ABSTRACT
Changes in environmental characteristics can affect habitat use by birds, impacting the number of individuals, number of species, and changing species composition and functional structure of assemblages. Metrics that evaluate the functional structure of biological assemblages constitute a complementary tool to the traditional taxonomic approach, because they quantify the differences between species by means of functional traits. We assessed the effect of environmental characteristics on the taxonomic diversity (species richness, species composition and number of individuals) and functional structure (functional richness, functional evenness, Rao's functional diversity, and community-weighted mean traits) of bird assemblages in northern Mato Grosso state, in the southwestern Brazilian Amazon. We sampled birds in 32 plots. At each plot birds were captured using mist nets, and eight environmental variables were measured: canopy openness, leaf litter, elevation, number of trees in three classes of DBH, soil clay content, and distance to nearest stream. To evaluate functional structure, we measured seven morphological traits from individuals of each bird species. Habitat variables had a significant effect on taxonomic diversity. However, the general functional structure was not affected. Elevation and distance to nearest stream were the main variables driving changes in taxonomic diversity and had a minor effect on functional richness. The other metrics of functional structure were not significantly affected by the set of environmental variables. Our results suggest that the sampled bird assemblages exhibit some functional tolerance (redundancy) to small-scale environmental variation, implying certain resilience to ecosystem modification. (AU)
Subject(s)
Birds , Classification , EcosystemABSTRACT
Abstract Atypical drought events have increasingly occurred in Brazil over the last years due to global climate changes. However, their consequences on aquatic biota in reservoirs are poorly known. We tested the hypothesis that macroinvertebrate communities are negatively affected by atypical drought events, given the sensitivity of many taxa to environmental changes. We predicted that: (a) there would be changes in limnological and sediment parameters between a regular year and an atypical year, (b) abundance and richness of the genera of Chironomidae and of exotic species would be higher due to the enhanced ability of these organisms to adapt to changes in the physical environment, and (c) community structure metrics (i. richness; ii. % richness; iii. abundance; iv. % abundance) would be affected by disturbance indices (i. Buffer Disturbance Index-BDI; ii. Local Disturbance Index-LDI; iii. Integrated Disturbance Index-IDI) in both years. The study was carried out in the reservoir of the Nova Ponte Hydroelectric Power Plant, state of Minas Gerais, comparing two sampling periods: a regular climatological year (2010) and an atypical drought year (2014). A total of 40 sampling sites were defined along the shore of the reservoir, and types of land use in the surrounding area of each site were measured, as well as physical habitat conditions, sediments, and benthic macroinvertebrate communities. Sampling was performed at these sites in the end of the rainy season in both years. The intensity of anthropogenic modifications was assessed at local scale and in the areas (buffers) surrounding the sampling sites using quantitative disturbance indices. There were striking differences in limnological parameters and sediment characteristics between sampling periods. Taxonomic richness was significantly lower in the drought year. As opposed to our predictions, richness and abundance of Chironomidae and exotic species did not increase with the atypical drought event. Besides, most community structure metrics showed a significant relationship with disturbance indices only during the regular climatological year, thus indicating that the large-scale effects of water stress may override the conditions of local habitats and the surrounding landscape. Therefore, in addition to a correct political-environmental management of water resources at local-scale, which includes maintaining the water quality and the riparian and landscape integrity, addressing large-scale climate issues is required for the maintenance of the ecological integrity of tropical reservoirs.
Resumo A ocorrência de episódios atípicos de seca vem crescendo nos últimos anos no Brasil em decorrência de mudanças globais no clima. Entretanto, as consequências disso para a biota aquática são ainda pouco conhecidas. Testamos a hipótese de que comunidades de macroinvertebrados são negativamente afetadas por eventos de seca atípica, dada a sensibilidade de muitos taxa às alterações ambientais. Nossas predições foram que (a) parâmetros limnológicos e características de sedimento seriam alterados em um ano de seca atípica, (b) encontraríamos maior abundância e riqueza de gêneros de Chironomidae e de espécies exóticas dada à alta capacidade destes organismos de adaptarem-se às mudanças no ambiente, (c) métricas de estrutura de comunidade (i. riqueza; ii. % riqueza; iii. abundância e iv. % abundância) seriam afetadas por índices de distúrbio (i. Índice de Distúrbio no Buffer-IDB; ii. Índice de Distúrbio Local-IDL e iii. Índice de Distúrbio Integrado-IDI) em ambos os anos. O estudo foi realizado no reservatório da Usina Hidrelétrica de Nova Ponte, Minas Gerais, comparando dois períodos amostrais: um ano climatológico normal (2010) e um ano de seca atípica (2014). Foram definidos 40 sítios amostrais na região litorânea do reservatório onde foram mensurados os tipos de usos do solo no entorno, condições de habitats físicos, características limnológicas na coluna d'água, sedimento e comunidades de macroinvertebrados bentônicos. A intensidade de alterações antrópicas foi avaliada em escala local e no entorno dos pontos amostrais (buffers) por meio de índices de distúrbio. Observamos diferenças expressivas nos parâmetros limnológicos e nas características dos sedimentos entre os dois períodos amostrais. A riqueza taxonômica foi significativamente menor no ano de seca. Ao contrário do esperado, os valores de riqueza e abundância de Chironomidae e de espécies exóticas não aumentaram com o evento extremo de seca. Paralelamente, a maioria das métricas de estrutura de comunidade apresentou relação significativa com os índices de distúrbio somente durante o ano climatológico normal, indicando que os efeitos de estresse hídrico em larga escala podem se sobrepor às condições locais de habitat e de paisagem circundante. Portanto, deve ser considerada não só a correta gestão político-ambiental de recursos hídricos em escala local, que inclui a manutenção da qualidade da água e da integridade da região ripária e uso do solo da região de entorno, mas também abordar questões climáticas em larga escala faz-se necessário para a manutenção da integridade ecológica em reservatórios tropicais.