We analyzed the distribution and diversity patterns of ground dwelling spiders in the main plant associations of the protected area known as Churince, in the Cuatro Ciénegas Basin, Coahuila, Mexico. Spiders were collected with pitfall ramp traps during the years 2011 and 2012. We found 29 families and 144 morpho-species. The most abundant families were Gnaphosidae, Lycosidae and Salticidae. The most common species were Gnaphosa sp. and G. hirsutipes. There were 4 new records for Mexico and 4 for the Chihuahuan Desert, including 2 possible new species of Sergiolus and Oecobius. The number of species was high in comparison when compared with other studies in the Chihuahuan and Sonoran deserts. The species abundances were fitted to the Fisher distribution. The rarefied richness was highest at sites with denser vegetation and high humidity. Dominance was high and richness low in sparsely vegetated sites. The wandering hunters were dominant in all sites, but the guild diversity was higher in sites with high plant complexity.

Abstract:Few reports have described the relationship between the distribution of frugivorous birds and vegetation successional changes in dry forests. We assessed the abundance and behaviour of frugivorous birds in early, intermediate and mature dry forests in the Balsas river basin, Guerrero, Mexico. We selected nine dry-forest fragments, three fragments per stage, in these three stages of succession. We analysed the vegetation, estimated bird abundances in 10-min count periods, and recorded the way birds process fruits in circular plots (11–15 plots per fragment, 123 plots in total). Birds were classified as seed predators (15% of all individuals in this study), pulp consumers (15%) or legitimate dispersers (70%). Bird abundance was higher in mature forests in the dry season, while abundance and richness of legitimate dispersers and seed predators were positively related to vegetation complexity. Mature forests have a high vegetation complexity and a high cover of Bursera species that produce fruit during the dry season. During the rains, abundance was higher in early-successional sites when the zoochorous plants produced fruit. Legitimate disperser migrants (i.e. Tyrannus vociferans, Myiarchus cinerascens and M. tyrannulus) were widespread, helping the establishment of zoochorous trees such as Bursera spp. in early-successional forests.

Abstract:The biotic province of the Sierra Madre del Sur presents a mosaic of woodlands at different successional stages due to frequent modifications in land use. In this study, we analyzed changes in woody flora across three successional stages of pine-oak forest: early, intermediate, and mature. Vegetation composition and diversity were characterized in 10 plots (each 0.28 ha). The mature stage had the highest values for species richness, abundance, and diversity. Pioneer plants were dominant in the early-successional site and may promote the establishment of late-successional species. The vegetation structure was more complex in the mature stage, where members of the Quercus genus were co-dominant with Pinus species. Pine tree richness was highest in the early-successional stage, and its abundance increased at the intermediate-successional site. These results suggest that Pinus species can grow in perturbed and sunny environments but also require favorable edaphic and microclimatic conditions, such as those found in intermediate woodlands. Results of this fieldwork support the initial floristic composition succession model, which suggests that species present at early stages will also occur in subsequent stages. Ecological succession may be considered to be a natural restoration process, and thus, conservation strategies should focus on maintaining distinct successional communities in addition to mature forests in order to preserve a high number of species.

Water, food and nutrition are three of the main factors that regulate the distribution and abundance of wildlife species in a given area. In Baja California Sur, Mexico, the bighorn sheep is one of the most appreciated species for its ecological and economic value within the peninsular desert ecosystem; however, many aspects of its biology, ecology and population status remain unknown. The objective of the present study was to evaluate the diet composition of the bighorn sheep, analyzing the seasonal use and availability patterns of the plant species consumed. Using two food selection indices, we tested the hypothesis that the bighorn sheep opportunistically selects plant species from its habitat in the southern zone of Sierra El Mechudo, Baja California Sur, Mexico. The vegetation was characterized by means of 50 linear transects measuring 100 m x 5 m (500 m 2). The diet of the bighorn sheep was evaluated through the microhistological analysis of feces. We calculated the percentage of in-vitro dry-matter digestibility and the digestible energy of forage consumed by sheep. The similarity of seasonal vs. annual diet was determined through a cluster analysis. From two food selection indices (Ivlev's electivity, Bonferroni), we estimated the proportion of use of plant species consumed by sheep to determine food preferences. In the habitat, we identified 21 families with 63 species in 2010 and 22 families with 50 species in 2011. Shrubs were the dominant forms. The analyses of faeces identified 47 species, consisting of 27 shrubs (62.1 %), 12 forbs (26.9 %), six trees (10.6 %), one succulent (0.2 %) and one unidentified species (0.1 %). The cluster analysis showed seven similar groups. Ivlev's and Bonferroni indices showed the selection of Bourrieria sonorae, Melochia tomentosa and Caesalpinia placida by bighorn sheep in 2010; in 2011, it selected Bursera epinnata, Caesalpinia placida and Larrea tridentata. Non-significant differences between seasons were observed regarding the composition of plant species in the diet. Shrubs were the dominant life forms, followed by trees and succulents. Shrubs were the preferred food foraged by sheep, accounting for 62.1 % of the diet; this finding is consistent with values reported for Arizona and California. Non-significant differences were observed in the percent in-vitro dry matter digestibility and digestible energy of the plant species foraged by sheep. However, we found that sheep grazed preferentially on four plant species, three shrubs and one tree, of high food quality. In this study, the bighorn sheep behaved like a specialist; therefore, we rejected the hypothesis that this species forages opportunistically on plant species. Studies on the diet of the bighorn sheep are valuable to develop management plans for the species and its habitat, since these provide information to better understand the extent of vegetation use and whether distribution sites are suitable and meet with the requirements for the conservation of the species and its populations.

Intra and interspecific competition for nectar play an important role in hummingbird communities. Larger sized species usually exclude smaller species from the rich floral resources. However, it has been recently postulated that the competitive advantages of a large body size decline as the evolutionary distance between the contending species increases. In this study, we analyzed dominance hierarchy dynamics in a hummingbird assemblage in central Mexico. By monitoring hummingbird territories established in three plant species through 1 year, we assessed the effects of energy within territories and the territory owners identity in the frequency of inter and intraspecific encounters. We also evaluated if these factors affect the dominance of larger species when they compete against smaller distantly related contenders. Our results show that their frequency of intraspecific encounters was related with the identity of the territory’s owner. On the contrary, the frequency of interspecific encounters was related with both the territory and the identity of the territory’s owner. We did not find a significant difference between the number of encounters dominated by larger and smaller species and their contenders. However, the increase in genetic distance between contenders was positively associated with a higher frequency of encounters dominated by small hummingbirds. Our results showed that the ecological factors and evolutionary relationships among contenders play important roles in the dominance hierarchy dynamics.