A system for categorizing the distribution of the Mesoamerican herpetofauna. — Larry .. The Herpetofauna of Chiapas, Mexico: composition, distribution, and. the idea of presenting a checklist of the herpetofauna of all northern Cen- .. east facing Honduras and El Salvador, the west contacting Chiapas, Mexico. Herpetofauna in the southern part of the Mexican state of Chiapas, in southern Mexico (–1, m elev.; Fig. 1). .. Scientific collections in Chiapas state; 8.
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Flores-Villela; Patterns of richness and endemism of the Mexican herpetofauna, a matter of spatial scale?
The goal of this study was to compare the richness and endemism patterns of Mexican species of amphibians and reptiles at different spatial scales. We used the best available dataset of distributional ranges generated from ecological niche models and employed geographically weighted regressions GWRs to test whether richness and endemism were related.
Patterns were found to vary with the scale used for richness and endemism, and these patterns were not coincident. The results showed that: Mexico is a diverse country in many different respects, with amphibians and reptiles being especially prominent. There are species of amphibian known from the country, which corresponds to 5.
The diversity of amphibians and reptiles is higher at tropical latitudes IUCN, In Mexico, this latitudinal pattern of richness has been repeatedly observed e. Among individual terrestrial vertebrate groups in Mexico, the most species-rich areas i.
Traditionally, it has been thought that the cause of pattern richness is an abundance of resources, such as net hrepetofauna productivity e.
Based on previous studies, we assume that, if the factors behind the patterns of richness and endemism differ, these patterns at different scales do not necessarily have to retain similar congruence, because the causal factors of each pattern — richness or endemism — are operating at different scales. We assume that two groups with different characteristics, particular ecological requirements and dissimilar evolutionary histories will not share richness and endemism patterns, and that the factors that influence their distribution and the structure of their communities will be different.
The goal of this study is to independently analyse the influence of spatial scale on patterns of richness and endemism of Mexican amphibians and reptiles and then to compare these two groups of vertebrates.
We obtained geographical information herpetofauja specimens of Mexican amphibians and reptiles from various museums. This database contains records of Mexican amphibians and reptiles, including insular records.
Subspecies were not used in the analyses. Locality records for individual species were checked for geographical outliers and, in cases in which it appeared that a particular record was based on a misidentification or faulty locality date, it was removed from the database.
This was accomplished with the help of Arc View 3. A polygon was generated for the geographical distribution of each species. However, the use of prediction models to approximate ranges helps to reduce biases that may exist herrpetofauna the absence of samples or collections.
Although it is impossible to entirely eliminate these biases by modelling, it diminishes their influence on the results. To model ranges, there are a variety of algorithms that operate under different assumptions Peterson et al.
GARP also gives a binary output presence—absence mapwhich aids in making a consensus of maps. We generated an ecological niche model for individual species. We also included variables of aspect, slope, topographic index and model of digital elevation US Geological Survey, One hundred models were generated for each species, using different criteria depending on the number of unique locality records that herpegofauna available.
After obtaining the consensus in raster format, each consensus was converted to vector form shape.
Afterwards, consensus maps were sometimes trimmed based on a literature review and knowledge of the region. Distribution range maps are available at http: Based on the distribution ranges obtained, richness maps were generated at different scales for the two groups.
Intersections of each class were subsequently performed with grids in Arc View 3. The scale of values was homogenized into five groups, 1—10, 11—30, 31—50, 51—70 and 71—90, to compare patterns of richness and endemism between both groups. We performed geographically weighted regressions for each of the four scales analysed to analyse the relationship between richness and endemism, and to take into account the spatial structure of the patterns.
This method allowed us to explore non-stationary relationships among variables i. We report only the average and standard deviations of these coefficients. We obtained records useful for analysis.
About 30 museum records were determined to be in error, usually because their purported provenance was far removed from their known distribution. Valid records represented valid species.
We obtained an ecological niche model for of these species, whereas most of the remaining are microendemic and have few unique records less than fiveexcept for Elgaria nanawhich is restricted to the Coronados Islands, Baja California, and climatic layers were not available for that area. Supporting Information Table S3 provides complete information. Richness and endemism analyses are based on these models. Reptiles exhibit the richest areas between 71 and 90 species both west and east of the Isthmus of Tehuantepec and in central Guerrero.
Notably, areas of moderate richness are present along the Sierra Madre Oriental and Occidental. For comparative purposes, the scale of values located at the bottom of the figure was used in all cases. At a scale of 0. For reptiles, the richest areas 51—70 species are found from central Veracruz Los Tuxtlas region and central Guerrero Omiltemi—Chilpancingo region into southern Oaxaca and southward to central Chiapas Fig.
At the finest scale of 0. Two relatively large areas stand out for their reptile richness 51—70 species: Further, five small areas are notable for their richness in reptiles 51—70 species: Areas with the highest richness of species for both amphibians and reptiles are mountainous, although they differ in location between amphibians and reptiles.
Sufficient locality records were available to model of these. There are endemic species of reptile in Mexico, and available records allowed us to model of these.
Finally, at the finest scale of 0. Three other regions are noteworthy because of their number of endemic reptiles 31—50 species: The richest areas of endemism in both amphibians and reptiles are found at moderate elevations in temperate zones, similar to the areas harbouring the highest species richness, but varying according to changes in spatial scale.
Linear regression values showing richness and endemism at different scales are presented in Table 1. Values of the local regressions between richness and endemism in amphibians are slightly higher than those for reptiles.
