| C. Ciências Biológicas - 5. Ecologia - 2. Ecologia Aquática |
|
| ECOLOGICAL FACTORS INFLUENCING AQUATIC BIRD COMMUNITIES IN ANAVILHANAS ARCHIPELAGO, CENTRAL BRAZILIAN AMAZONIA |
|
Renato Cintra 1
|
|
1. INPA - Ecologia
|
|
| INTRODUÇÃO: |
| The debate will never end among tropical ecologists on processes determining community structure and composition and ultimately the local biodiversity. Two major theories which have been often under test: 1) the Hubbell’s neutral defend the idea that natural communities are a conjunct of ecologically equivalent individuals belonging to a fixed number in local species which are part of a larger regional species pool (Hubbell 2001). However, this theory do not consider the differences in the individual responses to variation in the environs and local ecological conditions; 2) The niche theory, in contrast, assumes that communities results from a strong relationship between the patterns of biodiversity and the variability in ecological factors (physical disturbances, productivity, habitat availability) and interaction, such as competition with other species (Tilman, 1982; Tokeshi,1999).
Lake systems are useful to verify whether ecological factors and differences in spatial scales influence aquatic bird community composition, which may help to explain local and regional biodiversity, and are essential to guide management actions and conservation policies.
This study investigates how the richness, abundance, and composition of the aquatic bird communities of Anavilhanas archipelago, central Amazon, change on a local scale among black water lakes, and are influenced by lake shape, degree of isolation, physic-chemical properties (depth, water transparency, productivity) and habitat richness.
|
|
| METODOLOGIA: |
| The study was accomplished in the Anavilhanas archipelago, Rio Negro, Brazil. Bird surveys were conducted in 45 water bodies, aboard a speedboat at speed of 15 km/h and 15-20 m from the lake shore, in July, November-December 2007 and July 2008. The sample unit was the lake, which we contoured completely. A Garmin 76 GPS was used to record their geographical coordinates in order to obtain lake positions. Sampling effort was standardized by dividing the number of individuals of each bird species by the sizes (areas) of the lakes in which the species occurred. The species densities obtained were then used in the quantitative statistical analyses. Data on lake characteristics and habitats type (recorded every 10 seconds through direct observation but also using digital photos) were done simultaneously. Lake properties (perimeter, area) were digitalized from satellite images using Global mapper software. A rope graduated in meters with a Secchi disc and a 5 kg weight attached to its end was used to register lake water transparency and water depth. The concentrations (μmol l-1) of total nitrogen and total phosphorus in the water samples were determined through simultaneous analyses (Valderrama, 1981). To compare aquatic bird community among lakes, data matrices constructed from the bird surveys were subjected to non-metric multidimensional scaling (NMDS), and the resulting vectors in models of Multiple regression analysis using PC-ORD (MacCune and Mefford 1999) and SYSTAT (Wilkinson 1998), respectively. |
|
| RESULTADOS: |
| A total of 3626 individuals were recorded, distributed by 48 bird species; of these, 32 are aquatic, and 19 are primarily piscivorous. Seven species accounted for 70 % of all 32 species recorded. Aquatic and picivorous bird richness and abundance were not significantly related to water body shape and productivity but were directely influenced by water depth, transparency, lake isolation and habitat richness. Matrices of bird species by water body were subjected to multivariate analysis using non-metric multidimensional scaling (NMDS). Results of multivariate regression indicates that, for quantitative data (species abundance) and qualitative data (species presence/absence), the changes in composition of the aquatic birds community (using NMDS - axes 1 and 2 together as response variable) increased significantly as water body gets deeper, decreased with increase in water transparency, increased with increase in lake isolation, decreased with increasing in the habitat richness. The changes in picivorous community composition decreased significantly as lake water gets deeper and in more isolated lakes. The numerical analyses revealed a remarkably different behavior of the communities of aquatic birds and picivorous birds, the former changing significantly vis-à-vis lacustrine water body physical characteristics and local geography (water bodies isolation), and the latter being relatively less sensitive to variation in these parameters.
|
|
| CONCLUSÃO: |
| Similar in species composition, but showing lower bird abundance than those from white water varzea lakes in the Amazon (Cintra et al., 2007), the communities of birds associated with black water aquatic lakes at Anavilhanas comprise few abundant and a higher number of rare species. This is a typical pattern of large and pristine animal communities (Terborgh et al., 1990; 1997; Ricklefs and Schluter, 1993). Bird diversity in aquatic habitats in South America is about 292 species (Stotz et al.1996). Of the 48 species associated with aquatic environments that were recorded in Anavilhanas, 31 (64.6%) are dependent on aquatic habitats, and 17 (35.4 %) are mainly piscivorous, representing 10.6 % and 5.8 % of the continental total, respectively. Most of the 31 aquatic species are abundant, widespread, and occur in most aquatic environments in Anavilhanas (Cintra et al. 2007) and in Brazilian Amazonia (Pinto 1978; Cohn-Haft et al.1997; Petermann 1997; Cintra et al.2007). In general, the results support some predictions from Hubbell’s neutral theory and some from Tilman niche theory. The results indicate that water body physical characteristics (depth, water transparency), isolation and habitat richness are determinants of aquatic bird community composition in the black water lake systems in Central Amazonia. |
|
| Instituição de Fomento: CNPq |
|
| Palavras-chave: Aquatic bird community, Anavilhanas, Amazonia. |