Mexico City is one of 32 federal entities in Mexico. It is the capital of the country. It is located between 19°35'34"N and 19°2'54"N, and 98°56'25"W and 99°2154'W. It is bordered by the State of Mexico to the north, east, and west, and by Morelos to the south (Fig. 2). It covers 1,485 km², which represents 0.1% of the total area of Mexico. The urban area of Mexico City is in the Valley of Mexico, a large valley in the high plateaus in the center of Mexico, at an altitude of 2,240 m (Figs 2, 3; INEGI 2017; https://en.wikipedia.org/wiki/Mexico_City – accessed 17 December 2019).

Figure 2. 

Map of Mexico with Mexico City shown in red (modified from INEGI 2018).

Figure 3. 

Topographical map of Mexico City, Mexico (Source: CONABIO 1997).

The topography of Mexico City is highly variable, including an extensive high plateau in the northern half of the city, where the urban area sits, and mountains and volcanoes that reach up to 3,930 m of altitude (Volcán Ajusco) that surround the urban area mainly on its southern and western sides (Fig. 3). Mexico City is located in the physiographic province of the Neovolcanic Axis, sub-province of Lagos and Volcanes of Anahúac. Mexico City is divided into an urban development area, usually referred to as urban land (41% of the territory, mostly on the northern half of the city), and an ecological conservation area, referred to as conservation land (59% of the territory, mostly on the southern half of the city). Urban land primarily consists of the urbanized plain area of the city, whereas conservation land includes areas with natural ecosystems (Reygadas-Prado 2016). Natural vegetation is primarily distributed in the conservation land, and in general terms it is represented by forests (55.6%), agricultural areas (35.8%), grasslands (7.17%), and scrublands (1.43%) (Fig. 4; INEGI 2017). According to the Köppen climate classification modified by García (1998), the climate of Mexico City is broadly divided into Subhumid Temperate with summer rains, covering much of the city (Fig. 5). A Semicold Subhumid climate with summer rains is present in the highest parts of the mountains that surround the city, from the west-central part running diagonally to the southeastern end on the border with Morelos; and Semiarid Temperate with summer rains present in the east-northeast end of the city, including the Sierra de Santa Catarina in the eastern part of the city and a considerable portion of the northeastern end of the city in the boroughs of Gustavo A. Madero, Venustiano Carranza, and Iztacalco (Fig. 5).

Figure 4. 

Vegetation map of Mexico City, Mexico (modified from Dirección General de Geografía; INEGI 2016).

Figure 5. 

Climate map of Mexico City, Mexico (modified from García and Comisión Nacional para el Conocimiento y Uso de la Biodiversidad 1998).

Reygadas-Prado (2016) provided a regionalization of Mexico City based on biophysical characteristics that consists of six regions. The Forests and Ravines region is made up of the largest and best-preserved forest massifs and ravines found in the south and southwest of the city, occupying an area of 532.4 km². The principal forests in this region are oak, pine-oak, and pine forests, with some cloud forest relics in the vicinity of the Dínamos de Contreras. The Wetlands of Xochimilco and Tláhuac region is found in the Chinampas area of Xochimilco, San Gregorio, San Luis Tlaxialtemanco, Tláhuac and the lowlands of Tláhuac, occupying an area of 60.3 km². This region is located in the east-central parts of the city. The Urban Parks and Gardens region includes parks, gardens, forests, protected natural areas, and areas of environmental value located on urban land, and occupies an area of 607.3 km². It is found in the northern half of the city, except for the Sierra de Guadalupe, and two areas in the central and eastern parts of the city that represent the Sierra de Santa Catarina region. This region includes the urbanized area of Mexico City. The Mountains of Xochimilco and Milpa Alta region is found between the Urban Parks and Gardens and the Forests and Ravines regions, and it occupies an area of 237.5 km². It runs from west-central to eastern Mexico City. It consists of an area of forests fragmented by housing developments; however, important areas of oak, pine-oak, and pine forests are located in this region. The Sierra de Guadalupe region is located in northern Mexico City and includes the protected natural areas of Sierra de Guadalupe, La Armella, and Tepeyac National Park and occupies an area of 12.9 km². Its characteristic vegetation is xerophilous scrub. The Sierra de Santa Catarina region, located in eastern and central Mexico City, occupies an area of 31.4 km². The vegetation here is similar to the Sierra de Guadalupe, with an important area of grassland and a greater number of tree species for reforestation (Fig. 6; Reygadas-Prado 2016).