Interestingly, for both groups, the lowest correlation between richness and endemism occurs at the finest spatial scale of 0. GWRs between richness and endemism, richness and latitude, and endemism and latitude follow the same pattern, decreasing as the spatial scale decreases.
The average of the local r 2 and the standard deviations from the GWR are reported to represent the general pattern. Variation of richness—endemism, richness—latitude and endemism—latitude relationships of amphibians and reptiles of Mexico at different spatial scales.
The values were calculated with linear models LM for richness—endemism for comparative purposes only, and with geographically weighted regression GWR for all.
We hepretofauna the mean and standard deviations of local r 2 of GWR. Wiens defined patterns as assertions that are made after many observations suggesting a particular conformation of the properties of the system under examination. The above analyses demonstrate that the diversity patterns, richness and endemism, vary depending on the spatial scale of analysis in both groups. Chipas the coarsest spatial scale maps for both amphibians and reptiles, it is possible to observe a clear latitudinal pattern of species richness Fig.
These results reinforce the herpftofauna of previous studies with these and other groups, where there is a latitudinal gradient of species richness i. Ruggiero stated that there are nerpetofauna least three theories that try to explain the hrpetofauna gradient in species richness from the regional approach. In the case of Mexico, where the herpetofaunal patterns show highest richness in the south, this is the portion of the country in which the mainland is narrower, and so it is reasonable to rule out this hypothesis.
In this sense, to herpetofaunw more species of reptile at the regional level nationwideone would expect local communities of reptiles to generally exhibit higher richness. This prediction is fulfilled at any locality size different spatial scalesand there is always a larger chuapas of species of reptiles than amphibians. However, to explain herpetofana patterns, this hypothesis becomes redundant because there are more species chiappas the equator.
At the herpeyofauna scale of 0. A decrease in the number of species occurs in reptiles towards the centre of the chiapzs, which is surrounded by relatively species-rich areas at moderate elevations in the mountains. However, it was not possible herpetfauna appreciate the subtleties in the pattern of richness in northern Mexico probably because of the lack of locality records in this region, which was amended using species distribution models based on ecological niche.
At an even finer scale of 0. As a result, it is very difficult to discern a pattern associated with latitude or Neotropical effects, and this suggests that historical factors have been more important than environmental factors as causes of species richness. In addition, considering patterns at different scales of values one for each spatial scalealpha areas may be distinguished, in which local richness is very important, and beta areas, in which replacement contributes more to regional richness see Supporting Information Figs S1, S2.
In the former, rich areas remain when decreasing the grid size, whereas, in the latter, rich areas are diluted with hwrpetofauna grid size. The highest patterns of richness were obtained in southern Mexico, and this suggests a close relationship between climate and latitude, and climate and elevation. In the second group, historical reasons play an important role. Flores-Villela noted that isolation and the variety of environmental conditions owing to rugged topography were primary factors contributing to the radiation and differentiation of herpetofauna species see also Smith et al.
Although there is a widespread feeling among researchers advocating that explanations associated with processes that generate patterns of distribution and therefore richness are general to a certain degree, there is evidence which supports the possibility that there may be more than one mechanism involved in the generation of these patterns Gaston et al. However, it is very likely herpetofquna, in this herpetofauns case, historical processes, the convergence of faunas and historical climatic changes are the main causes of the richness in Mexico.
Such is the case for the salamanders of Mesoamerica. As the determination of endemism in this case is referred to a political entity, it makes sense that the ranges of most endemic species do not coincide with political boundaries. However, the distributional pattern of endemic species richness in amphibians and reptiles diverges from the coarsest to the finest spatial scales. This result suggests that factors promoting endemism patterns differ between amphibians and reptiles or, as a result of their different ecologies, the same causal factor acts differently in each group.
Mountain formations probably acted as a filter for most Mexican herpetofauna, so that Mexico served as a barrier to invading species from the north and south, and only 23 species extend from the USA, through Mexico, and into Central America Flores-Villela, It has been suggested that variation in climate seasonality favours endemism, and climate stability favours richness, and this is associated with explosive reproductive modes occurring in environments with marked climatic seasonality Gentry, Along the Pacific Coast, the predominant vegetation type is tropical deciduous forest high seasonalitywhereas, on the Gulf Coast, the dominant vegetation is evergreen forest low seasonality.
This may explain the herrpetofauna Table 1 of the relationship between richness and endemism across the country. Nevertheless, heroetofauna other areas, it might be assumed that isolation and divergence have occurred at the level of entire communities because of the limited dispersal abilities of both groups.
If the previous theory of complete community speciation is correct, this would provide a satisfactory explanation for the relationship between richness and endemism in Mexico at all spatial scalesreflected in the high scores of herppetofauna GWRs Table 1. Patterns of species herptofauna and endemism of the amphibians and reptiles of Mexico have been studied by various researchers and a basic understanding of these patterns is beginning to emerge.
The level of taxonomic and biogeographical understanding and, especially, the integration of information relating to museum specimens have advanced significantly in recent years. All of this, together with new tools permitting the modelling of the distribution areas of the species, has allowed us to obtain a more complete picture and has led to the re-analysis from new perspectives of the patterns of diversity and endemism.
The use of different spatial scales to examine the patterns of richness and endemism of the Mexican herpetofauna is one of the central contributions of this article, and this is the first time that the effect of spatial scale on the observed patterns has been considered explicitly and systematically.