Evidence of niche shift and invasion potential of Lithobates catesbeianus in the habitat of Mexican endemic frogs.

Invasive alien species are one of most severe threats to biodiversity and natural resources. These biological invasions have been studied from the niche conservatism and niche shifts perspective. Niche differentiation may result from changes in fundamental niche or realized niche or both; in biological invasions, niche differences between native and non-native ranges can appear through niche expansion, niche unfilling and niche stability. The American bullfrog Lithobates catesbeianus is an invasive species that can have negative impacts on native amphibian populations. This research examines the climate niche shifts of this frog, its potential range of expansion in Mexico and the risk of invasion by bullfrog in the habitats of 82 frog species endemic to Mexico, that based on their climatic niche similarity were divided in four ecological groups. The results indicate that species in two ecological groups were the most vulnerable to invasion by bullfrog. However, the climate niche shifts of L. catesbeianus may allow it to adapt to new environmental conditions, so species from the two remaining groups cannot be dismissed as not vulnerable. This information is valuable for decision making in prioritizing areas for conservation of Mexican endemic frogs.

Evaluación de análisis de endemicidad y PAE para identificar trazos generalizados, a partir de las serpientes del estado de Hidalgo, México / Evaluation of PAE and endemicity analysis for identifying generalized tracks using snakes in Hidalgo, Mexico

Resumen:Uno de los conceptos centrales en la Panbiogeografía es el trazo generalizado, el cual representa una biota ancestral que se ha fragmentado por eventos geológicos y puede recuperarse a través de distintos métodos, que incluyen el análisis de simplicidad de endemismos (PAE) y el análisis de endemicidad (AE). El PAE es un método frecuentemente utilizado para la identificación de trazos generalizados, mientras que el AE fue diseñado para encontrar áreas de endemismo, pero recientemente se ha usado también para identificar trazos generalizados. En este trabajo se evaluaron ambos métodos para la identificación de los trazos generalizados a partir de los datos de 84 serpientes distribuidas en el estado de Hidalgo, México. Con el PAE se obtuvo un trazo generalizado formado por tres trazos individuales (Agkistrodon taylori, Crotalus totonacus y Pliocercus elapoides), que corresponden a sinapomorfías que apoyan al clado principal. La prueba de robustez estadística mostró un soporte del 89 %, mientras que con el AE se identificaron dos áreas de endemismo con valores del índice de endemicidad de 2.71-2.96 y 2.84- 3.09 respectivamente, las cuales fueron transformadas a trazos generalizados; el primero formado por tres trazos individuales (Micrurus bernadi, Rhadinaea marcellae y R. quinquelineata) y el segundo formado por dos trazos individuales (Geophis mutitorques y Thamnophis sumichrasti). Estos trazos generalizados pueden considerarse un solo patrón de distribución, dada la cercanía geográfica y su topología. Al compararse los métodos se observó que ambos son útiles para la identificación de trazos generalizados, y aunque son independientes, se sugiere su uso de manera complementaria. Sin embargo, para una correcta aplicación e interpretación de los resultados, es necesario considerar las bases teóricas de cada método, así como la correcta elección del tamaño de las unidades de estudio. En el caso particular del AE si se utilizan tamaños de celda pequeños éstos pueden resultar ideales para la búsqueda de patrones biogeográficos a través de límites geopolíticos y esta información puede favorecer la realización de pro- puestas de conservación a nivel estatal que consideren a las especies con distribuciones restringidas, pues la pérdida de éstas representaría la extinción de linajes únicos.