Figure 6. 

Satellite map showing the topographic features of Mexico City (source: Comisión Nacional para el Conocimiento y Uso de la Biodiversidad 2003) and Regions of Mexico City according to Reygadas-Prado (2016): 1) Forests and Ravines; 2) Wetlands of Xochimilco and Tláhuac; 3) Urban Parks and Gardens; 4) Mountains of Xochimilco and Milpa Alta; 5) Sierra de Guadalupe; 6) Sierra de Santa Catarina.

Fifteen of the 18 species of amphibians found in Mexico City are endemic to Mexico. Two species are endemic to Mexico City (Eleutherodactylus grandis and Ambystoma mexicanum), one species has a spotty distribution in Mexico City and the State of Mexico, seven are distributed in central Mexico (Dryophytes plicatus [Brocchi, 1877], Ambystoma altamirani Dugès, 1895, Aquiloeurycea cephalica [Cope, 1865], Chiropterotriton orculus [Cope, 1865], Pseudoeurycea altamontana [Taylor, 1939], P. leprosa [Cope, 1869], and P. tlilicxitl Lara-Góngora, 2003), two are distributed in central Mexico and the Mexican Altiplano (Rana montezumae Baird, 1854, and Anaxyrus compactilis [Wiegmann, 1833]), one occurs in central Mexico, the Mexican Altiplano, the Sierra Madre Occidental, and the Sierra Madre Oriental (Dryophytes eximius [Baird, 1854]), and one occurs along the Neovolcanic Axis, the Sierra Madre Occidental, the Sierra Madre Oriental, and the Sierra Madre del Sur of Guerrero (Isthmura belli [Gray, 1850]). The three amphibian species not endemic to Mexico that inhabit Mexico City are species found in the United States and Mexico (Table 1). Twelve of the 14 species of lizards that occur in Mexico City are endemic to Mexico, six of the endemic species are restricted to a small area in the State of Mexico and Morelos and Mexico City, and in some cases the states of Puebla or Oaxaca (Sceloporus aeneus Wiegmann, 1828, S. anahuacus Lara-Góngora, 1983, S. mucronatus Cope, 1885, S. palaciosi Lara-Góngora, 1983, S. sugillatus Smith, 1942, and Plestiodon copei [Taylor, 1933]), and the other six endemics are widely distributed in the Neovolcanic Axis, including parts of the Sierra Madre Occidental, the Sierra Madre Oriental, and in some cases the Mexican Altiplano (Barisia imbricata [Wiegmann, 1828], Phrynosoma orbiculare [Linnaeus, 1758], Sceloporus scalaris Wiegmann, 1828, S. spinosus Wiegmann, 1828, S. torquatus Wiegmann, 1828, and Plestiodon brevirostris [Günther, 1860]). One of the non-endemic species ranges widely from southeastern United States, south through most of Mexico to southern Oaxaca (Sceloporus grammicus Wiegmann, 1828), and the other species ranges from central United States to Central America (Aspidoscelis gularis [Baird & Girard, 1852]) (Table 1). Twenty-one of the 29 species of snakes that inhabit Mexico City are endemic to Mexico. Of the eight snake species not endemic to Mexico that inhabit Mexico City, five are found in Canada and/or the United States and Mexico (Diadophis punctatus [Linnaeus, 1766], Micrurus tener Baird & Girard, 1853, Rena dulcis Baird & Girard, 1853, Thamnophis eques (Reuss, 1834), and Crotalus molossus Baird & Girard, 1853), one is found from Mexico to Central America (Pituophis lineaticollis [Cope, 1861]), and two range from the southern United States to Central America (Senticolis triaspis [Cope, 1866] and Thamnophis cyrtopsis [Kennicott, 1860]).

