Pablo Corcuera

Does the microarchitecture of Mexican dry forest foliage influence spider distribution

Abstract Spider species diversity has been associated with vegetation structure and stratification but there are few studies comparing the spider distribution in different shrubs and trees. In this study we analyzed the species distribution of the spider community of 11 shrub and tree species in two different study sites in a Mexican tropical dry forest. We present results from multivariate analyses that explain their distribution. A classification analysis based on spider abundances separated one shrub, Croton ciliatoglanduliferus, from the rest of the plant species. This was explained by the presence of large numbers of the oxyopid Peucetia viridans (Hentz 1832) on this plant. A second cluster segregated broad-leaved from small-leaved, bipinnate species. This was mainly due to higher spider abundances in the latter type of plants. Four vegetation variables were estimated and their influence on the species distribution was assessed by means of a principal components and regression analysis. With the exception of P. viridans, all spiders were positively associated with number of leaves and number of branchlets per 50 cm branch and negatively with foliage area.

Ground Spider Guilds and Functional Diversity in Native Pine Woodlands and Eucalyptus Plantations

Abstract Vegetation structure and floristics have a strong influence on the relative abundance of spider guilds and functional diversity of terrestrial arthropods. Human activities have transformed much of the temperate woodlands. The aim of this study was to test five predictions related to the guild distribution and functional diversity of the ground spider communities of Eucalyptus plantations and native pine woodlands in western Mexico. Spiders were collected every fortnight from September to November from 15 pitfalls positioned in each of the eight sites. We also assessed the cover of grasses, herbs, shrubs, and leaf litter in each site. We found that the abundances of ground hunters and sheet weavers between plantations and pine woodlands were different. Nevertheless, there was not a consistent difference between sites of each of the vegetation types. Most species of ground hunters, sheet web weavers, and many other hunters were associated with litter and the grass cover. Nonetheless, in some cases, species of different families belonging to the same guild responded to different variables. Wolf spiders were related to the grass Aristida stricta Micheaux, 1803, while the species of the other families of ground hunters were associated with leaf litter. One Eucalyptus plantation and one pine woodland had the highest functional diversity of all sites. These sites have a well developed litter and grass cover. Our study suggests that the abundance of litter and a high cover of grasses explain the occurrence of species with different traits, and these habitat components results in a high functional diversity.

Distribution of the community of frugivorous birds along a successional gradient in a tropical dry forest in south-western Mexico

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.

Susceptibility of Varroa destructor (Gamasida: Varroidae) to four pesticides used in three Mexican apicultural regions under two different management systems

ABSTRACT Mexico has five apicultural regions wich are defined according to their blooming period and geography. Varroa destructor Anderson and Trueman is controlled with pesticides and alternative treatments in all these regions. To determine the concentration-mortality response lines of V. destructor, bioassays with four pesticides that are used for its control in the Gulf of Mexico, Yucatan Peninsula and Central-Highland regions were conducted. The Burgerjon spraying tower was used to apply known concentrations of flumethrin, fluvalinate, amitraz and coumaphos. Lethal concentrations 50 (LC50) and resistance indexes were calculated with Probit analyses. In the Gulf region, the resistance indexes were: flumethrin, 659.43; fluvalinate, 21.83; amitraz, 12.77; coumaphos, 1.49×. In the Central-Highland region: flumethrin, 243.43; fluvalinate, 19.04; amitraz, 8.56; coumaphos, 1.22 x. In the Yucatan Peninsula region: flumethrin, 4057.32; fluvalinate, 199.57; amitraz, 26.55; coumaphos, 3.93×. These results suggest a resistance to flumethrin, fluvalinate and amitraz, with similar values in migratory beekeeping regions, and higher values in the non-migratory region. Coumaphos remained effective in V. destructor populations of the Gulf and Central-Highland regions.

Non weaving spiders on native woodlands and Eucalyptus plantations in Western Mexico: diversity and distribution patterns

Eucalyptus spp. are commonly planted, forming non-native plantations, including the tropics and their wildlife conservation value is relatively unknown. Recent studies have concluded that secondary forests and tree plantations are less diverse than well-developed tropical rain forests. However, introduced Eucalyptus stands harbored similar species richness to surrounding native woodland in temperate woodlands in North America though the identity of the species present may differ. Species composition, as well as dominance curves and differences in community structure add additional insight to understanding faunistic responses to replacement of native woodland by Eucalyptus plantations. Here, we compared species richness, diversity patterns, and the distribution of non-weaving spiders between native woodlands and Eucalyptus plantations in a temperate region of Mexico. We found more Lycosidae species in all plantation stands. Other community attributes were not consistently different between plantations and native woodlands. This is explained by similarities between, and differences within, the understory of the two main vegetation types. Multivariate analyses identified three spider groups and five spider species could be identified as indicators of these groups. A comparison of the number of species of the wandering spiders between the two vegetation types suggests a compensation pattern that is reported here for the first time.

