A conservation checklist of the amphibians and reptiles of Mexico City, with comparisons with adjoining states

Abstract Mexico City houses one of the most populous urban areas of the world, and the modification of its natural habitat likely influences the biological diversity found there. In particular, amphibians and reptiles are likely affected by these modifications. Herein, we present an updated list of the species of amphibians and reptiles that inhabit Mexico City. Mexico City harbors 65 species of amphibians and reptiles, which represent 21 families and 33 genera. These include 18 species of amphibians (nine anurans and nine salamanders) and 47 species of reptiles (14 lizards, 30 snakes [one introduced], and three turtles [one introduced]). Forty-eight of the amphibian and reptile species in Mexico City are endemic to Mexico, with two endemic to Mexico City. The most diverse region of Mexico City is the Forests and Ravines region, which is home to 43 species. Eleven species of amphibians and reptiles in Mexico City are IUCN listed, 16 are placed in a protected category by SEMARNAT (Secretaria del Medio Ambiente y Recursos Naturales), and 27 species are categorized as high risk by the EVS (Environmental Viability Score). Mexico City shares almost 94% of its species with the State of Mexico.


introduction
Since pre-Hispanic times the Basin of Mexico, upon which Mexico City (formerly Mexico, Distrito Federal) sits, caught the attention of the inhabitants of central Mexico. This large lake surrounded by fertile land was the location of important human settlements that, at the arrival of the Spaniards, were represented mainly by Tenochtitlan, which along with a large number of villages located around the basin reached over a million inhabitants (Wikipedia: https://es.wikipedia.org/wiki/Ciudad_ de_M%C3%A9xico -accessed 27 December 2019). At the arrival of the Spaniards, in 1519, the basin was occupied by a well-developed civilization whose economy revolved around the Chinampas that surrounded the lake (Fig. 1). With the Spanish conquest of Mexico, cattle were introduced to the basin and a radical transformation began, including the drying of the Basin and the felling of the forests that surrounded it. The population around the Basin began to decline to such extent that at the end of the 18 th century the number of inhabitants in Mexico City was only 120,000. It was not until the middle of the 20 th century that the population explosion began creating diverse and complex problems that today overwhelm Mexico City (Imaz 1989). Currently the population of Mexico City is approximately 8.9 million inhabitants; however, including the metropolitan area of the Valley of Mexico, which extends over the Basin of Mexico, the population totals 22 million inhabitants, the ninth most populated urban area in the world, and the largest in the Americas (Wikipedia: https://es.wikipedia.org/ wiki/Ciudad_de_M%C3%A9xico -accessed 27 December 2019).
The urban area of Mexico City covers almost the whole northern half of Mexico City sensu lato (previously Distrito Federal) and is rapidly expanding (e.g., Hernández-Flores et al. 2017), including through illegal development (Rodríguez López et al. 2017). The southern half of Mexico City sensu lato is occupied by mountains and ravines covered by extensive forests and grasslands, some of them highly fragmented by housing developments and cultivated fields. The air pollution is such that the governments of Mexico City and the State of Mexico created a program at the end of 1989 that limits motor vehicle use in the city. However, air pollution continued to increase despite the initial restrictions, and currently there are increased limitations on vehicle use. Spaces for new residential development within the city are fewer and the population continues to grow and demand more resources, increasing the production of waste, the emission of greenhouse gases, the number of fires, the illegal occupation of protected areas, and the depletion of available natural resources (Santibáñez-Andrade et al. 2015;SEMARNAT 2016;Heider et al. 2018). Increased urbanization around Mexico City proper has also affected rivers and streams (Caro-Borrero et al. 2016). This considerable modification of the natural habitat exerts a constant pressure on the biological diversity of Mexico City. Amphibians and reptiles are strongly affected by these changes, and there are species whose presence in Mexico City is known only from their original records (e.g., Geophis bicolor and G. petersi), or whose conservation status is quite tenuous (e.g., Eleutherodactylus grandis, Rana tlaloci, Ambystoma mexicanum, and Crotalus transversus).
Herein, we present an updated list of amphibians and reptiles that inhabit Mexico City in an effort to disseminate important information about its herpetofauna to help in their conservation. Previous recent efforts to catalog the herpetofauna of Mexico City reported a list of 18 species of amphibians and 39 species (one of them introduced) of reptiles from Mexico City (García-Vázquez and Méndez-de la Cruz 2016; García-Vázquez et al. 2016).

Physiographic characteristics
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 km 2 , 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).
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%), ag-  ricultural 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).
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 km 2 . 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 km 2 . 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 km 2 . 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 km 2 . 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 km 2 . Its characteristic vegetation is xerophilous scrub. The Sierra de Santa Catarina

