Habitat, water quality or geomorphological degradation in the streams: Which is most important for conserving an endemic amphibian of Central Mexico?

Amphibians are one of the most vulnerable vertebrate groups globally as a consequence of pollution and habitat degradation. To explore the environmental and anthropogenic variables that are currently influencing amphibian distribution in central Mexico, we used the Mexican endemic Mountain salamander (Ambystoma ordinarium) as a model. In particular, we evaluated which physicochemical water quality variables, river geomorphological structure, and habitat conditions provide the better environment for A. ordinarium populations. We generated a Multiple Factor Analysis model to identify the relationship of the different variables simultaneously. Our results showed a higher number of salamanders and better body condition animals in conserved sites. The change in the riverbed́s physical structure by increasing degradation influenced water quality and the substratés particle size. Changes included reducing the slope and water velocity, consequently decreasing dissolved oxygen content, increasing turbidity, dissolved solids, and particle embeddedness. This made habitat less suitable for Ambystoma. Results from the classification and regression tree model suggest that the most important variables related to higher salamandeŕs abundance were riverbed stability>12.5 and the slope bigger than 0.016. Also, individuals with better body condition were found in sites with slopes bigger than 0.02 and wider riparian vegetative zones (>3). Our study suggests that habitat deterioration by anthropogenic activities, such as deforestation of riparian vegetation, cattle ranching, and agriculture, that mainly impact the slope and flood-prone areas may start a detrimental cascade that may lead to local extinctions of the Mountain salamander. Therefore, to safeguard A. ordinarium, we first need to conserve their habitat, focusing the efforts not only on the riverbed, but also on the vegetation associated with the riverbank. The study provides insight into important variables that may be considered for future restoration projects for the A. ordinarum, emphasizing the zones in the rivers where these projects could occur.