Javier Alvarado-Díaz

Effects of Conversion of Dry Tropical Forest to Agricultural Mosaic on Herpetofaunal Assemblages

We explored the impact of forest conversion to agricultural mosaic on anuran, lizard, snake, and turtle assemblages of Neotropical dry forests. Over 2 years, we sampled 6 small watersheds on the west coast of Mexico, 3 conserved and 3 disturbed. The disturbed watersheds were characterized by a mosaic of pastures and cultivated fields (corn, beans, squash) intermingled with patches of different successional stages of dry forest. In each watershed, we conducted 11 diurnal and nocturnal time-constrained searches in 10 randomly established plots. We considered vulnerability traits of species in relation to habitat modification. Eighteen anuran, 18 lizard, 23 snake, and 3 turtle species were recorded. Thirty-six species (58%) occurred in both forest conditions, and 14 (22%) and 12 species (19%) occurred only in the conserved and disturbed sites, respectively. Assemblages responded differently to disturbance. Species richness, diversity, and abundance of lizards were higher in disturbed forests. Anuran diversity and species richness were lower in disturbed forest but abundance was similar in both forest conditions. Diversity, richness, and abundance of turtles were lower in disturbed forest. The structure and composition of snake assemblages did not differ between forest conditions. We considered species disturbance sensitive if their abundance was significantly less in disturbed areas. Four anuran (22%), 2 lizard (11%), and 3 turtle (100%) species were sensitive to disturbance. No snake species was sensitive. The decline in abundance of disturbance-sensitive species was associated with the reduction of forest canopy cover, woody stem cover, roots, and litter-layer ground cover. Anuran species with small body size and direct embryonic development were especially sensitive to forest disturbance. An important goal for the conservation of herpetofauna should be the determination of species traits associated with extinction or persistence in agricultural mosaics.

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.

A NEW MONTANE RATTLESNAKE (VIPERIDAE) FROM MICHOACAN, MEXICO

A new species of rattlesnake is described from the upper elevations of Cerro Tancítaro in Michoacán, in the western portion of the Transverse Volcanic Cordillera. This diminutive rattlesnake appears to be most closely related to several species also occurring at high elevations in Mexico and the southwestern United States including Crotalus intermedius, C. pricei, and C. transversus. The Tancítaro species is most similar to C. transversus, but differs in aspects of lepidosis and color pattern.

Multilocus species delimitation in the Crotalus triseriatus species group (Serpentes: Viperidae: Crotalinae), with the description of two new species

Members of the Crotalus triseriatus species group of montane rattlesnakes are widely distributed across the highlands of Mexico and southwestern USA. Although five species are currently recognized within the group, species limits remain to be tested. Genetic studies suggest that species may be paraphyletic and that at least one cryptic species may be present. We generate 3,346 base pairs of DNA sequence data from seven nuclear loci to test competing models of species delimitation in the C. triseriatus group using Bayes factor delimitation. We also examine museum specimens from the Trans-Mexican Volcanic Belt for evidence of cryptic species. We find strong support for a nine-species model and genetic and morphological evidence for recognizing two new species within the group, which we formally describe here. Our results suggest that the current taxonomy of the C. triseriatus species group does not reflect evolutionary history. We suggest several conservative taxonomic changes to the group, but future studies are needed to better clarify relationships among species and examine genetic patterns and structure within wide-ranging lineages.

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.

Diet of the Tepalcatepec Valley whiptail, Aspidoscelis calidipes (Squamata: Teiidae), in Michoacán, México

Abstract We investigated the diet of the endemic teiid lizard Aspidoscelis calidipes in the Balsas-Tepalcatepec Basin in the state of Michoacán, Mexico, during 2010 and 2011. We removed, analyzed, and identified stomach contents to order or family. The diet of A. calidipes consisted of 27 prey taxa and the dietary diversity was low (H′ = 0.45). Termites and ants were the most important prey items. Adult and juvenile lizards consumed greater proportions of termites than any other prey item by number, volume, and frequency. Diet diversity of juveniles was higher (H′ = 1.15) than that of adults (H′= 0.28). Dietary overlap between adults and juveniles was 49%.

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.

Does a Frog Change its Diet along a Successional Forest Gradient? The Case of the Shovel-Nosed Treefrog (Diaglena spatulata) in a Tropical Dry Forest in Western Mexico

Abstract Biologists have increasingly recognized the importance of secondary forests as facilitators of passive landscape restoration and recovery of faunal communities in landscapes fragmented by farming. To evaluate the role of secondary forests as providers of food resources for anurans, we studied the diet of the Shovel-Nosed Treefrog (Diaglena spatulata) from five vegetation stages of tropical dry forest (pasture, early forest, young forest, intermediate forest, and old-growth forest) on the coast of Jalisco, Mexico. We examined the stomach content of 97 individuals using a stomach-flushing method. We found 14 different types of prey (Class or Order) in the frogs diet. Araneae, Lepidoptera, and Orthoptera occurred in frogs from all five vegetation stages. We recorded the highest number of prey types (11) in the young and intermediate forest stages, and the highest prey volume and prey frequency in stomachs from frogs inhabiting the old-growth forest. We found no difference in size or body condition of frogs among vegetation stages, but there was a positive relation between size and body condition with the volume of stomach content. Our results suggest that D. spatulata presents high dietary plasticity and that secondary stages of dry tropical forest contribute to the persistence of this species in human-modified landscapes.