Materials and methods
We compiled our list of amphibians and reptiles for Mexico City using our fieldwork, a thorough examination of the literature, records from VertNet.org and Servicio de Descarga de Ejemplares del Sistema Nacional de Información sobre Biodiversidad (SNIB-CONABIO): Amphibians Ciudad de México and Reptiles Ciudad de México data bases. We included species in the list if they had confirmed records, either by direct observation, literature report, or through documented museum records or vouchers. We follow Frost (2020) and AmphibiaWeb (2020) for amphibian names and Uetz and Hošek (2019) for reptile names. We did not include some of the species in the Rüthling collection (AMNH) for Mexico City, as that collection includes specimens from a German School Collection, from Mexico City. These were donated to Rüthling, namely Sonora michoacanensis mutabilis Stickel, 1943 (paratypes: AMNH R-19714-6), Trimorphodon tau tau (Cope, 1870) (AMNH R-19718), Micrurus elegans elegans (Jan, 1858) (AMNH R-19720), and Thamnophis proximus (Say, 1823) (AMNH R-19809-10), but do not occur in Mexico City. In addition, some of the specimens in the German School Collection obtained by Rüthling were most likely not collected in Mexico City (Zweifel 1959). However, some of the specimens in the German School Collection donated to Rüthling could have been collected in Mexico City (e.g., Senticolis triaspis (Cope, 1866) [AMNH R-19838]), as there are two more records of this species in other collections: BMNH 1868.4.7.16 collected by Doorman and reported by Günther (1894: 115) and ENCB-IPN 7398 from San Gregorio, Xochimilco). Other specimens from the Rüthling collection donated by the German School are likely to occur in Mexico City (e.g., Tantilla bocourti (Günther, 1895) [AMNH R-19735]), but as no other records of the species are available, we decided not to include this species in our list.
We created species accumulation curves for the total herpetofauna, as well as amphibians and reptiles separately, using the year of the first recorded observation for each species. Such species accumulation curves likely provide a good estimate of potential herpetofaunal richness (see Raxworthy et al. 2012). In addition, we recorded the conservation status of each species based on the IUCN Red List 2019-2 (IUCN 2019), SEMARNAT (2019), and Environmental Vulnerability Scores from Wilson et al. (2013a, b) and Johnson et al. (2015). We determined the number of overlapping species with the two states that neighbor Mexico City using recent state lists (State of Mexico, Lemos-Espinal and Smith in press; Morelos, Lemos-Espinal and Smith in 2020).

Results and discussion
Mexico City harbors 65 species of amphibians and reptiles, which represent 21 families (two introduced: Typhlopidae Merrem, 1820 and Emydidae [Rafinesque, 1815]) and 33 genera (two introduced: Indotyphlops Hedges, Marion, Lipp, Marin & Vidal, 2014 and Trachemys Agassiz, 1857) (Tables 1, 2). These include 18 species of amphibians (nine anurans and nine salamanders) and 47 reptiles (14 lizards, 30 snakes [one introduced], and three turtles [one introduced]). It appears that this list of amphibian and reptile species is likely fairly complete given the shape of the species accumulation curves (Fig. 7). The species accumulation curves indicate a rapid accumulation of species in the late 1800s, followed by a slow gradual increase in species throughout the 20 th and early 21 st centuries, with a leveling off in recent years.
The two introduced species are Brahminy Blindsnake, Indotyphlops braminus (Daudin, 1803), and Huastecan Slider, Trachemys venusta (Gray, 1855). Two of the 63 native species are endemic to Mexico City: Great Piping Frog, Eleutherodactylus grandis (Dixon, 1957), and Axolotl, Ambystoma mexicanum (Shaw & Nodder, 1798). The latter species originally inhabited lakes in the State of Mexico and Mexico City but is currently only known from the remnants of Lake Xochimichilco (Frost 2020). The most species-rich amphibian family is Plethodontidae Gray, 1850, and the most species-rich reptile family is Phrynosomatidae Fitzinger, 1843 (Table 1).
We compiled a list of eight species (six amphibians, two reptiles: Table 3) that potentially occur in Mexico City based on their distribution along the border with Morelos and the State of Mexico. We used distributional records in Vertnet.org and the Sistema Nacional de Información sobre Biodiversidad (SNIB-CONABIO) for the two neighboring states and Mexico City to generate this list. As more herpetological work is done near the borders with the neighboring states, we believe that these "likely to occur" species will be recorded for Mexico City.

General distribution
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, andAnaxyrus 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 [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] [Kennicott, 1860]).

Habitat types
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 table 1. Amphibians and reptiles of Mexico City with distributional and conservation status. Region: (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) according to Reygadas-Prado (2016). Species with asterisk (Geophis bicolor and G. petersii), are records without a specific locality, assigned to a region that we consider the best fit, and species with a question mark (Lampropeltis polyzona and Micrurus tener) are records without a specific locality representing species with a wide range of habitat use, such that is not possible to assign them to a specific region.  pool for the city. This region occupies the second place in the territorial area of the city with 534.4 km 2 (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 (Tay-lor, 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 km 2 (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 (

Conservation status
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 SE-MARNAT 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. 2013aWilson et al. , 2013b.

Comparison with neighboring states
Mexico City shares more than 90% of its species (59 of 63 species = 93.7%,  (Taylor, 1940) southern Mexico City Tlalocohyla smithii (Boulenger, 1902) southern Mexico City Family Ranidae Rana spectabilis Hillis & Frost, 1985 southern Mexico City Class Reptilia Order Squamata Suborder Lacertilia Family Scincidae Plestiodon indubitus (Taylor, 1933) southern Mexico City Suborder Serpentes Family Colubridae Tantilla bocourti (Günther, 1895) southern Mexico City table 4. Summary of the numbers of species shared between Mexico City and neighboring Mexican states (not including introduced species). The percent of Mexico City species shared by a neighboring state are given in parentheses. Total refers to the total number of species found in Mexico City and two neighboring states (i.e., regional species pool) and the number in parentheses in this column is the percent of the regional species pool found in Mexico City. -indicates either Mexico City or the neighboring state has no species in the taxonomic group, or none of that specific taxon is shared between the states, thus no value for shared species is provided. 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. (2007Cruz et al. ( , 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).