RESUMO
Tropical dry forests (TDFs) are affected by land-use changes. These modifications impact their composition and arboreal structure, as well as the availability of food for several bird groups. In this study, we evaluated the foraging preferences in zoochorous trees of fruit-eating birds during the dry season of the year in three successional stages (early, intermediate, and mature) of TDFs in southern Mexico. The fruits of these trees are important in the diet of several birds during the dry season, a period during which food resources are significantly reduced in TDFs. We estimated foliar cover (FC) and foliage height diversity (FHD) of zoochorous trees in 123 circular plots. These variables were recognized as proxies of food availability and tree productivity. Foraging preferences were evaluated at the community level, by frugivore type, and by bird species. We evaluated the effect of the structural variables and the fruit size of zoochorous plants on fruit removal by birds and related the bird body mass and fruit size removed in the successional gradient. A total of 14 zoochorous tree species and 23 fruit-eating bird species were recorded along the successional gradient. Intermediate and mature stages showed greater fruit removal. The birds removed mainly B. longipes fruits across the three successional stages. The FHD and fruit size were important drivers in the selection of zoochorous trees and fruit removal by fruit-eating birds. Fruit size and bird body mass were positively related along the successional gradient. The results suggest that fruit removal by fruit-eating birds in the successional gradient can promote the demographic dynamics of several zoochorous tree species, especially of Bursera spp. along the TDFs.
RESUMO
Knowledge of bird species diversity along elevational gradients is key for understanding the distributional limits of species and, ultimately, for promoting measures that conserve biodiversity. In the present study, we evaluated changes in bird species richness, diversity, and endemism along an elevational gradient in the Sierra Madre del Sur in southern Mexico -a globally recognized biodiversity hotspot. Monthly bird surveys were carried out at localities with elevations of 1600, 1800, 2000, and 2200 m over the course of one year (2014-2015) covering an area of 2000 km2 (10 circular plots with a radius of 25 m per elevation site). Diversity was calculated in terms of effective number of species or Hill numbers, while the composition of bird species along the elevational gradient was analyzed by non-metric multidimensional scaling, and endemic bird species turnover was assessed with faunal congruence curves. Overall, a total of 118 bird species belonging to 35 families were recorded along the elevational gradient. Although we found that bird richness and diversity increased with increasing elevation, we also observed significant turnover in bird composition and endemic species, which were likely linked to forest types and conditions, as well as proximity of sites to urban centers. Assessing biodiversity patterns across elevational gradients in a well-recognized biodiversity reservoir advances both understanding of ecological patterns and aids conservation efforts and management of biological resources.