*Dirección para correspondencia Abstract ]]>
The Oaxacan Spiny-tailed Iguana Ctenosaura oaxacana is a restricted species to the Isthmus of Tehuantepec in Southern Oaxaca, Mexico. This reptile is one of the less known iguanid species. We censustracked a population in the South of Niltepec, Oaxaca, Mexico from May 2010 to April 2011. Throughout one year, a total of 10 line transects were situated and recorded in the study area to determine relative abundance and density, and habitat ]]>
C. oaxacana population on the Southeastern limit of species range. Although this species has a very restricted distribution and is in danger of extinction, C. oaxacana has a high population density when compared to other Ctenosaura species. A total of 108 individuals were recorded throughout the study. Dry forest (33.75ind/ha) and Nanchal ]]>
B. crassifolia (Nanchal); C. alata (grassland); Tabebuia sp., Genipa americana, G. sepium, Acacia sp., Ficus sp. and Haematoxylon sp. (dry forest); G. sepium, Acacia sp. and Guazuma ulmifolia (riparian ]]>
C. erecta (mangrove). Live trees hollows and branches were used by species. Main threats to the species are excessive hunting and habitat loss. Furthermore, grassland fires are still common in the study area during the dry season, which can result in habitat loss and territorial displacement of individuals.
La Iguana de Cola Espinosa ]]>
Ctenosaura oaxacana es una especie restringida al Istmo de Tehuantepec en el Sureste de Oaxaca, México. Este reptil es uno de los iguánidos menos conocidos. Entre Mayo 2010 y Abril 2011 hicimos el seguimiento de una población al Sur de Niltepec, Oaxaca, México. A lo largo de un año, se colocaron y monitorearon un total de diez transectos en el área de estudio, para determinar la abundancia relativa, densidad y uso de hábitat (selva seca, Nanchal, pastizal, vegetación riparia y manglar) de la especie. Esta ]]>
C. oaxacana en el límite sureste de la distribución conocida para la especie. Aunque esta especie posee una distribución muy restringida y se encuentra en peligro de extinción, C. oaxacana presenta una alta densidad poblacional comparada con otras especies de Ctenosaura. Se registró un total de 108 individuos a lo largo del ]]>
B. crassifolia (Nanchal); C. alata (pastizal); Tabebuia sp., Genipa americana, G. sepium, Acacia sp., Ficus sp. y Haematoxylon sp. (selva seca); G. ]]>
sp. y Guazuma ulmifolia (vegetación riparia); y C. erecta (manglar). La especie utilizó agujeros y ramas de árboles vivos. Las principales amenazas para la especie son la cacería excesiva y la pérdida de hábitat. Además, la quema de pastizales sigue siendo común en el área de estudio durante la temporada seca, lo que puede resultar en la pérdida de hábitat y el desplazamiento territorial de los individuos.
Palabras clave:Ctenosaura oaxacana, uso de hábitat, abundancia, densidad, Oaxaca.
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The Oaxacan Spiny-tailed Iguana (Ctenosaura oaxacana, Köhler & Hasbún 2001) named by the local people as “guiou” (in “zapoteco” language), and which prior to 2001 was named as five-keeled Spiny-tailed Iguana (C. quinquecarinata, Gray 1842), is a critically endangered species restricted to the Pacific versant of the Isthmus of ]]>
2 with six to ten surviving subpopulations highly isolated due to deforestation, frequent habitat burning, and poaching. Total population size is not known, but an occurrence of fewer than 2 500 mature individuals is expected on the basis of current habitat conditions, population size which is further expected to decline by at least 30% over the next 10 years if current rates of habitat loss continue (Köhler & ]]>
Despite their importance, there have been very few studies on the species. Records on C. oaxacana are very scarce; and only reported for tropical deciduous forest at altitudes ranging from sea level to 250m. The only records from Salina ]]>
et al. (1996) reported the occurrence of the species in San Mateo del Mar,Municipality of San Mateo del Mar. ]]>
et al. 2005). Additional records were reported from Cerro Piedra Larga, an isolated mountain massif in Eastern Oaxaca, located 100km to the West of the Isthmus of Tehuantepec, a major biogeographic barrier separating the heart of Mexico from Northern Central America (Peterson
et al. 2004, Köhler 2004). Recently, Martín-Regalado et al. (2011) recorded the presence of the species close to the Tehuantepec municipality.
Biological information of C. oaxacana is scarce, and with the only available ]]>
C. oaxacana, and determine its ]]>
Material and Methods
The study area of approximately ]]>
2 is located in the North of Inferior lagoon at the South of the Isthmus of Tehuantepec, Oaxaca (16º22’00” N - 9 4º35’12” W and 16º24’10” N - 94º34’47” W), which is also near to the Montecillo Santa Cruz community, Municipality of San Francisco del Mar. This region is located Northeast of the Istmica-Chiapaneca coastal plain, which is situated between Sierra Madre de Chiapas and Pacific Ocean (Zizumbo & Colunga 1982).
