RESUMO
A comparative study on forests and grasslands in three ecoregions (Humid Chaco, Espinal, and Paranaense) was conducted in two protected areas in northeastern Argentina: Iberá National Park and Mburucuyá National Park. The effects of habitat heterogeneity (vegetation cover) on terrestrial ant (Formicidae) assemblages were analyzed and compared. The habitat heterogeneity hypothesis-which predicts that when environmental structural complexity increases, the species richness will also increase-was tested. Two sites were selected in each ecoregion. A forest and a grassland were surveyed in each site, using unbaited pitfall traps from October 2013 to February 2014. Overall, 5,465 ants belonging to 37 species were collected, 32 of which were present in forests and 26 in grasslands. Solenopsis invicta Buren (Hymenoptera: Formicidae) and Pheidole radoszkowskii Mayr (Hymenoptera: Formicidae) were the most abundant species. Formicidae assemblages were compared in terms of abundance, species richness, and diversity between habitats and ecoregions. The results of this study support the habitat heterogeneity hypothesis, since we found a higher diversity of ants in more structured habitats (i.e., forest) in the three ecoregions analyzed. Also, the ant assemblages differed both between habitats and between ecoregions. Our findings provide the first assessment of terrestrial ant assemblages in natural habitats of the three ecoregions in Corrientes Province, Argentina.
Assuntos
Formigas , Animais , Argentina , Ecossistema , Florestas , PradariaRESUMO
The spatial habitat heterogeneity hypothesis posits that habitat complexity increases the abundance and diversity of species. In tropical forests, lianas add substantial habitat heterogeneity and complexity throughout the vertical forest profile, which may maintain animal abundance and diversity. The effects of lianas on tropical animal communities, however, remain poorly understood. We propose that lianas have a positive effect on animals by enhancing habitat complexity. Lianas may have a particularly strong influence on the forest bird community, providing nesting substrate, protection from predators, and nutrition (food). Understory insectivorous birds, which forage for insects that specialize on lianas, may particularly benefit. Alternatively, it is possible that lianas have a negative effect on forest birds by increasing predator abundances and providing arboreal predators with travel routes with easy access to bird nests. We tested the spatial habitat heterogeneity hypothesis on bird abundance and diversity by removing lianas, thus reducing forest complexity, using a large-scale experimental approach in a lowland tropical forest in the Republic of Panama. We found that removing lianas decreased total bird abundance by 78.4% and diversity by 77.4% after 8 months, and by 40.0% and 51.7%, respectively, after 20 months. Insectivorous bird abundance and diversity 8 months after liana removal were 91.8% and 89.5% lower, respectively, indicating that lianas positively influence insectivorous birds. The effects of liana removal persisted longer for insectivorous birds than other birds, with 77.3% lower abundance and 76.2% lower diversity after 20 months. Liana removal also altered bird community composition, creating two distinct communities in the control and removal plots, with disproportionate effects on insectivores. Our findings demonstrate that lianas have a strong positive influence on the bird community, particularly for insectivorous birds in the forest understory. Lianas may maintain bird abundance and diversity by increasing habitat complexity, habitat heterogeneity, and resource availability.