andean sites was reductions in their geographical range in the preceded by changes in the relative abundance recent past in central Chile. Human activities of the generalist Octodon degus and O. bridgesi have been suggested as the major cause of local in stratigraphical (i.e., temporal) sequences. extinction of O. bridgesi in the Andes and in the While O. degus became progressively more coastal range close to Santiago (Simonetti abundant in recent times, O. bridgesi became 1989a, Simonetti & Saavedra 1998). In the scanty, coupled to the historical reduction of Andes of central Chile, local horticulturalist vegetative cover (Simonetti 1989a). reduced vegetation cover ca. 1,500 years ago to Although central Chile has been obtain agricultural lands, determining the characterized by a long history of human disappearance of O. bridgesi, a dense vegetation presence (Aschmann 1991), local extinction specialist, from the area (Simonetti 1989a). The observed for other Octodontid species can not be same habitat reduction was driven in the coastal directly associated to human disturbance. range of central Chile ca. 200 years ago, due to Octodon degus for example, uses preferentially the development of intense wood cutting and habitats with low vegetation cover, being 388 SAAVEDRA ET AL. regularly found in human-modified habitats Timber extraction, forestry, or live stock (Mann 1978, Meserve et al. 1984). Based on grazing has been developed in central Chile habitat preferences, O. degus should have been more intensively than in other area of the favored by human-induced changes in habitat country (Miller 1980). Other human-induced cover (Simonetti 1989a). Nevertheless, O. degus disturbances like introduction of exotic showed a reduction in its southern limit, where predators and competitors like black rat (Rattus elevated human disturbance has been also rattus), rabbits (Oryctolagus cuniculus), or goats recognized (Miller 1980). Interestingly, A. (Capra hircus), might also have negative effects fuscus experienced range reduction during on native octodontids (Simonetti 1983, Jaksic Holocene. Due to its fossorial habits, habitat 1998). Introduced goats for example reduced destruction by domestic cattle has been vegetation cover by consuming native advanced as a causal factor to explain its range vegetation. This reduction favors the presence of reduction (Muñoz-Pedreros 2000). Nevertheless, rabbits, which also feed on native vegetation, S. cyanus is also a fossorial taxon that was not reducing overall food and habitat resources for affected in their geographic range, suggesting native species like O. degus, and probably that human activities do not have equivalent reducing its abundance (Simonetti 1983). effects on the persistence of different species. Holocene records for Octodontids evidence Factors like climate seem not to be the elevated dynamism of Chilean rodent important in explaining the ancient rodent assemblages, indicating that present-day patterns dynamics shown here, since the changes in of rodent distribution have been achieved very distributional range occurred in the last 1,500 recently. This fact must be acknowledged when years, where no significant alterations in faunal analyses are made. For example when climate are registered (Villagrán & Varela comparing Mediterranean areas, small mammals 1990, Villagrán 1994). Nevertheless, the of central Chile are regarded as poor in species occurrence of other significant climate changes richness (e.g., Glanz 1977). Acknowledging the like Pleistocene glaciations (Villagrán 1984) fact that present assemblages are very recent, might probable have affected rodent and have been mostly shaped by human- distribution at the beginning of the Holocene, associated factors, intercontinental comparisons and their study must be accomplished to should include species recently extinct like complete the Holocene history of this group. Octodon bridgesi and Aconaemys fuscus. This Likewise, due to methodological limitations long-term perspective should also be applied imposed by zooarchaeological analysis (Rosen when population surveys are developed for 1988, Reitz & Wing 1999) changes in elaborate evolutionary, conservation, and Octodontid distribution advanced by us should management analysis. be regarded as hypothesis. Particularly, the ancient distributions proposed for these rodents must be considered as the minimum ACKNOWLEDGMENTS distributional range observed for Octodontid species in the past. The fact that they are based This work has been financed by FONDECYT on the manifest presence of the taxon in a site, grants 2990120, 1990067, 1990027, 1990049, does not prevent the extension of ranges if 1950036, 1940106, 1921040. BS is a doctoral other records are registered in new fellow of CONICYT. archaeological sites. Geographic reduction of Octodontids occurred in all cases due to extinction of peripheral populations: southern limit for O. degus and O. LITERATURE CITED lunatus, and northern limit for O. bridgesi and A. fuscus. 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Associate Editor: Pablo Marquet Received October 29, 2002; accepted May 12, 2003