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Climate is tropical with mean annual temperature of 27.6°C, mean annual rainfall of 800mm (INEGI 1995), and with clearly defined seasons. The rainy season occurs from May to October with an intra-estival drought in August, while the dry season occurs from November to April, particularly drastic weather conditions occurs during late winter and early spring (Zizumbo & Colunga 1982).
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Montecillo Santa Cruz presents five habitat types: 1- Grassland: open and plain areas, flooding during wet season, and characterized by a forb stratum of grasses, herbs, scattered isolated “morro” trees (Crescentia alata Kunth 1819), and shrubs. The most frequent plants are grass species such as Aristida sp. and Trisetum sp. 2- Nanchal: semi open ]]>
Byrsonima crassifolia (L.) Kunth (1822), a common species form South-Southeast Mexico. 3- Dry forest: close areas of thorny and deciduous shrubs, and trees up to four meters high. The most frequent species are Acacia farnesiana (L.) Willd. (1806), Casearia sp., and Aristida sp. 4- ]]>
Aristida sp., Gliricidia sepium (Jacq.) and Celtis iguanaea (Jacq.) Sarg. are the characteristic species. 5- Mangrove: characterized by two species, Rhizophora mangle L. ]]>
Conocarpus erecta L. (Farías 2004, Sántiz 2005, Lorenzo et al. 2008). No rocky terrain occurs at any surveyed habitat types (Pérez-García et al. 2001).
Local people from Montecillo Santa ]]>
et al. 2008).
Monitoring: Data were obtained from four field surveys of eight days (from 0900-1 500h), from May 2010 to April 2011, and during the dry and rainy seasons. Two lineal transects of a total length of 500m and variable width each based on distance sampling proposed by Thomas et al. (2010), were evaluated per vegetation type. Transects were located randomly per vegetation type, with at least 500m separating them. Each transect was visited once a day by two persons; we visually inspected the branches of the trees and ]]>
C. oaxacana. Geographical coordinates (eTrex Vista, 3-15m precision, Garmin, Kansas) of each observed individual was recorded. Seasonal and ]]>
et al. 2010). Comparison of relative abundance between habitat types was analyzed by a non-parametric Wilcoxon test (Motulsky 1995).
Whenever possible, we took high-quality photographs of the specimens observed. The photographs were added to the Image Database of the National ]]>
Habitat use data were analyzed ]]>
X2) test to assess significant differences in habitat use by C. oaxacana and the expected occurrence based on the availability of each type of habitat in the area. Bonferroni intervals were applied for each statistical significant difference observed to determine whether or not selection of habitat type existed (Neu et al. 1974, Byers
et al. 1984).
Results
New records of C. oaxacana were reported for the North border of the Inferior lagoon, in the ]]>
Highest relative abundance and density were estimated for dry forest, ]]>
Table 1). Comparisons between habitat types showed no significant differences between dry forest and Nanchal (W=15, p=0.0808), and neither between habitat types showing the lowest values such as comparison between riparian vs. grassland and riparian vs. mangrove (W=39, p=0.4674). Differences between seasons had similar results. In regard to rainy season and dry season, dry forest and Nanchal were the habitat types which showed highest values on relative abundance and density for both rainy and dry seasons. ]]>
Habitat use analysis showed that C. oaxacana preferred dry forest, followed by Nanchal and mangrove, whereas they avoided grassland and riparian vegetation (Table 2). There was no difference in habitat use between males and females.