Abstract:One of the most important concepts in Panbiogeography is the generalized track, which represents an ancestral biota fragmented by geological events that can be recovered through several methods, including Parsimony analysis of endemicity (PAE) and endemicity analysis (EA). PAE has been frequently used to identify generalized tracks, while EA is primarily designed to find areas of endemicity, but has been recently proposed for identifying generalized tracks as well. In this study we evaluated these methods to find generalized tracks using the distribution of the 84 snake species of Hidalgo. PAE found one generalized track from three individual tracks (Agkistrodon taylori, Crotalus totonacus and Pliocercus elapoides), supported by 89 % of Bootstrap, and EA identified two generalized tracks, with endemicity index values of 2.71-2.96 and 2.84-3.09, respectively. Those areas were transformed to generalized tracks. The first generalized track was retrieved from three individual tracks (Micrurus bernadi, Rhadinaea marcellae and R. quinquelineata), and the second was recovered from two individual tracks (Geophis mutitorques and Thamnophis sumichrasti). These generalized tracks can be considered a unique distribution pattern, because they resembled each other and agreed in shape. When comparing both methods, we noted that both are useful for identifying generalized tracks, and although they can be used independently, we suggest their complementary use. Nevertheless, to obtain accurate results, it is useful to consider theoretical bases of both methods, along with an appropriate choice of the size of the area. Results using small-grid size in EA are ideal for searching biogeographical patterns within geopolitical limits. Furthermore, they can be used for conservation proposals at state level where endemic species become irreplaceable, and where losing them would imply the extinction of unique lineages. Rev. Biol. Trop. 64 (4): 1611-1624. Epub 2016 December 01.

Beta Diversity in a Highly Heterogeneous Area: Disentangling Species and Taxonomic Dissimilarity for Terrestrial Vertebrates.

Quantifying differences in species composition among communities provides important information related to the distribution, conservation and management of biodiversity, especially when two components are recognized: dissimilarity due to turnover, and dissimilarity due to richness differences. The ecoregions in central Mexico, within the Mexican Transition Zone, have outstanding environmental heterogeneity and harbor huge biological richness, besides differences in the origin of the biota. Therefore, biodiversity studies in this area require the use of complementary measures to achieve appropriate information that may help in the design of conservation strategies. In this work we analyze the dissimilarity of terrestrial vertebrates, and the components of turnover and richness differences, among six ecoregions in the state of Hidalgo, central Mexico. We follow two approaches: one based on species level dissimilarity, and the second on taxonomic dissimilarity. We used databases from the project "Biodiversity in the state of Hidalgo". Our results indicate that species dissimilarity is higher than taxonomic dissimilarity, and that turnover contributes more than richness differences, both for species and taxonomic total dissimilarity. Moreover, total dissimilarity, turnover dissimilarity and the dissimilarity due to richness differences were positively related in the four vertebrate groups. Reptiles had the highest values of dissimilarity, followed by mammals, amphibians and birds. For reptiles, birds, and mammals, species turnover was the most important component, while richness differences had a higher contribution for amphibians. The highest values of dissimilarity occurred between environmentally contrasting ecoregions (i.e., tropical and temperate forests), which suggests that environmental heterogeneity and differences in the origin of biotas are key factors driving beta diversity of terrestrial vertebrates among ecoregions in this complex area.

[Evaluation of PAE and AE for identifying generalized tracks using snakes in Hidalgo, Mexico]. / Evaluación de análisis de endemicidad y PAE para identificar trazos generalizados, a partir de las serpientes del estado de Hidalgo, México.

One of the most important concepts in Panbiogeography is the generalized track, which represents an ancestral biota fragmented by geological events that can be recovered through several methods, including Parsimony analysis of endemicity (PAE) and endemicity analysis (EA). PAE has been frequently used to identify generalized tracks, while EA is primarily designed to find areas of endemicity, but has been recently proposed for identifying generalized tracks as well. In this study we evaluated these methods to find generalized tracks using the distribution of the 84 snake species of Hidalgo. PAE found one generalized track from three individual tracks (Agkistrodon taylori, Crotalus totonacus and Pliocercus elapoides), supported by 89 % of Bootstrap, and EA identified two generalized tracks, with endemicity index values of 2.71-2.96 and 2.84-3.09, respectively. Those areas were transformed to generalized tracks. The first generalized track was retrieved from three individual tracks (Micrurus bernadi, Rhadinaea marcellae and R. quinquelineata), and the second was recovered from two individual tracks (Geophis mutitorques and Thamnophis sumichrasti). These generalized tracks can be considered a unique distribution pattern, because they resembled each other and agreed in shape. When comparing both methods, we noted that both are useful for identifying generalized tracks, and although they can be used independently, we suggest their complementary use. Nevertheless, to obtain accurate results, it is useful to consider theoretical bases of both methods, along with an appropriate choice of the size of the area. Results using small-grid size in EA are ideal for searching biogeographical patterns within geopolitical limits. Furthermore, they can be used for conservation proposals at state level where endemic species become irreplaceable, and where losing them would imply the extinction of unique lineages.