Ireri Suazo-Ortuño

High Resilience of Herpetofaunal Communities in a Human-Modified Tropical Dry Forest Landscape in Western Mexico:

Secondary forests are replacing mature primary forests in the tropics because of increasing demand for agricultural land to support the growing human population. It is important to determine the potential of these secondary forests to support old-growth forest species, particularly threatened animal groups such as reptiles and amphibians. Moreover, existing studies are biased towards tropical rain forests, even though tropical dry forests (TDF) are comparatively more threatened. Here we examine how different TDF successional stages support old-growth forest species of amphibians and reptiles in the Chamela region, western Mexico. Over the course of two years we conducted seven surveys for amphibians and reptiles in 15 one-ha plots representing four different stages of the succession chronosequence of the TDF, ranging from pasture to old-growth forest. We found that anurans, lizards and snakes did not differ greatly in abundance and species richness among vegetation successional stages. Moreover, dominant species were shared among most of the vegetation stages, indicating low habitat specialization. Herpetofauna species composition did not differ among vegetation stages, and species turnover among stages was relatively low. These results differ greatly from those found in some tropical rainforest sites, where characteristics of herpetofauna communities differ markedly among vegetation successional stages. Our results suggest that secondary TDF in human-dominated landscapes might support substantial reptile and amphibian diversity.

DIET OF THE MEXICAN MARBLED TOAD (BUFO MARMOREUS) IN CONSERVED AND DISTURBED TROPICAL DRY FOREST

Abstract We collected data on diet of the marbled toad (Bufo marmoreus) on conserved and disturbed areas of tropical dry forest on the coast of Jalisco, Mexico, during 2000 and 2001. Although the diet of B. marmoreus consisted of 19 prey taxa, the moderately low dietary diversity measure (H′ = 1.51) reflected the dominance in the diet of only 3 groups of prey: ants, beetles, and termites. Toads in the conserved area consumed greater proportions of ants (36.7% by volume), whereas toads in disturbed forest consumed greater proportions of beetles (53.1% by volume). Diet diversity was significantly lower in the disturbed area. However, abundance, size, and weight of toads was similar in both areas, suggesting that prey availability was not affected by disturbance.

Predicting Ambystoma ordinarium Habitat in Central Mexico Using Species Distribution Models

Abstract Amphibian diversity in Neotropical mountains habitats is at risk, particularly those species associated with stream habitats at altitudes >500 m above sea level (a.s.l.). This pertains especially to the amphibian diversity of Mexico, where the number of species is high on the central and southwestern highlands. In the present study, we predicted the potential distribution of Ambystoma ordinarium using a Geographic Information System modeling approach. We used survey data from 2013 to 2015 and historical data reported in databases and literature, and employed environmental variables from the WorldClim–Global Climate Data Project. Our results indicate that a single factor, Mean Diurnal Range, contributed most to the model, followed by other factors (Minimum Temperature of the Coldest Month and Precipitation of the Driest Month). The conservative predicted distribution was 5256 km2, especially in areas have dynamic aquatic ecosystems (e.g., small streams). The highest probability of occurrence of the species at locations of 1900–2900 m a.s.l., with 13.7–16.3°C diurnal terrestrial air temperatures, and annual precipitation of 829–1454 mm. In these areas, native forest vegetation has decreased by almost 250 km2, and native grassland by 280 km2. Agricultural activities, human settlements, and secondary succession vegetation increased by 160, 120, and 330 km2, respectively. We infer that A. ordinarium is susceptible to changes in habitat, with most of the constraint on the distribution of this species arising from deforestation, increased urbanization and agricultural activities. Based on our model, and a recent genetic study, we suggest that the population of this species from lower elevations could be considered a different taxon. Consequently, the relative species distribution boundaries should be redefined, and appropriate monitoring programs redesigned to support conservation of the Michoacan stream salamander.

Habitat quality affects the incidence of morphological abnormalities in the endangered salamander Ambystoma ordinarium

Identification of early warning signals previous to the occurrence of population decline or extinction is a major challenge for the conservation of animal species. Prevalence of morphological abnormalities in a population can be one of these signals. We registered morphological abnormalities in the salamander Ambystoma ordinarium. We also evaluated the relation between habitat quality and the prevalence of abnormalities in this species. We used scores from rapid bioassessment protocols (RBPs) to assess the habitat quality of streams inhabited by A. ordinarium. A preliminary survey indicated that of 29 streams where this species has been historically registered, 13 might have few or no A. ordinarium. The association between habitat quality and the incidence of morphological abnormalities was evaluated in these 16 streams. Of 502 sampled individuals, 224 (44.62%) had at least one body abnormality. Of the 224 individuals with body abnormalities, 84 (37.5%) presented more than one abnormality. Of a total of 5,522 evaluated morphological characters, 344 (6.74%) were abnormal. Partial loss of gills and missing digits were the most frequent abnormalities. Results of a binomial logistic regression indicated that the probability of a character of an individual to be abnormal was significantly associated with habitat quality; as the levels of the quality of the habitat increased, the prevalence of morphological abnormalities decreased. These results suggest that RBPs are a quick and useful method for assessing the habitat quality of streams inhabited by A. ordinarium. Given that RBPs provide rapid and cost-effective assessments of the ecological health of aquatic ecosystems, it will be important to test if the RBPs protocols can be used to rapidly assess habitat quality for other species of stream amphibians. The negative association between habitat quality and the prevalence of morpohological abnormalities that we found indicates that habitat condition plays an important role in the high number of abnormalities registered in A. ordinarium. Therefore, our results suggest that one of the several negative effects of habitat degradation on amphibians is an increase in the frequency of morphological abnormalities with marked consequences for the survival and general fitness of aquatic amphibians.