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Mean perch heights were 1.23±0.32 (n=30) in Nanchal, 2.11±0.30 (n=9) in grassland, 1.90±0.56 (n=54) in dry forest, 1.91±0.28 (n=9) in mangrove and 2.3±0.37 (n=6) in riparian vegetation. At Nanchal, the B. crassifolia shrub was the only species observed as refuge and perch, while at the grassland the C. alata tree was the preferred refuge and perch species observed. At dry forest
C. oaxacana used Tabebuia sp., Genipa americana (Linneaus 1759), G. sepium, Acacia sp., Ficus sp. and Haematoxylon sp. as refuge and perch. We registered one case in which an individual was observed occurring in a ground hole, but we cannot determine if it corresponded to a common refuge or ]]>
G. sepium, Acacia sp. and Guazuma ulmifolia Lam (1789) were the vegetation species used as perch and refuge. At mangrove, C. erecta was the only species used as refuge, but we observed an individual perching on R. mangle branches. In all cases live trees hollows and branches were used ]]>
Discussion
On the basis of available information on species distribution, this study reports a new C. ]]>
population in the Southeastern limit of the species range (Köhler & Hasbun 2001, Köhler 2004). However, more surveys are needed, in particular to the Southeast of the study area, where local people say they have seen the occurrence of the species. Additional sites to the East of the Isthmus of Tehuantepec, near the border of the state of Chiapas (CONABIO 1999), characterized by dry forest should also be surveyed. Moreover, is necessary to extensively survey the area between our new records and the former reported populations in Niltepec. These areas ]]>
Up to date, there is no empirical data on relative density and abundance for any reported population of the species. The little information available has been indicated by Köhler (1995) and Köhler & Hasbun (2001). Density data for the most closely ]]>
C. quinquecarinata, on a wildlife refuge in Nicaragua estimated 28 individuals, with a density of 0.93ind/ha (Robleto 2010); which is a density value very low compared with our results. About other species, Teran (2006) reported a maximum value of 3.1ind/ha in Honduras (C. similis), while Zurita-Carmona et al. (2009) reported a maximum value of 1.01ind/ ha in Mexico (C. pectinata). In both ]]>
C. oaxacana density. Although the population density of C. oaxacana seems high when compared with other species, it is significant to note that this species has a restricted distribution in Southern Oaxaca, Mexico. Additionally, we know that C. oaxacana have a specific preference to dry forest. ]]>
In the dry forest habitat, C. oaxacana density reached values of 33.75ind/ha. However, the preferred habitat (dry forest) is not the most abundant habitat type. Villa & Scott (1967) reported that C. quinquecarinata prefers dry forest trees and roots, while Robleto (2010) reported the greatest number of specimens recorded in the scrub and dry forest. ]]>
Although Köhler (1995) recorded a single individual per tree in its report, during our ]]>
As Köhler & ]]>
C. oaxacana, but local people reported that the species is slightly hunted because is too small to be an important source of food (Carrillo-Reyes, pers. comm.). Similarly, Robleto (2010) in Nicaragua, were C. quinquecarinata densities was lower than
C. oaxacana, reported the same major threats. Furthermore, grassland fires during the dry season are common in the study area, which can results in habitat loss and territorial displacement of individuals. As well, high degree of habitat loss and fragmentation in the study area (Carrillo-Reyes, pers. comm.) might affect both the distribution and density of the species. Further studies are needed concerning issues such as reproduction, diet, and behavior of C. oaxacana in Mexico.
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Acknowledgments
We thank the municipal and communal authorities of Montecillo Santa Cruz and San Francisco del Mar, Oaxaca, especially to all local families. We are grateful to the students from UNICACH and UJED for their help during the fieldwork. We thank the financial support from Programa de Mejoramiento del Profesorado ]]>
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*Correspondencia: Tamara Rioja: Sustentabilidad y Ecología Aplicada, Universidad de Ciencias y Artes de Chiapas, Lib. Norte Pte. No.1150, Lajas Maciel, Tuxtla Gutiérrez, Chiapas, México; tamararioja@gmail.com. Oikos: Conservación y Desarrollo Sustentable, A.C., San Cristóbal de las Casas, Chiapas, México. Arturo Carrillo-Reyes: Sustentabilidad y Ecología Aplicada, Universidad de Ciencias y Artes de Chiapas, Lib. Norte Pte. No.1150, Lajas Maciel, Tuxtla Gutiérrez, Chiapas, México. Oikos: Conservación y Desarrollo Sustentable, A.C., San Cristóbal de las Casas, Chiapas, México; acarrillo@oikos.org.mx Eduardo Espinoza-Medinilla: Sustentabilidad y Ecología Aplicada, Universidad de Ciencias y Artes de Chiapas, Lib. Norte Pte. No.1150, Lajas Maciel, Tuxtla Gutiérrez, Chiapas, México; eespinoza@unicach.edu.mx Sergio López-Mendoza: Sustentabilidad y Ecología Aplicada, Universidad de Ciencias y Artes de Chiapas, Lib. Norte Pte. No.1150, Lajas Maciel, Tuxtla Gutiérrez, Chiapas, México; slopez@unicach.edu.mx 1. Sustentabilidad y Ecología Aplicada, Universidad de Ciencias y Artes de Chiapas, Lib. Norte Pte. No.1150, Lajas Maciel, Tuxtla Gutiérrez, Chiapas, México; tamararioja@gmail.com, eespinoza@unicach.edu.mx, slopez@unicach.edu.mx 2. Oikos: Conservación y Desarrollo Sustentable, A.C., San Cristóbal de las Casas, Chiapas, México; acarrillo@oikos.org.mx
Received 04-XI-2011.Corrected 10-V-2012.Accepted 12-VI-2012.
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