Distribution of Peucetia viridans (Araneae: Oxyopidae) on Croton ciliatoglandulifer

ABSTRACT Peucetia viridans (Hentz) lives almost exclusively on Croton ciliatoglandulifer (Ortega) in the dry forests of western Mexico. This spider is usually found on pubescent shrubs. Within their host plants, P. viridans has been associated with plant height and cover, as well as with number of flowers or inflorescences in anthesis. Flowers can be used as cues of good habitat conditions or because they attract prey detected by the spider. In this study, we assessed the importance of flowers, plant cover, and plant exposure (sun/shade) on the spider distribution in five 50-plant transects. In a field experiment, we also compared the number of spiders between controls, plants from which inflorescences were removed, and plants with artificial inflorescences. The results from the transects indicate that, when the number of flowers per spider is high, spiders were more abundant in exposed locations, which presumably offer better microclimatic conditions; when flowers become scarce, food may be more difficult to find and the spider distribution become strongly associated with the number of flowers, where they are more likely to find prey. Spider abundances on the experimental plot decreased on plants from which flowers were removed in comparison to control plants. Spider abundance increased on those in which artificial inflorescences were added. The similarity between plants with natural and artificial inflorescences suggests that spiders use flowers as cues of good microhabitats instead of prey visitors, which are significantly less abundant on artificial inflorescences.

Spatiotemporal variation in the structure and diet types of bird assemblages in tropical dry forest in southwestern Mexico

ABSTRACT Tropical dry forest is one of the most threatened ecosystems in the Neotropics as a result of agriculture, cattle ranching, and timber extraction. The effects of disturbance on the bird communities of this ecosystem have not been well studied. In this study, we evaluated changes in the richness, abundance, and diversity of birds and their diet types in the following land uses in southwestern Mexico: agroecosystem, palm grove, forest edge, and undisturbed forest. Visual and auditory sampling was performed for 1 year (August 2014 to July 2015) in 40 circular plots with a radius of 30 m (10 plots per land use). Differences in the composition and the abundance of bird species in plots of distinct land use were analyzed by a non-metric multidimensional scaling (NMDS) ordination to determine similarity among the data. In total, 101 species from 29 families were found in the study sites. The agroecosystem presented the greatest species richness (70 species), followed by undisturbed forest (57). Overall abundance of birds differed significantly among land uses. Bird abundance and dominance, in addition to the abundance of diet types, also varied significantly among land uses and between dry and rainy seasons. We found species of open habitats as well as species dependent on undisturbed forest fragments. The results suggest that seasonal variation in the abundance of birds is mainly determined by the availability of food resources and other local environmental factors. The abundance of carnivorous, granivorous, omnivorous, insectivorous, and frugivorous birds was higher at disturbed sites while the abundance of nectarivorous birds was higher in the undisturbed forest. The species composition of the undisturbed forest was most distinct among the land uses. Our results showed that the comparison of diet types was more useful for understanding the effect of land-use changes than the sole evaluation of the structural patterns of bird assemblages.

Factors affecting the dominance hierarchy dynamics in a hummingbird assemblage

Abstract 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.

Myiarchus flycatchers are the primary seed dispersers of Bursera longipes in a Mexican dry forest

We evaluated the seed dispersal of Bursera longipes by birds along a successional gradient of tropical dry forest (TDF) in southwestern Mexico. B. longipes is an endemic tree to the TDF in the Balsas basin. The relative abundance of frugivorous birds, their frequency of visits to B. longipes and the number of removed fruits were recorded at three study sites with different stages of forest succession (early, intermediate and mature) characterized by distinct floristic and structural elements. Flycatchers of the Myiarchus and Tyrannus genera removed the majority of fruits at each site. Overall, visits to B. longipes were less frequent at the early successional site. Birds that function as legitimate dispersers by consuming whole seeds and regurgitating or defecating intact seeds in the process also remove the pseudoaril from seeds, thereby facilitating the germination process. The highest germination percentages were recorded for seeds that passed through the digestive system of two migratory flycatchers: M. cinerascens and M. nutingii. Perch plants, mainly composed of legumes (e.g., Eysenhardtia polystachya, Acacia cochliacantha, Calliandra eryophylla, Mimosa polyantha), serve also as nurse plants since the number of young individuals recruited from B. longipes was higher under these than expected by chance. This study shows that Myiarchus flycatchers are the most efficient seed dispersers of B. longipes across all successional stages. This suggests a close mutualistic relationship derived from adaptive processes and local specializations throughout the distribution of both taxa, as supported by the geographic mosaic theory of coevolution.

Residency in white-eared hummingbirds (Hylocharis leucotis) and its effect in territorial contest resolution

Background Territory owners usually defeat intruders. One explanation for this observation is the uncorrelated asymmetry hypothesis which argues that contests might be settled by an arbitrary convention such as “owners win.” We studied the effect of territorial residency on contest asymmetries in the white-eared hummingbird (Hylocharis leucotis) in a fir forest from central Mexico. Methods Twenty white-eared male adult hummingbird territories were monitored during a winter season, recording the territorial behavior of the resident against intruding hummingbirds. The size and quality of the territory were related to the probability that the resident would allow the use of flowers by the intruder. Various generalized models (logistical models) were generated to describe the probabilities of victory for each individual resident depending on the different combinations of three predictor variables (territory size, territory quality, and intruder identity). Results In general, small and low quality territory owners tend to prevent conspecific intruders from foraging at a higher rate, while they frequently fail to exclude heterospecific intruders such as the magnificent hummingbird (Eugenes fulgens) or the green violetear hummingbird (Colibri thalassinus) on any territory size. Our results showed that the identity of the intruder and the size and quality of the territory determined the result of the contests, but not the intensity of defense. Discussion Initially, the rule that “the resident always wins” was supported, since no resident was expelled from its territory during the study. Nevertheless, the resident-intruder asymmetries during the course of a day depended on different factors, such as the size and quality of the territory and, mainly, the identity of the intruders. Our results showed that flexibility observed in contest tactics suggests that these tactics are not fixed but are socially plastic instead and they can be adjusted to specific circumstances.