The most diverse region of the city is the Forests and Ravines region, which is home to 43 species (13 amphibians, 30 reptiles), which represents 70.5% of the species pool for the city. This region occupies the second place in the territorial area of the city with 534.4 km² (36.0% of the surface of Mexico City). This region is in the best conservation state and is where there is the possibility of rediscovering species known only from historical records such as Geophis bicolor Günther, 1868, Geophis petersii Boulenger, 1894, and Rhadinaea taeniata (Peters, 1863), or finding new species records such as for Eleutherodactylus nitidus (Peters, 1870), Exerodonta smaragdina (Taylor, 1940), and Tantilla bocourti (Günther, 1895). This region also has a high number of species listed in an IUCN protected category (7 amphibians, 1 reptile), listed in a SEMARNAT protected category (6 amphibians, 7 reptiles), and categorized as high risk by the EVS (7 amphibians, 15 reptiles). The second most diverse region of Mexico City is the Urban Parks and Gardens that hosts 34 species (13 amphibians, 21 reptiles). This region occupies the largest area of the city with 607.3 km² (40.9% of the surface of Mexico City). It is also the most populated region and is dominated by urban habitats, which are generally not suitable for most amphibians and reptiles. However, it has two important urban parks, the Pedregal de San Angel Ecological Reserve (REPSA) and the Chapultepec Forest, where the largest number of species has been recorded for this region. The number of species in this region listed in an IUCN protected category (6 amphibians, 2 reptiles), listed as protected by SEMARNAT (6 amphibians, 7 reptiles), and categorized as high risk by the EVS (6 amphibians, 8 reptiles) is also high. The Wetlands of Xochimilco and Tláhuac and the Mountains of Xochimilco and Milpa Alta, and the Sierra de Guadalupe host similar numbers of amphibian and reptile species and also have similar numbers of species included in the IUCN and SEMARNAT lists or categorized as high risk by the EVS. In the Wetlands of Xochimilco and Tláhuac, 20 species (6 amphibians, 14 reptiles) are present, of which four are listed by the IUCN, five by SEMARNAT, and 10 are categorized as high risk by the EVS. In the Mountains of Xochimilco and Milpa Alta, 19 species (6 amphibians, 13 reptiles) are found, of which two are listed by the IUCN, four by SEMARNAT, and nine are categorized as high risk by the EVS. In the Sierra de Guadalupe, 23 species (6 amphibians, 17 reptiles) occur, of which one is listed by the IUCN, five by SEMARNAT, and eight are categorized as high risk by the EVS. The Sierra de Santa Catarina region is like an island, a mountain with disturbed vegetation surrounded by urban habitats. It has an area of only 31.4 km² (2.1% of the area of Mexico City; Fig. 7) and harbors 13 species of reptiles. However, the government of Mexico City mentioned the presence of two amphibians and 14 reptiles, with only eight reptile species included in the SEMARNAT list (Gobierno del Distrito Federal [= Mexico City] 2005). None of the reptile species in this region are included in the IUCN list, three are in the SEMARNAT list, and four are categorized as high risk by the EVS. Our observations of the distribution of amphibians and reptiles in Mexico City are broadly consistent with the findings of García Vázquez and Méndez de la Cruz (2016) and García Vázquez et al. (2016).

Eleven of the 63 species (17.5%) of amphibians and reptiles in Mexico City are included in the IUCN Red List (i.e., Vulnerable, Near Threatened, or Endangered), 17 (27.0%) are placed in a protected category (excluding NL and Pr, this last category is equivalent to the LC category of IUCN) by SEMARNAT, and 27 species (42.9%) are categorized as high risk by the EVS (Fig. 8; Table 2). For amphibians, 38.9% (7 of 18 species) are included in the IUCN Red List and are protected by SEMARNAT, and 50.0% (9 species) are at high risk according to the EVS (Fig. 8; Table 2). For reptiles, 4.4% (2 of 45 species) are listed by the IUCN, 22.2% (10 species) are protected by SEMARNAT, and 40.0% (18 species) are at high risk according to the EVS (Fig. 8; Table 2). These results suggest that the amphibians of Mexico City are considered to be of relatively high conservation concern at a global and national scale (IUCN and SEMARNAT lists), but there are even greater conservation concerns based on the EVS. The limited distribution of half of the amphibian species that inhabit Mexico City, coupled with the loss of available habitat, places them in a delicate conservation status. For example, the Axolotl, Ambystoma mexicanum, which is listed as Critically Endangered by the IUCN and In Danger of Extinction by SEMARNAT, currently appears to be limited to Lake Xochimilco and faces threats such as introduced predators, illegal collection, and pollution (Griffiths et al. 2004; Contreras et al. 2009; Recuero et al. 2010). On the other hand, reptiles are of lesser conservation concern than amphibians according to the IUCN and SEMARNAT lists, but not the EVS list (Fig. 8), which is a reflections that EVS uses more variables in determining country-level conservation status than either the IUCN or SEMARNAT (see Wilson et al. 2013a, 2013b).

Figure 8. 

Percentage of species included in the IUCN Red List or listed by SEMARNAT, and the Environmental Vulnerability Score (EVS). A Amphibians B reptiles. Green is percentage in Data Deficient and Least Concern (IUCN); Not Listed and Subject to Special Protection (we regarded the category of Subject to Special Protection in SEMARNAT equivalent to IUCN’s Least Concern) (SEMARNAT); low and medium EVS. Red is percentage in protected categories or high EVS. N is the number of species assessed by each agency.

Mexico City shares more than 90% of its species (59 of 63 species = 93.7%, Table 4), with the State of Mexico, such that the herpetofauna of Mexico City is practically contained in that of the State of Mexico. Both the city and state are in the Basin of Mexico, which is included in the physiographic province of the Neovolcanic Axis, and all of Mexico City belongs to the sub-province of Lagos y Volcanes de Anáhuac, which also forms a part of the State of Mexico. Thus, the topographic and physiographic characteristics shared by these two entities result in a great similarity of their biological diversity, including their herpetofaunas. Additionally, the State of Mexico surrounds Mexico City on three sides (west, north, and east), and this, coupled with the small territorial area of Mexico City, results in a nesting of the species richness of Mexico City in the species richness of the State of Mexico. There are four species that Mexico City does not share with the State of Mexico. These include Eleutherodactylus grandis, which is limited to the Pedregal de San Angel in the Urban Parks and Gardens region; Ambystoma mexicanum, currently limited to two wild populations, one in the channels of Lake Xochimilco and a second in the remnants of Lake Chalco, both in southern Mexico City, where it faces serious conservation problems (Zambrano-González et al. 2003; Recuero et al. 2010); Geophis petersi, a snake with secretive habits, which is difficult to find and known only from the type series; and Rena dulcis, reported by Méndez de la Cruz et al. (2007, 2009) in the Pedregal de San Angel.

Geophis petersi was collected by H. Doorman in 1868 and its type locality at Mexico City was questioned and restricted to Pátzcuaro, Michoacán by Smith and Taylor (1950); however, Downs (1967) pointed out that this restriction was unjustified and that the presence of G. petersi at the southern tip of the Mexican Altiplano seems reasonable. Due to the secretive habits and presence of similar habitats in the State of Mexico, it is possible that G. petersi also inhabits the State of Mexico but not yet recorded from there. A similar situation occurs for R. dulcis, the other species not yet recorded in the State of Mexico, but due to its secretive habits and tiny size, this snake might also likely occur in the State of Mexico.

Mexico City shares 49 of its amphibians and reptiles with Morelos (77.8%; Table 4). The lower percentage of shared species compared to the State of Mexico is partly due to the fact that Morelos is not within the Basin of Mexico; however, part of it is included in the physiographic province of the Neovolcanic Axis, subprovince of Lagos y Volcanes de Anáhuac. In addition, less temperate forest is present in Morelos, and Morelos is smaller compared to the State of Mexico (Lemos-Espinal and Smith 2020). These characteristics result in fewer species shared with Morelos than with the State of Mexico. Seven of the 14 species that Mexico City does not share with Morelos probably inhabit this latter state, but they have not been recorded yet (Ambystoma velasci, Sceloporus anahuacus, Diadophis punctatus, Geophis bicolor, G. petersi, Thamnophis melanogaster, and T. pulchrilatus) (Lemos-Espinal and Smith 2020).